Mutual inhibition effects of elevated CO₂ and climate change on global forest GPP

The impact of CO₂ fertilization on enhancing global forest gross primary productivity (GPP) is acknowledged, but its interaction with climate factors-air temperature (Tem), precipitation (Pre), vapor pressure deficit (VPD), and radiation (Rad)-remains unclear. In this study, global forest GPP trends from 1982 to 2018 were examined using BEPS, NIRv, FLUXCOM, and revised EC-LUE datasets, with interannual trends of 5.618 (p < 0.01), 5.831 (p < 0.01), 0.227, and 6.566 g C m^-2 yr^-1 (p < 0.01), respectively. Elevated CO₂ was identified as the primary driver of GPP trends, with the dominant area ranging from 51.11% to 90.37% across different GPP datasets. In the NIRv and revised EC-LUE datasets, the positive impact of CO₂ on GPP showed a decrease of 0.222 g C m^-2 yr^-1, while the negative impact of Rad increased by 0.007 g C m^-2 yr^-1. An inhibitory relationship was found between the actual effects of elevated CO₂ and climate change on GPP in most forest types. At lower latitudes, Tem primarily constrained CO₂ fertilization, while at higher latitudes, VPD emerged as the key limiting factor. This was mainly attributed to the potential trade-off or competition between elevated CO₂ and climate change in influencing GPP, with strategic resource allocation varying across different forest ecosystems. This study highlights the significant inhibitory effects of elevated CO₂ and climate change on global forest GPP, providing insights into the dynamic responses of forest ecosystems to changing environments.