Regulation of water use in three contrasting coffee (Coffea arabica) cultivars

Water use and hydraulic architecture were studied in the coffee ( Coffea arabica) cultivars San Ramon, Yellow Caturra and Typica. They differed in growth habit, crown architecture, basal sapwood area, and total leaf area. Sap flow, stomatal conductance (gs), crown conductance (gc), apparent hydraulic conductance of the soil-leaf pathway (Gt), leaf water potential ( YL ) and the stomatal decoupling coefficient ( W ) were assessed over a range of soil moisture and during partial defoliation treatments. Xylem vulnerability to loss of hydraulic conductivity was also determined for excised lateral branches. Sap flow, g c, and Gt were greatest in Typica, with and without irrigation. Yellow Caturra had intermediate values of sap flow, gc, and Gt comparable to that of San Ramon when irrigated, but these were dramatically reduced without irrigation. Withholding water decreased gs more in Typica and Yellow Caturra. Typica experienced substantially lower YL when water was withheld, and xylem vulnerability curves revealed Typica to be less susceptible to loss of hydraulic conductivity. Relationships between declining Gt and loss of hydraulic conductivity predicted from YL and xylem vulnerability curves were distinct for each cultivar, and suggested that caution is needed when extrapolating results obtained with excised branches to behavior of intact plants in the field. A common linear relationship between sap flow and sapwood area was found for three cultivars. Yellow Caturra had the highest ratio of leaf area to sapwood area (LA/SA). Variation in gc, transpiration ( E), and Gt was negatively correlated with variation in LA/SA, as was variation in leaf area-specific hydraulic conductivity of excised lateral branches. E and gc were positively correlated with G t. E and Gt peaked at intermediate values (10 m2) of whole-plant leaf area. W was greatest in Yellow Caturra, which had the greatest leaf area and a dense crown, and was smallest in Typica, which had an open crown. Differences in W were attributable primarily to differences in boundary layer conductance. Plants of each cultivar that were 40% defoliated had sap flow comparable to untreated plants. Despite their contrasting crown morphologies and hydraulic architecture, the three cultivars shared common relationships between water use and hydraulic architectural traits.