Centre for Ecology Evolution and Environmental Changes, Faculdade de Ciências da Universidade de Lisboa, Lisboa, Portugal.
PPG - Ecologia, Instituto de Biologia, Universidade Estadual de Campinas, Campinas, Brazil.
Glob Chang Biol. 2018 Oct;24(10):4894-4908. doi: 10.1111/gcb.14403. Epub 2018 Aug 16.
Predicted droughts and anthropogenic water use will increase groundwater lowering rates and intensify groundwater limitation, particularly for Mediterranean semi-arid ecosystems. These hydrological changes may be expected to elicit differential functional responses of vegetation either belowground or aboveground. Yet, our ability to predict the impacts of groundwater changes on these ecosystems is still poor. Thus, we sought to better understand the impact of falling water table on the physiology of woody vegetation. We specifically ask (a) how is woody vegetation ecophysiological performance affected by water table depth during the dry season? and (b) does the vegetation response to increasing depth to groundwater differ among water-use functional types? We examined a suite of physiological parameters and water-uptake depths of the dominant, functionally distinct woody vegetation along a water-table depth gradient in a Mediterranean semi-arid coastal ecosystem that is currently experiencing anthropogenic groundwater extraction pressure. We found that groundwater drawdown did negatively affect the ecophysiological performance of the woody vegetation. Across all studied environmental factors, depth to groundwater was the most important driver of ecophysiological adjustments. Plant functional types, independent of groundwater dependence, showed consistent declines in water content and generally reduced C and N acquisition with increasing depths to groundwater. Functional types showed distinct operating physiological ranges, but common physiological sensitivity to greater water table depth. Thus, although differences in water-source use exist, a physiological convergence appeared to happen among different functional types. These results strongly suggest that hydrological drought has an important impact on fundamental physiological processes, constraining the performance of woody vegetation under semi-arid conditions. By disentangling the functional responses and vulnerability of woody vegetation to groundwater limitation, our study establishes the basis for predicting the physiological responses of woody vegetation in semi-arid coastal ecosystems to groundwater drawdown.
预计干旱和人为用水将增加地下水降低速率，并加剧地下水限制，特别是对地中海半干旱生态系统而言。这些水文变化可能会引起植被在地下或地上的不同功能响应。然而，我们预测地下水变化对这些生态系统的影响的能力仍然很差。因此，我们试图更好地了解地下水位下降对木本植被生理学的影响。我们特别提出以下问题：（a）在旱季，地下水位深度如何影响木本植被的生态生理表现？（b）植被对地下水增加深度的响应是否因水分利用功能类型而异？我们在一个地中海半干旱沿海生态系统中，沿着地下水位深度梯度，研究了一套生理参数和主要的、功能上不同的木本植被的水分吸收深度，该生态系统目前正受到人为地下水开采的压力。我们发现，地下水下降确实会对木本植被的生态生理表现产生负面影响。在所有研究的环境因素中，地下水深度是生态生理调整的最重要驱动因素。植物功能类型，与地下水依赖无关，随着地下水深度的增加，表现出水分含量的持续下降，一般减少 C 和 N 的获取。功能类型表现出明显的生理工作范围，但对更大的地下水位深度表现出共同的生理敏感性。因此，尽管存在水分来源利用的差异，但不同功能类型之间似乎出现了生理趋同。这些结果强烈表明，水文干旱对基本生理过程有重要影响，限制了半干旱条件下木本植被的性能。通过分离木本植被对地下水限制的功能响应和脆弱性，我们的研究为预测半干旱沿海生态系统木本植被对地下水下降的生理响应奠定了基础。
