甘南地区二氧化碳施肥效应对生态系统的影响

Fertilization effect of carbon dioxide on ecosystems in Gannan,China

陆地生态系统是全球第二大碳库,其碳收支一直是气候变化研究的热点领域,而研究二氧化碳(CO_(2))施肥效应又是全球变化碳循环领域较为关注的前沿部分。CO_(2)与生态系统关系复杂,当前仍无法厘清CO_(2)对陆地生态系统碳循环的影响作用。基于太阳辐射数据、气温数据及归一化植被指数数据等,利用光能利用率遥感模型,模拟2019年甘南地区的碳循环,选取三个指标,即GPP(陆地生态系统总初级生产力)、NPP(净初级生产力)和NEP(净生态系统生产力)来分析甘南地区植被固碳的时空变化特征及CO_(2)施肥效应。结果表明:(1)甘南地区2019年植被固碳总量约为2611 tC。甘南地区生态系统GPP、NPP和NEP季节性特征明显,其值均在夏季达到最高;而在空间上,GPP、NPP表现为东高西低的特征,NEP呈现出北高南低的分布特征。(2)CO_(2)对GPP、NPP存在正向的施肥效应,分别增加了14.4%和14.3%;而对NEP具有负向反馈效应,使其减少了0.3%,并且CO_(2)对NEP的影响整体也表现为北高南低的特征。研究揭示出:虽然CO_(2)在提升GPP和NPP时,正向的施肥效应明显,但是对甘南地区的NEP,即固碳量来说,CO_(2)的影响却很有限。因此在研究CO_(2)施肥效应时不应一概而论,生态地理环境对其的影响不可忽视。研究可以为揭示陆地生态系统碳循环的动态机制提供一定的理论依据。

Terrestrial ecosystems are the second largest carbon pool in the world,and their carbon budget has always been a hot field in climate change research.Any slight change in the ecosystem will cause changes in the global carbon cycle and budget,and the study of fertilization effect of carbon dioxide(CO_(2))is the forefront part of global change carbon cycle.The relationship between CO_(2)and ecosystem is complex,and the effect of CO_(2)on carbon cycle of terrestrial ecosystem is still unclear at present.Current studies normally use the gross primary productivity(GPP)and net primary productivity(NPP)to study the impacts of CO_(2)fertilization effect on ecosystem carbon sequestration,even though they do not completely explore the autotrophic and heterotrophic consumption of ecosystems.The net ecosystem productivity(NEP)used to study the fertilization effect of CO_(2)on ecosystem carbon sequestration is more accurate and more valuable,but the related research is still relatively insufficient,currently.In this study,based on temperature data,solar radiation data,and normalized difference vegetation index data from remote sensing,a light energy utilization model was used to simulate the carbon cycle in Gannan,China in 2019.Three key carbon cycle indicators,namely GPP,NPP,and NEP were selected to analyze the spatial and temporal variation characteristics of ecosystem carbon sequestration and CO_(2)fertilization effect in Gannan.The results showed that:(1)the total amount of carbon sequestration by ecosystem in Gannan in 2019 was about 2611 tC.The seasonal characteristics of GPP,NPP and NEP in Gannan were obvious,and their values reached the highest in summer.From the spatial perspective,the GPP and NPP were characterized by high in the east and low in the west while NEP was characterized by high in the north and low in the south in Ganan.(2)CO_(2)had positive fertilization effect on GPP and NPP,which increased by 14.4%and 14.3%,respectively;However,it had a negative feedback effect on NEP,reducing it by 0.3%,and the overall influence of CO_(2)on NEP was characterized by high in the north and low in the south in Ganan.This study reveals that although the positive fertilization effect of CO_(2)is obvious in promoting GPP and NPP,the effect of CO_(2)on NEP,namely carbon sequestration,is very limited in Gannan.Therefore,we should not make generalizations when studying the effects of CO_(2)fertilization.The impacts of ecological geography on it cannot be ignored.This study can provide a certain theoretical basis for revealing the dynamic mechanism of terrestrial ecosystem carbon cycle.