Assessing the impacts of dry-heat extremes on grassland gross primary productivity across mainland China using multi-source remote sensing data

Background aridity shapes ecosystem traits and governs the pattern of grassland gross primary productivity (GPP) loss under dry-heat extremes. However, in response to the intensification of such events, how the spatial heterogeneity of background aridity affects grassland GPP responses remains unclear. Furthermore, the trade-off between GPP loss rate (G lr ) and loss intensity (G li )—where higher G lr is generally associated with lower G li and vice versa—serves as a key indicator of ecosystem stability. The breakdown of this trade-off (i.e., trade-off decoupling), marked by concurrent directional changes in both G lr and G li , indicates that grassland productivity is in a highly unstable state. To systematically elucidate the regulatory role of background aridity and reveal the actual state of the G lr -G li trade-off under dry-heat extremes, this study utilized multi-source daily remote sensing data from mainland China's grasslands during 1985–2018 to quantify the G lr and G li , identify the dominant drivers of GPP, and assess the G lr -G li trade-off. The results indicated that compared to drought events (DEs) and heatwave events (HEs), the G lr and G li induced by compound drought-heatwave events (CDHEs) increased with increasing background aridity, specifically manifesting as lower than DEs and HEs in humid and semi-humid zones, but higher than DEs and HEs in semi-arid and arid zones. Increased background aridity significantly amplified G lr under dry-heat extremes. Compared to humid and semi-humid zones, G lr in semi-arid and arid zones increased by 54.67%, 80.50%, and 288.11% under DEs, HEs, and CDHEs stress, respectively. Soil moisture (SM) was the dominant factor regulating GPP under dry-heat extremes, and its regulatory capacity strengthened with increasing background aridity. Compared to DEs and HEs, the regulatory capacity of SM on GPP was strongest under CDHEs stress. Dry-heat extremes led to a significant breakdown of the G lr -G li trade-off, and increased background aridity exacerbated this trade-off decoupling. Specifically, compared to humid and semi-humid zones, the spatial extent without a G lr -G li trade-off in semi-arid and arid zones increased by 12.18%, 22.99%, and 14.10% under DEs, HEs, and CDHEs stress, respectively. Except in arid zones, CDHEs caused more severe G lr -G li trade-off decoupling compared to DEs and HEs. Across mainland China, a transition occurred from low G lr and G li in the southwest to high G lr and G li in the northeast, highlighting the vulnerability of grassland GPP in the semi-arid zones of North China and the transition zones between semi-arid and semi-humid/humid zones. These findings provide critical implications for risk management under intensifying dry-heat extremes in China. • Increased background aridity amplified GPP loss rate under dry-heat extremes. • Increased background aridity enhanced soil moisture's dominance over GPP under dry-heat extremes. • Increased background aridity exacerbated the breakdown of the GPP loss rate-intensity trade-off under dry-heat extremes.