Study on evapotranspiration and canopy photosynthesis during and after rainfall in a Japanese cypress forest

概要

Abstract
ｼﾞｬｵ ﾘﾝｼﾞｪ

JIAO LINJIE
Thesis title
Study on evapotranspiration and canopy photosynthesis during and after
rainfall in a Japanese cypress forest
（降雨中・直後のヒノキ林における蒸発散および群落光合成に関する研究）
This study used an enclosed-path gas analyzer for the continuous ecosystem
fluxes observation in a temperate evergreen coniferous (Japanese cypress) forest in the
Asia monsoon area. In canopy-wet period, simulation of different interception
situations (wet area ratio and water storage capacity) by a multilayer model was
combined with eddy covariance measurement to evaluate interception evaporation from
the abaxial surface of leaves, and the relationship between abaxial interception and wet
canopy photosynthesis. For the canopy-dry period, the gas exchange of dry canopy at
different periods after wetness ended was compared and evaluated to verify the lasting
effect of rainfall improving dry canopy gas exchange. The comparison of the simulated
and observed latent heat flux(λE) suggests the occurrence of interception evaporation
from both sides of leaves at the wet Japanese cypress forest canopy. This phenomenon
is more likely to happen after heavy rainfall, while the abaxial surface may not be fully
wet as the adaxial surface after small rainfall. The comparison of the simulated and
observed net ecosystem exchange (NEE) suggests that the abaxial surface of Japanese
cypress leaves was only partly wet by interception during and after rainfall, thus the
wet canopy can maintain depressed photosynthesis. The averaged and accumulated
NEE showed the wet canopy CO2 uptake is mainly contributed by the photosynthesis
at the post-rainfall canopy-wet period rather than during-rainfall period. The increased
gas exchange (λE and NEE, and canopy conductance) was found at the dry canopy
immediately after wetness ended, suggesting the positive effect of rainfall-induced leaf
wetness on forest gas exchange. These results indicate the ecological value of rainfallinduced leaf wetness to the temperate evergreen coniferous forest gas exchange and
revealed the mechanism of wet Japanese cypress canopy maintaining gas exchange. ...