Vol.3, No.6, 835-843 (2012) Agricultural Sciences
Biomass production and distribution in seedlings of
Coffea arabica genotypes under contrasting nursery
environments in southwestern Ethiopia
Taye Kufa
Ethiopian Institute of Agricultural Research, Jimma Research Center, Jimma, Ethiopia; kufataye@yahoo.com
Received 18 June 2012; revised 28 July 2012; accepted 8 August 2012
In Ethiopia, the natural forests with the occur-
rence of wild Arabica coffee gene pools are un-
der constant threats, largely due to anthropo-
genic activities. The study was conducted to
compare the variability among the wild arabica
coffee genotypes in biomass assimilation and
allocation patterns under varying light and irri-
gation condit ions at the Ji mma Research Ce nter,
southwest Ethiopia. The treatments included ir-
radiance (moderate and full sunlight), irrigation
(well watered and water stressed) regimes and
twelve coffee genotypes of different geographi-
cal areas. One-year-old seedlings were used to
impose the environmental stresses and to re-
cord dry mass of leaves, main stem, primary
branches and root growth. Each organ was se-
paretly oven-dried and total dry matter produc-
tion and allocation patterns were measured and
analyzed. The results depicted highly significant
differences between the contrasting irradiance
and irrigation regimes as well as among coffee
genotypes for most of the parameters consid-
ered. Accordingly, root, leaf, stem, whole-shoot
and total biomass assimilation and root parti-
tioning were higher for unshaded, water stressed
and Harenna genotypes from the respective
treatment groups. Significantly the lowest and
highest root and shoot biomass values were
recorded for Berhane-Kontir and Harenna geno-
types, respectively. Likewise, coffee seedlings
significantly differed in root dry mass and root
to shoot ratio, dry matter partitioning due to the
main and combined treatment effects. Most ac-
cessions had relatively lower assimilations in
shade as compared to full sun light conditions.
Conversely, leaf share was significantly high
under moderate shade environments and for
irrigated and Berkane-Kontir genotypes. The total
dry matter share varied for the seedling growth
parts (root = 22%, leaf = 35%, stem = 43% and
whole shoot = 78%). The root growth followed
the order of Harenna > Yayu > Bonga > Berhane-
Kontir populations, which were grouped into
three broad cluster classes. The reverse was
true for the leaf and whole-shoot partitioning,
demonstrating the interplay betw een above- and
below-ground growth parts partly due to geno-
type, environment and/or their interactions. As a
whole, the study demonstrates the need to con-
sider both dry matter assimilation and parti-
tioning patterns in identifying desirable geno-
types and optimum environm ents for future bree-
ding program in Ethiopia.
Keywords: Ecological Physiolo gy; Environment;
Genetic Diversity; Seedling Growth Response; Wild
Ethiopian Coffee Population
The montane rainforest areas in Ethiopia are the only
known center of origin and genetic diversity for the
highland arabica coffee (Coffea arabica L.). In its origi-
nal natural habitats, arabica coffee occurs in the multi-
strata of forest ecosystems and thus it is a shade-adapted
plant. Its response to light has caused it to be tradition-
ally considered a heliophobic plant requiring high, some-
what dense cover in a plantation. Today, the cultivation
of coffee in open sun is not uncommon in most coffee
producing countries, though its sustainability is ques-
tionable. It is known that coffee trees with high produc-
tivity potential are capable of high yields when they are
cultivated intensiv ely without shade [1,2].
Although arabica coffee is said to be a shade-loving
plant with greater quantum utilization efficiency for
photosynthesis, excessive shading or light interception
by the upper two to three canopy strata of various tree
species would decrease growth and productivity of the
Copyright © 2012 SciRes. OPEN ACC ESS
T. Kufa / Agricultural Sciences 3 (2012) 835-843
crop, as the plant spends much of its photosynthetic ac-
tivities for maintenance. On the other side, if the light
intensity is too high, there will be inadequate reaction
centers in the leaves of the crop to accommodate the
light energy and convert it into biochemical energy. As a
result, the coffee trees excessively photo-respires and
eventually most of the stored carbohydrates become de-
pleted. Consequently, the trees may suffer from a serious
dieback mostly due to excessive fruit load via enhanced
flowering in full sunlight compared to shade conditions
and coffee production limitations and coffee shade inter-
actions [3,4]. Besides, excessive evapo-transpiration and
severe drought stress, death of actively growing shoot
parts, seasonal crinkling of leaves, frost damage and
subsequent yield reduction are common problems ob-
served in unshaded coffee orchards [5].
It is known that photosynthesis in coffee follows the
C3 or Calvin cycle pathway, as coffee plants placed in
darkness after a period of light produce a burst of CO2
following photorespiration [6]. Work done in Kenya [7]
revealed that about 95% of the biomass of a plant are
derived from the carbohydrates manufactured in the
green parts by the process of photosynthesis and the re-
maining 5% come from mineral elements absorbed by
the roots. Large regular yields of coffee can be obtained
only when both the carbohydrates and mineral element
supplies within the tree are adequa te to meet the needs of
the developing fru its and the shoots and roots which will
support the following year’s crop. The capacity of the
plant to produce carbohydrate depends mainly on the
total green (mainly leaf) area engaged in photosynthesis
and the net photosynthetic rate per unit green surface
area [7]. The same author showed that dry matter pro-
duction in any crop depends upon leaf area index, struc-
ture of the canopy, photosynthetic rate per unit of leaf
area and strength of the metabolic sinks in attracting as-
The physiological mechanisms involved in the adapta-
tion of the juvenile trees to light have remained less in-
vestigated in the diverse coffee germplasm collections at
the center of origin and genetic diversity. Shade plants
essentially follow strategies of optimum use and conser-
vation of available energy. The need to know how the
coffee plant accumulates and partitions dry matter to the
various plant organs under a given management cannot
be overemphasized. Moreover, this information is nec-
essary as a selection criterion for coffee cultiv ars as well
as for determining optimum management levels [6,7].
This aspect, however, has not yet deserved attentions in
the evaluation of the immense arabica coffee genetic
resources grow i ng u nder wide ecologies.
The growth and seed production of a plant is a result
of the integrated processes of photosynthetic carbon di-
oxide assimilation and subsequent partitioning and utili-
zation of the assimilated carbon. This requires efficient
translocation of photo-assimilates to the developing plant
parts [8,9]. However, there is little information on the
phenotypic plasticity and biomass partitioning of coffee
trees under varying light gradients in heterogeneous field
conditions. To this effect, understanding the influence of
environmental stress pressures such as direct solar radia-
tion on growth and physiology of coffee plant is impor-
tant to examine the coping mechanisms involved in the
shade-adapted Arabica coffees. The natural coffee forests
with the occurrence of maximum plant diversity include-
ing the wild coffee genetic resources are under continu-
ous threats of erosion due to several factors and needs
urgent conservation measures [10]. According to [11],
nowadays, it is not uncommon to see coffee tree drying
symptoms due to climate changes that have resulted in
physiological disorders between vegetative and repro-
ductive growths. This is associated with continuous
flowering and heavy crop loads as a result of changes in
weather patterns with erratic rainfalls. The situation is
aggravated by the outbreak of insect pests and diseases,
requiring new corrective strategies to revive Arabica
gene pools from possible fast and irreversible losses.
Hence, this study would provide baseline research in-
formation on the use of growth traits in the selection of
coffee genotypes in breeding program for sustainable
management and conservation of coffee genetic diversity
and its healthy environments. Therefore, this ex-situ ex-
periment was carried out to compare the variability in
biomass prodution and allocation patterns in seedlings of
arabica coffee germplasm accessions under varying nur-
sery irradiance and irrigation conditions at Jimma Re-
search Center in southwest Ethiopia.
2.1. The Study Site
The experiment was conducted at a common nursery
garden of the Jimma Research Center, southwest Ethio-
pia (7˚46'N, 36˚0'E, 1750 m.a.s.l). This is a national cof-
fee research coordinating center were about 5960 live
coffee germplasm are found in field gene banks for re-
search work. The area receives adequate amount of rain-
fall with an average rainfall of 1595 mm per annum dis-
tributed into 173 days. The driest season lasts between
December and January. The average maximum and mini-
mum air temperatures are 25.9˚C and 11.2˚C, respec-
tively, the coldest month being December [12].
2.2. Experimental Treatments and Design
Ripe red coffee cherries were collected in 2004/2005
from four wild coffee populations in the montane rain-
forests of southeastern and southwest Ethiopia. The
Copyright © 2012 SciRes. OPEN ACC ESS
T. Kufa / Agricultural Sciences 3 (2012) 835-843 837
recommended ideal potting medium [13] was prepared
from topsoil and decomposed coffee husk at the respect-
tive proportion of 3:1 (v/v) and firmly filled in black
plastic pots (volume = 5.8 L) perforated at the bottom.
The plant plastic pots were arranged on nursery seedbed
and the prepared coffee seeds were sown in each pot.
The recommended post-sowing nursery operations were
applied [14] and the seedlings were uniformly managed
under partial shade conditions and irrigated at every
four-day intervals.
After one-year of ex situ estab lishment under common
garden, the shade treatment was applied for three con-
secutive dry months between March and May. In this
case, seedlings were divided into equal halves to impose
the contrasting shade and irrigation treatments. The
studied environmental modification treatments included
shading levels (moderate shading and full solar light in-
terception), two irrigation treatments (well-watered and
water deficit) and twelve coffee germplasm genotypes of
different geographical origins in Ethiopia. The central
five coffee seedlings were used to record destructive
growth parameters for each treatment. These include dry
weight of leaves, main stem, primary branches and root
system. The roots were immersed and washed in clean
water to remove adhering soil. Subsequently, each plant
part was separately oven-dried at 105˚C for 24 h and
weighed using a sensitive balance. Finally, total dry
matter production and allocation patterns were deter-
mined in seedlings of arabica coffee germplasm acces-
sions under contrasting nursery microclimatic varables
(Table 1) monitored and described [12].
2.3. Data Analysis
The statistical analysis was accomplished using SAS
Table 1. Microclimate variables in the studied full sunlight and
moderately shaded coffee nursery site at Jimma Research Cen-
Temperature (˚C)
Variable RH (%) Air Soil
Time of day * **
Night 80.97 ± 9.97a 16.56 ± 1.74b 19.10 ± 7.16
Day 70.82 ± 6.03b 20.47 ± 2.01a 23.83 ± 4.23
Shading level Ns Ns Ns
Full sun 73.42 ± 8.57 18.75 ± 3.17 24.03 ± 5.95
Shaded 78.36 ± 9.52 18.28 ± 2.46 18.90 ± 5.60
Mean 75.89 18.51 21.46
CV (%) 3.17 3.58 30.42
Time* shade Ns Ns Ns
Ns = Not significant; *P < 0.05; **P < 0.001. Means with the same letter is
not different from each other according to Tukey test at P = 0.05.
for Windows version 8.1 (SAS Institute Inc., Cary, NC).
Two-way analysis of variance (ANOVA) was computed
for each growth variable considered in a factorial ex-
periment arranged in a randomized complete block de-
sign with three replications. Principal component analy-
sis was computed to compare the variability among the
coffee germplasm accessions. Moreover, treatment means
were ranked according to Tukey test at P = 0.05, when-
ever the F-test showed significant differences. Figures of
significant interactions were made with the Sigma Plot
SPW9.0 (SYS TAT So ft wa r e, Inc.) .
3.1. Biomass Production
3.1.1. Shoot Biomass
Significantly (P < 0.001) higher stem (main stem and
branch) biomass (17.48 ± 2.49 g) was obtained from un-
shaded plots than from those in partial shade environ-
ments. In addition, insignificantly higher leaf dry weight
(13.58 g) was found for sun-exposed seedlings (Tab le 2).
Similarly, most shoot growth parameters were signifi-
cantly higher for water deficit subjected seedlings. Hence,
significantly (P < 0.05) higher leaf dry mass and main
stem plus branch (P < 0.05) were obtained for non-irri-
gated than for well-watered seedlings. With regard to
shade or irrigation, stem biomass was higher (17.48 g) in
the open sun than the shade (15.60 g) with about 11%
difference. Coffee accessions significantly (P < 0.05)
differed in stem dry weigh t, with average results ranging
from 14.36 ± 1.85 to 19.08 ± 2.01 g for Berhane-Kontir
(III-2) and Harenna (I-1) seedlings, respectively (Table
2). Most accessions had relatively lower growth re-
sponses in shade cond itions as compared to the su n plots.
As a result, higher dry mass of leaf, root and total dry
matter were recorded for seedlings exposed to direct
sunlight (Figure 1). The results depict significant differ-
ences among accessions in root dry mass and root to
shoot ratio; the values followed the descending order of
Harenna > Yayu > Bonga > Berhane-Kontir accessions.
3.1.2. Root Biomass
A significantly ( P < 0.01) higher root dry weig ht (8.93
g) was obtained from unshaded than from partially
shaded seedlings (7.89 g), where a reduction of about
12% was noted. The difference between watering re-
gimes was also significant (P < 0.01) for root dry mass
and was higher for drought-stressed (8.90 g) than for
well-irrigated (7.92 g) seedlings. In the same manner,
coffee accessions significantly differed (P < 0.01) in root
dry mass. Consequently, the lowest (III-1 = 6.48 g) and
highest (I-2 = 10.43 g) average values were obtained
from Berhane-Kontir and Harenna seedlings, respec-
Copyright © 2012 SciRes. OPEN AC CESS
T. Kufa / Agricultural Sciences 3 (2012) 835-843
Copyright © 2012 SciRes.
Table 2. Shoot and root growth (means ± S.D) of seedlings of arabica coffee genotypes under varying irradiance and irrigation re-
Treatment LDW (g) SDW (g) RDW (g) R:S TDM (g)
Irradiance Ns ** **
Ns **
Open sun 13.58 ± 1.59 17.48 ± 2.49a 8.93 ± 1.64a 0.29 ± 0.03 39.99 ± 5.31a
Moderate shade 13.06 ± 0.91 15.60 ± 1.55b 7.89 ± 1.52b 0.28 ± 0.04 36.54 ± 3.13b
Irrigation * * **
Ns **
Water stressed 13.68 ± 1.40a 17.14 ± 2.53a 8.90 ± 1.52a 0.29 ± 0.03 39.72 ± 4.95a
Well-watered 12.95 ± 1.12b 15.94 ± 1.81b 7.92 ± 1.66b 0.27 ± 0.04 36.81 ± 3.92b
Genotype Ns * ** ** *
I-1 13.25 ± 0.80 19.08 ± 2.01a 10.02 ± 1.1 1a 0 .31 ± 0.04ab 42.34 ± 3.43a
I-2 13.06 ± 0.89 18.47 ± 2.09ab 10.43 ± 1.23a 0.33 ± 0.01a 41.95 ± 4.03ab
I-3 13.73 ± 1.85 16.63 ± 1.78ab 9.22 ± 0.95ab 0.31 ± 0.02ab 39.57 ± 4.52ab
II-1 13.63 ± 1.78 16.65 ± 2.47ab 8.30 ± 1.44abc 0.28 ± 0.02abc 38.58 ± 5.57ab
II-2 12.34 ± 0.66 15.52 ± 1.33ab 7.97 ± 1.11abc 0.28 ± 0.03abc 35.82 ± 2.90ab
II-3 12.81 ± 0.68 15.29 ± 1.66ab 8.15 ± 1.34abc 0.29 ± 0.04abc 36.24 ± 2.84ab
III-1 11.91 ± 0.51 14.84 ± 1.45ab 6.48 ± 1.09c 0.25 ± 0.04 bc 33.23 ± 1.93b
III-2 12.97 ± 1.29 14.36 ± 1.85b 7.22 ± 1.66bc 0.27 ± 0.04abc 34.54 ± 4.2 1a b
III-3 14.37 ± 1.4 5 16.11 ± 2.41ab 6.86 ± 1. 2 0b c 0.23 ± 0.03 c 37.33 ± 4.65ab
IV-1 13.87 ± 0.76 17.16 ± 1.50ab 8.67 ± 0.30abc 0.28 ± 0.02abc 39.69 ± 2.09ab
IV-2 14.41 ± 0.67 18.06 ± 1.24ab 9.39 ± 1.00ab 0.29 ± 0.01abc 41.87 ± 2.81ab
IV-3 13.52 ± 2.12 16.29 ± 3.37ab 8.23 ± 2.43abc 0.27 ± 0.05abc 38.03 ± 7.63ab
Mean 13.32 16.54 8.41 0.28 38.26
CV (%) 7.95 9.35 10.72 9.31 8.20
Ns = Not significant; *, ** and *** = significant at P < 0.05, P < 0.01 and P < 0.001, respectively. Means followed by same letter with in a column are not differ-
ent from each other (Tukey test at P = 0.05). Abbreviations: LDW = leaf dry weight, SDW = stem dry weight, RDW= root dry weight, R:S = root to shoot ratio,
TDM = total dry matter.
igure 1. Biomass yield and root to shoot ratio of coffee accessions under full sunlight and shaded conditions.
T. Kufa / Agricultural Sciences 3 (2012) 835-843 839
tively (Table 2). In general, the Harenna seedlings had a
higher root mass than the others, particularly the Ber-
hane-Kontir accessions, which had a low root biomass
ranging between 6.48 and 7.22 g. This was less than the
overall average root dry mass of 8.41 g. The ratios of
root to shoot dry mass of the seedlings also significantly
differed among the coffee accessions, but not between
irradiance and irrigation levels. The absence of signifi-
cant differences due to shade and irrigation suggests that
the duration of the treatments was too short to considera-
bly change root biomass accumulation. However, root to
shoot ratio of some seedlings surpassed those in shadow
conditions. The significantly lowest (III-3 = 0.23) and
highest (I-2 = 0.33) root to shoot values were determined
for the Berhane-Kontir and Harenna accessions, respec-
tively. The root to shoot ratio result was higher for the
Harenna as compared with those from Berhane-Kontir
coffee germpl asm (Figure 2).
3.1.3. Total Biomass
The analysis of variance comparing the total dry matter
production of coffee seedlings depicts significant (P <
0.01) differences between the two shade and irrigation
treatments as well as due to accessions (P < 0.05). Sig-
nificantly (P < 0.001) higher total dry matter yield (3 9.99
± 5.31 g) was obtained from the full sun light than from
the shaded plots. There was abou t 9% reducetion in total
dry matter production of seedlings in moderately shaded
seedlings as compared to those in open sunlight. Simi-
larly, significantly (P < 0.01) higher total dry matter was
obtained from drought-stressed than well-watered seed-
lings. The results also reveal sign ificantly lowest (III-1 =
33.23 g) and highest (I-1 = 42.34 g) total biomass from
the Berhane-Kontir and Harenna coffee accessions, re-
spectively (Table 2, Figure 2). Accessions from Harenna
(I-2 = 41.95 g) and Berhane-Kontir (III-2 = 34.54 g) had
the next maximum and low average values, respectively,
though no significance was detected among the other
accessions. The results of the destructive parameters
manifested that the coffee germplasm accessions were
grouped into three broad classes. The first group con-
sisted of a mixture of accessions from Yayu (IV-1 and
IV-2), Bonga (II-1), Berhane-Kontir (III-3) and Harenna
(I-3). Wher eas, the Bong a and Harenna populatio ns were
classified into the second and the third group (Figure 3).
3.2. Biomass Partitioning
The amount of total dry mass partitioned to the root
part was comparable between shade treatments, though it
was higher in full sun irradiance (22.22% ± 1.89%) and
drought stressed (22.35% ± 2.02%) seedlings. In contrast,
leaf partitioning was significantly different according to
the level of shade (P < 0.001) and irrigation (P < 0.05).
As a result, the mean values ranged from 34.11% ± 2.19%
Figure 2. Root and shoot dry mass for seedlings of wild coffee
accessions under (a) full sunlight and (b) shaded conditions.
Figure 3. Principal component analysis for destructive growth
parameters of coffee seedlings maintained under optimal envi-
ronmental conditions.
to 35.89% ± 2.92% and 34.63% ± 2.50% to 35.37% ±
2.90% between full sun and shade and drought-stressed
and irrigated seedlings, respectively. Furthermore, in full
sunlight, the stem plus branch part shared significantly (P
< 0.05) more of the total assimilates (43.67% ± 1.55%)
as opposed to seedlings in partial shade conditions (Ta-
ble 3).
The total dry matter yield distributed to leaf and total
shoot part was, however, not altered due to irrigation
regimes. Hence, the average leaf and shoot shares ranged
between 43.03% ± 1.75% and 43.30% ± 1.53% and
77.66% ± 2.02% and 78.67% ± 2.68 %, respectiv ely. Th is
was similar to the slightly higher assimilate amounts
(78.55% ± 2.81%) stored in the shoot part of shaded
seedlings, though the allocation to the root part was low
(Table 3). This corresponds with the more luxurious
shoot growth of coffee seedlings at resource rich envi-
ronments as opposed to deep root systems in drought-
stressed situations. The coffee accessions from Berhane-
ontir had significantly (P < 0.01) the lowest (18.3%) K
Copyright © 2012 SciRes. OPEN AC CESS
T. Kufa / Agricultural Sciences 3 (2012) 835-843
Ta b le 3. Total dry matter partitioning patterns (means ± SD) in seedlings of Arabica coffee genotypes under varying nursery envi-
Treatment Root Leaf Stem Whole-shoot
Irradiance Ns *** * Ns
Open sun 22.22 ± 1.89 34.1 1 ± 2.19b 43.67 ± 1.55a 77.78 ± 1.90
Moderate shade 21.45 ± 2.81 35.89 ± 2.92a 4 2.66 ± 1.58b 78.55 ± 2.81
Irrigation Ns * Ns Ns
Water stressed 22.35 ± 2.02 34.63 ± 2.50b 43.03 ± 1.75 77.66 ± 2.02
Well-watered 21.33 ± 2.68 35.37 ± 2.90a 4 3.30 ± 1.53 78.67 ± 2.68
Genotype ** ***
Ns **
I-1 23.68 ± 1.89ab 31.33 ± 1.14de 45.00 ± 1.55 76.33 ± 1.89bc
I-2 24.82 ± 0.87a 31.21 ± 1.61e 43.98 ± 1.19 75.18 ± 0.87c
I-3 23.33 ± 0.66ab 34.62 ± 0.99bc 42.05 ± 0.73 76.67 ± 0.66bc
II-1 21.48 ± 1.19abc 35.38 ± 0.92bc 43.15 ± 1.05 7 8.53 ± 1.19abc
II-2 22.16 ± 1.45abc 34.52 ± 1.50c 43.32 ± 1.48 77.84 ± 1.44abc
II-3 22.37 ± 2.04abc 35.51 ± 3.48abc 42.13 ± 2.20 77.64 ± 2.04abc
III-1 19.50 ± 3.15bc 35.87 ± 1.09abc 44.64 ± 2.90 80.50 ± 3.15ab
III-2 20.75 ± 2.89abc 37.71 ± 3.00ab 41.54 ± 0.57 79. 25 ± 2 .89abc
III-3 18.34 ± 1.86c 38.62 ± 2.52a 43.05 ± 1.16 81.66 ± 1.85a
IV-1 21.88 ± 1.32abc 34.94 ± 1.00bc 43.18 ± 1.73 78.13 ± 1.33abc
IV-2 22.39 ± 0.92abc 34.47 ± 1.07cd 43.15 ± 0.76 77.62 ± 0.93abc
IV-3 21.38 ± 2.81abc 35.81 ± 2.85abc 42.82 ± 0.74 78.62 ± 2.81abc
Mean 21.84 35.00 43.17 78.16
CV (%) 7.67 3.18 3.30 2.14
Ns = Not significant; *, ** and *** = significant at P < 0.05, P < 0.01 and P < 0.001, respectively. Means followed by the same letter(s) with in a column are not
different from each other (Tukey test at P = 0.05).
root partitioning as compared to the Harenna seedlings,
which had the highest (38.6%) root share. The results
indicate significant differences among accessions in the
patterns of total biomass partitioned in leaf (P < 0.001)
and shoot (P < 0.01) growth organs. Consequently, the
values ranged between 31.2% and 38.6% for leaves and
between 75.2% and 81.7% for the shoot. Under ideal
shade and irrigation regimes, differences among acces-
sions in the allocation of total biomass were not signifi-
cant. However, low leaf partitioning was observed in th e
Harenna accessions as compared to those from the
Bonga and Berhane-Kontir forests. Maximum leaf por-
tioning was also observed in one of the accessions from
the Yayu populations (IV-3 = 35.8%). On the other hand,
stem plus branch partitioning was comparable among
coffee genotypes, with the values ranging between 41.5
and 44.6% for III-2 and III-3 of the Berhane-Kontir ac-
cessions, respectively (Table 3, Figure 4).
4.1. Biomass Assimilation
The results show significantly higher shoot dry mass
Figure 4. Total dry matter partitioning to root and shoot parts
in seedlings of Arabica coffee germplasm accessions.
production in unshaded and progressively droughted
coffee seedlings. This could in part be related to low
stomatal conductance and concomitantly lower rate of
net carbon assimilation in shade and irrigated plants
compared to short-term drought-stressed plants [15].
Moreover, a reduced leaf growth was noted in shade
compared to sun plots, and such smaller leaf area may
alter assimilate partitioning among the tree organs and
Copyright © 2012 SciRes. OPEN ACC ESS
T. Kufa / Agricultural Sciences 3 (2012) 835-843 841
decrease shoot dry matter yield, in part indicating the
effect of micro-climatic variables at coffee nurseries
(Table 1). This suggests that a major mode of adjustment
to reduced soil water demand by the coffee seedlings, at
least in the early stages of soil moisture deficit irrigation,
could consist of the maintenance of nearly constant as-
similation on an area ba sis through a reductio n in the rate
of increase in average leaf size. This indicates that leaf
expansion can be accompanied by growth and develop-
ment as well as accumulation and synthesis of the leaf
cell components. Similar results were also reported for
field-grown robusta coffee [16].
On the other hand, coffee accessions significantly dif-
fered in stem dry weight with the lowest and highest av-
erage results obtained from the Berhane-Kontir and
Harenna seedlings, respectively. This could reflect the
variations among the coffee genotypes in growth rate and
productivity, which in turn depend upon stem nature
(stiff or flexible) and size of water conducting tissue [17].
The results of dry matter production and partitioning are
in line with the maximum hydraulic conductance meas-
ured in full sun light and irrigated seedlings [12]. More-
over, other finding [18] also indicated the enhanced wa-
ter use of the arabica coffee populations with a decreased
rainfall gradient in Ethiopia. This could be associated,
among others, with the specific growth responses in-
cluding increased number of lateral roots, higher root to
shoot ratio as well as decreased leaf-specific area in
drought-stressed coffee seedlings [19].
In this regard, many other authors [20-22] pointed out
that plants withstand drought stress by drought tolerance
(higher biomass allocation to vegetative organs and root
to shoot ratio) , whereas drough t escape strategies invo lve
early flower set and leaf senescence. According to the
work done [16], water deficit led to marked decreases in
net carbon assimilation rate and to a lesser extent in
stomatal conductance, regardless of the low and high
nitrogen levels. In Ethiopia, variations among coffee
varieties were found [23] due to soil moisture deficit
irrigation and their capacity to establish in more stressful
field conditions. This concurs with the previous findings
[13] that underlined similar patterns of total dry matter
production and allocation in Arabica coffee seedlings due
to varied potting media blends. The response of the cof-
fee seedlings could also suggest a drought-stress resis-
tance strategy investing more of the daily biomass pro-
duction in the root system, while penalizing the shoot
system. This may be explained due to the differences in
root and shoot growth habits and thus hydraulic conduc-
tance in coffee seedlings as elucidated [19].
4.2. Biomass Partitioning
The amount of total dry mass partitioned to the root
part was comparable between the shade and irrigations
regimes, though the results were higher for partially
shaded and well-irrigated seedlings. By contrast, the cof-
fee accessions significantly (P < 0.001) differ in total
biomass share to root, leaf and whole shoot part. For
maximum rate of production of dry matter within the
plant as a whole it is important that a high proportion of
assimilates as possible should be returned to the leaf tis-
sue, which will further increase the productive capacity
of the plant, and that expenditure of dry matter on the
rest of the plant (stems, petioles and roots) should be no
more than is required to efficiently support the leaves
and supply sufficient mineral nutrients and water. The
overall rate of utilization of assimilates in leaf production
depend upon the rate of new leaf initiation, the rate of
growth and final leaf size and the branching habit [24].
Under field conditions, assimilate utilizatio n may be lim-
ited by various external factors including temperature,
and the supply of water and mineral elements [1]. How-
ever, there is evidently some homeostatic mechanism
maintaining a given root-shoot balance under any given
set of conditions, and this in turn implies an interplay
between growth in root and shoot components [25].
Changes in the partitioning of dry matter between roots
and shoots brought about by environmental factors sug-
gest that when the size of the source is reduced, the
growth of organs most remote from it is often particu-
larly affected [26]. Similarly, assimilate allocation in
plants was found to be affected by water deficit stress
conditions [15]. Hence, the manner in which dry matter
is partitioned between the different parts of the plant is
clearly of great importance both in natural vegetation and
in crop plants.
In essence, the growth and seed production is a result
of the integrated processes of photosynthetic carbon di-
oxide assimilation and subsequent partitioning and utili-
zation of the assimilated carbon. This requires efficient
translocation of photo-assimilates to the developing plant
parts [8,9]. A method of studying energy allocation in
plants that requires separating individual plants into
component tissues has been reported [27] according to
their function, and expressing energy allocation as a
proportion of total biomass stored in each tissue type.
Ther e are several r easons why weight is used to measu re
biomass allocation patterns. According to available in-
formation [8,20], energy content and dry weight equally
reflect energy allocation pattern and dry weight is re-
ported to reflect the integration of all physiological
processes throughout the growing season. In addition,
dry weight reflects the functional aspects of all assimila-
tion [28].
In many crop species, increased yields of improved
cultivars have been related to changes in partitioning as
opposed to increase in total biomass [29]. In the tall,
Copyright © 2012 SciRes. OPEN AC CESS
T. Kufa / Agricultural Sciences 3 (2012) 835-843
mature field-grown Arabica coffee trees in Kenya, shoot
growth is reported to be associated with seasonal changes
in dry matter distribution within the [7]. Green-house-
grown Arabica coffee cultivar-Ruiru 11 showed that dry
matter partitioning to above- and below-ground parts
varied with accessions [27]. The present finding could be
explained in terms of the variations in morphological
growth natures in seedlings of the same coffee popula-
tions [30]. This corroborates with the prev ious results [13]
on the influence of potting media on dry matter yield and
allocation in coffee seedlings. Cognizant of the impor-
tance of coffee, its high genetic erosion in the centers of
origin and minimal conservation efforts emphasized the
need for immediate conservation meas- ures to safeguard
the sustainability of the global coffee industry [10].
The study depicted that biomass production and dis-
tribution patterns in coffee seedlings varied due to geno-
types and environmental modifications, singly and/or in
combinations. The present findings provide an insight
research information to evaluate and character ize growth
response of coffee germ plasm accessions to the induced
heat and water stress environments. This contributes to
identify and develop drought tolerant arabica coffee cul-
tivars against the expansion of coffee cultivation to open
sun fields and marginal sites coupled with changing cli-
matic variables. It can be concluded that dry matter pro-
duction and partitioning patterns in the various growth
organs of coffee seedlings can be considered and used as
selection criteria in future breeding program. This would
also demonstrate the variability among the Ethiopian
coffee diversity in biomass assimilation and allocation
and the need to maintain optimum nursery environments
for production of high quality coffee seedlings. Ho wever,
better understanding on underlying adaptation mechan-
nisms involved in coffee genetic divesities calls for detail
ecophysiologcal and breeding works under specific
ecological zones, prodution systems and field manage-
ment practices for sustainable use and preservation of
arabica coffee genetic resources and its ideal environ-
ments in Ethiopia.
The author would like to appreciate the financial support from the
German Federal Ministry for Education and Research (BMBF) and the
Ethiopian Institute of Agricultural Research (EIAR). My deepest thanks
also go to Alemseged Yilma for his versatile and untiring technical
supports to the success of the study.
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