Abstract
Understanding the influences of climatic changes on water use efficiency (WUE) of Tibetan alpine meadows is important for predicting their long-term net primary productivity (NPP) because they are considered very sensitive to climate change. Here, we collected wool materials produced from 1962 to 2010 and investigated the long-term WUE of an alpine meadow in Tibet on basis of the carbon isotope values of vegetation (δ 13Cveg). The values of δ 13Cveg decreased by 1.34‰ during 1962–2010, similar to changes in δ 13C values of atmospheric CO2. Carbon isotope discrimination was highly variable and no trend was apparent in the past half century. Intrinsic water use efficiency (W i) increased by 18 μmol·mol–1 (approximately 23.5%) during 1962–2010 because the increase in the intercellular CO2 concentration (46 μmol·mol–1) was less than that in the atmospheric CO2 concentration (C a, 73 μmol·mol–1). In addition, W i increased significantly with increasing growing season temperature and C a. However, effective water use efficiency (W e) remained relatively stable, because of increasing vapor pressure deficit. C a, precipitation, and growing season temperature collectively explained 45% of the variation of W e. Our findings indicate that the W e of alpine meadows in the Tibetan Plateau remained relatively stable by physiological adjustment to elevated C a and growing season temperature. These findings improve our understanding and the capacity to predict NPP of these ecosystems under global change scenarios.
Highlights
The Tibetan Plateau, referred to as the Earth’s “third pole,” is highly sensitive to climate change, and climate warming has been widely observed here during the past several decades [1,2]
water use efficiency (Wi) increased by 23.5% from 1962 to 2010, which was an increase of 3.20% per 10 μmolÁmol–1 increase in Ca
Mean vapor pressure deficit (VPD) in the growing season increased by 0.11 kPa; as a result, the observed water use efficiency (We) did not increase significantly from 1962 to 2010 (Fig 4C)
Summary
The Tibetan Plateau, referred to as the Earth’s “third pole,” is highly sensitive to climate change, and climate warming has been widely observed here during the past several decades [1,2]. Stable WUE of Tibetan Alpine Meadow generally increases with increasing promotion of plant growth by precipitation or increased water use efficiency (WUE) related to the leaf area index [4]. The observed increases in growing season temperature (GST) and Ca in the Tibetan Plateau may increase Rubisco enzyme activity, stimulate leaf photosynthesis, enhance NPP, and result in higher WUE [5,6]. We assumed that the WUE of alpine meadows would increase under scenarios of warming and increasing Ca and result in higher NPP in the Tibetan Plateau as shown by Piao and others [2]
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