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Spatial Variability in Water Relations of Wild Coffea arabica Populations in the Montane Rainforests of Ethiopia
... At Harenna, soil water contents were inversely and highly significantly influenced by bulk density, which is site-specific response perhaps due to its peculiar bimodal rainfall pattern and seasonal climate variations. This is in agreement with the spatial variability in water relations of these sites (Kufa and Burkhardt, 2011). Since both the volume of pore spaces and soil solids determine the bulk density of a given soil medium, soils with a high proportion of pore space to solids have lower bulk densities as compared to more compact soil with less pore spaces. ...
... This supports the findings on the spatial variability of soil organic carbon (Law et al.2009), soil nutrients (Sokouti and Mahdian, 2011) and water relations (Kufa and Burkhardt, 2011). ...
... Moreover, soil bulk density was significantly and indirectly related to saturated water-holding capacity, percolation rates and hydraulic conductivity of the soil as it has been reported by Kufa and Burkhardt (2011). This indicates the compactness of the soil with reduced pore spaces and decreased soil water content at field capacity. ...
The study focused on assessing soil physical properties under natural coffee forest ecosystems in southeast and southwest Ethiopia. For this, the Harenna, Berhane-Kontir, Bonga and Yayu forest coffee soils were collected from three sub-sites and two soil depth ranges at each area. Hence, a total of 24 soil samples were analyzed for major soil physical properties using the standard procedures. The results depicted significant differences among the coffee forests in soil texture particles (silt and sand), bulk density, soil moisture content, water holding capacity, permanent wilting point and available water holding capacity. The proportions of silt followed the order of Berhane-Kontir,Bonga,Yayu and Harenna soils. In contrast, the highest sand and clay contents were from Yayu and Harenna soils, respectively, possibly reflecting their variations in soil weathering process and parent materials, among others. Likewise, there were significant differences between soil depths in most soil physical parameters. In contrast to the increased clay and available water content, the silt and sand particles declined with the decrease in depth, indicating the more vulnerability of forest soils to erosion loss. The results also depicted that clay was negatively correlated with silt particles at all study areas. In contrast, the association between soil water contents at field capacity and permanent wilting point was direct and highly significant at most locations. In conclusions, the findings showed considerable site-specific variations in major soil physical properties and provided soil quality evidences for knowing and promoting natural coffee forest habitats in Ethiopia and elsewhere.
... Similarly, relative leaf water content and leaf thickness of accession H-857/98 were significantly higher, while the rate of recovery was higher for accession H-857/98 and 74110 [11]. Drought resistant coffee genotypes tend to increase root lengths in order to uptake deep soil moisture water through their deep root systems and decrease leaf area in order to improve plant water status [12][13][14]. Deeper root systems of tolerant clones enabled them to gain greater access to water towards the bottom of the pots and, therefore, to maintain more favorable internal water status for longer than drought-sensitive clones [15]. In general, among the Harerege coffees tested in this experiment, accession H-857/98 and H-856/98 showed the least stress score, higher total dry matter yield, higher relative leaf water content, better root-to-shoot ratio, and a higher rate of recovery after re-watering [11]. ...
... Tadesse (2019) [4] reports that the highest ETo value was recorded in March (4.61 mm day-1) and the lowest in July (2.91 mm day-1) while the monthly mean coffee ETc ranged from 80.9 mm (November) to 131.11 mm (April). The coffee ETc for the Jimma zone is a good indicator and benefits the coffee farmers in planning the water resources of the area for best agricultural water management practices [4,[33][34][35]. ...
Rainfall rarely meets the time with the required amount of water application for plant growth because of spatial and
temporal variability and due to this there was a low production. Thus, for a sustainable increase in agricultural
production and productivity, the intervention of irrigation is essential. Jimma Agricultural Research Center has been
conducting a lot of irrigation and water harvesting research and also generated essential research findings for its
mandate area from its establishment for the last one and half a decade. The objective of this review is to document
the major achievement of Irrigation and water harvesting, challenges and future prospects. The study was conducted
by reviewing the secondary data documents available on the web and through interviewing the previous researchers
who conducted research and also research documents that are available in the library of the Jimma Agricultural
Research center. Accordingly, the major research activities conducted in Jimma Agricultural Research Center under
the irrigation and water harvesting program on coffee crops were, Dry matter partitioning and physiological responses
of Coffea arabica varieties to soil moisture deficit stress at the seedling stage in Southwest Ethiopia, Growth Response
of Hararghie Coffee Accessions to Soil Moisture Stress at Seedling, Sensitivity of coffee Genotypes to Drought
Induced by Soil Drying at Early Growth stages, Growth and plant water relations of Arabica coffee in response to
deficit irrigation, Determination of Optimal irrigation scheduling for coffee and Estimation and mapping of coffee
water requirement using models. The major challenges were lack of irrigation infrastructure, lack of green house and
shelter, and lack of laboratory equipment. The future irrigation research will focus on climate change, salinity, ground
water monitoring, watershed-based irrigation, modelling, more advanced technology such as GIS and remote sensing.
Keywords: Achievements; Challenges; Coffee; Irrigation; Water harvesting
... Tadesse (2019) [4] reports that the highest ETo value was recorded in March (4.61 mm day-1) and the lowest in July (2.91 mm day-1) while the monthly mean coffee ETc ranged from 80.9 mm (November) to 131.11 mm (April). The coffee ETc for the Jimma zone is a good indicator and benefits the coffee farmers in planning the water resources of the area for best agricultural water management practices [4,[33][34][35]. ...
... The same findings demonstrated that the southeastern and southwestern coffee germplasm accessions were found to follow opportunistic and conservative ways of water use strategies, respectively. The substantial variations in root growth characteristics are in agreement with the findings under field conditions (Kufa and Burkhardt, 2011), indicating the consistency of root traits and in part underlined the diversity in adaptation mechanisms as pointed out by Sobrado (2003). ...
Root characteristics of coffee seedlings were studied with the main objective to compare the variations among twelve Coffea arabica germplasm accessions under contrasting nursery environments at Jimma Research Center, southwest Ethiopia.
Coffee seedlings from four wild coffee populations, namely, Harenna, Bonga, Berhane-Kontir and Yayu were ex-situ established under common nursery settings. The treatments included coffee germplasm accessions, shadings (moderate
shade and full sunlight) and irrigation levels (well-watered and water-stressed). One-year-old coffee seedlings were used to record root growth traits from five central seedlings per plot and the data were analyzed using SAS software. Coffee accessions significantly differed in most root characteristics. The longest and
shortest lateral roots were obtained from Yayu and Harenna seedlings, respectively. Berhane-Kontir accessions had significantly the lowest root volume as opposed to the highest value for the Harenna seedlings. Significantly higher root
dry biomass was obtained from unshaded than from shaded seedlings. The difference between watering regimes was also significant for root dry biomass and it was higher for water-stressed than for well-irrigated seedlings. Coffee accessions
were significantly differed in root proliferation and dry biomass and consequently, the lowest and highest average values were obtained from Berhane-Kontir and Harenna seedlings, respectively. The Harenna seedlings had a higher root mass
than the others, particularly the Berhane-Kontir accessions. The ratios of root to shoot dry biomass of the seedlings were significantly differed among coffee accessions, but not between shade and irrigation levels. The significantly lowest and highest root to shoot values was determined for the Berhane-Kontir and
Harenna accessions, respectively. Hence, Harenna genotypes can be considered as parents in coffee improvement programs under limiting water conditions.
The coffee research community has maintained a long ongoing debate regarding the implications of shade trees in coffee production. Historically, there has been contrasting results and opinions on this matter, thus recommendations for the use of shade (namely in coffee agroforestry systems) are often deemed controversial, particularly due to potential yield declines and farmers' income. This study is one of the first demonstrating how several Coffea arabica cultivars respond differently to shade with respect to yield. By standardising more than 200 coffee yield data from various in-field trials, we assembled the so-called "Ristretto" data pool, a one of a kind, open-source dataset, consolidating decades of coffee yield data under shaded systems. With this standardised dataset, our meta-analysis demonstrated significant genotypic heterogeneity in response to shade, showing neutral, inverted U-shaped and decreasing trends between yield and shade cover amongst 18 different cultivars. These findings encourage the examination of C. arabica at the cultivar level when assessing suitability for agroforestry systems. Comparison of productivity is also encouraged across a range of low to moderate shade levels (10-40%), in order to help elucidate potential unknown optimal shade levels for coffee production.
Climate change is posing a major challenge to coffee production worldwide leading to a need for the development of coffee cultivars with increased drought tolerance. In several plant species, the use of DREB genes in crop improvement has achieved promising results to desiccation tolerance engineering. Recent studies reported CcDREB1D specific patterns of expression in Coffea canephora and functional evidence of this gene involvement in drought stress responses. However, knowledge on natural diversity of this gene is largely unknown. In this context, this study aimed at evaluating the sequence variability of the DREB1D gene in several Coffea genotypes. Nucleotide variation in promoters and coding regions of this gene were evaluated in a population consisting of 38 genotypes of C. canephora, C. arabica and C. eugenioides, most of them characterized by different phenotypes (tolerance vs. susceptibility) in relation to drought. The genetic diversity of the loci revealed different haplotypes for the promoter and coding regions. In particular, our findings suggest association between drought tolerance and the genetic variations on DREB1D promoter regions, but not with those from its corresponding coding regions. Gene expression studies revealed up-regulated expression of DREB1D gene upon drought mainly in leaves of drought-tolerant clones of C. canephora, and in response to drought, high, and low temperatures in leaves of C. arabica, suggesting a key role of this gene in coffee responses to abiotic stress.
Coffee is native to shady environments, but often grows and yields better without shade. Thus, it may be reasoned that coffee
leaves should display enough plasticity to acclimate themselves to contrasting light environments. However, little is known
about mechanisms associated with such plasticity in coffee. This work aimed, therefore, to explore differences in leaf photoprotective
mechanisms. Plants were grown in the field and received either 48 or 100% natural light. Evaluations were made using outer
leaves from the sun-facing sides of the coffee hedgerow in Viçosa (Brazil) in August and October, when growth and photosynthetic
rates are expected to be minimal and maximal, respectively, and in December, when temporary depressions in those variables
are common. Regardless of light treatments, coffee leaves showed: (1) very low photosynthetic rates (generally below 2.5μmolm−2s−1), (2) chronic photoinhibition in August (dry, cool season) that was accompanied by strong loss of pigment concentration,
and (3) discrete, dynamic photoinhibition in October and December (rainy, warm season). Compared with shaded leaves, sunlit
leaves generally exhibited lower pigment concentration, lower quantum yield of electron transport, steeper inclinations and
similar electron transport rate. Total ascorbate pool tended to be larger in sunlit than in shaded leaves (but with similar
redox state), whereas activities of key antioxidant enzymes, as well as malondialdehyde accumulation and electrolyte leakage,
were similar between those leaf types. As a whole, the photosynthetic apparatus of the coffee tree showed a low phenotypic
plasticity to varying irradiance.
Shade trees reduce the stress of coffee (Coffea spp.) and cacao (Theobroma cacao) by ameliorating adverse climatic conditions and nutritional imbalances, but they may also compete for growth resources. For example, shade trees buffer high and low temperature extremes by as much as 5 °C and can produce up to 14 Mg ha−1 yr−1 of litterfall and pruning residues, containing up to 340 kg N ha−1 yr−1. However, N2 fixation by leguminous shade trees grown at a density of 100 to 300 trees ha−1 may not exceed 60 kg N ha−1 yr−1. Shade tree selection and management are potentially important tools for integrated pest management because increased shade may increase the incidence of some commercially important pests and diseases (such as Phythphora palmivora and Mycena citricolor) and decrease the incidence of others (such as Colletotrichum gloeosporioides and Cercospora coffeicola). In Central America, merchantable timber production from commercially important shade tree species, such as Cordia alliodora, is in the range of 4−6 m3 ha−1 yr−1.
The relative importance and overall effect of the different interactions between shade trees and coffee/cacao are dependent upon site conditions (soil/climate), component selection (species/varieties/provenances), belowground and aboveground characteristics of the trees and crops, and management practices. On optimal sites, coffee can be grown without shade using high agrochemical inputs. However, economic evaluations, which include off-site impacts such as ground water contamination, are needed to judge the desirability of this approach. Moreover, standard silvicultural practices for closed plantations need to be adapted for open-grown trees within coffee/cacao plantations.
The dynamics of growth (shoot and root dry weights, surface areas, hydraulic conductances, and root length) were measured
in seedlings of five neotropical tree species aged 4–16 months. The species studied included two light-demanding pioneers
(Miconia argentea and Apeiba membranacea) and three shade-tolerant young- or old-forest species (Pouteria reticulata, Gustavia superba, and Trichilia tuberculata). Growth analysis revealed that shoot and root dry weights and hydraulic conductances and leaf area all increased exponentially
with time. Alternative methods of scaling measured parameters to reveal differences that might explain adaptations to microsites
are discussed. Scaling root conductance to root surface area or root length revealed a few species differences but nothing
that correlated with adaptation to light regimes. Scaling of root surface area or root length to root dry weight revealed
that pioneers produced significantly more root area and length per gram dry weight investment than shade-tolerant species.
Scaling of root and shoot hydraulic conductances to leaf area and scaling of root conductance to root dry weight and shoot
conductance to shoot dry weight also revealed that pioneers were significantly more conductive to water than shade-tolerant
species. The advantages of scaling hydraulic parameters to leaf surface area are discussed in terms of the Ohm's law analogue
of water flow in plants.
This study was carried out in pioneer and successional forest tree species in a lower montane tropical forest with seasonal rains. We tested whether pioneer species feature high hydraulic conductance allowing them to use water profusely at leaf level. Conversely, forest species may have relatively low hydraulic conductance accompanied with better control over water use. This may lead in turn to pioneer species being at a relatively higher risk of shoot water potential falling below the threshold value at which cavitations occur compared to forest. Specific hydraulic conductance (K
s) measured during the wet season was comparable between pioneers and forest species. During drought, K
s was significantly reduced, and species of both plant groups responded to this by modifying the relationship between conducting area and leaf area (Huver value), such that leaf specific conductivity (K
l) was unaffected. Thus, leaf area seemed to be adjusted to maintain constant hydraulic sufficiency during drought. Pioneer species were more efficient in conducting water to their leaves but had low control over water use compared to forest species. A trade-off between water transport and leaf water use efficiency was suggested. These ecophysiological differences may have an impact on the performance of the species occupying contrasting habitats. Nonetheless, drought-induced embolisms occurred in trees growing in both open and forest habitats. Overall, during drought, adjustment of leaf area occurred in order to maintain a homeostasis of some physiological traits (leaf-specific conductivity and carbon assimilation).
Especially in the less favorable areas (altitude < 800 m and mean air temperature > 25 °C) that predominate in Central America,
there is a renewed interest in managing Arabica coffee (Coffea arabica L.) under shade after three decades of promoting intensively managed coffee systems planted in full sun with highly productive
dwarf cultivars. The presence of shade trees, especially leguminous species, improves soil fertility (organic matter content
and nutrient cycling) and enhances coffee plantation sustainability (Beer et al., 1998; Soto-Pinto et al., 2000). In suboptimal
coffee producing areas with low altitude, shade trees greatly reduce excessive solar irradiance and buffer large diurnal variations
in air temperature and humidity that are detrimental to coffee physiology (Gutiérrez et al., 1994; Siles and Vaast, 2002).
In mountainous areas, associated trees decrease soil erosion and nutrient leaching, especially nitrogen (Babbar and Zak, 1995).
Therefore, shade trees play an important role in the Central American region due to the valuable impact of coffee agroforestry
(AF) systems on the environment and natural resources such as preservation of biodiversity, soil conservation, water quality,
buffering effect around protected areas, reduced pressure on forests, and carbon sequestration (Somarriba et al., 2004). In
this region with a long-lasting reputation for commercializing quality coffee, shade can also contribute to the production
of high-quality coffee as demonstrated in Guatemala (Guyot et al., 1996), Costa Rica (Muschler, 2001), and Honduras (Decazy
et al., 2003). Nonetheless, trees associated to coffee are mainly legume species (Erythrina spp. and Inga spp.) with no timber values that are pruned periodically to avoid large decreases in coffee production due to competition
for light, nutrients and water during the dry period (Beer et al., 1998). Indeed, timber trees are less common in coffee AF
systems of Central America despite the fact that timber could greatly help farmers to diversify their income.
Drought-deciduous and evergreen species coexist in tropical dry forests. Drought-deciduous species must cope with greater seasonal leaf water-potential fluctuations than evergreen species and this may increase their susceptibility to drought-induced xylem embolism. The relationship between water transport efficiency and leaf life-span were determined for both groups. They differed in seasonal changes of both, wood water content (W
c) and wood specific gravity (G). During the dry season, the W
c in drought-deciduous species declined and the minimum value was recorded when leaf fall was complete. At this time, the volumetric fraction of gas (V
g) increased indicating air entry into xylem vessels. In contrast, W
c, G and V
g changed only slightly throughout the year for evergreen species. Maximum hydraulic conductivity of drought-deciduous species was 2–6 times that of the evergreen species. but was severely reduced at leaf fall. In the evergreen species, similar water conductivities were measured during wet and dry seasons. The trade-off between xylem water transport capacity and leaf lifespan found in species coexisting in this forest reveals the existence of contrasting but successful adaptations to this environment. Drought-deciduous species maximize production in the short term with higher water transport efficiency which leads to the seasonal occurrence of embolisms. Conversely, the behaviour of evergreen species with reduced maximum efficiency is conservative but safe in relation to xylem embolism.