Delayed autumn leaf senescence date prolongs the growing season length of herbaceous plants on the Qinghai-Tibetan Plateau

摘要

Plant phenological shifts on the Qinghai-Tibetan Plateau (QTP) have been a hot research topic during the recent decade. Most previous studies based on remote sensing data suggest that earlier spring green-up is the main contributor to the prolonged vegetation growing season on the QTP. Given the large uncertainties of satellite-derived phenology, this study collected a large number (1455+ records) of long-term and continuous ground phenological observation data across the QTP. Based on these data, we conducted comprehensive analyses of temporal changes in spring green-up date (GUD), autumn leaf senescence date (LSD), and growing season length (GSL) of herbaceous plants from 1981 to 2017 through ordinary least squares regression and meta-analysis, and evaluated the relative contribution of shifts in GUD and LSD to change in GSL using the C-index. Results showed that the overall trends of GUD, LSD, and GSL insignificantly advanced at a rate of -0.17 days/decade, significantly delayed at a rate of 5.29 days/decade, and significantly lengthened at a rate of 5.46 days/decade, respectively. On average, the relative contribution of LSD shift to GSL change was 69.3% which was more than twice that of GUD shift (30.7%). Therefore, it was mainly the delayed LSD, rather than an advanced GUD, that prolonged GSL of QTP herbaceous plants, which was contrary to the prevailing conclusion reported by studies based on remote sensing data. Besides, among three functional groups of herbaceous plants, we found that change trends and patterns of the growing seasons seemed to be more favorable to the growth of forbs, which might shift community structure and further influence ecosystem function. Our study suggests that the importance of autumn phenology has been underestimated on the QTP, and more attention should be paid to the shift in autumn phenology and its influences on ecosystem structure and function under global warming.