Coupled biogeochemical cycling of water, silicon and cations in a temperate forest-shale system.

该项目的重点是了解温带森林树木（枫树，橡树）的水获取和他们的策略，以获取矿物质营养，特别是钙和硅之间的联系。 树木作为强大的“泵”，带来了土壤水和地下水，并作为土壤湿润和干燥的季节，树木转移他们的水源需要。 这项调查将使用氢和氧的同位素来追踪宾夕法尼亚州中部一个仪器密集的地球化学研究地点的这些变化，该研究地点是NSF临界区观测站网络的一部分。 树木在吸收水分的同时，也从土壤中吸收养分。 研究人员将测试关于矿物质营养源如何随着水源的变化而变化的想法。 树木吸收所需的养分，当落叶发生时，将它们回收到土壤中。 一个问题是，在营养收支中，从深层“挖掘”营养物质有多重要。 如果树木不能开采养分，那么它们就只能储存在浅层土壤和现存植被中。一些证据表明，在某些物种中，树根会将水渗漏到浅层土壤中-一种可能的解释是，它们这样做是为了在水分胁迫期间从干燥的浅层土壤中获得养分。 锶的同位素和锗与硅、锶与钙的比例将被用来更明确地检验这些假设。 这是建立在研究人员以前在热带系统中进行的矿物营养循环的工作基础上的。森林和地球化学循环对气候变化的反应是一个重要的考虑因素，因为碳和水循环可能会产生反馈。 大多数气候模式的预测是降水模式的变化更大，即使在总体较湿润的条件下，干旱期也会增加。 更适合这些可变条件的物种的水和养分获取策略可以预测物种在适应温带森林气候变化方面的成功模式。 如果这些物种即使在土壤水分供应不足的情况下也能更好地获取养分，它们也可能在二氧化碳水平增加的情况下增加对二氧化碳的利用。 提高我们对水循环和养分循环之间的耦合的理解至关重要，以便更好地预测这些重要生态系统对气候变化的反应及其对碳和水循环的未来影响。

This project is focused on understanding the linkages between water acquisition by temperate forest trees (maples, oaks) and their strategies to acquire mineral nutrients, especially calcium and silica. Trees act as powerful "pumps" to bring up soil water and groundwater, and as the soil wets and dries through the season, trees shift their water sources as needed. The investigation will employ isotopes of hydrogen and oxygen to trace those shifts in a heavily instrumented biogeochemistry study site in central Pennsylvania, part of the NSF Critical Zone Observatory network. At the same time as they acquire water, trees acquire nutrients from the soil. Investigators will test ideas about how mineral nutrient sources may change as water sources change. Trees take up nutrients they need, and when leaf drop occurs, recycle them to the soil. One question is how important is the "mining" of nutrients from deep levels in the nutrient budget. If trees cannot mine nutrients, then they are limited to the store that is in shallow soil and in standing vegetation. Some evidence suggests that in some species tree roots leak water to shallow soils - one possible explanation is that they do this to make nutrients available from otherwise dry, shallow soils during times of water stress. Strontium isotopes and the ratios of germanium to silicon and strontium to calcium will be used to test these hypotheses more explicitly. This builds on previous work on mineral nutrient cycles the investigators have carried out in tropical systems.The response of forests and of biogeochemical cycles to climate change is an important consideration because of the possible feedbacks on the carbon and water cycles. A prediction of most climate models is for more variable precipitation patterns, with increased periods of drought even under overall wetter conditions. Water and nutrient acquisition strategies for species that are better suited to these variable conditions may predict success patterns among species in adapting to climate change in temperate forests. Such species may also be able to increase their utilization of CO2 under increased CO2 levels if they are better able to acquire nutrients even under conditions of low soil water availability. It is critical to improve our understanding of the coupling between water and nutrient cycles in order to better predict the response of these important ecosystems to climate change, and their future impacts on the carbon and water cycles.