Spring phenology is an important indicator of vegetation dynamics and plays an important role in vegetation activity and ecosystem functions. Understanding the spring phenology of vegetation and its response to climate change are important for projecting regional ecosystem carbon exchange.

Temperatures influence the spring phenology of vegetation and to understand the mechanism needs to investigate separate impacts of maximum temperature (Tmax) and daily minimum temperature (Tmin) on spring phenology.

Recently, researchers at Northeast Institute of Geography and Agroecology of Chinese Academy of Sciences investigated the changes of the start date of the vegetation growing season (SOS) for the temperate grasslands in China, and explored the effects of monthly Tmax, Tmin and precipitation on the SOS across different grassland vegetation types. This results were published in Agricultural and Forest Meteorology.

Scientists found that the SOS significantly advanced during 1982-2015, controlled mainly by spring precipitation as well as spring and winter temperatures, with differing degrees of influence among vegetation types.

Although warmer temperatures generally led to advanced SOS, the seasonal effects of daytime and nighttime warming on the SOS of temperate grasslands in China were revealed for the first time to be asymmetric, with Tmax more influential in winter and Tmin more influential in spring.

An increase of 1°C in winter Tmax and spring Tmin would advance SOS by 0.42 and 1.34 days, respectively, compared with effects of 0.24 or 0.64 days for 1°C increases in winter Tmin or spring Tmax.

Given the global asymmetry in daytime and nighttime warming, this study highlighted the asymmetric effects of daytime and nighttime warming on the SOS of temperate grasslands, and suggested that the impacts of seasonal Tmax and Tmin should be considered separately in the SOS modules of terrestrial ecosystem models for temperate grasslands.

This work was supported by the National Natural Science Foundation of China, the National Key Research and Development Program of China, and the Excellent Young Scientists Foundation of the Northeast Institute of Geography and Agroecology of Chinese Academy of Sciences.