Variability and Changes in Climate, Phenology, and Gross Primary Production of an Alpine Wetland Ecosystem

Lijuan Cui,Wei Li,Xiangming Xiao,Xiaoyong Cui,Paul Kardol,Sanxiang Huang,Yanbin Hao,Yangong Du,Xiaoming Kang,Huai Chen

doi:10.3390/rs8050391

Abstract

Quantifying the variability and changes in phenology and gross primary production (GPP) of alpine wetlands in the Qinghai–Tibetan Plateau under climate change is essential for assessing carbon (C) balance dynamics at regional and global scales. In this study, in situ eddy covariance (EC) flux tower observations and remote sensing data were integrated with a modified, satellite-based vegetation photosynthesis model (VPM) to investigate the variability in climate change, phenology, and GPP of an alpine wetland ecosystem, located in Zoige, southwestern China. Two-year EC data and remote sensing vegetation indices showed that warmer temperatures corresponded to an earlier start date of the growing season, increased GPP, and ecosystem respiration, and hence increased the C sink strength of the alpine wetlands. Twelve-year long-term simulations (2000–2011) showed that: (1) there were significantly increasing trends for the mean annual enhanced vegetation index (EVI), land surface water index (LSWI), and growing season GPP (R2 ≥ 0.59, p < 0.01) at rates of 0.002, 0.11 year−1 and 16.32 g·C·m−2·year−1, respectively, which was in line with the observed warming trend (R2 = 0.54, p = 0.006); (2) the start and end of the vegetation growing season (SOS and EOS) experienced a continuous advancing trend at a rate of 1.61 days·year−1 and a delaying trend at a rate of 1.57 days·year−1 from 2000 to 2011 (p ≤ 0.04), respectively; and (3) with increasing temperature, the advanced SOS and delayed EOS prolonged the wetland’s phenological and photosynthetically active period and, thereby, increased wetland productivity by about 3.7–4.2 g·C·m−2·year−1 per day. Furthermore, our results indicated that warming and the extension of the growing season had positive effects on carbon uptake in this alpine wetland ecosystem.

Highlights

Wetlands only cover 3%–8% of the Earth’s land surface, but store 15%–30% of the world’s terrestrial soil carbon [1,2], indicating that they play an important role in the global carbon (C) cycle and potentially have a significant impact on global climate change [3,4,5]
The land surface phenology defined by GPPEC and land surface water index (LSWI)
Our study showed that the land surface phenology of the Zoige alpine wetland, as described by the satellite vegetation indices, in particular the water-related vegetation indices (e.g., LSWI), corresponds well with the phenological patterns based on ecosystem physiology, as measured by the eddy covariance method

Summary

Introduction

Wetlands only cover 3%–8% of the Earth’s land surface, but store 15%–30% of the world’s terrestrial soil carbon [1,2], indicating that they play an important role in the global carbon (C) cycle and potentially have a significant impact on global climate change [3,4,5]. Vegetation phenology is a fundamental determinant affecting the processes of carbon, water, and energy exchange in wetland ecosystems [6,7]. Phenology determines the timing and duration of the photosynthetically active canopy and drives annual carbon uptake in wetland ecosystems [8,9,10]. Changes in the global and regional climate, such as rising global mean temperatures and changing precipitation regimes [11,12,13], have significantly affected wetland vegetation dynamics and carbon dynamics. Warming may stimulate plant phenological development, increase nutrient mineralization rates, and lengthen the growing season, which in turn may increase plant primary production and carbon sequestration [14,15]. Quantifying the relationships among climate change, phenological variability, and vegetation production is crucial for investigating accurate

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Conclusion