Plant nutrition as Earth System Science: understanding the links between plant nutrient gain and soil carbon storage.

我们不完全了解植物如何从土壤中获取养分。这使得模拟陆地生态系统中的碳(C)循环以及了解陆地碳储量如何对全球变化作出反应变得困难。该奖学金项目旨在提高我们对植物营养的理解，从而提高我们准确预测气候和陆地C循环之间反馈的能力。植物从土壤中获取养分的方式，尤其是氮(N)，是决定土壤有机质（SOM）分解速度的重要因素，因此也决定了土壤中储存了多少碳。例如，已知植物及其相关的共生根真菌（菌根菌）通过产生能够降解抗性更强的有机化合物的酶来“启动”SOM分解。最近的证据还表明，植物吸收养分的形式，无论是无机（矿物）离子还是含c的有机分子，都对SOM的分解速度有影响。问题是，虽然我们知道存在复杂的植物介导的土壤碳储存效应，但我们对它们的了解还不够好，无法将它们纳入碳循环模型。目前的知识表明，在北极等营养有限的环境中，植物营养可能对土壤C的储存有很大影响。北极生态系统储存了大量的C -约。全球陆地碳总量的35-45%存在于北极和永久冻土中。北极土壤C在变暖条件下的未来是高度不确定的，也是NERC研究的重点（例如，通过最近的500万英镑北极研究计划）。特别迫切需要了解北极环境中植物营养与土壤C储存之间的相互作用，这将是研究金活动的重点。长期以来，人们一直认为无机氮离子提供了植物所需的大部分氮，但现在越来越多的证据表明，有机形式的氮在维持植物生长中也起着重要作用。因此，除了对全球碳循环的影响外，了解有机氮营养对作物生产和粮食安全也有潜在的影响。由于现有技术受到实验人工制品的限制，到目前为止，有机氮对植物的相对重要性一直无法测量。这项研究首次提出了新的同位素方法，可以量化有机氮对植物的重要性。这些新技术包括种植同位素与土壤不同的植物，以便追踪从土壤中吸收含碳有机养分进入植物组织的过程（连续耗尽放射性碳（CDER）标记）。还将在北极实地进行实验，利用植物和土壤的同位素特征来测试不同条件下植物养分需求与SOM分解之间的联系。所提出的技术将使定量测试植物营养影响土壤分解的方式成为可能。这些新信息将用于更新碳循环模型，以改善植物养分吸收的表现，并测试环境变化对北极土壤碳储存的未来影响。该项目的成果将大大提高我们对植物营养和北极C种群对全球变化的脆弱性的理解。

We do not fully understand how plants access nutrients from the soil. This makes it difficult to model carbon (C) cycling in terrestrial ecosystems - and to know how terrestrial C storage might respond to global change. This fellowship project aims to improve our understanding of plant nutrition and by doing so increase our ability to accurately predict feedbacks between climate and the terrestrial C cycle.The ways in which plants obtain nutrients from the soil, and especially nitrogen (N), are known to be important in determining how quickly soil organic matter (SOM) decomposes and therefore how much C is stored in soils. For example, plants and their associated symbiotic root fungi (mycorrhizas) are known to "prime" SOM decomposition by producing enzymes capable of degrading more resistant organic compounds. Recent evidence also suggests that the form in which plant take up nutrients, whether as inorganic (mineral) ions or as C-containing organic molecules, has an impact on rates of SOM decomposition. The problem is that whilst we know that complex plant-mediated effects on soil C storage exist, we do not understand them well enough to include them in models of the C cycle. Current knowledge suggests that plant nutrition may have a large impact on soil C storage in nutrient-limited environments such as the Arctic. Arctic ecosystems store large amounts of C - approx. 35-45% of total global terrestrial C is found in Arctic and permafrost soils. The future of Arctic soil C under warming conditions is highly uncertain and is a focus of NERC research (e.g. through the recent £5m Arctic Research Programme). There is a particularly pressing need to understand the interactions between plant nutrition and soil C storage in Arctic environments and this is where the fellowship activities will be concentrated. It has long been assumed that inorganic N ions provide most of the N that plants need but there is now growing evidence that organic forms of N also play an important role in sustaining plant growth. In addition to implications for the global C cycle, understanding organic N nutrition therefore has potential ramifications for crop production and food security.The relative importance of organic N to plants has been impossible to measure until now because existing techniques are limited by experimental artefacts. This fellowship proposes new isotopic methods that can quantify the importance of organic N to plants for the first time. These novel techniques include growing plants which are isotopically distinct from the soil, in order to trace the uptake of C-containing organic nutrients from the soil into plant tissues (Continuous Depleted Radiocarbon (CDER) labelling). Experiments will also be carried out at Arctic field sites, in which the isotopic signatures of plants and soils will be used to test the linkages between plant nutrient demand and SOM decomposition under different conditions. The proposed techniques will make it possible to quantitatively test the ways in which plant nutrition impacts decomposition in soils. This new information will then be used to update C cycle models to improve representation of plant nutrient uptake, and test the future impact of environmental change on soil C storage in the Arctic. The outcome of this project will be a significant improvement in our understanding of plant nutrition and of the vulnerability of Arctic C stocks to global change.