The Latitude Trend On Photosynthesis Seasonality And Its Mechanism For Tropical Forests In Mainland Southeast Asia

Tropical forests are characterized by vast biomass,complex structures and mega-biodiversity.However,the adaptation processes of these forests to seasonal water availability are less understood,especially those located in the monsoonal and mountainous regions of tropical Southeast Asia.We used three methods together to address the latitude trend on photosynthesis seasonality in mainland southeast Asia.They are large scale remote sensing,eddy flux and ecosystem processes model.The remote sensing analysis were majorly used to discover the regional and general patterns on photosynthesis seasonality.We also carried correlation analysis for the spatial data to determine the major factor which could explain the photosynthesis seasonality spatially.In order to give a solid seasonal pattern,both sun-induced fluorescence and enhanced vegetation index were engaged in this study.The eddy flux data was used to confirm patterns findings suggested by regional analysis on the one hand.On the other,we take the advantage of high temporal resolution of this dataset for the physiological analysis.The reason for us to introduce ecosystem processes model in this study is to separate the contribution of physiological regulation and intrinsic rhythm of plants.Photosynthesis production is the start point of ecosystem energy flow and nutrient cycling.It also the key for terrestrial ecosystem carbon sequestration.Therefore,this study has both theoretical and practical significance.Given the severe forest destroy in the study region,it also has a strong emergence for us to carry this study.We believe our study could contribute to the understanding of our target scientific question in the following ways.First,we observed a clear and regular latitude trend on photosynthesis seasonality for forests in Mainland Southeast Asia.For forest near the equator,there clear bimodal seasonality.Along with increase of latitude,the double peak shifted into single peak.On the other hand,the seasonality becomes stronger and mean photosynthesis rate decreased as latitude increases.Second,for the forest exhibit double peak photosynthesis seasonality,dry spell could reduce stomatal openness but in a very limited way.The light-saturated photosynthesis rate was maintained or even higher during the dry spells.This was controverse for evergreen forest grow in seasonal climate and exhibit single peak photosynthesis seasonality.Third,all methods suggest the incident solar radiation at the top of atmosphere(R_TOA)play significant role in contribute to photosynthesis seasonality.This contribution was very clear for regions near equator.The effect of climate seasonality will act confounding effect on photosynthesis seasonality which cover the contribution of R_TOA.Fourth,we proposed a new hypothesis which could explain how R_TOA affect leaf seasonal rhythm,and subsequently on photosynthesis seasonality.More importantly,we give it a solid evolutionary account for this explanation.