Gas exchange characteristics of tea (Camellia sinensis) in subtropics

Abstract

The patterns of net photosynthetic rate (P_N), transpiration rate (E), stomatal conductance (g_s), leaf water potential (ψ_L) and water use efficiency (P_N/E) of intact leaves and stem diameter in field grown tea (Camellia sinensis (L) O. Kuntze), clone T78 representing �China� jat were evaluated at monthly intervals during 1999 and 2000. The maximum value of P_N was recorded in October when relative humidity was very high, air temperature, soil moisture (Sm) were moderate and photosynthetic photon flux density (PPFD) was maximum, P_N was lowest in August, when humidity and soil moisture were highest, and PPFD were lowest. Higher values of g_s were recorded during July/August (rains) and lowest in March/April (summer). ψ_L decreased from �1.6 MPa in August to �2.8 MPa in May. Decrease in E was more pronounced during March and April. The maximum value of P_N was recorded up to a VPD of 2.3 in October; there after P_N declined slowly. In general, a reduction in g_s with higher VPD values was observed. Maximum P_N/E observed in March and decreased during rains. P_N was positively correlated with PPFD, E, g_s, P_N/E and VPD. A positive correlation between Chl content and P_N also existed. Higher rate of stem diameter (SD) increment observed during June to August (rains) and lowest increment was recorded during December (winter), January, and April/May. The correlation between SD and P_N was found negative. In general, higher SD coincided with higher ψ_Land E.

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