Vegetation structural change and CO2 fertilization more than offset gross primary production decline caused by reduced solar radiation in China

Abstract

Terrestrial gross primary production (GPP) is the largest carbon flux from the atmosphere to the terrestrial ecosystems. However, how GPP dynamics respond to vegetation structural change (VSC), climate change, and rising CO2 concentration are still unclear. In this study, we developed a process-based model (i.e., Farquhar GPP Model) to characterize GPP dynamics in China from 2001 to 2016, and further identify the dominant drivers for GPP variation related to VSC, climate change, and rising atmospheric CO2 through model scenario design. During the study period, VSC showed an overwhelmingly positive impact on annual total GPP (i.e., 39.2 Tg C yr−1, P<0.001), followed by the fertilization effect of rising CO2 (i.e., 11.9 Tg C yr−1, P<0.001). However, climate variation would be expected to have an overall negative effect (i.e., -9.9 Tg C yr−1, P<0.001), which is primarily related to the decline of the incoming solar radiation over this period. Consequently, China's GPP showed a remarkable upward trend (i.e., 40.5 Tg C yr−1, P<0.001) during the study period. Our study highlighted the strong positive GPP contribution from VSC, which is mainly related to forest increase under the background of forest cover changes primarily from widespread forest conservation and restoration programs implemented in China since the late 1990s. Therefore, our study suggests that forest conservation and restoration could effectively increase terrestrial ecosystem GPP, despite the negative effects of climate change.