Journal of Biosciences and Medicines, 2014, 2, 33-50 Published Online March 2014 in SciRes. http://www.scirp.org/journal/jbm http://dx.doi.org/10.4236/jbm.2014.21005 How to cite this paper: Ssenku, J.E., et al. (2014) Assessment of Seedling Establishment and Growth Performance of Leu- caena leucocephala (Lam.) De Wit., Senna siamea (Lam.) and Eucalyptus grandis W. Hill ex Maid. in Amended and Untreated Pyrite and Copper Tailings. Journal of Biosciences and Medicines, 2, 33-50. http://dx.doi.org/10.4236/jbm.2014.21005 Assessment of Seedling Establishment and Growth Performance of Leucaena leucocephala (Lam.) De Wit., Senna siamea (Lam.) and Eucalyptus grandis W. Hill ex Maid. in Amended and Untreated Pyrite and Copper Tailings Jamilu Edirisa Ssenku1*, Mohammad Nta l e 2, Ingvar Backéus3,4, Hannington Oryem-Origa1 1Department of Biological Sciences, College of Natural Sciences, Makerere University, Kampala, Uganda 2Department of Chemistry, College of Natural Sciences, Makerere University, Kampala, Uganda 3School of Natural Sciences, Technology and Environmental Studies, Södertörn University, Huddinge, Sweden 4Department of Plant Ecology and Evolution, Uppsala Universit y , Uppsala, Sweden Email: *jssenku@g mail.co m Received 18 January 2014; revised 23 February 2014; accepted 2 March 2014 Copyright © 2014 by autho rs and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativ ecommon s.org/l icenses/by /4.0/ Abstract Growth and survival performance of Leucaena leucocephala (Lam.) De Wit., Senna siamea Lam. and Eucalyptus grandis W. Hill ex Maid. in amended and untreated pyrite and copper tailings were evaluated under field conditions. The physico-chemical characteristics of the pyrite soil and tail- ings were determined. Growth in height, basal diameter and later dbh, relative growth rate due to height (RGRh) and basal diameter (R GRd) and survival were determined every after six months. A split block experimental design was used and the data collected were analyzed using a statistical package R, with an additional package lme4. Tailings and pyrite soils had extremely low pH, poor nutritional status, low organic matter content and elevated concentrations of available heavy metals as compared to the unpolluted soils and treated pyrite soil and copper tailings. Growth performance was extremely poor on the untreated pyrite soil and copper tailings for all the spe- cies but significantly enhanced by the application of compost and limestone. Treatment had a sig- nificant effect on all parameters at all sites. Eucalyptus gran dis displayed a higher potential of phytomass accumulation than Leucaena leucocephala and Senna siamea. Even though Leucaena leucocephala grew fastest reaching reproductive maturity in 7 months after planting, relative *Corresponding author.
J. E. Ssenku et al. growth rates of the three species were not significantly different at all sites. The three species can be used for phytostabilisation of the tailings at Kilembe tailings dam sites (KTDS) after treatment while at Low polluted pyrite trail site (LPPTS) and Highly polluted pyrite trail sites (HPPTS) Senna siamea is more suitable as Eucalyptus grandis and Leucaena leucocephala are susceptible to at- tacks by Syncerus caffer (Buffalos) and Kobus kob thom asi (Uganda Kob). Keywords Seedling Establishment; Growth Performance; Py rit e; Phyt os tabiliz ation ; Taili ngs; QEC A 1. Introduction Copper mining activities in Kilembe that lasted for close to 30 years from 1956 to 1982 generated an enormous volume of cobaltiferous pyrite wastes to the tune of 1.13 million metric tonnes that were stockpiled near Kasese town, 11 km east of the mines [1]. Flotation tailings to the tune of 15 million metric tonnes were dumped in various areas in Kilembe valley in which the fast flowing River Nyamwamba is located [2]. In total there are four tailings dams in the area. The cobaltiferous pyrite wastes and the tailings dams have remained acidic and devoid of vegetation for the last 30 years. The acid mine drainage emanating from these wastes has over the years polluted the nearby ecosystems without any mitigation measures instituted leading to wide spread envi- ronmental pollution in Queen Elizabeth Conservation Area (QECA) [1] and old Kilembe Copper Mining Area. In QECA the acid mine drainage from the wastes scarred and damaged shallow rooted vegetation creating bare ground over a large area, now popularly referred to as the pyrite trail, originally covering a total area of about 150 hectares and a distance of about 11 km to Lake George [1]. Mitigation of the pollutio n most especiall y after closure o f mining areas is still a glo bal challenge mos t espe- cial ly in the de velop ing worl d d ue to the exo rbit ant cost s involve d whe n conve ntiona l techni ques s uch as le ach- ing of pollutant, vitri fication, electro-kinet ic tr eat ment , exca vatio n and off-site treatment a re deployed [3]. Such methods are expensive and technically limited to small areas. Amongst the various strategies adopted for re- moval of toxic heavy metals from the contaminated sites, phytoremediation has emerged as an economical, eco-friendly and aesthetically acceptable technology in the recent years [4]-[10]. It is a technique that in- volves the use of plants and soil microbes for removal and cleaning of pollutants from the soil including heavy metals. Among the plants used in phytoremediation, trees are preferred to the shallow rooted plants because of their ability to treat t he contaminants at gr eater depths, as their roots ha ve the potential to penetrate more deeply into the ground. However, their success largely depends on their establishment and growth performance on sites to be remediated. In this study, one naturalized leguminous tree species Leucaena leucocephala (Lam.) De Wit. (Family Fabaceae), one exotic leguminous tree species Senna siamea (Lam.) H. S. Irwin & Barneby (Family Fabaceae) and one non leguminous fast-growing tree species Eucalyptus grandis W. Hill ex Maid (Family Myrtaceae) were used in the field to assess their gro wth pe rfo rma nce d uri ng the rec lama ti on and red evel op ment of polluted and degraded soils. Selection of the legumes has received justification from recent studies on plant communities of metal contaminated areas. Surveys of plant species surviving in long term heavy metal con- taminated environments have revealed that legumes constitute a dominant portion of the populations in these communities [11], hence having potential for phytoremediation. Eucalyptus grandis is a tree species exhibit- ing great environmental plastic ity, with the ability to gro w in impoverished or marginal soils and to accumu- late high quantities of heavy metals [12] while Senna siamea has been applied as a hyper-accumulator plant for biorem ediat i on of fly ash dumps els ew he re [13]. The three selected tree species have characteristics that were hoped to enhance the phytoremediation of pol- luted and degraded soils. The tree species are locally kno wn to be resistant to draught and ter mites, fast growing and produce vast amount of seeds. Senna siamea and Leucaena leucocephala are legumes capable of enhancing nitrogen fixation, hence improving soil fertility of the nutritionally impoverished tailings and pyrite soils. By gro win g very fa s t t he ne w veg eta ti on c o ver will mi nimiz e soil er o sio n a nd l i xi via ti on of ha z ar d o us hea v y meta l s to aquifers or river systems by controlling direct rainfall impacts on bare soils and promoting the retention of
J. E. Ssenku et al. water within the rhizosphere. Pla nt gro wth re quir e ments ar e ke y co mpone nts t hat de ter mine the gro wth a nd s urvi val of intr od uced tree s [14] in a phytoremediation process. However, mine spoil habitats are nutritionally impoverished; characterized by low nitrogen mineralization rates, low phosphate availability, low soil organic matter, poor soil structure, com- pacted sub-soil, poor drainage and low water holding capacity [15]. Like any other plant species, reduction of soil phytotoxicity is a precondition for growth of legumes on highly metal contaminated sites [11]. Limestone and compost have been reported to improve substrate fertility by increasing plant nutrients and organic matter content, and neutr alizing acidit y [16]. On the basis of being abundant and locally available, limestone and com- post were selected for the study. Limestone was added to neutralize the acidity while compost was to improve upon t he water -holdi ng capacit y and the i mpoverished nutritio nal status of the soils or taili ngs respecti vely. T he main purpo se of soil amendments was initia lly to facilitate the estab lishment of the test trees before growing on their own abilities beyond the treat soil layers. Comparatively, scanty information is available on the response of many woody species commonly used in ecological restoration as compared to the grass species. Similarly, there is no information on the field perfor m- ance of Leucaena leucocephala, Senna siamea and Eucalyptus grandis in the phytoremediation of tailings and mine wastes p olluted soils tha t are character ised with hetero genous di stribution of hea vy metals as in this study area. The aim of t his study was to assess the impact of the treatments on the survival and growth performance of the selected tree species. It was hypothesized that seedli ng establishment a nd survival and growth perfor mance of the experimental tree species d id not vary with site a nd treatment factor. 2. Materials and Methods 2.1. Study Area The study area comprised of the pyrite trail (PT) in QECA located at the geographical coordinates of latitude 0˚8'53.03"N, longitude 30˚4'27.53"E and altitude of 949 meters above sea level and the four tailings dams in the vicinity of Kilembe Town area located at latitude of 0˚11'16.12"N, longitude of 30˚1'11.43"E and altitude of 1243 meters above sea level (Figure 1). The study site experiences a tropical climate wit h rainfall whic h is bi-modally distributed with the wetter pe- riods occurring from March to Ma y and August to November. During the study period from May 2010 to Feb- ruary 2013, the temperatures for pyrite trail site showed minima ranging from 20.1˚ to 17.4˚C and maxima ranging from 29.2˚ to 33.8˚C. Records of temperatures for the Kilembe tailings dams were not available, but being located at higher altitude it was always cooler than the pyrite trail site which lies within the floor of the western arm of the great East African Rift Valley. The tailings dams are flattened at the top, characterised by longitudinal rows of depressions and elevations that were formed during the heaping process and gullies formed as result of water erosion. The flattened top is characterised by very fine polluted powdery soils that are easily transferred into nearby gardens and River Nyamwamba by eolian dispersal during the dry season. The pyrite trail is characterised by bare patches dotted with trees of Acacia gerrardi i Benth and Balanites aegyptiaca (L.) Del. and islets of vegetation composed of Capparis tormentosa Lam., Phytolacca dodecandra L Hérit., Fim- bristyl is ferru gin ea (L.) Vahl, Imperata cylindrica (L.) P. Beauv, Sporobolus pyramidalis P. Beauv., Typha lati- folia L. Cynodon dactylon (L.) Pers. covers most of the regenerated part of the pyrite trail. The surrounding vegetation consists largely of Acacia savannah woodland. 2.2. Experimental Design The study area was categorised into four study sites coded as Kilembe tailing dams site (KTDS), low polluted pyrite trail site (LPP TS), highly polluted pyrite trail site (H PPTS) and unpolluted site ( UPS). The categor isation was based on the results of the geochemical survey of the e ight zones that were mapped out covering the entire study area. A split block experimental design was used with site as a blocking factor and amendment type as a treatment factor categorised into untrea ted (UT) , limestone (LS), c ompost (Co mp) and limestone + compost (LS + Comp) and the tree species grown. 2.3. Establishment of Pilot Restoration Plots A total of 12 restoration and 3 control plots measuring 15 m × 15 m were demarcated in different randomly
J. E. Ssenku et al. Figure 1 . Location of the experimental sites at the tailings dams in Kilembe and the pyrite trail in QECA. selected parts of the control and polluted area. Three plots were established on Kilembe tailings dams, three in the control and nine p lots in the p yrite trail in QEC A. Using hoes and the pick axes where necessary, the soils in the plots were dug up to the depth of 40 cm, and the large hard crumbs crashed to get the finest soil particles possible. Each plot was split into four sub-plots each measuring 7 m × 7 m, separated from each other by one meter (Figure 2(a)). In order to avoid anthropogenic and wild animal interference in the pyrite trail, the plots were fenced off by planting a live fence of Euphorbia trirucalli L. strengthened by reeds and Eucalyptus poles. 2.4. Treatment of Sub-Plot s Like any other plant species, reduction of soil phytotoxicity is a precondition for growth of legumes on highly metal contaminated sites [11]. Therefore, two abundant and locally available treatment materials limestone and compost were selected for the study. Limestone was added to neutralize the acidity while compost was for im- provement of the water holding capacity and the impoverished nutritional status of the soils and tailings. The plo ts at UP S and one o f the four sub-plots in each plot at KTDS, LPPTS and HPPTS were not subjected to any treatment that would res ult in significant change in physico-chemical characteristics except for the initial hoeing. Three treatment types were designed and randomly assigned to the remaining three sub-plots in each plot. One of the sub-plots in each plot at KTDS, LPPTS and HPPTS was treated with limestone at a rate of 2 tons per sub-plot . Anothe r sub -plot was treated with compost at a rate of 1 ton per sub-plot. The r emainin g sub-plot was treated with a mixture of the two amendment materials prepared by thoroughly mixing 0.5 ton of wet compost wit h 1 to n of limestone. T he tre atment ma t erials appli ed were then thoroughly mixed with the residual soil of the sub-plot by overtur ning t hem withi n the sub -plot fo ur times. This was followed b y regular watering to field c a- pacity and allowing the treated pyrite soils and copper tailings to homogenize for a period of one month.
J. E. Ssenku et al. (a) (b) Figure 2 . Design of the experimental plots: (a) Layout of the sub-plots; (b) Planting of the experimental trees. 2.5. Raising and Planting of Seedlings Seeds of Leucaena leucocephala, Senna siamea and Eucalyptus grandis were secured, planted and raised at the nursery beds of the Afforestation and Soil Conservation Project of the Catholic Diocese of Kasese. Fifteen day old healthy seedlings of each species were selected and pure stands of each species planted (Figure 2(b)) in five different plots of which one was selected from the UPS, one from KTDS and the three from LPPTS &HPPTS. 2.6. Physico-Chemical Characterization of Copper Tailings and Pyrite Soil Samples Each time growth parameters were measured in the field, rhizospheric copper tailings and pyrite soils were sam- pled. Their physico-chemical characterisation was done at National Agricultural Research Laboratories (NARL) at Kawanda follo wing standard p rocedures. Soil pH (soil: deionised water = 1:2.5 w/v) was determined using a calibrated pH meter, organic matter content by Walkley-Black potassium dichromate wet oxidation [17] as de- scribed by [18] while total nitrogen was determined by the semi-micro Kjeldahl method [19]. Extraction of available phosphorous and heavy metals was done using Mehlich 3 extractant. In brief, the soil sample was dried in an o ven at 45 ˚C for 48 hours. The dried sample was pulverized to pass through a 2 mm sieve to remove any coarse particles. The sample was then sub-sampled to a very fine powder in a mortar. The dry sample (3 g) was weighed into a 50 ml centrifuge vial and 30 ml of Melich 3 extractant was added. T he mixture was then shaken at 200 rpm for 5 minutes and later left to stand for 10 minutes for settling before centrifuging at 2000 rpm for 5 minutes. The available phosphorous in the extract was determined following Ammonium Molybdate-Ascorbic acid method [20] using a UV/Visible spectrophotometer at 860 nm. The heavy metal concentrations representing largely available concentrations for plant uptake was determined with an atomic absorption spectrophotometer (SHIMADZU AA-6800). 2.7. Determination of Survival Rate and Growth Performance of the Tree Species The survival rate for each species under different treatments at the four sites was monitored throughout the study period. At regular time intervals of 6 months the number of trees surviving in each sub-plot was counted and recorded. The percentage survival of each species under the different treatments was calculated as the number of tree s sur vivi ng b y the e nd o f ea ch sa mplin g pe rio d di vide d by the numb er of tre e see dli ngs pl anted in a s ub-plot (64 see dlings) mult iplied by 100. For growth performance, five trees were selected from each sub-plot and labelled. At regular intervals of six months, stem heights of the labelled trees were measured using common measuring tape [21] while basal di-
J. E. Ssenku et al. ameter was measured slightly above the root collar by using a vernier calliper [22]. Growt h performance of the trees under each treatment was then evaluated as the mean relative growth rates in height (RGRh) and mean rela- tive growth rate in diameter sl ightly above ro ot collar (RGRd) usi ng the for mulae o f classi c growth ana lysis b e- low [22] [23]. 21 log log fh ih ee h RGR tt − = − (1) where: RGRh = heig ht relati ve gro wth rate, loge = the nat ural logarithm, ih = mean height of the seedling at t1, fh = mean height of the seedling at t2 and t2 − t1 = the period between two successive measurements (6 months). 12 log log fd id ee d RGR tt − = − (2) where: RGRd = dia meter relative gro wth rate, loge = the natural logarithm, id = mean diameter of the seedling at t1, fd = mean diameter of the seedling at t2 and t2 − t1 = the period between two successive measurements (6 months). After 18 months of growth, diameter at breast height (dbh) was measured at 4.5ft (137 cm) above ground level using diameter tape (d-tape). Non quantifiable growth features of the trees were regularly observed and recorded. 2.8. Data Ana ly si s Data collected were analyzed using a statistical package R (version 2.13.2) developed by R development Core Team [24], with an additional package lme4 [25]. Prior to any statistical analysis, data distributions were checked for normality and homogeneity of variances. Data with strong deviations from the normal distribution or that were heteroscedastic were log-transformed and analyzed with parametric tests. Variability in means among parameters with data that were both normally distributed and homoscedastic were analyzed with analysis of variance (ANOVA) followed by a post-hoc test (Tukey Honest Significa nt Multiple C ompariso n) with means considered to be significantly different at p ˂ 0.05. Correlation between growth and survival performance and physico-chemical characteristics were explored. A generalised linear mixed model (GLMM) was fitted to ana- lyse variabilit y of so il ph ysico -chemical characteristics and the growth performance of the tree species. For each parameter, the model was tested for normality and homogeneity of variance by the normal (Q-Q) plot and the plot of residuals against fitted values respectively. In case of strong deviations from normality or homoscedas- ticity, data were log-transformed before analysis. 3. Results 3.1. Physico-Chemical Characteristics of Soils The physic o-chemical characteristics of the untreated and treated tailings and pyrite soils are pr esented in Table 1. All the untreated copper tailings and pyrite soils had extremely low pH ranging between 2.96 ± 0.35 - 4.36 ± 0.89, poor nutritional status with re spect to total nitrogen a nd available phosphorous, low or ganic matter content and elevated concentrations of available heavy metals as compared to the unpolluted soils. The pH of the treated soils var ie d wit hi n the ra n ge o f ac id ic to sl ightl y al ka li ne wit h mean va lues r angi ng between 4.33 ± 0.78 - 7.70 ± 0.44 while that of unpolluted soils ranged between 5.88 ± 0.49 - 6.25 ± 0.61. Application of the amendment ma- terials improved the organic matter content most especially for compost and limestone+compost treated soils, available phosphorous and total nitrogen content. Total nitrogen content was generally higher with compost treatment for all the tree species. All the treatments effectively reduced rhizospheric available concentrations of heavy metals for all tree species at all sites. 3.2. Height and Diameter of the Seedlings of the Experimental Tree Species The genotypic characteristics of the seedlings with respect to height and diameter varied significantly (ANOVA, p < 0.05). Regarding dia meter, Leucaena leucocephala had highest diameter of 0.380 ± 0.020 cm, followed by Eucalyptus grandis with mean diameter of 0.256 ± 0.013 cm and lowest in Senna siamea at 0.232 ± 0.019 cm
J. E. Ssenku et al. Table 1. Mean (±SEM, n = 4), pH, organic matter content and concentrations of total nitrogen and available phosphorous and heavy metals in untreated, treated and unpolluted soils. The abbreviation OM, TN and AP denotes organic matter, total nitrogen and available phosphorous respectively. Sit e Tree species Treatment Melich 3 extractable concentratio ns of heav y me t als ( mg· kg−1) pH OM (%) TN (mg·kg−1) AP (mg·kg−1) Cu Co Ni Pb KTDS E. grandis UT 3.73 ± 0.25 3.11 ± 1.08 0.14 ± 0.06 2.46 ± 0.40 14.32 ± 2.38 14.98 ± 2. 89 3. 90 ± 0. 54 2.04 ± 0.12 LS 6.88 ± 0. 91 2.94 ± 0.50 0.13 ± 0.04 17.31 ± 5.43 7.86 ± 1.52 4.68 ± 1.31 0.90 ± 0.35 1.58 ± 0.25 Comp . 5.67 ± 0.89 4.30 ± 0.67 0.23 ± 0.07 70.27 ± 18.43 8.76 ± ± 1.00 5.87 ± 1.16 1.54 ± 0.33 0.89 ± 0.10 LS + Comp 6.61 ± 0.83 3.92 ± 1.33 0.19 ± 0.06 42.71 ± 9.04 9.04 ± 1.85 3.40 ± 0.82 1.25 ± 0.47 0.53 ± 0.15 Senna siamea UT 4.75 ± 0. 82 3.97 ± 1.05 0.20 ± 0.09 10.74 ± 3.63 27.75 ± 3. 31 15. 22 ± 1. 44 4. 00 ± 0. 47 2.53 ± 0.79 LS 7.43 ± 0. 28 4.87 ± 1.06 0.25 ± 0.07 24.92 ± 6.41 9.91 ± 2.02 2.90 ± 0.29 1.17 ± 0.63 0.40 ± 0.09 Comp . 6.40 ± 0.72 6.27 ± 1.62 0.34 ± 0.11 89.67 ± 17.02 9.12 ± 0. 99 6.30 ± 0.73 1.27 ± 0. 51 0.16 ± 0.01 LS + Comp 7.16 ± 0.78 5.99 ± 0.62 0.31 ± 0.07 76.69 ± 10.27 9.11 ± 1. 33 4.56 ± 1.17 2.29 ± 0. 43 0.39 ± 0.16 L. leucocephala UT 4.51 ± 0.39 3.14 ± 0.72 0.15 ± 0.01 1.79 ± 0.16 13.61 ± 4.60 15.65 ± 4. 18 4. 17 ± 0. 52 1.09 ± 0.34 LS 7.83 ± 0. 37 4.51 ± 1.09 0.20 ± 0.06 25.49 ± 11.72 6.22 ± 0. 82 3.47 ± 1.04 2.64 ± 0. 81 0.58 ± 0.12 Comp . 6.70 ± 1.17 5.84 ± 0.89 0.24 ± 0.07 204.00 ± 73.10 7.12 ± 1. 96 1.47 ± 0.19 2.77 ± 0.95 0.63 ± 0.11 LS + Comp 7.56 ± 0.47 5.22 ± 0.97 0.22 ± 0.06 104.06 ± 32.17 9.26 ± 2. 87 3.56 ± 0.055 2.26 ± 0.24 0.79 ± 0.19 LPPTS E. grandis UT 2. 96 ± 0. 35 3.76 ± 0.84 0.14 ± 0.04 21.65 ± 5.98 15.02 ± 1. 98 93. 29 ± 17. 48 10. 09 ± 1. 16 1. 62 ± 0. 32 LS 6.95 ± 0. 76 3.22 ± 0.47 0.16 ± 0.03 30.18 ± 6.67 5.66 ± 1.27 44.70 ± 8.23 4.29 ± 1.56 0.54 ± 0.10 Comp . 4.33 ± 0.78 9.16 ± 1.19 0.33 ± 0.11 125.61 ± 27.16 6.43 ± 1. 40 36.78 ± 3.12 5.57 ± 1.47 0.38 ± 0.12 LS + Comp 6.75 ± 0.68 5.25 ± 0.73 0.22 ± 0.06 63.97 ± 19.41 7.10 ± 1. 57 35.67 ± 5.59 4.93 ± 1.15 0.37 ± 0.09 Senna siamea UT 2.99 ± 0. 56 5.15 ± 1.33 0.25 ± 0.08 26.28 ± 5.07 12.43 ± 1. 35 88. 48 ± 14. 27 15. 88 ± 2. 33 1. 62 ± 0. 24 LS 6.92 ± 0. 71 5.16 ± 1.79 0.26 ± 0.06 37.86 ± 12.43 6.95 ± 1. 70 28.82 ± 5.75 3.69 ± 0.62 0.43 ± 0.10 Comp . 4.53 ± 0.36 9.18 ± 1.50 0.37 ± 0.14 139.38 ± 31.21 5.12 ± 1. 93 53.10 ± 8.33 6.30 ± 1.65 0.69 ± 0.02 LS + Comp 6.50 ± 0.65 6.26 ± 1.77 0.27 ± 0.07 64.63 ± 17.54 7.68 ± 1. 29 33.42 ± 2.48 2.64 ± 0.57 0.71 ± 0.21 L. leucocephala UT 4.36 ± 0.89 1.36 ± 0.18 0.09 ± 0.02 5.02 ± 0.49 16.18 ± 3.53 49.70 ± 11. 6 13. 22 ± 3. 49 1. 75 ± 0. 21 LS 7.58 ± 0. 37 1.56 ± 0.30 0.09 ± 0.03 18.26 ± 3.54 7.20 ± 1.38 10.65 ± 1.11 6.29 ± 0.96 0.51 ± 0.10 Comp . 6.94 ± 1.13 4.31 ± 0.59 0.25 ± 0.07 157.76 ± 25.57 4.83 ± 0. 98 9.21 ± 0.81 4.96 ± 1. 61 0.42 ± 0.06 LS + Comp 7.57 ± 0.39 1.84 ± 0.15 0.21 ± 0.06 78.19 ± 10.34 6.22 ± 1. 00 5.92 ± 0.66 6.40 ± 2. 00 0.51 ± 0.13 HPPTS E. grandis UT 3. 26 ± 1. 00 1.80 ± 0.19 0.11 ± 0.05 9.31 ± 2.92 37.65 ± 8.89 125.11 ± 25. 01 29.20 ± 9.04 2.46 ± 1. 09 LS 7.02 ± 0. 33 1.89 ± 0.25 0.13 ± 0.04 38.04 ± 3.50 7.17 ± 1.01 36.78 ± 4.96 3.91 ± 1.86 1.13 ± 0.27 Comp . 6.83 ± 0.67 4.36 ± 0.80 0.17 ± 0.06 280.17 ± 51.66 5.83 ± 1. 34 18.63 ± 1.39 7.82 ± 2.74 0.48 ± 0.13 LS + Comp 7.02 ± 0.55 3.77 ± 0.13 0.17 ± 0.05 172.75 ± 28.56 7.92 ± 1. 69 21.81 ± 0.53 4.69 ± 1.62 0.75 ± 0.23 Senna siamea UT 3.39 ± 1. 22 1.50 ± 0.15 0.09 ± 0.01 12.29 ± 3.03 40.58 ± 7. 58 107. 89 ± 19. 76 9.78 ± 3.08 1.26 ± 0.14 LS 7.37 ± 0. 56 1.59 ± 0.18 0.21 ± 0.06 13.95 ± 3.25 14.76 ± 4. 04 15. 09 ± 4. 96 2. 80 ± 0. 70 0.76 ± 0.17 Comp . 4.60 ± 1.21 4.01 ± 0.36 0.15 ± 0.04 127.88 ± 14.58 18.75 ± 1. 80 31. 62 ± 5. 95 3. 22 ± 0. 96 0.81 ± 0.11 LS + Comp 7.30 ± 0.72 1.63 ± 0.14 0.13 ± 0.04 41.16 ± 8.42 11.84 ± 2. 26 29. 32 ± 8. 77 3. 66 ± 0. 93 0.73 ± 0. 16 L. leucocephala UT 4.50 ± 0.81 1.57 ± 0.17 0.11 ± 0.02 20.13 ± 3.27 36.14 ± 6. 92 72. 19 ± 12. 62 10. 42 ± 0. 66 1. 36 ± 0. 14 LS 7.70 ± 0.44 2.21 ± 0.31 0.13 ± 0.01 36.11 ± 5.17 6.94 ± 1.98 11.69 ± 2.46 2.53 ± 0. 74 1.09 ± 0.27 Comp . 6.64 ± 0.81 4.42 ± 0.80 0.17 ± 0.03 125.56 ± 22.46 7.06 ± 1.06 11.19 ± 3.56 3. 72 ± 1. 01 0.63 ± 0.15 LS + Comp 7.55 ± 0.64 2.24 ± 0.37 0.14 ± 0.03 80.82 ± 16.97 10.35 ± 2.66 12.92 ± 2.79 2. 58 ± 0. 68 0.72 ± 0.19 Unpolluted E. grandis 6.24 ± 0.61 9.83 ± 1.93 0.39 ± 0.08 40.92 ± 4.45 4.25 ± 0. 77 4.50 ± 0.96 2.5.71 ± 0. 06 0.28 ± 0.03 Senna siamea 6.24 ± 0. 56 9.04 ± 1.12 0.37 ± 0.04 42.70 ± 4.47 4.09 ± 0.42 4.65 ± 0.14 2.96 ± 0. 01 0.15 ± 0.04 L. leucocephala 5.88 ± 0. 49 9.84 ± 1.92 0.39 ± 0.09 50.69 ± 6.75 5.54 ± 0. 66 5.04 ± 0.11 3.00 ± 0.19 0.18 ± 0.01
J. E. Ssenku et al. (Figure 3). Seedling dia meter was significantly higher in Leucaena leucocephala than in the other two species (Tukey’s test, p < 0.05), but there were no significant differences between those of Eucalyptus grandis and Senna siamea (Tuke y’s test, p > 0.05). Eucalyptus grandis seedling height was the highest at 24.88 ± 1.370 cm, followed b y that of Leucaena leucocephala at 11.20 ± 0.255 cm and lowest in Senna siamea at 6.90 ± 0.210 cm. The mean seedling height of each species significantly differed from each other (Tuke y’s t est, p < 0.05). 3.3. Final Diameter and Height Attained by the Trees after 18 Months of Growth Assessment of species growth performance was based on diameter and height attained at a particular time and site and their respective relative growth. For Eucalyptus grandis the diameters ranged between 2.88 ± 0.85 cm for the untreated sub-plot at the HPPT S to 10.26 ± 1.72 cm for the limestone + compost sub-plot at the LPPT S (Table 2). Eucalyptus grandis trees grown in the compost, limestone + compost sub-plots at all sites and lime- stone subplot at LPPTS had relatively higher diameters in the range of 4.18 ± 0.29 cm to 6.98 ± 0.83 cm as compared to those grown in the limestone treated sub-plots at KTDS and HPPTS with diameter of 4.18 ± 0.29 cm and 6.98 ± 0.83 cm respectively. With the exceptional case of trees grown in the limestone treated sub-plots at KTDS, all the trees grown in the amended sub-plots at all sites performed better than the trees grown in the E. grandisS. siameaL. leucocephala Height (cm) 0 5 10 15 20 25 30 E. grandisS. siameaL. leucocephala Diameter (cm) 0.0 0.1 0.2 0.3 0.4 0.5 aa b a b c (i) (ii) Figure 3 . (i) Mean hei ght and (i i) basal d iameter o f the seedlin gs (n = 10). B ars follo wed by dif ferent l etter in each case are significantly different (Tukey, p < 0.05). Error bars denote SEM. Table 2. Mean diameters and heights attained by the tree species under different treatments at the different sites after 18 months of growth. Site Treatment Eucalypt us g randis Senna siamea Leucae na glauca Dia met er Hei gh t Dia m et er Hei gh t D i am et er Hei g h t KTDS Unt rea t ed 3.68 ± 0. 2 8c 159.80 ± 48.3c 3.72 ± 0. 13c 146.60 ± 28.05c 2.62 ± 0. 3 5d 141.20 ± 26.84e Limestone 4.18 ± 0. 29c 180.00 ± 35.64c 5.60 ± 0. 6 2c 334.80 ± 26.78c 5. 78 ± 0.5 1ce 454 .20 ± 33.03d Compost 9.60 ± 0. 9 9d 722.80 ± 66.63ad 8.16 ± 0. 54d 503 .00 ± 47.64ad 6.10 ± 0. 9 0ce 344.60 ± 19.38bc LS+C o m p . 9.62 ± 0.6 1d 753 .80 ± 36.16ad 7.98 ± 0. 7 9d 543.00 ± 21.82ad 6.48 ± 0. 49e 384.40 ± 35.28bd LPP TS U n t rea t ed 3.93 ± 1. 0 5c 234.00 ± 60.11c ** ** 2.38 ± 0. 6 1d 8 1 . 2 0 ± 8. 35f Limestone 9.20 ± 0. 47ad 773.20 ± 16.50d 5.32 ± 0.7 0 ad 202.80 ± 23 .15d 6.16 ± 0. 75ce 321.00 ± 27 .78ab Compost 8.27 ± 0. 2 5bd * 6.78 ± 0.91bd 293 .60 ± 16.59be 4.88 ± 0.86c 271.40 ± 39.94a LS+C o m p . 10.26 ± 1. 72d 847.20 ± 128.89d 6.32 ± 0. 5 3d 293.00 ± 27.26d 6.54 ± 1. 29e 385.60 ± 26.02bd HPPTS Unt r eat ed 2.88 ± 0. 8 5c 157.75 ± 50.86c 3.05 ± 0.80c 101.50 ± 20.47c 4.60 ± 0. 56ad 188.33 ± 14.84a Limestone 6.98 ± 0. 8 3b 467.40 ± 87.31b 3.39 ± 0.7 4b 109.20 ± 20.39b 4.88 ± 0.7 5abc 298.20 ± 22.02ab Compost 8.60 ± 1. 1 0ad 714.20 ± 11.34ad 4.50 ± 0. 7 3ad 145.00 ± 26.94ad 5.13 ± 0. 49bc 270.00 ± 09.16ac LS+C o m p . 7.72 ± 0. 8 2ab 577.60 ± 38.36 ab 5.23 ± 0. 97ab 225.25 ± 32.02ab *** *** Unpolluted. 6.32 ± 0. 3 4b 501.80 ± 22.12b 6.24 ± 0.27 b 471.80 ± 24.95b 5.16 ± 0.64ce 310.00 ± 10 .00ab Values a re means ± SEM (n = 5). Means with different letters withi n the columns for a particula r species and site indicate si gnifi cant di fferen ce b e- tween va lues; Tuke y’s test , (P < 0.05). *Mis sing valu es due t o destructi on of the sub -plot b y buffalos; **Mi ssing va lues due to survi val; ***Mis sing value due to attack by Uganda Kob.
J. E. Ssenku et al. unpolluted site with resp ect to d ia meter. H ei ght fo r Eucalyptus grandis ranged from 157.75 ± 50.86 cm for trees grown in the untreated sub-plot at HPPTS to 847.20 ± 128.89 cm for the trees grown in limestone + compost sub-plot at LPPTS. Apart from the trees grown on the limestone treated sub-plot at KTDS and HPPTS, all the trees in the treate d plots were sig nificantly taller than those gro wn in the unpolluted site (Tuke y’s test, p < 0.05). For Senna siamea diameter range was in the order of 3.05 ± 0.80 in the untreated sub-plot s at HPP TS to 8 .16 ± 0.54 cm in the compost treated sub-plots at KTDS. Senna siamea trees grown in the compost, limestone + compost at KTDS and LPPTS had significantly wider diameters than the rest of the trees in untreated and treated sub-plots and at the unpolluted site (Tukey’s test, p < 0.05). Height was in the range of 101.50 ± 20.70 cm to 543.00 ± 21.82 cm in the limestone + compost sub-plot at KTDS. It is only trees grown in the compost and limestone +compost sub-plots at KTDS that were significantly taller than those grown at the unpolluted site (Tukey’s tes t, p < 0.05). In the case of Leucaena leucocephala, diameter was in the range of 2.38 ± 0.61 cm in the untreated sub-plots at LPPTS to 6.54 ± 1.29 cm at the same site. It is only trees grown on compost and limestone + compost sub- plots at KTDS and LPPTS that had significantly higher diameters than trees grown at the unpolluted site (Tu- key’ s test, p < 0.05). Heights ranged fro m 81.20 ± 8.35 cm for trees grown on the untreated sub-plot at LPP TS site to 385.60 ± 26.02 cm for trees grown on limestone + compost sub-plot at the same site. Among the trees gro wn on t he tr eate d s ub-plots it was only tree s gro wn on compo st and lime stone + compo st; and limesto ne and limestone + compost sub-plots at LPPTS that were significantly taller than those grown at the unpolluted site (Tukey’s tes t, p < 0.05). Means for species:treatment effect extracted from the model for the entire growth period show Eucalyptus grandis with the highest a verage height and dia meter that considerably varied among the treatment (Figure 4). Mean average height attained by Eucalyptus grandis for the different treat ments wa s in the or der of li mestone + compost > compost > limestone > untreated while for average diameter was in the order of co mpost > limestone + compost > limestone > untreated. Mean average height and diameter attained for Senna siamea and Leucaena leucocephala were within the same range with minimal variations across treatments. 3.4. dbh of the Three Tree Species after 18 Months of Growth Results of dbh after 18 months of growth are presented in Figure 5. Eucalyptus grandis dbh ranged between 1.10 ± 0.43 cm for trees grown on the untreated soil to 7.34 ± 1.43 cm for trees grown on limestone + compost treated pyrite soils at the LPPTS. The latter trees and those grown on limestone treated soils at LPPTS had Figure 4. M eans and respecti ve 95% co nfiden ce interval s extracted from th e model for Species :Treatment e ffect on avera ge height , average diameter, RGBh and RGRd. The symbols , , , and represent Compost, limestone + compost, limestone, and un treated respectively. 0100 30050 A.Height(cm) S.siamea E.grandisL.leucoc 0.00 0.10 0.20 0 .3 R GRH(c m/c m/ S.siamea E.grandisL.leucoc 1234567 A .Diame te r(c m S.siamea E.grandisL.leucoc 0.0 0.10.2 0.3 RGRD(cm/cm S.siamea E.grandisL.leucoc
J. E. Ssenku et al. Unpolluted KTDS LPPTS HPPTS dbh (cm) 0 1 2 3 4 5 6 7 Unpolluted KTDS LPPTS HPPTS dbh (cm) 0 1 2 3 4 5 Unpolluted Untreated Limestone Compost Limestone+compost Senna siamea Leucaena leucocephala aab dd c ab bb ab c abc ae abc e bd cd be cd d Unpolluted KTDS LPPTS HPPTS dbh (cm) 0 2 4 6 8 10 b dd ab ac d a a bc d b ab bc Eucalyptus grandis Figure 5. Mean dbh (n = 5) of each tree species attained after 18 months of growth at different sites and treatment. Bars followed by different letters for a particular species are significantly different (Tukey’s, p < 0.05). Some bars are missing owing to failure of trees for a particular treat ment to reach dbh measurable heigh t. significantly higher dbh than those grown on the unpolluted soils. For Senna siamea dbh was in the range of 1.07 ± 0.208 cm for the untreated tailings to 5.40 ± 0.628 cm in the limestone + compost tailings bo th at KTDS. Trees grown on the limesto ne + compost treated soils had s ignificantly higher dbh than those grown at the un- polluted site (T uke y’s test, p < 0.05). Senna siamea trees gro wn on untreated p yrite soils at LP PT S and HPPTS, and compost treated pyrite at HPPTS and Leucaena leucocephala trees grown on untreated soils and soils treated with lime stone + compost at HPPTS had not reached the height of 4.5 ft above the ground at which dbh measurements were taken and were therefore taken to be 0 cm. Leucaena leucocephala trees grown on lime- stone and li mestone + compost treated soils at KTDS had significantly hi gher diameter than those grown o n the unpolluted so ils. 3.5. Relative Growth Rate Performance of the Tree Species Results of relative gro wth due to dia meter RGRd and hei g ht RGRh are presented in Table 3 . Relative growth rate was higher for all the species in the first month of growth but later declined to the lowest rates in the last six months of growth. A similar trend was observed for the trees gro wn on unpolluted soils. Site did not have sig- nificant effect on both RGRd (χ2 = 0.19, df = 2, p > 0.05) and RGRh (χ2 = 6.77, df = 2, p > 0.05) Table 4. Simi- larly both RGRh and RGRd did not vary significantl y across tr ee species (χ2 = 0.07, df = 2, p > 0.05) and (χ2 = 0.14,
J. E. Ssenku et al. Table 3. Variation of RGDd and RGDh (cmcm−1month−1) of the tree species with ti me under differen t treatments at t he dif- ferent sites. Site Spec i es Treatment 6 Map 12 Map 1 8 Map RGDd RGDh RGDd RGDh RGDd RGDh KTDS E. gra ndis Un treated 0.200 ± 0. 021a 0.122 ± 0.179 a 0.172 ± 0.016 a 0.148 ± 0.036a 0.0 72 ± 0.017 a 0.0 36 ± 0.011 ab Limestone 0.254 ± 0.045b 0. 192 ± 0.044b 0.130 ± 0.034 ab 0.1 10 ± 0.059 a 0.082 ± 0. 041a 0.029 ± 0. 016a Compost 0.438 ± 0. 02 6c 0.374 ± 0.036c 0.120 ± 0.031b 0.132 ± 0.01 6a 0.048 ± 0.010 a 0.056 ± 0. 017b LS + C omp 0.4 20 ± 0.014c 0.380 ± 0.029c 0.126 ± 0.011b 0.1 24 ± 0. 019a 0.0 57 ± 0.025 a 0.0 65 ± 0.028 ab Sen a si am ea Untre at ed 0.314 ± 0.050a 0.408 ± 0.013a 0.122 ± 0.035 a 0.062 ± 0. 018a 0.0 30 ± 0.016 a 0.035 ± 0.019a Limestone 0.332 ± 0.060 a 0.456 ± 0. 029b 0.160 ± 0.024 a 0.136 ± 0.026b 0.0 43 ± 0.020 a 0.0 55 ± 0.013 ab Compost 0.386 ± 0. 051a 0.510 ± 0.019c 0. 146 ± 0. 035a 0.152 ± 0. 013b 0. 062 ± 0.021 a 0.0 54 ± 0.013 ab LS + C omp 0.3 62 ± 0.028 a 0.498 ± 0.016a 0.1 66 ± 0.009a 0. 1 66 ± 0.011b 0.065 ± 0. 021a 0.065 ± 0. 012b L . leuc oc epha la Untreated 0.198 ± 0.043a 0.372 ± 0. 028a 0.0 96 ± 0.029a 0.014 ± 0. 005a 0.0 28 ± 0.019a 0.033 ± 0.018a Limestone 0.306 ± 0.025b 0. 468 ± 0.022b 0.1 02 ± 0.016a 0.058 ± 0. 013bc 0.044 ± 0.007 a 0.084 ± 0. 015b Compost 0. 2 62 ± 0.031b 0. 450 ± 0.012b 0.1 20 ± 0.030a 0.0 48 ± 0.019b 0.0 80 ± 0.017b 0. 0 73 ± 0.024b LS + C omp 0.2 78 ± 0.015b 0. 4 40 ± 0.007b 0.114 ± 0.018 a 0. 0 84 ± 0.017c 0.082 ± 0.023b 0. 068 ± 0.018b LPPTS E. grandis Untreated 0.134 ± 0. 077a 0.098 ± 0. 019a 0.1 60 ± 0.079a 0.093 ± 0. 064a 0.0 85 ± 0.032a 0.105 ± 0.050a Limestone 0.265 ± 0.061b 0. 239 ± 0.044b 0.1 59 ± 0.040a 0. 1 02 ± 0.043ab 0.0 54 ± 0.010 ab 0.0 73 ± 0.021 a Compost 0.386 ± 0. 04 0c 0.319 ± 0.070c 0.1 49 ± 0.042a 0.1 63 ± 0.052b 0.0 29 ± 0.008a - L + Comp 0.3 91 ± 0. 039c 0.3 77 ± 0.042c 0.1 11 ± 0. 027a 0.070 ± 0.029a 0.073 ± 0. 015b 0.0 85 ± 0.027a Senna siamea Untreated 0.104 ± 0.055a 0.160 ± 0. 031a - - - - Limestone 0.302 ± 0.024b 0. 306 ± 0.017b 0.138 ± 0.019 ab 0.1 20 ± 0.028 a 0.0 82 ± 0.012b 0.139 ± 0.017a Compost 0. 3 46 ± 0.031b 0.392 ± 0.029c 0.170 ± 0.007a 0. 1 84 ± 0.017b 0.046 ± 0. 018a 0.053 ± 0. 016b LS + C omp 0.3 70 ± 0.049b 0.400 ± 0.020c 0.118 ± 0. 044b 0.148 ± 0. 025ab 0.0 63 ± 0.013 a 0.077 ± 0.011b L . leuc oc epha la Untreated 0.188 ± 0.047 a 0.282 ± 0.024a 0.0 74 ± 0.036a 0.020 ± 0.012 a 0.041 ± 0.013a 0.024 ± 0. 007a Limestone 0.210 ± 0.044 a 0.382 ± 0. 013b 0.170 ± 0. 035b 0.0 92 ± 0.008b 0.0 85 ± 0.020a 0.081 ± 0.004b Compost 0.2 22 ± 0.045 ab 0. 3 86 ± 0.025b 0.170 ± 0. 037b 0.1 02 ± 0.065b 0.0 29 ± 0.010a 0.041 ± 0.019 a LS + C omp 0.3 06 ± 0.054b 0.4 50 ± 0.024 ab 0.1 30 ± 0.023 ab 0.0 96 ± 0.011b 0.0 38 ± 0.011a 0.043 ± 0. 019a HPPTS E. grandis Unt re ated 0.184 ± 0. 077a 0.098 ± 0. 011a 0.1 60 ± 0.079a 0.094 ± 0.014a 0.057 ± 0. 039a 0.094 ± 0.008a Limestone 0.265 ± 0.061b 0. 239 ± 0.044b 0.1 59 ± 0.040a 0. 1 02 ± 0.043ab 0.0 79 ± 0.038 a 0.098 ± 0.014a Compost 0.386 ± 0. 04 0c 0.319 ± 0.070c 0.1 49 ± 0.042a 0.1 63 ± 0.012b 0.0 49 ± 0.023a 0. 0 56 ± 0.023b LS + C omp 0.3 91 ± 0.039c 0.3 77 ± 0.041 0.111 ± 0. 027a 0.070 ± 0. 001a 0.0 40 ± 0.022a 0.046 ± 0.019b Senna siamea Unt re at ed 0.150 ± 0.023a 0.152 ± 0.026a 0.236 ± 0.018 a 0.242 ± 0. 016a 0.0 64 ± 0.022 a 0.042 ± 0.027a Limestone 0.264 ± 0.056b 0. 268 ± 0.027b 0.144 ± 0.049b 0.1 64 ± 0.038b 0.0 65 ± 0.032a 0.029 ± 0.011a Compost 0.2 40 ± 0.014 ab 0. 2 85 ± 0.007b 0.2 25 ± 0.091 ab 0.1 75 ± 0.078 ab 0.0 47 ± 0.029 a 0.043 ± 0.007a LS + C omp 0.2 83 ± 0.005b 0. 3 13 ± 0.005b 0.1 60 ± 0.000 ab 0.1 80 ± 0.036 ab 0.0 48 ± 0.013 a 0.035 ± 0.002a L . leuc oc epha la Untreated 0.135 ± 0.049 a 0.2 75 ± 0.064 ab 0.1 95 ± 0.049 a 0.105 ± 0.064a 0.0 45 ± 0.011a 0.035 ± 0. 026a Limestone 0.200 ± 0.058ab 0.220 ± 0.072b 0. 167 ± 0.048 a 0.200 ± 0.069a 0.0 43 ± 0.029 a 0.036 ± 0.023a Compost 0. 2 32 ± 0.026b 0.384 ± 0. 018a 0.1 50 ± 0.021 a 0.145 ± 0.019a 0.0 28 ± 0.003 a 0.095 ± 0.021b LS + C omp 0.171 ± 0.025a 0.233 ± 0.048b 0. 214 ± 0.023 a 0.176 ± 0.046a - - Unpolluted E. grandis 0.3 90 ± 0.008 0.352 ± 0. 007 0.1 08 ± 0.00 5 - 0.0 37 ± 0. 014 - Senna siamea 0. 3 90 ± 0.016 0.4 58 ± 0.012 0.1 16 ± 0.007 0.1 30 ± 0.078 0.0 45 ± 0. 009 0. 119 ± 0.024 L. leucocephala 0.1 46 ± 0.027 0.160 ± 0.0147 0.153 ± 0.020 0.397 ± 0.003 0. 107 ± 0.060 0.071 ± 0. 005 Values a re means ± SEM (n = 5). Means with different letters withi n the columns for a particula r species and site indicate significant di fference be- tween values; Tukey’s test, (p < 0.05).
J. E. Ssenku et al. Table 4. S urvival p er fo rmance of t he tree species und er different treatments with ti me at the differen t study sites. Eucalyptus grandis Senna siamea Leuc aena leuc oc e p hala Tim e Ti m e Ti m e Site Treatment 6 Map 12 Map 18 Map 6 Map 12 Map 1 8 Map 6 Map 1 2 Map 18 Map KTDS Un t rea t ed 100.00 59.38 43.75 96.88 76.56 43.75 90.63 65.63 39.06 Limestone 98.44 75.00 71.88 89.06 71. 88 67.19 97.69 92.19 90.63 Comp ost 100.00 79.69 78.13 100.00 95.31 93.75 95.31 92.19 92.19 LS + comp. 98.44 84.38 76.56 98.44 92.19 92.19 92.19 78.13 78.13 LPP TS U n tr ea t ed 3 7.50 12.50 3.57 87.50 51.56 0.00 46.94 2.04 2.04 Limestone 92.86 33.30 33.30 100.00 91.84 85.71 77.55 51.02 48.98 Comp ost 71.43 67.86 66.07 100.00 69.39 67.35 77.55 44.90 44.90 LS + comp. 87.76 87.76 81.63 93.88 67.35 67.35 91.84 85.71 83.67 HPPTS Unt rea t ed 51.56 7.81 1.56 63.27 44.90 14.29 12.24 4.08 2.04 Limestone 84.38 62.50 59.38 89.29 44. 90 44.90 28.57 18.37 18.37 Comp ost 95.92 81.63 73.47 45.24 11.90 7.14 53.03 36.73 32.65 LS + comp. 95.92 71.43 69.39 66.67 35.71 35.71 18.37 10.20 10.20 Unpolluted 81.97 N/A 69.30 93.47 93.47 90.95 51.76 51.76 56.25 N/A—No record ta ken after destru ction by Buffalos. Map denotes month after planting. df = 2, p > 0.05) respectively, but significantly varied across treatments (χ2 = 18.75, df = 3, p < 0.001 ) a nd (χ2 = 26.37, df = 3, p < 0.001). Relative growth for all the tree species grown on untreated soils remained lower than that of the trees grown on the unpolluted a nd treated co pper tailings and pyrite soils. 3.6. Survival Performance of the Tree Species Survival performance for all species was remarkably poor on untreated soils at all sites ranging between 1.56% at HPPTS to 43.75 at KTDS for Eucalyptus grandis; 0.00% at LPPTS to 14.29% at HPPTS for Senna siamea and 2.04% at LPPTS and HPPTS to 39.06% at KTDS for Leucaena leucocephala (Table 4). Survival of the three tree species on treated soils was generally high ranging between 33.30% on limestone treated soils at LPPTS to 78.13% on compost treated soils at KTDS for Eucalyptus grandis; from 7.14% on compost treated soils at HPPTS to 93.75% on compost treated soils at KTDS and 10.20% on compost treated soils at HPPTS to 92.19% on compost treated soils at KTDS. At HPPTS the survival performance of Senna siamea on treated soils was lo wer than that for the trees of the same species grown on untreated soils at both KTDS and HPPTS. Sur- vival performance of the tree species was significantly affected by site and treatment (χ2 = 6.76, df = 2, p < 0.05) and ( χ2 = 26.37, df = 3, p < 0.001) respectively, but did not vary significantly across the tree species (χ2 = 0.14, df = 2, p > 0.05). 3.7. Site, Treatment and Time Effects on the Growth Performance and Survival Performance of the Tree Species Results of the model test showed that variation in average height, average diameter, RGRh, RGRd and survival were significant due to time and treatment (Table 5) (p < 0.05). Variation in average height and survival per- formance of the tree species due to site was significant (p < 0.05 and p < 0.001 respectively) but on the other hand not sta tisticall y significa nt with re spect to a verage dia meter, RGRh and RGRd (p > 0.05). Apart from RGRh
J. E. Ssenku et al. Table 5. Significance tests of Time, Site, Species and Treatment and their interactions on Average height, Average diameter, RGRh, RGRd and Survival performance by the model. Factors Av. height Av. di ameter RGRh RGRd Survival Tim e *** *** *** *** *** Site * NS NS NS *** Tree species *** *** NS NS *** Trea t men t *** *** *** *** ** Sit e:S p eci es NS NS NS NS *** Sit e:Tr ea t men t NS NS NS NS NS Spec i es: Tr eam en t NS NS NS NS NS Spec i es: Tim e NS NS NS * NS Level of significance: ***p < 0.001, **p < 0.01, *p < 0.05 and NS (not signifi cant), p > 0.05. and RGRd all the other parameters varied significantly amongst the three tree species (p < 0.05). Interactive ef- fects of Species:Treatment and Site:Treatment had no significant effect on all parameters while Site:Species and Species:Time had significant effects on only survival and RGRd respectively (p < 0.05). 3.8. Relationships between Growth and Survival Performance and Soil Physico-Chemical Characteristics Computation of correlation coefficients showed that pH, organic matter, available phosphorous and total nitro- gen were positively correlated with all the growth performance parameter and survival performance as sho wn in Table 6. pH had a significant positive correlation with height, RGRh, RGRd and survival (p < 0.05) but with basal dia meter the corr elation was not si gnifican t (p > 0.05). Soil orga nic matter co ntent was positi vely and si g- nificantly correlated with basal diameter, height and survival (p < 0.05) but had an insignificant positive correla- tion with relative growth rate (p > 0.05). Pho sphor ous had si gnif icant p osit ive cor relat ion wit h only RGRh and surviva l while total nitro gen correlation was not only significant with basal diameter. Heavy metals had negative correlations with some parameters. Copper had significant negative correlation with basal diameter and height (p < 0.05) but on the contrary had significant po sitive correlati on with r elative growth a nd surviva l per formance (p < 0.05 ). Cobal t had a ne gative correlation with survival that was not significant and insignificant positive correlation with RGRh, height, and basal diameter. It was only positively and significantly correlated with RGRd. Nickel had significant positive correlation with relative growth rate and insignificant negative correlation with all the other parameters. Lead was positively and significantly correlated with relative growth rate (p < 0.01) but positively and not signifi- cantly correlated with survival. Its correlation with height and basal diameter was negative. 3.9. Observable Growth Features Field observations were made on growth features of the tree species under different treatments. Eucalyptus grandis grown on untreated soils had developed chlorotic purple leaves. Such leaves were not observed in Eucalyptus grandis growing on unpolluted soils but occasionally occurred in some pockets of treated soils. Fo- liage density was observed to be very high in the ea rl y sta ges of growth for the tree s grown on treated so ils most especiall y for compost and limesto ne + co mpost treated soils but relative ly lower for thos e gro wn on unpolluted soils. The tr e e s maintained their foliage b oth in dry and wet seaso ns. Senna siamea grown on untreated soils also developed chlorotic yellow leaves which were totally not observed on the trees grown on unpolluted soils but occasionally occurred on trees grown on treated pyrite and tailings. Foliage density was remarkably higher for trees gro wn on treated tailin gs at KT DS and unpolluted soils, lo wer for p lants gro wn on t reated pyrite so ils and very low on untreated soils. Symptoms of chlorosis were not observed in Leucaena lecocephala but there were fluct uatio ns in folia ge densi t y with more lea ves l ost d uri ng the dr y seaso n. R oot ing p atte rn va rie d with ti me a nd site.
J. E. Ssenku et al. Table 6. Correlation coefficients (r) between soil physico-chemical characteristics and growth and survival performance para meters. Para m et er pH OM P N Cu Co Ni Pb Basal diam e te r 0.06NS 0.23* 0.16NS 0.07NS −0.32 ** 0.06NS −0.09NS −0.4 1 ** Heigh t 0.22* 0.21* 0.11NS 0.19* −0.18 * 0.05NS −0.10NS −0.18 NS RGRd 0.27** 0.04NS 0.12NS 0.33** 0.45** 0.20* 0.37** 0.35** RGRh 0.29** 0.11NS 0.20* 0.34** 0.44** 0.14NS 0.29* 0.35** Survival 0.30** 0.54** 0.46** 0.38** 0.37** −0.17NS −0.003NS 0.13NS NS = not significant, *level of signi ficance: p < 0.05, **level of significance: p < 0.01. The tap root was still positively geotro pic for all the species at KTDS and treatment but at LP PT S and HPPT S the tap roots had turned out to be negatively geotropic. Secondary roots were thin in untreated soils and thick in treated soils growing super ficially. Nodulation was species specific occurring only on roots of Leucaena leuco- cephala and absent on roots of Senna siamea and as expected on roots of Eucalyptus grandis. Nodulation was only observed on young roots of Leucaena leucocephala grown on unpolluted soils and treated pyrite and tail- ings but not in the untreated pyrite and co pp er tailings. Des pite insecticid al pr op erties o f Leucaena leucocephala, it was prone to a tta c k by small insects that fed on the tips. 4. Discussions Growth performance of plant species is a consequence of multitude of factors comprising of among others cli- matic factors, so il (substrate) physico-c hemical characteristics and genetic potential. Seedling height and diame- ter for the three species differed significantly despite being raised under the same environmental settings. The three species be long to different gener a and families in case of Eucalyptus grandis and most likely p ossess di f- ferent genetic potentials for expression of the characters. Growth and establishment of the three tree species on untreated soils was extremely poor. Even Eucalyptus grandis with pro ven environmental pla sticity, its ability to gro w in i mpove ri s hed o r mar g i nal soil s and abilit y to a ccum ulate hig h qua ntities o f heavy metal s [12], co ul d not cope up especially at LPPTS and HPPTS. Generally, the failure of the three species to grow and establish themselves could partly be due to extremely acidic pH range of 2.96 to 4.36 that was characteristic of the untreated soils and far below the pH range of 6.0 - 7.0 that is ideal for growth of many plant species [26]. At such pH ranges growth is also adversely affected due to increased metal toxicities such as magnesium or manganese and reduced population of nitrogen fixing bacte- ria [27]. Acco rd ing to [28], at a pH of 2.4 there is a high mobility of ele ments s uch a s Zn, C u, Fe a nd Mn whic h become phytotoxic and adversely affect growth. In the current study higher availability of Cu, Co, Ni and Pb were observed (Table 2), in untreated soils as compared to unpolluted and treated soils. T he availability of Cu, Ni and Pb could have had an adverse effect as depicted by correlation results with basal diameter and height (Table 5). The reduction in nitrogen fixing bacteria might be responsible for the absence of nodulation in Leu- caena leucocephala growing on untreated soils. Poor growth and hindrance of nodulation of Leucaena leuco- cephala has also been reported in soils with low soil pH lower than 5.5 [29] while best growth occurs in soils with pH from 6.0 to 7.5 [30] which were characteristic of limestone and limetone + compost treated soils. In this study relative growth rate was adopted for inter-specific comparison of the tree species due to their significant differences in average height and diameter among the seedlings [31]. Both RGR h and RGRd did not vary significantly across species (p > 0.05) and site but vari ed significantly with treat ment and time (p < 0.05). This implies that the treatments were effective regardless of species and site. T he signific ant variatio n with time may be ascribed to the usual pattern of growth followed with time, entailing slow growth rates in the initial stages, faste r growth in the expone ntial pha s e and ver y s lo w growth i n s tationary phase. Average height and diameter were considered as proxies for phytomass accumulation. The average heights and diameter measured were reflective of the species phytomass accumulation potential. Phytomass production by the tree species in a given period of time and its ability to accumulate heavy metals are very crucial for the success of phytoremediation. For the three species average height and diameter were substantially low for the trees gro wn on untreated soils (Figure 5), but sig nificant ly impro ved for the trees gro wn on treated soils for all
J. E. Ssenku et al. the species. The inability of the trees to grow and accumulate phytomass on the untreated pyrite and tailings demonstrated their lo w potential to remediate them through either phytoextraction or phytostabilisation and the need for application of amendment materials. Nitr ogen a nd pho sphoro us are the ele ment s that mo st co mmonl y limit tr ee gro wth [32]. P lants gr own on a cid soils commonly undergo phosphorous deficiency [33]. Their low concentrations as compared to unpolluted and treated so ils could have also significa ntl y retarded gro wth of the trees in untreated soils. It has been reported that phos pho r o us d efic ient p la nts s how an e nha nc ed exud a tion o f ca r bo xylic ac id s, suc h as citric and malic acid [34]. Carboxylate exudation could play a role in the mobilization of heavy metals in the rhizosphere and enhance their uptake to levels that are ph yto toxic and thus p r ohibitive to growth. However, as per the model results, the treatments were effective regardless of the species and site at which the species was grown. Average height and diameter for Eucalyptus grandis were substantiall y higher tha n tho se of the two leguminous species which had comparably similar diameter and heights for the three treatment regimes. The superiority Eucalyptus grandis demonstrated over Senna siamea and Leucaena leucocephala may not nec- essarily be linked with the species adaptability to the harsh soil condition but rather to the species’ genetic potential since the roots had not penetrated to the deeper levels that were extremely harsh. The higher gro wth rate of the species on treate d soils is attrib uted to r educ tion o f the ava il abil ity of the hea vy metal s thr o ugh cha n ge of p H o f soil to slightly alkaline in most of the soils and binding of heavy metals by the relatively high organic matter. The organic matter has freq uently bee n repor ted to have a domina nt role in controlling the behaviour of copper in the soil because it p ossesse s important bindi ng site for the ele ment in compost and a mended soils [35]. Nitro- gen a nd phosphorous that most commonly li mi t tree growth [32], were relatively more abundant in treated soils Survival of the plant is one of the basic parameters to study the growth performance of the plants under a given set of environmental conditions [36]. Survival performance was generally poor on untreated soils for all the species most especially at LPPT S and HPPTS. Survival of the tree was under the in fluence of both climatic, physicochemical characteristics of soils and destructions by wild animals. Climatic conditions at KTDS could have favoured the survival of the trees more as compared to the other sites. Based on previous records of rainfall totals KTDS receives mean annual rainfall of 1370 mm while LPPTS and HPPTS receive 890 mm [37]. During the study period, temperatures at LPPTS and HPPTS ranged between 17.4˚C to 33.8˚C but KTDS being loc ated at higher altitude it was always coole r than the pyrite trail site. W ith such climatic conditi ons at KTDS as com- pared to LPPTS and HPPTS, the evapotranspiration rates could have been low leading to higher water retention and e nhanc ement of survival of the trees. Contrary to the expectations, survival performance and growth of Senna siamea was very poor on compost treated so ils at HPPTS. Treatment with compost adjusted the mean soil pH to 4.12 which is be low the pH of 5.5 - 7.5 at which it gro ws best [38], thus high mortalit y of the seedlings. Si milarly, survival of Eucalyptus grandis on compost treated soils at LPPTS and on unpolluted soils was remarkably low. This was due to frequent attacks to this species by Syncerus caffer (Buffalos) that defoliated and uprooted the trees. Similarly Leucaena leuc o- cephala survival was lower at LPPTS and HPPTS partly due to frequent browsing by Kobus kob thomasi (Uganda kob), despite the physical barriers that were put in place to restrict their access to the plant. This points to the uns uitability of t his species for phytoremediatio n in pro tected area as it ma y in t urn se rve a s lin k thro ugh which heavy metals may be channelled into food chains of wild life. Survival performance was positively and strongly correlated with pH, organic matter, available phosphorous, total nitrogen as expected and strangely with available copper. The strange relationship with copper could have been due the decline in survival performance with time as the rhizospheric available copper did, due to phytoextraction by the trees. Trees grown on untreated pyrite and tailings were characterised with low foliage density and chlorotic leaves in contrast with those grown on unpolluted and treated pyrite and tailings which had high foliage density and green leaves. Higher availability of the heavy metals in untreated pyrite and tailings as compared to those treated with limestone and compost could have lead to high uptake of heavy metals leading to chlorosis, as a result of decreased rate of chlorophyll biosynthesis and content [39]. Chlorosi s may also b e attr ibuted to the de ficiency of nutrients such as nitrogen, magnesium that usuall y characteri s e tail ing s and pyrite soils. Roots are necessary for the gro wth and development of a plant and their modific ation s have an e ffect o n other plant parts [40]. T he roots formed by the trees growing on untreated soils were observed to be thin as compared to those for med by tre es gro wing o n treated taili ngs and p yrite so ils a nd unpo lluted soils, le adi ng to p oo r gr o wth. The relatively higher concentration of available heavy metals could have inhibited root elongation through in- terference with cell division, including inducement of chromosomal aberrations and abnormal mitosis as sug-
J. E. Ssenku et al. gested by [41]-[44]. Upon absorption, compartmentalization and accumulation of heavy metals occur in the vacuoles of ro ot ce lls thus li mitin g heav y metal tr ansp orta tion to shoo ts [45], co nse q uen tl y c ul mi na ti n g i nto r o o t cell metabolism disorders and depressed root growth [46]. Senna siamea lacked nodules and this in conformity with earlier reports in which it has been reported as a non-nodulating woody legume [47]. Failure of nodulation of Leucaena leucocephala in untrea ted soils may be attrib uted to low pH of the untreated ta ilings and pyrite soils. In acid soils malformation of roots of Leucaena leucocephala, po or gro wth o f the ent ire plant, poo r surviva l of Rhizobium and impairment of its nodulation have been reported [29]. The curving of the roots could be associ- ated with the uneven vertical distribution of heavy metals and other physico-chemical characteristics, with the deeper layers of the soil p rofiles possessi ng levels that are pro hibitive to gro wth. This explanation is in line with observation of [16] that p lan t r oo ts gro w sele cti vel y int o t he s oil, tak ing a dva nta ge o f the hig h de gre e of heter o- geneity in the distribution of heavy metals, by avoiding the most contaminated part of the mine tailings. Thus the chan ge in di rect ion of growth following c oncentration grad ie nts may result into s uch deformity in roots. 5. Conclusion Pyrite and copper tailings were extremely acidic with relatively higher concentrations of available heavy metals, low organic matter content and deficient in nutrients. Proper establishment and growth of Eucalyptus grandis, Senna siamea and Leucaena leucocephala on untreated pyrite and copper tailings is unattainable. T hus, applica- tion of amendments purposely to boost the establishment of the species during a phytoremediation programme is recommended. The three species have great potential for phytostabilisation of pyrite and copper tailings. How- ever, Senna siamea would be preferred to Eucalyptus grandis and Leucaena leucocephala in QECA a s t heir u se is limited by the potential attacks from Syncerus caffer and Kobus kob thomasi respectively. Acknowledgements The autho rs ac kno wledge Sida -S AREC fo r the fina ncia l su ppo rt exte nded thro ugh M aker er e Uni vesrit y and Na- tional Agriculture Research Laboratories (NARL) for the physico-chemical analyses of the soil samples. References [1] O ryem-Origa, H., Makara, A. and Tusiime, F.M. (2007) Propagule Establishment in the Ac id -Mine Polluted Soils of the Pyrite Trail in Queen Elizabeth Nati onal Park, U ganda. African Journal of Ecology, 45, 84-90. http://dx.doi.org/10.1111/j.1365-2028.2007.00743.x [2] Muwanga, A., Oryem-Origa, H., Maksara., A., Hartwig, T., Ochan, A., Owor, M., Zachmann, D. and Pohl, W. (2009) Heavy Metals and Their Uptake by Plants in the River Nyamwamba-Rukoki-Kamulikwezi-Lake George System, Western Ug anda. African Journal of Science and Technology, Science and Engineering Series, 10, 60-69. [3] Barceló, J. and Poschenrieder, C. (2003) Phytoremediation: Principles and Perspectives. Contribution to Science, 2, 333-344. [4] Cecchi, C.G.S. and Zanchi, C. (2005) Phytoremediation of Soil Polluted by Nickel Using Agricultural Crops. Envi - ronmental Management, 36, 675-681. http://dx.doi.org/10.1007/s00267-004-0171-1 [5] Liu, X., Peng, K., Wang, A., Lian, C. and Shen, Z. (2010) Cadimium Accumulation and Distribution in Populations of Phytolacca americana L. and the Role of Transpiration. Chemosphere, 78, 11 36-1141. http://dx.doi.org/10.1016/j.chemosphere.2009.12.030 [6] Sylwia, W., Anna, R., Ewa, B., Stephanc, C. and Maria, A.D. (2010) The Role of Subcellular Distriution of Cadmium and Phytochelatins in th e Generation of Distinct Phenotypes of AtPCS1 -and CePCS3 Exp ressing Tobacco. Journal of Plant Physiology, 167, 981-988. http://dx.doi.org/10.1016/j.jplph.2010.02.010 [7] Huang, H., Yu, N., Wang, L., Gupta, D.K., He, Z., Wang, K., Zhu, Z., Yan, X., Li, T. and Yang, X. (2011) The Ph yto- remediation Potential of Bioenergy Crop Ricinus communis for DDTs and Cadmium co-Contaminated Soil. Biore- source Technology, 102, 11034-11038. http://dx.doi.org/10.1016/j.biortech.2011.09.067 [8] Santana, K.B., de Almeida, A.F., Souza, V.L., Mangabeira, P.A.O., Silva, D., da, C., Gomes, F.P., Dutruch, L. and Loguercio, L.L. (2012) Physiological Analyses of Genipa americana L. Reveals a Tree with Ability as Phytostabilizer and Rhizofilterer of Chromium Ions for Phytoremediation of Polluted Watersheds. Environmental and Experimental Botany, 80, 35-42. http://dx.doi.org/10.1016/j.envexpbot.2012.02.004 [9] Stingu, A., Volf, I., Popa, V.I. and Gostin, I. (2012) New Approaches Concerning the Utilisation of Nat ural Ammend- ments in Cadmium Phytoremediation. Industrial Crops Products, 35, 53-60. http://dx.doi.org/10.1016/j.indcrop.2011.06.005
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