The carbon sink in pantropical biomes play a crucial role in modulating the inter-annual variations of global terrestrial carbon balance and is threatened by extreme climate events. However, it has not been carefully examined whether an increase in tropical gross primary productivity (GPP) can compensate the decrease during precipitation anomalies. Using the asymmetry index (AI) and multiple GPP products, we assessed responses of pantropical GPP to precipitation anomalies during 2001-2022. Positive AI indicates that GPP increases are greater than GPP decreases during precipitation anomalies, and vice versa. Our results showed an average negative pantropical GPP asymmetry, that is, GPP decreases exceeded the GPP increases during precipitation anomalies. In addition, a positive AI was found in tropical hyper-arid and arid regions, which is opposite to the negative AI observed in tropical semi-arid, sub-humid, and humid regions. This suggest that tropical GPP asymmetry changes from positive to negative as the moisture increases. Notably, a significant decreasing trend of negative AI was observed over the entire tropical region, indicating that the negative effect of inter-annual precipitation variations on pantropical vegetation productivity has enhanced. Considering the model predicted increasing climate variability and extremes, the negative impact of precipitation variability on tropical carbon cycle may continue to intensify. Lastly, the divergence in AI estimates among multiple GPP products highlight the need to further improve our understanding of the response of tropical carbon cycle to climate changes, especially for the tropical humid regions.

Plain Language Summary Tropical biomes play an essential role in controlling the global carbon balance but has been threatened by extreme climate events recently. Whether the increase in tropical GPP can compensate the GPP decrease during precipitation anomalies is still poorly known. In this study, we found an average negative asymmetric GPP response to precipitation anomalies over the entire tropics during 2001-2022, that is, GPP decreases exceeded the GPP increases during precipitation anomalies. Meanwhile, we found that the tropical GPP was shifted from positive asymmetry to negative asymmetry as the moisture increases. Besides, a significantly decreasing trend of GPP asymmetry was observed over the study period, suggesting that the negative effect of inter-annual precipitation variations on pantropical GPP has intensified.