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

Water use, hydraulic properties and xylem vulnerability to cavitation were studied in the coffee (Coffea arabica L.) cultivars San Ramon, Yellow Catur ra and Typica growing in the field under similar environmental conditions. The cultivars differed in growth habit, crown morphology and total leaf sur face area. Sap flow, stomatal conductance (g(s)) crown conductance (g,), ap parent hydraulic conductance of the soil-leaf pathway (G(t)), leaf water po tential (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 C aturra. The cultivars had similar g, when well watered, but withholding wat er decreased g, more in Typica and Yellow Caturra than in San Ramon. Typica had substantially lower YL near the end of the unirrigated period than the other cultivars (-2.5 versus -1.8 MPa), consistent with the relatively hig h sap flow in this cultivar. Xylem vulnerability curves indicated that Typi ca was less susceptible to loss of hydraulic conductivity than the other cu ltivars, consistent with the more negative YL values of Typica in the field during the period of low soil water availability. During soil drying, wate r use declined linearly with relative conductivity loss predicted from vuln erability curves. However, cultivar-specific relationships between water us e and predicted conductivity-loss were not observed because of pronounced h ysteresis during recovery of water use following soil water recharge. All c ultivars shared the same functional relationship between integrated daily s ap flow and G(t), but they had different operating ranges. The three cultiv ars also shared common functional relationships between hydraulic architect ure and water use despite consistent differences in water use under irrigat ed and dry soil conditions. We conclude that hydraulic architectural traits , rate of water use per plant and crown architecture are important determin ants of short- and long-term variations in the water balance of Coffea arab ica.