The Influence Factors Of Carbon Flux Of Grassland In The Loess Hilly Region Of Northern Shaanxi

Grassland is an important component of the terrestrial ecosystem.Therefore strengthen the study of grassland has important practical significance for maintaining ecological balance in northwest of China and strengthen regional soil erosion manage even can further clarify the global carbon balance.This study taking Tarragon-Artemisia vestita grassland in Loess Hilly Region of China for research objects.Using a three year data set of eddy covariance flux measurements of CO2 fluxes(NEP,net ecosystem productivity;GEP,gross ecosystem productivity;RE,ecosystem Respiration)in 2012-2014.Reliable CO2 flux data were obtained by data processing and quality control.We discussed the biological and environmental controls on the CO2 flux at different time scales.In addition,we found the studies by eddy covariance which included 15 grasslands in China.We analyzed the spatial variation characteristics and influence factors of CO2 fluxes.The main results can be summarized as follows:(1)The Tarragon-Artemisia vestita grassland in Loess Hilly Region of China is a net carbon sink,carbon sequestration capacity is higher than temperate grassland in China.NEP presented seasonal variation characteristics.At the growing season,the value of NEP is the highest but in autumn and winter is the lowest.NEP in 2012-2014 were 250.33 g Cm-2yr-1?339.94 g Cm-2yr-1?318.99 g Cm-2yr-1,respectively.(2)GEP presented seasonal variation characteristics,the value in 2012-2014 were 433.2 g Cm-2yr-1?476.1 g Cm-2yr-1?453.7 g Cm-2yr-1,respectively(CV=4%).The value of RE were 182.9 g Cm-2yr-1?136.2 g Cm-2yr-1?134.7 g Cm-2yr-1,respectively.The value of RE in peak season is higher than that in begin and last growing season at monthly scale.(3)Analysis on single factors,Ta is the most impotent factor for NEP and GEP at daily scale,but the factors are not clear for RE at daily scale.The most impotent factor for NEP,GEP and RE is EVI,and the other factors are Ta,P and Rn in turn.(4)The results showed in complex influence with many factors.NEP and GEP at daily scale were mainly affected by Rn,Ta and VPD,NEP at monthly scale was influenced by Ta and EVI,GEP at monthly scale was affected by Ta,EVI and VPD.Besides,RE at daily scale was influenced by Ta and VPD while RE at monthly scale was only affected by EVI.The results also showed that Ta played a dominative role for Rn through its effects on CO2 flux,EVI could improve the influence of Ta,while VPD could reduce the impact of Rn and Ta.(5)Seasonal drought decreased NEP and GEP but made no significantly influence in RE.NEP and GEP were mainly affected by Ta and SWC at the stage of drought stress.(6)Grassland ecosystem carbon fluxes(NEP,GEP and RE)in China had the spatial variation characteristics,the relationship with latitude is quadratic function.The values of carbon fluxes are the highest when the latitude reach 36-37°N.(7)MAP,MAT and EVI are the impotent factors for the spatial variation characteristics of grassland ecosystem carbon fluxes.The relationship between MAP and GEP,RE is quadratic function.The relationship between MAT and NEP,RE is liner.The relationship between EVI and NEP,GEP,RE is liner.