Connor Elise W, Hawkes Christine V
Department of Integrative Biology, University of Texas at Austin, Austin, TX, 78712, USA.
Oecologia. 2018 Oct;188(2):355-365. doi: 10.1007/s00442-018-4212-5. Epub 2018 Jun 29.
Climatic patterns are expected to become more extreme, with changes in precipitation characterized by heavier rainfall and prolonged dry periods. Yet, most studies focus on persistent moderate changes in precipitation, limiting our understanding of how ecosystems will function in the future. We examined the effects of extreme changes in precipitation on leaf-level and ecosystem CO and HO exchange of three native C4 bunchgrasses (Andropogon gerardii, Panicum virgatum, and Sorghastrum nutans) over 3 years. Grasses were grown in three precipitation treatments: extreme dry, mean, and extreme wet based on historical rainfall records. After 3 years, plants were 45% smaller in the extreme dry treatment relative to the mean and extreme high treatment, which did not differ. We also found that an extreme decrease in precipitation caused reductions of 55, 40, and 40% in leaf-level photosynthesis (A), stomatal conductance (g), and water use efficiency (WUE), respectively. Extreme increases in precipitation inhibited leaf-level WUE, with a 44% reduction relative to the mean treatment. At the ecosystem level, both an extreme increase and decrease in precipitation reduced net CO and water fluxes relative to plants grown with mean levels of precipitation. Net water fluxes (ET) were reduced by an average of 74% in the extreme dry and extreme wet treatment relative to mean treatment; net carbon fluxes followed a similar trend, with average reductions of 68% (NEE) and 100% (R). Unlike moderate climate change, extreme increases in precipitation may be just as detrimental as extreme decreases in precipitation in shifting grassland physiology.
气候模式预计将变得更加极端，降水变化的特征是降雨增多和干旱期延长。然而，大多数研究集中在降水持续的适度变化上，这限制了我们对未来生态系统功能的理解。我们研究了3年期间降水极端变化对三种本土C4丛生禾本科植物（糙毛须芒草、柳枝稷和苏丹草）叶片水平和生态系统的二氧化碳及水汽交换的影响。根据历史降雨记录，将这些禾本科植物种植在三种降水处理条件下：极端干旱、平均降水和极端湿润。3年后，与平均降水和极端高降水处理相比，极端干旱处理下的植物小45%，而后两者之间没有差异。我们还发现，降水极端减少分别导致叶片水平光合作用（A）、气孔导度（g）和水分利用效率（WUE）降低55%、40%和40%。降水极端增加抑制了叶片水平的水分利用效率，相对于平均处理降低了44%。在生态系统水平上，与在平均降水水平下生长的植物相比，降水的极端增加和减少都降低了净二氧化碳和水分通量。相对于平均处理，极端干旱和极端湿润处理下的净水分通量（ET）平均降低了74%；净碳通量也呈现类似趋势，平均降低68%（NEE）和100%（R）。与适度气候变化不同，降水极端增加在改变草地生理方面可能与降水极端减少一样有害。
