Water utilization, plant hydraulic properties and xylem vulnerability in three contrasting coffee (Coffea arabica)...

Water use, hydraulic properties and xylem vulnerability to cavitation were studied in the coffee (Coffea arabica L.) cultivars San Ramon, Yellow Caturra and Typica growing in the field under similar environmental conditions. The cultivars differed in growth habit, crown morphology and total leaf surface area. Sap flow, stomatal conductance (g(s)), crown conductance (g(c)), apparent hydraulic conductance of the soil-leaf pathway (G(t)), leaf water potential (Psi(L)) and xylem vulnerability to loss of hydraulic conductivity were assessed under well-watered conditions and during a 21-day period when irrigation was withheld. Sap flow, g(c), and G(t) were greatest in Typica both with and without irrigation, lowest in San Ramon, which was relatively unresponsive to the withholding of irrigation, and intermediate in Yellow Caturra. The cultivars had similar g(s) when well watered, but withholding water decreased g(s) more in Typica and Yellow Caturra than in San Ramon. Typica had substantially lower Psi(L) near the end of the unirrigated period than the other cultivars (-2.5 versus -1.8 MPa), consistent with the relatively high sap flow in this cultivar. Xylem vulnerability curves indicated that Typica was less susceptible to loss of hydraulic conductivity than the other cultivars, consistent with the more negative Psi(L) values of Typica in the field during the period of low soil water availability. During soil drying, water use declined linearly with relative conductivity loss predicted from vulnerability curves. However, cultivar-specific relationships between water use and predicted conductivity loss were not observed because of pronounced hysteresis during recovery of water use following soil water recharge. All cultivars shared the same functional relationship between integrated daily sap flow and G(t), but they had different operating ranges. The three cultivars also shared common functional relationships between hydraulic architecture and water use despite consistent differences in water use under irrigated and dry soil conditions. We conclude that hydraulic architectural traits, rate of water use per plant and crown architecture are important determinants of short- and long-term variations in the water balance of Coffea arabica.