Coffee is an important crop in the global south. However, ongoing changes in the climate system reinforce the need to quantify coffee plants' ecological and eco-physiological traits to assure coffee production in the future. One way to assess how environmental changes affect coffee performance is via leaf traits, most notably leaf carbon and nitrogen concentrations (to reflect the nutrient status), leaf stable carbon isotope composition (δ 13 C) to determine intrinsic water use efficiency (WUEi), and specific leaf area (SLA) to describe carbon gain relative to water loss within a plant canopy as these traits are related to yields. Therefore, we sampled coffee plants growing at contrasting elevations using a space-for-time substitution approach for warming and superimposed a canopy cover gradient to assess whether increasing canopy cover could modulate responses to temperature. Three coffee shrubs were sampled in each of 59 coffee farms in southwest Ethiopia across elevations of 1500-2160 m a.s.l. and along canopy cover gradients from open to deep shade. Soil nutrient concentrations, light availability, soil temperature and moisture were quantified for each coffee shrub. Elevation and shade tree canopy cover significantly and interactively affected WUEi. Elevation was found to be the driving factor for microclimate and soil factors which indirectly influenced both SLA and WUEi. Both of these coffee leaf traits are moderately governed by soil temperature whereas leaf N and C:N are mainly controlled by soil temperature and soil chemical variables. As elevation increased, WUEi kept increasing at light (< 35%) to intermediate shade levels (35-65%), and the values decreased at dense shade levels (65-100%) at high elevations, suggesting that coffee plants growing at high elevations with light shade can assimilate more CO 2 with minimum evaporative water loss. SLA declined with elevation. Leaf N and leaf C:N responded negatively and positively to shade canopy cover, respectively. In sum, elevation and canopy cover interactively determined microclimate and coffee leaf traits. Our findings are useful to adjust the intensity of shade, along with other tree-level management tools, to modulate climate-change effects on coffee at the farm level.
Green coffee bean quality and biochemistry are influenced by environmental variables. The present study was designed to study the influence of soil temperatures and soil chemistry on bean physical attributes, bean quality (assessed by three internationally trained, experienced and certified Q-grade cuppers licensed by the Specialty Coffee Association (SCA) Coffee Quality Institute (CQI) and biochemistry of green coffee beans). The study was performed in 53 farms in southwest Ethiopia distributed along an elevational gradients (1500 -2160 m a.s.l.) and with varying shade canopy cover (open to dense shade). A total of 159 individual coffee trees were sampled. Shade tree canopy cover, soil temperature, and soil chemistry as well as coffee management intensity were quantified as explanatory variables. Green bean quality was negatively correlated to soil temperatures. On the other hand, hundred bean mass and green bean biochemistry (caffeine, trigonelline and chlorogenic acid contents) were negatively correlated to soil temperatures but positively to soil chemistry. During the coffee fruit development period (flowering to fruit maturity), temperature appeared to be a driving factor influencing coffee bean quality and biochemistry. Total specialty quality was significantly associated with soil chemistry , in which 84% of the variation could be explained by soil chemical variables. This study is the first to demonstrate the relationship between soil temperatures and chemistry in coffee bean quality and green bean biochemical compositions. Although the relative importance of factors such as air temperatures and humidity and soil moisture are missing from this study, we find that soil temperatures and soil chemistry have a strong effect on coffee bean quality and biochemistry. Overall, climate change, which generally involves a substantial increase in mean temperatures of tropical regions, could be expected to have a negative impact on coffee bean quality and biochemistry.
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