Inner Mongolian grassland plant phenological changes and their climatic drivers.

Global warming is widely believed to extend the length of plant growing season (LOS) through advancing the start (SOS) and delaying the end (EOS) of plant growing season. However, divergent directions of phenological changes under current climate warming have been frequently reported but poorly understood. Here we collate the long-term filed phenological and climatic records at 8 sites in Inner Mongolian grassland to assess how climate changes regulate the phenological variations with divergent directions and magnitudes in this region. We found that the spring climatic changes (e.g., changes in air temperature and precipitation during March and April) correlate well with variations in SOS. However, our in situ observations show divergent changes in SOS across space, which can be attributed to the generally insignificant changes of climates during the preseasons of SOS. The climate warming prior to the end of plant growing season (EOS) was generally significant at most sites. Nevertheless, the effects of such warming on changes in EOS were possibly overshadowed by the impacts of precipitation in this arid/semi-arid region. As a result, the temporal variations in EOS distribute divergent directions and magnitudes across space and species. Using climate attributes during the preseason of EOS alone can hardly explain changes in EOS. Alternatively, by introducing changes in SOS as an additional driving factor, variations in EOS can be well represented. We therefore infer that plant phenologies can divergently response to current global warming (depending on the seasonal patterns of warming). Moreover, other influential factors such as precipitation and the interactions between the timings of different phenological stages are also needed in predicting the phenological dynamics.