Nutrient controls on the terrestrial carbon cycle: how does phosphorus deficiency influence plant respiration?

这个项目将提高我们量化磷限制和温度对植物组织呼吸影响的能力。生物体和生态系统的碳平衡在很大程度上取决于光合作用和呼吸作用之间的平衡。在全球范围内，目前陆地上的呼吸作用比光合作用略小，这意味着陆地生态系统被认为是大气二氧化碳的“汇”，减缓了大气中二氧化碳浓度的持续上升。陆地呼吸总量的很大一部分被认为来自树木，因此了解决定植物呼吸的因素对于了解地球系统的陆地部分是如何工作的至关重要。然而，尽管它很重要，但只有有限的数据可以帮助我们量化世界上大片地区的植物呼吸。例如，虽然我们知道植物生长最重要的营养物质(氮和磷)限制了植物的新陈代谢，但我们几乎没有关于磷缺乏如何限制植物呼吸从而限制碳平衡的信息。我们对植物呼吸对温度的反应也知之甚少：目前，我们的全球陆地生态系统模型对此做出了可能是错误的大假设。当我们考虑到：(I)全球30%的陆地表面可能是缺磷的；(Ii)全球磷供应可能在不到100年的时间里严重下降；(Iii)全球气候变暖可能会在本世纪增加植物呼吸(但我们不知道增加多少)，显然有迫切需要解决这个问题。我们将对多种植物的呼吸作用进行测量。我们将首先使用受控环境箱来控制植物的营养供应。然后，我们将把这一点与在磷和氮受到不同限制的选定森林地区进行的实地测量结合起来，以便将我们实验工作的数据与真实的生态系统进行比较。我们在热带南美洲和新西兰的野外选址利用了关于可能的磷限制的现有知识，并将使我们能够解决生物多样性如何影响磷-呼吸关系的问题。最后，我们将分析我们的数据，使我们能够将我们的发现纳入数学模型，用于计算陆地表面和我们的气候如何相互作用。我们的项目将使我们能够：(I)量化缺磷如何影响呼吸；(Ii)量化缺磷对植物呼吸的温度依赖性的影响。我们将能够将我们的结果与现有关于植物组织新陈代谢和氮浓度之间关系的工作联系起来，并将结果纳入特定地点和全球模拟框架。该项目对NERC来说具有很高的成本效益，利用了国际设施和项目合作伙伴的时间，为该项目提供了零成本。这项工作还将与NERC资助的现有研究方案直接挂钩，项目调查人员已经是该方案的一部分。该项目将填补我们在理解全球生态和地球系统运行方面的一个重大空白。

This project will advance our ability to quantify the influence of phosphorus limitation and temperature on plant tissue respiration. The carbon balance of an organism and of an ecosystem is strongly dependent on the balance between photosynthesis and respiration. Globally, respiration on land is at present very slightly smaller than photosynthesis, meaning that terrestrial ecosystems are thought to be a 'sink' for atmospheric carbon dioxide, slowing the continual rise in carbon dioxide concentration in the atmosphere. A large fraction of the total respiration from land is thought to come from trees, so understanding what determines plant respiration is central to understanding how the terrestrial component of the Earth system works. However, despite its importance, only a limited amount of data are available to help us quantify plant respiration over large regions of the world. For example, although we know that the most important nutrients for plant growth (nitrogen and phosphorus) limit plant metabolism, we have almost no information on how phosphorus deficiency limits plant respiration, and hence the carbon balance. We also know only a little about how plant respiration responds to temperature: currently our global models of terrestrial ecosystems make large assumptions about this that may be wrong. When we consider that: (i) 30% of the global land surface may be phosphorus-deficient; (ii) the global phosphorus supply may seriously decline in under 100 years; and (iii) global climatic warming is likely to increase plant respiration this century (but by how much we don't know), there is clearly a strong and urgent need to address this issue. We will make measurements of respiration on a wide range of plant species. We will first use controlled-environment chambers to control the supply of nutrients to plants. We will then couple this with field measurements made in selected forested regions where phosphorus and nitrogen are differentially limiting, in order to compare the data from our experimental work to real ecosystems. The choice of our fieldsites in tropical South America and New Zealand makes use of existing knowledge about likely phosphorus limitations and will allow us to also address the issue of how biodiversity affects the phosphorus-respiration relationship. Finally we will analyse our data to enable us to incorporate our findings into mathematical models used to calculate how the land surface and our climate interact. Our project will enable us: (i) to quantify how phosphorus deficiency affects respiration; (ii) to quantify the influence of phosphorus deficiency on the temperature dependence of plant respiration. We will be able to link our results to existing work on the relationship between plant tissue metabolism and nitrogen concentration, and to incorporate the results into site-specific and global modelling frameworks. The project is highly cost efficient to NERC, making use of international facilities and project partner time supplied at zero cost to this project. This work will also link directly into existing research programmes funded by NERC of which the project investigators are already a part. The project will fill a signficant gap in our understanding of global ecology and the functioning of the Earth system.