Climatic Mechanism of Delaying the Start and Advancing the End of the Growing Season of Stipa krylovii in a Semi-Arid Region from 1985-2018

Plant phenological variations depend largely on temperature, but they cannot be explained by temperature alone in arid and semi-arid regions. To reveal the response mechanisms of grassland phenology to climate change, the effects of temperature, moisture and light at the start (SOS), peak (POS) and end (EOS) of the growing season for Stipa krylovii (S. krylovii) in Inner Mongolian grassland was analysed from 1985-2018 with partial least squares (PLS) regression. The results showed that the SOS was significantly delayed at a rate of 5.4 d/10a (change over 10 years), while POS and EOS were insignificantly advanced, which were inconsistent with the existing understanding that climate warming advances the SOS and delays the EOS. The vapor pressure deficit (VPD) in July, maximum air temperature (T-max) in September of the previous year, diurnal temperature range (DTR) from mid-February to mid-March, and T-max from late March to mid-April of the current year were the critical factors and periods triggering the SOS, which contributed to 68.5% of the variation in the SOS. Additionally, the minimum air temperature (T-min) occurred from mid-December to late December, and precipitation (PRE) occurred from mid-June to late July for POS, which could explain 52.1% of POS variations. In addition, T-max from late August to early September influenced the EOS with an explanation of 49.3%. The results indicated that the phenological variations in S. krylovii were the result of the combined effects of climatic conditions from the previous year and the current year. Additionally, an increase in the preseason DTR delayed the SOS, and excessive summer precipitation induced an earlier POS, while warming in early autumn induced an earlier EOS, reflecting the adaptation mechanism of the perennial dense-cluster herbaceous plants in semi-arid regions to climate change. These findings could enrich the understanding of plant phenology in response to climate change.