Forests of the future: what, when and how will trees get their water?

随着不断增加的二氧化碳浓度改变了地球看待其对植被影响的方式，地球的大气层正在发生变化。在一些地方，地球变得越来越绿，世界各地的树木似乎正在改变它们用水的方式。这些变化将影响全球的森林和水资源，但到目前为止，我们还没有办法测试树木未来将如何应对更高的二氧化碳。该项目将通过使用一种全球独一无二的实验设备来帮助填补这一重要缺口，该设备正在人为地提高英国中部一片古老橡树林(BIFoR Face)的二氧化碳浓度。就树木水分利用的变化而言，这可能会减少，因为气孔打开的频率会减少，或者树冠叶面积可能会增加(二氧化碳施肥效应)，从而创造更高的整体蒸腾速率。这些关于“多少”的问题很重要，但还有一个关键的问题，也就是树木正在吸收和使用的是“哪些”水，这一问题至今仍被忽视。该项目将利用稳定同位素作为一种方法，在BIFoR二氧化碳富集化实验(FACE)中追踪树木在生长季节所使用的水，以获得对未来森林将使用哪些水的第一次机械洞察。这项工作将具有重要的意义，将直接告知我们如何看待未来的森林和集水区。森林再生努力正在全球范围内扩大，并被广泛认为提供了许多有益的生态系统服务，但这些未来的森林对不断变化的水和气候动态的适应能力如何还是一个高度不确定的问题。这个项目将为它们如何应对水分压力，以及我们如何看待它们的种植和管理提供重要的见解。最后，这项工作还将通过研究结果是否可能在更大范围内适用，特别是树木所用的水如何反过来改变土壤和河流的可用水，从而改变下游水资源的供应，为集水区水管理提供信息。这些对森林和水资源的影响将直接与环境署的项目合作伙伴和合作者以及林业部门的其他合作伙伴合作，使学生能够将研究转化为政策实践。

The earth's atmosphere is changing, with increasing CO2 concentrations changing the way the planet looks through its impact on vegetation. The earth is getting greener in some places, and trees all over the earth appear to be changing the way they use water (refs). These changes will impact forests and water resources globally, but until now we have not had a way to test how trees will actually respond to higher CO2 in the future. This project will help fill this important gap by using a globally unique experimental facility that is artificially enhancing the CO2 concentrations of an old growth oak forest in central UK (BIFoR FACE).In terms of changes to tree water use, this may decrease because stomata will open less frequently, or alternatively the canopy leaf area may increase ('CO2 fertilization effect'), creating higher overall transpiration rates. These questions over "how much" are important, but there is also the critical, and as yet overlooked, question of "which" water is being taken up and used by trees. This project will utilise stable isotopes as a method to trace the water being used by trees over the growing season at the BIFoR CO2 enrichment experiment (FACE) to gain the first mechanistic insights into which water the forest of the future will use.This work will have important implications that will directly inform how we think about forests and catchments of the future. Forest regeneration efforts are expanding globally and are widely recognised as providing many beneficial ecosystem services, but how resilient these forests of the future will be with changing water and climate dynamics is highly uncertain. This project will provide critical insights into how they might respond to water stress, how we might think about their planting and management. Finally, this work will also inform catchment water management by examining whether how the results might apply at larger scales, specifically how the water being used by trees in turn changes the water available for soils and rivers and hence the supply of water resources downstream. These forest and water resource implications will be worked on directly with project partners and collaborators in the Environment Agency, as well as other partners in the forestry sector, allowing the student to also translate research into policy practice.