Effect of leaf wetness on canopy gas exchange has not been highlighted so far. Current studies have not reached a consensus on whether leaf wetness inhibits or stimulates canopy evapotranspiration and photosynthesis with respect to the type of vegetation, and few of them worked over forest canopies. Seasonal variation of canopy conductance for Japanese cypress forest has been documented, while the discussion about its variation relating to leaf wetness is insufficient.
We combined the method of eddy covariance and wetness sensor monitoring with the big-leaf analysis to evaluate the variation of canopy conductance (g_c) at different wetness situations (wet, wet-free and dry). Wetness sensors were attached to leaves at three heights of the canopy. 8-10 sensors were deployed in random at each height. The signal voltage of the sensor shows the wetness duration and intensity.
Low R_n (net radiation) and VPD (vapor pressure deficit) limited the process of photosynthesis and evapotranspiration for the wet canopy. A surge of gc and evapotranspiration was detected over the wet-free periods rather than the dry and wet periods.