Lemoine Nathan P, Griffin-Nolan Robert J, Lock Abigail D, Knapp Alan K
Department of Biology, Colorado State University, Fort Collins, CO, USA.
Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO, USA.
Oecologia. 2018 Dec;188(4):965-975. doi: 10.1007/s00442-018-4265-5. Epub 2018 Sep 29.
Climate change will alter global precipitation patterns, making it increasingly important that we understand how ecosystems will be impacted by more frequent and severe droughts. Yet most drought studies examine a single, within-season drought, and we know relatively little about the impacts of multiple droughts that occur within a single growing season. This distinction is important because many plant species are able to acclimate physiologically, such that the effects of multiple droughts on ecosystem function deviate significantly from the effects of cumulative, independent droughts. Unfortunately, we know relatively little about the ability of dominant species to acclimate to drought in drought-sensitive ecosystems like semi-arid grasslands. Here, we tested for physiological acclimation to multiple drought events in two dominant shortgrass steppe species: Bouteloua gracilis (C) and Elymus elymoides (C). Neither species exhibited physiological acclimation to drought; leaf water potential, stomatal conductance, and photosynthesis rates were all similarly affected by a single, late period drought and a second, late period drought. Biomass was lowest in plants exposed to two droughts, but this is likely due to the cumulative effects of both an early and late period drought. Our results suggest that late period droughts do exert weaker effects on biomass production of two dominant shortgrass species, but that the weaker effects are due to ontogenetic changes in plant physiology as opposed to physiological acclimation against multiple droughts. As a consequence, current ecosystem models that incorporate grass phenology and seasonal physiology should provide accurate predictions of primary production under future climates.
气候变化将改变全球降水模式，因此了解生态系统将如何受到更频繁、更严重干旱的影响变得越发重要。然而，大多数干旱研究都只考察单一季节内的干旱情况，而对于单一生长季节内多次干旱的影响，我们所知甚少。这种区别很重要，因为许多植物物种能够在生理上适应环境，以至于多次干旱对生态系统功能的影响与累积的、独立的干旱影响有显著差异。遗憾的是，对于半干旱草原等干旱敏感生态系统中优势物种适应干旱的能力，我们了解得相对较少。在此，我们测试了两种短草草原优势物种：细茎针茅（Bouteloua gracilis）和穗状披碱草（Elymus elymoides）对多次干旱事件的生理适应性。这两个物种均未表现出对干旱的生理适应；叶片水势、气孔导度和光合速率在受到单次后期干旱和第二次后期干旱时受到的影响都相似。遭受两次干旱的植物生物量最低，但这可能是早期和后期干旱共同作用的累积效应所致。我们的研究结果表明，后期干旱对两种短草优势物种生物量生产的影响确实较弱，但这种较弱的影响是由于植物生理的个体发育变化，而非对多次干旱的生理适应。因此，纳入了禾本科物候学和季节性生理学的当前生态系统模型应该能够准确预测未来气候下的初级生产力。
