Abstract
The directionality of the response of gross primary productivity (GPP) to climate has been shown to vary across the globe. This effect has been hypothesized to be the result of the interaction between multiple bioclimatic factors, including environmental energy (i.e. temperature and radiation) and water availability. This is due to the tight coupling between water and carbon cycling in plants and the fact that temperature often drives plant water demand. Using GPP data extracted from 188 sites of FLUXNET2015 and observation-driven terrestrial biosphere models (TBMs), we disentangled the confounding effects of temperature, precipitation and carbon dioxide on GPP, and examined their long-term effects on productivity across the globe. Based on the FLUXNET2015 data, we observed a decline in the positive effect of temperature on GPP, while the positive effects of precipitation and CO2 were becoming stronger during 2000–2014. Using data derived from TBMs between 1980 and 2010 we found similar effects globally. The modeled data allowed us to investigate these effects more thoroughly over space and time. In arid regions, the modeled response to precipitation increased since 1950, approximately 30 years earlier than in humid regions. We further observed the negative effects of summer temperature on GPP in arid regions, suggesting greater aridity stress on productivity under global warming. Our results imply that aridity stress, triggered by rising temperatures, has reduced the positive influence of temperature on GPP, while increased precipitation and elevated CO2 may alleviate negative aridity impacts.
Highlights
Terrestrial gross primary productivity (GPP), the total carbon uptake by photosynthesis of plants per ground area at the ecosystem scale, is the largest component of the global carbon cycle (Beer et al 2010) and helps to offset anthropogenic emissions of CO2 (Battin et al 2009)
On the basis of FLUXNET2015 data, when not considering CO2, we found that the positive effect of temperature on GPP showed a significant decrease between 2000 and 2014 across the globe
Between 1980 and 2010, the positive effect of temperature on GPP showed a significant decrease at the global scale, whereas a significant increase in the positive effect of precipitation was observed since 1980
Summary
Terrestrial gross primary productivity (GPP), the total carbon uptake by photosynthesis of plants per ground area at the ecosystem scale, is the largest component of the global carbon cycle (Beer et al 2010) and helps to offset anthropogenic emissions of CO2 (Battin et al 2009). Global climate change has greatly altered GPP across different geographic regions (Zhang et al 2009, Garbulsky et al 2010, Anav et al 2015, Burley et al 2016, Hao et al 2018). Many studies have shown that year-toyear variability of GPP is largely driven by the variations of energy- and water-related climate variables, including temperature, solar radiation, precipitation as well as CO2 (Nemani et al 2003). The directionality of the changes in GPP in response to these climate variables can be both positive and negative across different regions and periods. The interactive effects of water and energy further complicate the predictions of the spatio-temporal changes in their effects on the GPP under global warming (Zhao and Running 2010). A global analysis is imperative to clarify the responses of the GPP to climate drivers in order to reconcile observed contradictory relationships, and to more accurately predict the impacts of global climate change on carbon cycling
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