| Co-Investigator(Kenkyū-buntansha) |
MONJI Nobutaka Osaka Prefecture Univ., Graduate School of Agriculture and Biological Sciences, Professor, 大学院・農学生命科学研究科, 教授 (20111982)
HAMOTANI Ken Osaka Prefecture Univ., Graduate School of Agriculture and Biological Sciences, Assistant Professor, 大学院・農学生命科学研究科, 講師 (30264815)
MACHIMURA Takashi Osaka Univ., Graduate School of Engineering, Associate Professor, 大学院・工学研究科, 助教授 (30190383)
TAKAGI Kentaro Hokkaido Univ., Field Science Center for Northern Biosphere, Research Associate, 北方生物圏フィールド科学センター, 助手 (20322844)
OKADA Keiji Hokkaido Univ., Graduate School of Agriculture, Research Associate, 大学院・農学研究科, 助手 (30333636)
|
|---|
| Research Abstract |
An extremely important objective of long-term observations of CO_2 flux is to improve the understanding of climatic effects on the CO_2 exchange process between terrestrial ecosystems and the atmosphere for predicting net CO_2 ecosystem exchange (NEE). Nevertheless, reports that address NEE remain limited for Asian ecosystems. This paper reports the three-year measurement of NEE over a manmade Japanese larch forest in northern Japan, which is one of the most important forests for forestry in this area, using an eddy covariance technique with an open-path system from 2001 to 2003. Differences of the phase and amplitude between gross primary production (GPP) and ecosystem respiration (RE) in their seasonal variation were reflected on the seasonal course of NEE. Meteorology, LAI, and the photosynthetic physiology of vegetation controlled seasonal variation of GPP ; on the other hand, that of RE was mainly determined by temperature. Although PPFD was the most important meteorological facto
… More
r for GPP, high VPD reduced CO_2 assimilation under high PPFD conditions. Interannual variations in GPP, RE, and NEE occur according to environmental factors. Annual sums of NEE, GPP and RE were: -472, -1574, and 1103 gC M^<-2> y^<-1> for 2001 ; -503, -1543, and 1040 gC m^<-2> y^<-1> for 2002 ; and -524, -1667, and 1143 gC m^<-2> y^<-1> for 2003. Those values were estimated using u^* threshold of 0.2 m s^<-1>. Three-year averages of NEE, GPP, and RE were -499±26 (Standard deviation), -1595±65, and 1095±52 gC m^<-2> y^<-1>, respectively, which suggests that the larch forest worked as a large carbon sink. Difference in annual GPP among three years was larger than that of annual RE, which mainly caused interannual NEE variation. In 2003, the ecosystem absorbed the most carbon because of the most negative GPP with the largest PPFD occurs during the foliate season in spite of the largest annual RE. In spring, the ecosystem began to photosynthesize about two weeks earlier in 2002 than in other years because of early snowmelt and larch foliation. In contrast, during the summer season, GPP was less negative in 2002 than in other years because of small maximum GPP (P_<max>) and low PPFD. One reason for the small P_<max> may be the higher daytime precipitation frequency because leaf surface wetness restricted CO_2 assimilation through stomatal regulation caused by loss of Rubisco. Another possibility is early germination, which reduced photosynthetic N-use efficiency because of decreased N allocation to Rubisco with the change of leaf structure. Less
|
