Ecophysiological responses of Pinus massoniana to the CO_(2) enrichment

The net photosynthetic rate(Pn), stomotal conductance(gs), transpiration rate (E)and water use efficiency (Wue) were measured using a LI-6400 portable photosynthesis system for Pinus massoniana. In this experiment, the CO_2 concentration were set at three levels: 360 μmol·mol~(-1)?800 μmol·mol~(-1)?1 200 μmol·mol~(-1). The result showed that: under present CO_2 concentration(360 μmol·mol~(-1)) and 1 000 μmol·m~(-2)·s~(-1) of light intensity, the Pn of conifer leaves are 3.46 μmol·m~(-2)·s~(-1), E are 0.273 mmol.m~(-2).s~(-1), gs are 0.0254 mmol.m~(-2).s~(-1). Under these conditions, the light saturation and compensation points are (1 800±2) μmol·m~(-2)·s~(-1) and (24±2) μmol·m~(-2)·s~(-1). When CO_2 concentration reaches 1 200 μmol·mol~(-1), the light saturation points decreased by 200 μmol·m~(-2)·s~(-1), and the light compensation points increased by 4 μmol·m~(-2)·s~(-1). From 50 μmol·m~(-2)·s~(-1) to (2 000) μmol·m~(-2)·s~(-1), the mean Wue of conifer are as follows:19.163 μmol·mmol~(-1) under CO_2 concentration 1 200 μmol·mol~(-1), 12.912 μmol·mmol~(-1)under 800 μmol·mol~(-1), 11.192 μmol·mmol~(-1) under 360 μmol·mol~(-1). So, the effect of the leaves of Pinus massoniana to the CO_2 enrichment decreases the E and gs , but increase the Wue.