Spatio-temporal variations of spring phenology of Plantago asiatica and Taraxacum mongolicum in the Tibetan Plateau from 2000 to 2011

Plant phenology is strongly controlled by climate and has become a sensitive bio-indicator to study the plant response to climate change. Since the high altitude, permafrost geography and harsh physical environment of the Tibetan Plateau (TP), the phenology shift in the TP was thought to be more sensitive than many other regions. However, the study of phenology in the TP was greatly limited by the lack of ground-observed phenological data. In this study, we collected the phonological records of first leaf date (FLD) and the first flowering date (FFD) of two herbaceous species (Plantago asiatica and Taraxacum mongolicum) both from 14 stations across the TP during 2000-2011 and analyzed the spatio-temporal variations of spring phenology. The results showed that the onset dates of FLD and FFD exhibited strong dependence on latitude, longitude and altitude because the onset dates of spring phenology occurred earlier at warmer locations. The sensitivities of spring phenology temperature varied among stations and earlier phenological events showed more negative temperature sensitivity except for the FFD of Taraxacum mongolicum. But the relationship between spring phenology and precipitation was not clear. Though the diverse trends of spring phenology of Plantago asiatica and Taraxacum mongolicum were found, the differences between the onset dates of FLD of the two species tended to increase (P < 0.05). However, the differences between the onset dates of FFD of the two species showed a reducing tendency (P < 0.01). These findings can help us to better understand the responses of plants to climate change in alpine ecosystem and provide information for phenology modelling.