Ratio of photosynthetically active radiation to global solar radiation above forest canopy in complex terrain:measurements and analyses based on Qingyuan Ker Towers  

作　　者：Shuangtian Li Qiaoling Yan Tian Gao Xingchang Wang Qingwei Wang Fengyuan Yu Deliang Lu Huaqi Liu Jinxin Zhang Jiaojun Zhu 

机构地区：[1]CAS Key Laboratory of Forest Ecology and Silviculture,Institute of Applied Ecology,Chinese Academy of Sciences,Shenyang 110016,China [2]Qingyuan Forest CERN,National Observation and Research Station,Chinese Academy of Sciences,Shenyang 110016,China [3]CAS‑CSI Joint Laboratory of Research and Development for Monitoring Forest Fluxes of Trace Gases and Isotope Elements,Institute of Applied Ecology,Chinese Academy of Sciences(CAS),Shenyang 110016,China [4]University of Chinese Academy of Sciences,Beijing 100049,China [5]Center for Ecological Research,Northeast Forestry University,Harbin 150040,China

出　　处：《Ecological Processes》2024年第2期204-217,共14页生态过程(英文)

基　　金：supported by the National Key R&D Program of China(2016YFC0500300);the Strategic Leading Science&Technology Programme,CAS(XDA23070100);National Natural Science Foundation of China(31870533)

摘　　要：Background Understanding of the ratio of photosynthetic photon flux density(Q_(p))to global solar radiation(R_(s))(Q_(p)/R_(s))is crucial for applying Rsto ecology-related studies.Previous studies reported Q_(p)/R_(s)and its variations based on measurements from a single observatory tower,instead of multi-site-based measurements over complex terrains.This may neglect spatial heterogeneity in the terrain,creating a gap in an understanding of how terrain affects Q_(p)/R_(s)and how this effect interacts with meteorological factors.Methods Here the Qingyuan Ker Towers(three towers in a valley with different terrains:T1,T2,and T3)were utilized to measure Qpand Rsover mountainous forests of Northeast China.An airborne LiDAR system was used to generate a digital elevation model,and sky view factor of sectors(SVF_(s))divided from the field of view of tower's pyranometer was calculated as a topographic factor to explain the variations of Q_(p)/R_(s).Results The results identified significant differences in Q_(p)/R_(s)of the three towers at both daily and half-hour scales,with larger differences on clear days than on overcast days.Q_(p)/R_(s)was positively correlated with SVF_(s)of T1 and T3,while this correlation was negative with that of T2.The effect of SVF_(s)on Q_(p)/R_(s)interacted with clearness index,water vapor pressure and solar zenith angle.Random forest-based importance assessment demonstrated that explanation(R^(2))on Q_(p)/R_(s)was improved when SVF_(s)was included in the predictor variable set,indicating that incorporating terrain effects enhances the prediction accuracy of Q_(p)/R_(s).The improvement in the R^(2)values was more pronounced on clear days than on overcast days,suggesting that the effect of terrain on Q_(p)/R_(s)depended on sky conditions.Conclusions All findings suggested that Q_(p)/R_(s)is affected by terrain,and integrating terrain information into existing Q_(p)/R_(s)models is a feasible solution to improve Q_(p)/R_(s)estimates in mountainous areas.

关 键 词：Photosynthetic photon flux density Clearness index Water vapor pressure Solar zenith angle TERRAIN Sky view factor 

分 类 号：P422.1[天文地球—大气科学及气象学] S718.5[农业科学—林学]