Contrasting responses of grassland water and carbon exchanges to climate change between Tibetan Plateau and Inner Mongolia
Contrasting responses of grassland water and carbon exchanges to climate change between Tibetan Plateau and Inner Mongolia
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青藏高原与内蒙古草原水碳交换对气候变化的响应对比
DOI：
10.1016/j.agrformet.2017.11.034
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发表时间：
2018-02-15
影响因子：
6.2
通讯作者：
Piao, Shilong
中科院分区：
文献类型：
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作者：
Liu, Dan;Li, Yue;Piao, Shilong
中国青藏高原（TP）和内蒙古（IM）的草原生态系统在减缓气候变化以及粮食和畜牧业生产中发挥着重要作用。在过去的三十年里，这两个地区的气温越来越高，降水状况也不断变化。然而，目前尚不清楚气温升高和降水变化在多大程度上调节高山（TP）和温带（IM）草原的水和碳通量。在这里，我们首先使用涡协方差数据（TP 中的三个站点和 IM 中的 6 个站点）优化基于过程的碳和水通量模型，并根据暴露于一系列年温度和降水异常的优化模型来分析模拟的碳和水通量。我们发现，青藏高原草原的净生态系统-大气碳交换（NEE）变化相对较小，因为生态系统呼吸（R-e）和总初级生产力（GPP）随着多个地点的变暖以相当的速度增加（R-e：22.1 +/- 21.4 g C m（-2）年（-1）°C-1，GPP：22.43 +/- 36.41 g C m（-2）年（-1） C-1 度），这是由于草原的呼吸作用可能无法超过可用的光合作用供应。 IM草原的NEE随着变暖而增加（生态系统的碳损失更多），这主要是因为在温暖引起的可用水分减少的情况下，GPP比R-e下降得更快，并且Re对变暖的敏感性（1.17+/-3.56 g C m（-2）年（-1）℃-1）远小于GPP（15.53 +/- 15.91 g C m（-2）年（-1）℃-1）。这些结果表明，水是内陆草原的主要限制因素，但在TP草原则不然。与变暖相反，我们发现TP草原的水和碳通量对干燥和湿润的响应不对称（即在干燥条件下大幅减少，在湿润条件下小幅增加），但在IM草原中几乎呈线性响应。因此，我们强调，调节水和碳循环对变暖的响应的基本过程在青藏高原和内陆草原之间有着根本的不同，水分是内陆草原的主要限制因素，而青藏高原草原更受热条件的限制。我们的结果还表明，变暖将显着刺激生态系统碳净流失到大气中，但不会显着增加内蒙古草原的蒸散量，这可能为加速气候变化提供正反馈。相反，变暖不会显着影响生态系统碳交换，但会显着增强青藏高原草原的ET，这可能为缓解高寒草原的气候变化提供负反馈。
The grassland ecosystems in Tibetan Plateau (TP) and Inner Mongolia (IM) of China play important roles in climate change mitigation and food and livestock production. These two regions have increasingly experienced higher temperatures and changing precipitation regimes over the past three decades. However, it remains uncertain to what extent rising temperature and varying precipitation regulate the water and carbon fluxes across alpine (TP) and temperate (IM) grasslands. Here, we first optimize a process-based model of carbon and water fluxes using eddy-covariance data (three sites in TP and six sites in IM), and analyze the simulated carbon and water fluxes based upon the optimized model exposed to a range of annual temperature and precipitation anomalies. We found that the changes in net ecosystem-atmosphere carbon exchange (NEE) of TP grassland are relatively small because the ecosystem respiration (R-e) and the gross primary productivity (GPP) increase at comparable rate with warming across multiple sites (R-e: 22.1 +/- 21.4 g C m(-2) year(-1) degrees C-1, GPP: 22.43 +/- 36.41 g C m(-2) year(-1) degrees C-1), which is due to the possibility that grasslands cannot respire more than the available supply of photosynthesis. The NEE of IM grassland increases (more carbon loss from ecosystem) with warming, which is mainly because GPP decreases faster than R-e under warm-induced reduction in moisture availability, and the sensitivity of Re to warming (1.17 +/- 3.56 g C m(-2) year(-1) degrees C-1) is much smaller than that of GPP (15.53 +/- 15.91 g C m(-2) year(-1) degrees C-1). These results indicate that water is the major limiting factor in IM grasslands, but not in TP grasslands. In contrast to warming, we found an asymmetric response of water and carbon fluxes to drying and wetting in TP grasslands (i.e. a large decrease under the drying condition and a small increase under the wetting condition) but almost a linear response in IM grasslands. We therefore highlight that the underlying processes regulating the responses of water and carbon cycles to warming are fundamentally different between TP and IM grasslands, with the moisture being the major limiting factor in IM while grasslands in TP are much more limited by thermal conditions. Our results also imply that warming would significantly stimulate the net ecosystem carbon loss to atmosphere but not significantly enhance ET in IM grasslands, which may provide a positive feedback to accelerate climate change. Inversely, warming could not significantly affect the ecosystem carbon exchange but significantly enhance ET in TP grasslands, which may provide a negative feedback to mitigate climate change in alpine grasslands.