Interception and Gas Exchange Feature of a Temperate Evergreen Coniferous Forest in Asian Monsoon Area during and after Rainfall by using Multilayer Model

Abstract:

Correct evaluation of evapotranspiration and photosynthesis during and after rainfall is important for understanding the water circulation and carbon sink function of forests in Monsoon area with frequent rainfall events. The shape of coniferous leaf causes the possibility of interception by both leaf surfaces, and thus limits gas exchange by blocking the stomatal during the rainfall. However, measuring the actual interception in leaf scale and gas exchange during and after rainfall are difficult.

In this study, we used the enclosed path infrared gas analyser to improve the results of applying eddy covariance method in a temperate evergreen coniferous forest in central Japan (FLUXNET code: KEW). Meanwhile, by using a SVAT multilayer model, we simulated the wetness profile and latent heat flux (λE) of the wet canopy in two situations: free gas exchange with interception only by the adaxial surface (model 1) and no gas exchange with interception by both surfaces (model 2).

The simulation shows wetness and VPD profile is getting increasingly homogeneous with the upgrading of rainfall intensity, which is corresponding to the results by wetness sensors’ monitoring. The relationship between measured, simulated λE and VPD (vapor pressure deficit) shows that both model 1 and model 2 are close to measured λE in low VPD situation, while model 1 is closer to measured data in high VPD situation than model 2. This result indicates the potential of gas exchange activity from wet canopy. Carbon uptake shown by the annual daytime NEE (net ecosystem exchange) from wet canopy also agrees with this point.