Drought impacts to plant growth can be indicated by changes in key functional traits. However, previous research has focused on aboveground trait responses to precipitation deficits, with less emphasis on concomitant belowground impacts and deep soil drought from groundwater depletion. We assessed changes in a suite of aboveground and belowground traits of a dominant plant, Phragmites communis, in response to an experimental gradient of underground watertable depth. Our study occurred within the northeastern Inner Mongolia region, where changes to groundwater tables have been pervasive in recent years. In general, the results indicate that both aboveground and belowground traits responded positively, yet eventually negatively, to continual increases in watertable depth, indicative of reduced access to soil moisture as watertable depths increased. Key adjustments include changes to the ratio of coarse roots to fine roots, and the distribution of fine roots within the soil profile. These changes in belowground traits had strong correlations with changes in aboveground traits. In particular, specific root length of fine roots was positively correlated with leaf area, height, and aboveground biomass, whereas root biomass was linked to leaf area, specific root length of coarse roots, and root length density. Fine and coarse root production also had positive and negative relationships with aboveground biomass, respectively, suggestive of biomass allocation tradeoffs. We suggest that biomass production responses of this species to changes in watertable depths may largely be driven by interactions between the distribution of fine and coarse roots in the soil profile and changes to leaf area.

中文翻译：

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优势植物对地下水位变化的地上和地下性状响应之间的关系

干旱对植物生长的影响可以通过关键功能性状的变化来表明。然而，先前的研究集中在地上性状对降水不足的反应上，而较少地关注地下的伴随影响和地下水枯竭引起的深层土壤干旱。我们评估了优势植物芦苇（Phragmites communis）的一系列地上和地下性状的变化，以响应地下地下水位的实验梯度。我们的研究发生在内蒙古东北地区，近年来地下水位的变化无处不在。总的来说，结果表明，地下和地下性状均对地下水位的持续增加有积极的反应，但最终却是负面的，这表明随着地下水位的增加，土壤水分的获取减少。关键的调整包括改变粗根与细根的比例，以及细根在土壤剖面内的分布。地下性状的这些变化与地下性状的变化具有很强的相关性。特别是细根的根长与叶面积，高度和地上生物量呈正相关，根生物量与叶面积，粗根的比根长和根长密度有关。细根和粗根的产生也分别与地上生物量有正相关和负相关，这表明生物量分配存在一定的权衡。我们认为，该物种对水深变化的生物量生产响应可能主要由土壤剖面中细根和粗根的分布与叶面积的变化之间的相互作用所驱动。