Control of transpiration in three coffee cultivars: the role of hydraulic and crown architecture

Abstract 

Water use and hydraulic architecture were studied in the coffee (Coffea arabica) cultivars San Ramon, Yellow Caturra and Typica growing in the field under similar environmental conditions. The cultivars differed in growth habit, crown architecture, basal sapwood area and total leaf surface area. Transpiration per unit leaf area (E), stomatal conductance (g _s), crown conductance (g _c), total hydraulic conductance of the soil/leaf pathway (G _t) and the stomatal decoupling coefficient, omega (Ω) (Jarvis and McNaughton 1986) were assessed over a range of soil moisture and during partial defoliation treatments. The relationship between sap flow and sapwood area was linear and appeared to be similar for the three cultivars. Variation in g _c, E, and G _t of intact plants and leaf area-specific hydraulic conductivity (k _l) of excised lateral branches was negatively correlated with variation in the ratio of leaf area to sapwood area. Transpiration, g _c, and g _s were positively correlated with G _t. Transpiration and G _t varied with total leaf area and were greatest at intermediate values (10 m²) of leaf area. Omega was greatest in Yellow Caturra, the cultivar with the greatest leaf area and a dense crown, and was smallest in Typica, the cultivar with an open crown. Differences in omega were attributable primarily to differences in leaf boundary layer conductance among the cultivars. Plants of each cultivar that were 40% defoliated maintained sap flows comparable to pretreatment plants, but expected compensatory increases in g _s were not consistently observed. Despite their contrasting crown morphologies and hydraulic architecture, the three cultivars shared common relationships between water use and hydraulic architectural traits.