Increasing influence of minimum temperature on grassland spring phenology in arid Central Asia

Abstract

The dynamics of grassland spring phenology in arid Central Asia (ACA) are critical for the regional carbon cycle, ecological security, and social stability. Nonetheless, the mediating effects of climatic elements on grassland start of season (SOS) and trends in the relative contributions to the SOS in the ACA have not been sufficiently investigated. In this study, we explored the mediating effects of daily maximum temperature (TMX), daily minimum temperature (TMN), vapor pressure deficit (VPD), and soil moisture (SM) on grassland SOS and trends in the relative contributions of TMX, TMN, VPD, SM to SOS in the ACA from 1982 to 2022. We found that the grassland SOS in the ACA showed an advancing trend of 0.28 days/yr. Rising TMX and VPD contributed to the advance of SOS, and the delaying effects of TMN and SM were offset by the indirect effects of TMX and VPD. TMX and TMN had asymmetric effects on SOS, with SOS advanced or delayed for increases in TMX or TMN, respectively. TMX was the dominant factor controlling the SOS, with the largest relative contribution (47.93 % of the ACA). Over the past 41 years, the relative contributions of SM and VPD to SOS showed a non-significant decreasing trend, TMX remained unchanged, and TMN showed a highly significant increasing trend. Under sustained future warming, TMN may undergo more accelerated warming than TMX, and the advance of SOS due to increased TMX may be further offset, potentially leading to the supplantation of TMX by TMN in its impact on SOS. Our results emphasize that characterization of the phenological response should account for the mediating effects of climatic elements and trends in relative contributions.