During the last decade, Jatropha curcas L. ( J. curcas) has gained much attention worldwide as biofuel crop. Although its cultivation is promoted in the Sahel, there is a surprising lack of data on its water use regulation and growth in this region. Here, we investigated, in semi-controlled conditions, leaf transpiration and growth of six accessions of J. curcas at seedling stage under natural changing in vapour pressure deficit (VPD) and progressive soil drying in Senegal. The experimental layout was a randomized complete bloc design and after 3 months of growth arranged to a split-plot at the implementation of water stress to facilitate irrigation. Under well water condition, there was no significant difference between accessions for leave transpiration that was positively correlated to VPD with high values recorded between 13 h and 14 h pm. Accessions of J. curcas used in this study showed closed thresholds at which transpiration declined except accession from Ndawene that threshold was lower (0.30). There is no significant difference between accessions for growth during the experimentation period. In 3 months, we recorded 23.57 g for the aboveground dry biomass and seedlings had about 14 leaves and 24.3 cm height. Positive linear correlation was recorded between aboveground biomass and root dry weight (p < 0.0001) and between total biomass and collar diameter (p < 0.0001) as well as between leaf area and leaf dry weight (p < 0.0001). In natural climatic conditions in Sahel zone, cultivation of J. curcas might need complement irrigation for a better growth of seedlings especially during the dry season.
Jatropha curcas (J. curcas), an oil-seed shrub of Euphorbiaceae family, has been identified as an important source of biodiesel [
In many countries of West Africa, cultivation of J. curcas, presented as a potential source of biodiesel and accessible energy for rural populations, is encouraged. The government of Senegal launched in 2007 the national program for biofuel entitled “Programme National Biocarburant” [
Due to limited rainfall and hot temperature in Sahelien zone where J. curcas cultivation is planed and the fact that assimilation of carbon by plant incurs water costs [
The experiment was conducted at the outdoor conditions at the Regional Research Centre for the Improvement of Crop Adaptation to Drought (Ceraas). Six accessions selected from the J. curcas collection of ENSA (Ecole Nationale Supérieure d’Agriculture) were used based on seeds weight and rainfall of origins in order to have accessions with contrasted seeds weight and contrasted rainfall considering the collection sites in Senegal (
Plastic Pots with 20 cm height, 21 cm in diameter and a volume of 5 L were used for the experimentation. The pots were filled with 8 kg of soil to a 16.5 cm height. The soil used was of Ferra-sols type, composed of sand (91% - 95%) and clay (3.5% - 5.6%), with low organic matter (0.27% - 0.34%), low nitrogen (0.16% - 0.19‰), and low pH (6 - 6.5).
Pots with dry soil were weighted (DW) before saturating with water and allow draining freely until there was no water lost by draining and pots were weighted again (SW). So, water holding capacity (WHC) of soil in the pot was determined as.
WHC = DW − SW (1)
where WHC is water holding capacity, DW is the weight of the pot with dry soil and SW the weight of the pot when saturated with water.
A total of 126 pots were used (21 pots for each of the six accessions). Distance between pots and between lines was 0.5 m. Three seeds were directly sown per
Accession | Rainfall of origin (Bourou, 2012) [ | 100 Seed-weight (g) | Length (mm) | Breadth (mm) | Thickness (mm) |
---|---|---|---|---|---|
Ndawene | 500 - 900 mm | 65.06 ± 1.64 | 17.68 ± 0.11 | 10.86 ± 0.06 | 8.32 ± 0.07 |
Mako Foukola | 900 - 1100 mm | 72.76 ± 0.75 | 18.63 ± 0.03 | 11.02 ± 0.01 | 8.46 ± 0.02 |
Barkeyel | 500 - 900 mm | 71.94 ± 0.65 | 18.38 ± 0.02 | 11.13 ± 0.01 | 8.63 ± 0.02 |
Bantancountou | 900 - 1100 mm | 74.09 ± 0.80 | 18.86 ± 0.01 | 11.02 ± 0.01 | 8.66 ± 0.03 |
Latmingue | 500 - 900 mm | 58.89 ± 0.48 | 17.87 ± 0.05 | 11.09 ± 0.03 | 8.55 ± 0.01 |
Mampatim | 900 - 1100 mm | 77.83 ± 0.20 | 19.02 ± 0.04 | 11.36 ± 0.01 | 8.91 ± 0.01 |
pot. Two weeks after sowing, seedlings were thinned to one plant per pot. To monitor temperature and humidity, a Thermo-hygrometer (Hobo® Pro Series Temp H08-032-08, RH © 1998 ONSET) has been programmed and suspended in the experimental site to record temperature and humidity at each ten minutes. All the plants were kept at 90% WHC by manual irrigation and allow to grow until 3 months in a random complete design (
The day before the beginning of transpiration measurements (3 months after sowing), 90 uniform seedlings (15 seedlings per accession) were chosen and water saturated and allow to drain freely overnight. Thereafter, early on the next day, all the 90 pots were bagged in a transparent plastic bag wrapped around the base of plant stem to prevent soil evaporation [
Evaporative demand was estimated by calculating vapour pressure deficit (VPD) each 10 minutes along the day of measurement according to [
VPD = ( 1 − RH / 100 ) ∗ SVP (2)
where RH is relative humidity and SVP is saturated vapour pressure
SVP ( Pascals ) = 610.7 ∗ 10 7.5 T / ( 237.3 + T ) (3)
T is the air temperature (˚C).
The day following the two days of the measurement of seedling transpiration
under natural VPD, the corresponding 30 seedlings used (5 per accession) were harvested and leaf area of each seedling was measured through a scanner (EPSON expression 10000XL, model J181A) using WinRhizo pro V2008b application to determine leaves area. Due to variation of leaf area from seedling to seedling, transpiration was computed as water loss per unit of leaf area and called transpiration rate (TR). Rooting observations revealed that the plants had fully explored the pot soil volume. Thus, all the transpirable soil water content was accessible to the plants. Dry weight of leaves was determined after oven-drying (70˚C) until constant weight (72 h). Specific leaf area (SLA) was calculated as the ratio between the leaf area and the corresponding dry weight.
The remaining 60 seedlings (10 per accession) were arranged in a split-plot layout. Water stress was the main factor and accessions the secondary factor in order to facilitate pots irrigation (
conditions. Throughout the experiment, pots were weighted daily during 3 weeks at 9 h am to calculate seedling transpiration and soil water content.
The daily transpiration (Tr) was calculated based on the weights before and after watering and corrected for water added back following the equation:
Tr = Weight n − 1 − Weight n + WaterAdded n − 1 (4)
Weightn−1, Pot weight at day n − 1; Weightn, Pot weight at day n; WaterAddedn−1, quantity of water added in the pot at day n − 1 when transpiration exceeded 200 g.
The daily transpiration (Tr) values were normalized twice to facilitate comparison between seedlings. First, to minimize day to day variation resulting from changes in evaporative demand, values of daily transpiration of the individual stressed plants were expressed relative to the mean of the control seedlings (well-watered seedlings of the same accession), yielding daily transpiration ratio (DTR).
DTR = Tr stressed / Tr watered (5)
Trstressed corresponds to the daily transpiration of individual stressed seedling. Trwatered corresponds to the mean of daily transpiration of the 5 well watered seedlings belonging to the same accession with the stressed one.
The daily transpiration ratio (DTR) of each seedling was normalized by dividing each DTR value over time by the average of the DTR value of the seedling recorded in the first 3 days of measurements when there were still no water limitation effects. This second normalization gave the normalized transpiration ratio (NTR), which accounted for seedling to seedling variation in transpiration within the same accession and determined as:
NTR = DTR n / DTR 3dayMean (6)
DTRn, Daily Transpiration Ratio of day n; DTR3dayMean; mean of Daily Transpiration Ratio of the first 3 days of measurement.
The soil water status was monitored using the fraction of transpirable soil water (FTSW) as recommended by [
FTSW = ( WT n − WT f ) / TTSW (7)
TTSW = WT s − WT f (8)
where WTn is the pot weight on a given date n, WTs pot weight at water saturation (before applying water stress) and WTf the pot weight at the end of experimentation when transpiration rate of stressed plants was lower than 10% of the control, TTSW is the total transpirable soil water.
A one way Analysis of variance (ANOVA), with accession as factor, was performed for each investigated parameters before water stress imposition (randomized bloc design with 6 accession); using R software. When significant effect was recorded (P ≤ 0.05), the test of Tukey’s honestly significant differences was used for the comparison and grouping of means. When pots were arranged in split-plot during the water stress imposition, only the computed FTSW were used for analysis to compare accessions. FTSW thresholds where NTR initiates its decline were computed with SAS software using a plateau regression procedure as described by [
Variation in TR was closely linked to natural changing of VPD as illustrated in
VPD and reached its maximum when VPD values were at its maximum between 12:30 and 14:30 (GMT). After that, TR declined progressively. The TR for all the accessions were closed at sunrise and at sunset while largest variation was recorded at high values of VPD. The highest value of TR (76.4 mg・cm−2・h−1 corresponding to 11.78 mmol・m−2・s−1) was recorded in Mako Foukola accession whereas the lowest (48.65 mg・cm−2・h−1 corresponding to 7.51 mmol・m−2・s−1) was recorded in Bantancountou Accession. However, no significant difference of the accessions for Transpiration rate (TR) was recorded according to the Anova test (P > 0.05) considering the different periods of the day.
The accessions with high Transpiration rates recorded the higher total water transpired per plant throughout the day (
No rain was recorded during the experimentation.
Five of the six accessions didn’t present a significant difference for their fraction transpirable soil water (FTSW) threshold according to the Anova test (P > 0.05) as represented in
Accession | FTSW Threshold | Standard Error | Approximate 95% IC |
---|---|---|---|
Bantancountou | 0.3893a | 0.0276 | 0.3301 - 0.4485 |
Barkeyel | 0.3916a | 0.0166 | 0.3561 - 0.4271 |
Latmingué | 0.4362a | 0.0134 | 0.4076 - 0.4649 |
MakoFoukola | 0.3907a | 0.019 | O.3500 - 0.4313 |
Mampatim | 0.3753a | 0.0134 | 0.3466 - 0.4041 |
Ndawène | 0.3021b | 0.0128 | 0.2746 - 0.3295 |
Value with the same letter are not statistically different; IC, confidence interval.
Seedlings growth in the six accessions was similar during the first three months of sowing (
Transpiration rate (TR) followed the pattern of natural VPD variation throughout the day. This might be explained by an adjustment of stomatal response of J. curcas seedling in relation to change in VPD as it has been reported in Acacia tortilis [
Parameters | Accession | |||||
---|---|---|---|---|---|---|
Ban | Bar | Lat | Mako | Mam | Nda | |
Aboveground DW (g) | 18.64 ± 1.28 | 22.34 ± 3.25 | 25.97 ± 2.85 | 25.26 ± 4.20 | 24.79 ± 3.09 | 24.55 ± 1.24 |
Collar D (mm) | 16.24 ± 0.32 | 18.26 ± 1.18 | 19.89 ± 0.68 | 19.18 ± 1.68 | 18.55 ± 0.88 | 18.82 ± 0.44 |
LA (cm2) | 512.01 ± 40.72 | 616.56 ± 104.12 | 712.30 ± 139.46 | 816.84 ± 129.73 | 638.10 ± 92.92 | 753.83 ± 58.90 |
Number of leave | 12.00 ± 0.54 | 12.80 ± 1.15 | 15.60 ± 1.28 | 14.20 ± 1.31 | 13.40 ± 1.36 | 14.40 ± 0.67 |
Height (cm) | 23.20 ± 0.33 | 22.30 ± 1.07 | 24.50 ± 2.01 | 25.90 ± 1.56 | 23.80 ± 1.79 | 26.10 ± 1.00 |
Root DW (g) | 2.82 ± 0.20 | 3.30 ± 0.59 | 4.01 ± 0.30 | 3.25 ± 0.57 | 3.55 ± 0.34 | 3.02 ± 0.34 |
SLA (cm2・g−1) | 110.65 ± 2.84 | 104.03 ± 0.47 | 108.50 ± 2.77 | 112.30 ± 1.52 | 110.09 ± 1.97 | 109.51 ± 1.09 |
Stem DW (g) | 11.15 ± 1.18 | 13.10 ± 1.91 | 15.44 ± 2.08 | 14.78 ± 0.54 | 15.59 ± 2.23 | 14.67 ± 0.66 |
Ban: accession of Bantancountou; Bar: accession of Barkeyel; Lat: accession of Latmingue; Mako: accession of MakoFoukola; Mam: accession of Mampatim; Nda: accession of Ndawene. DW: dry weight; collar D: collar diameter; LA: leaf area; SLA: specific leaf area.
Dcollar | LeafArea | LeafDw | RootDw | |
---|---|---|---|---|
Leaf Area | 0.6852 (0.0000) | |||
Leaf dry weight | 0.6794 (0.0000) | 0.9862 (0.0000) | ||
Root dry weight | 0.7255 (0.0000) | 0.6495 (0.0001) | 0.6674 (0.0001) | |
Aboveground biomass | 0.8199 (0.0000) | 0.7718 (0.0000) | 0.7720 (0.0000) | 0.8888 (0.0000) |
Values in bracket are the probabilities of Pearson test. Dcollar, collar diameter; LeafDW, leaf dry weight; RootDw, root dry weight.
cristatum (11.99 mmol H2O m−2 s−1) and Cleistogenes squarrosa (10.31 mmol H2O m−2 s−1), and on Acacia tortilis in Senegal (8 mmol・m−2・s−1) as revealed by [
No difference was observed between the accessions for TR despite of the different noted in rainfall of the collection sites. So, the distribution of J. curcas throughout the country is not based on differences strategies in water use at seedling stage under well watered conditions regardless to the time of the day. This might be explained by the vegetative propagation of J. curcas, mainly via exchange of cuttings, across the country as described by [
Under well watered conditions, water loss by J. curcas is positively correlated to VPD as reported by [
In Sahel area, because of high VPD, cultivation in large scale of J. curcas will probably cause a high water loss from soil via transpiration especially during the wet season where water is available for J. curcas plants that present at this period high leaves surface. High evapo-transpiration of J. curcas, under increased atmospheric demand and non-water limited conditions, has been reported [
Accessions of J. curcas used in this study showed closed thresholds at which transpiration declined except accession from Ndawene. The stomata control of leaves transpiration in response to water depletion in the soil didn’t vary much between the accessions. This might be explained by a low genetic differentiation between accessions as J. curcas is spread mainly by cutting in Senegal [
Considering the concordance of transpiration of J. curcas accessions originated of different rainfall conditions in our study (
This is inconsistent to results of [
Seedlings of J. curcas reduce their transpiration rate only when the fraction of transpirable soil water (FTSW) fell below 0.5. This strategy allows J. curcas seedling to grow under climate with low to moderate soil moisture. This characteristic is an advantage for J. curcas seedlings in low to moderate rainfall zones. The mean FTSW threshold at which transpiration dropped was 0.39. Therefore, we can say that irrigation at about 50% field capacity seems to be sufficient to ensure growth of J. curcas seedlings. [
The declining of transpiration at FTSW threshold (0.39) indicated that physiological parameters of J. curcas seedling are affected by a severe water stress. These results corroborate the fact that under severe water stress conditions, transpiration rate of J. curcas seedlings is not correlated to the increase of its leaves surface area as reported by [
The relationship between fraction transpirable of soil water (FTSW) and normalized transpiration rate (NTR) are comparable to that fund for many species [
Seedlings growth of the six accessions was similar during the first 3 months of sowing. Therefore, in the base of the growth parameters measured, it will be difficult to identify accessions presenting the best growth during the first 3 months after sowing. [
Seedling growth in our study was low to that reported by [
Seedling growth of the different accessions has been affected by severe water stress as reported for shrubs species [
I am grateful to Dr SINE and to M. FABRE for their comments and advices regarding the material and methods. I’m also thankful to Mrs. SAMBAKHE for her help in statistical analysis.
Ouattara, B., Diédhiou, I., Belko, N. and Cissé, N. (2018) Growth and Transpiration of Jatropha curcas L. Seedlings under Natural Atmospheric Vapour Pressure Deficit and Progressive Soil Drying in Semi-Arid Climate. Agricultural Sciences, 9, 639-654. https://doi.org/10.4236/as.2018.96044