| Summary: | To investigate the physiological responses and latex yield of rubber trees under irrigation management, an experiment was established at Songkhla Province, southern Thailand. The sap flow of rubber trees was measured by heat-pulse technique. First, the anatomy of sapwood and the optimum depth for implanting the sap flow sensor probe were determined. Then, the diurnal changes of the physiological responses (sap flow, leaf water potential, and stomatal conductance) and latex yield under three regimes of irrigation (T1: no irrigation, T2: irrigation at 1.0 crop evapotranspiration (ETc) and T3: irrigation at0.5 ETc) were determined. The results showed that xylem vessels in sapwood were homogeneous and the optimum depth for implanting the sap flow sensor probes was 10 mm beneath the cambium. In the measurements of diurnal changes of the physiological responses, it was found that stomatal conductance and sap flow rates were related to radiation. Sap flow and stomatal conductance increased from the morning to the midday. Then they decreased slowly during the afternoon. However,leaf water potential changes showed an opposite effect. Among the three treatments, the results showed that sap flow, leaf water potential and stomatal conductance in T2 were highest. The trees in T2 also exhibited the highest latex yield from April to July 2006, which was significantly different from those of T3 and T1. This implied that latex yield increased with an increase of sap flow.
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