Projecting terrestrial responses to increasing atmospheric CO2 concentration and feedbacks to the climate system requires a thorough understanding of how rising levels of carbon dioxide affect plant processes (CO2 fertilization effects). Although experiments using higher CO2 have shown that elevated CO2 (eCO2) generally enhances plant productivity, the extent of enhancement varies substantially across ecosystems for reasons that remain unclear. Using data from CO2 enrichment experiments, we analyzed interactions of eCO2 with water supply and their impacts on aboveground net primary productivity (ANPP).
Results/Conclusions
We found that the CO2 enhancement of ANPP is sensitive to annual precipitation and this sensitivity differs significantly for ecosystems with different lifeforms. The difference is likely related to the capacity of leaf area extension in wet years, which consequently affects responses of plant productivity to eCO2. By using empirical data, we developed a general equation between enhanced leaf area index (LAI) and enhanced ANPP, which can be applied to remote sensing observations for quantifying eCO2 impacts on terrestrial productivity. Using LAI and net primary production (NPP) data derived from MODIS, we estimated that terrestrial NPP has increased by ~ 1.93 PgC/yr due to eCO2 enhancement over the last decade. Equivalently, eCO2 enhancement could have added ~0.10 PgC/yr to terrestrial carbon sink and accounted for 80% of the enhanced terrestrial C sink over this time.