Spatial and temporal variations in plant water-use efficiency inferred from tree-ring, eddy covariance and atmospheric observations
Spatial and temporal variations in plant water-use efficiency inferred from tree-ring, eddy covariance and atmospheric observations
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DOI：
10.5194/esd-7-525-2016
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发表时间：
2016-01-01
影响因子：
7.3
通讯作者：
Cox, Peter M.
中科院分区：
文献类型：
--
作者：
Dekker, Stefan C.;Groenendijk, Margriet;Cox, Peter M.
植物水分利用效率（WUE）是指植物通过光合作用吸收的二氧化碳与通过蒸腾损失的水分之比，是衡量陆地生物圈功能的一个非常有用的指标。用水效率预计将随着大气二氧化碳的增加而增加，但随着大气蒸发需求的增加而下降——这可能是由于近地表温度的增加或相对湿度的减少而引起的。我们使用来自树木年轮的δ C-13测量值，以及来自Fluxnet站点的涡动相关测量值，来估计WUE对CO2和大气湿度亏缺变化的敏感性。这使我们能够在仪器全球气候记录的整个时期，基于大气气候和二氧化碳的变化，重建WUE的分数变化。我们估计，从1900年到2010年，总体WUE增加了48±22%，这是最新地球系统模型模拟的两倍多。这种长期趋势在很大程度上是由二氧化碳的增加所驱动的，但由于温度和相对湿度的变化，显著的年际变率和区域差异也很明显。在一些人口密集的地区，如西欧和东亚，用水效率的增长率在过去20年里急剧下降。我们基于数据的分析表明，用水效率的增加通常超过了地球系统模型所模拟的结果——这意味着这些模型要么低估了光合作用的增加，要么低估了蒸腾作用的减少。
Plant water-use efficiency (WUE), which is the ratio of the uptake of carbon dioxide through photosynthesis to the loss of water through transpiration, is a very useful metric of the functioning of the land biosphere. WUE is expected to increase with atmospheric CO2, but to decline with increasing atmospheric evaporative demand - which can arise from increases in near-surface temperature or decreases in relative humidity. We have used Delta C-13 measurements from tree rings, along with eddy covariance measurements from Fluxnet sites, to estimate the sensitivities of WUE to changes in CO2 and atmospheric humidity deficit. This enables us to reconstruct fractional changes in WUE, based on changes in atmospheric climate and CO2, for the entire period of the instrumental global climate record. We estimate that overall WUE increased from 1900 to 2010 by 48 +/- 22 %, which is more than double that simulated by the latest Earth System Models. This long-term trend is largely driven by increases in CO2, but significant inter-annual variability and regional differences are evident due to variations in temperature and relative humidity. There are several highly populated regions, such as western Europe and East Asia, where the rate of increase of WUE has declined sharply in the last 2 decades. Our data-based analysis indicates increases in WUE that typically exceed those simulated by Earth System Models - implying that these models are either underestimating increases in photosynthesis or underestimating reductions in transpiration.