Complex responses of spring vegetation growth to climate in a moisture-limited alpine meadow.

Hasbagan Ganjurjav,Hongbao Guo,Yue Li,Xujuan Cao,Yan Liang,Matthew A Williamson,Wangzha Jiangcun,Erda Lin,Wenquan Zhu,Qingzhu Gao,Yunfan Wan,Mark W Schwartz

doi:10.1038/srep23356

Abstract

Since 2000, the phenology has advanced in some years and at some locations on the Qinghai-Tibetan Plateau, whereas it has been delayed in others. To understand the variations in spring vegetation growth in response to climate, we conducted both regional and experimental studies on the central Qinghai-Tibetan Plateau. We used the normalized difference vegetation index to identify correlations between climate and phenological greening, and found that greening correlated negatively with winter-spring time precipitation, but not with temperature. We used open top chambers to induce warming in an alpine meadow ecosystem from 2012 to 2014. Our results showed that in the early growing season, plant growth (represented by the net ecosystem CO2 exchange, NEE) was lower in the warmed plots than in the control plots. Late-season plant growth increased with warming relative to that under control conditions. These data suggest that the response of plant growth to warming is complex and non-intuitive in this system. Our results are consistent with the hypothesis that moisture limitation increases in early spring as temperature increases. The effects of moisture limitation on plant growth with increasing temperatures will have important ramifications for grazers in this system.

Highlights

Various authors hypothesized that the observed delays in the spring phenology may be driven by: (a) longer times required for chilling, or vernalization, caused by warmer winter temperatures[23]; (b) anthropogenic factors, such as grassland degradation[27]; (c) complex thaw– freeze processes associated with warming[27]; or (d) or drought[28]
The climate of the central Qinghai-Tibetan Plateau has been warmed by approximately 2.5 °C of the mean annual temperature since 1982, at an estimated rate of 0.6 °C per decade (Fig. 1, Table 1)
The Qinghai-Tibetan Plateau, with a below-freezing mean annual temperature, is a cold grassland ecosystem. It is characterized by a summer monsoon, which delivers over 90% of the annual rainfall during the summer months, making this region a global outlier in the seasonal distribution of moisture among cold grassland environments

Summary

Introduction

Sensed data for the region, readily available from the National Oceanic and Atmospheric Administration, have been used to observe changes in greenness on the Qinghai-Tibetan Plateau using the Normalized Difference Vegetation Index (NDVI)[13,23,24]. We evaluated the hypothesis that temperature and moisture interact to control spring vegetation growth To test this hypothesis, we conducted both regional and field studies on the central Qinghai-Tibetan Plateau. The goal of our study was to better understand the variations in spring vegetation growth in response to climate

Objectives

Methods

Results

Conclusion