New pathways of plant nutrition and resource partitioning in terrestrial ecosystems: testing the ecological role of DON

传统上，无机氮在陆地生态系统植物营养中的重要性一直占据中心地位。然而，最近的研究已经开始挑战这一点，表明植物也可以以氨基酸的形式使用溶解的有机氮（DON）。植物利用DON的能力日益增强，并与土壤中的微生物竞争这一氮池，导致对陆地氮循环和控制植物氮可用性的过程进行彻底的反思。这种新思维的另一个令人惊讶的结果是，它重新引发了关于植物群落中物种共存的资源分配作用的辩论。事实上，已经表明，一些植物物种在吸收不同化学形式的氮（无机和有机）的能力上存在差异，因此使它们能够避免与邻居竞争土壤氮。如果植物在野外这样做，它将为它们在自然群落中共存提供一种机制，从而有助于维持植物多样性。尽管人们越来越认识到DON在陆地生态系统中的作用，但最近的研究表明，它对植物营养和资源分配的重要性在不同的生态系统中有显着差异。这种变异性导致了这样一种想法，这仍然是未经检验的，即植物使用的DON是最重要的植物营养和物种共存（即通过基于化学形式的资源分配）在低生产力的生态系统中，DON的相对可用性无机N（DIN）是高的，由于低的DON池的微生物周转率。这就是我们希望在这项研究中测试，我们的总体假设是，DON的植物的可用性，以及合作的植物物种的能力，分区土壤氮库的基础上的化学形式的N，是最大的在低生产力的生态系统中，DON占主导地位的土壤氮库。我们将采取一个整体的，基于现场的方法来测试这一假设，使用一个很好的特点和无处不在的梯度草原生产力，加上非破坏性的稳定和放射性同位素示踪剂的方法，使我们能够跟踪这些生态系统中的DON组件的营业额和命运。我们相信，我们的数据将提供新的见解陆地氮循环和DON在植物营养和资源分配，这是植物多样性的基础上的作用。

Traditionally, the importance of inorganic nitrogen for plant nutrition in terrestrial ecosystems has taken centre stage. Recent studies, however, have started to challenge this, showing that plants can also use dissolved organic nitrogen (DON) in the form of amino acids. This growing awareness of the ability of plants to use DON, and compete with microbes in the soil for this pool of N, has led to radical rethinking about terrestrial N cycling and the processes that control N availability to plants. Another surprising outcome of this new thinking is that it has rekindled debates about the role of resource partitioning for species co-existence in plant communities. Indeed, it has been shown that some plant species differ in their ability to uptake different chemical forms of N, both inorganic and organic, which therefore allows them to avoid competition with their neighbours for soil N. If plants do this in the field, it would provide a mechanism for them to co-exist in natural communities, thereby contributing to the maintenance of plant diversity. Despite this growing awareness of the role of DON in terrestrial ecosystems, recent research has shown that its importance for plant nutrition and resource partitioning varies markedly across different ecosystems. This variability has led to the idea, which remains untested, that plant use of DON is of most importance for plant nutrition and species coexistence (i.e. via resource partitioning based on chemical form) in low productivity ecosystems where the relative availability of DON to inorganic N (DIN) is high, due to low of rates of microbial turnover of the DON pool. This is what we wish to test in this study, our overarching hypothesis being that the availability of DON to plants, and the ability of co-exisiting plant species to partition the soil N pool based on chemical forms of N, is greatest in low productivity ecosystems where DON dominates the soil N pool. We will take a holistic, field based approach to test this hypothesis, using a well characterised and ubiquitous gradient of grassland productivity, coupled with non-destructive stable and radioisotope tracer approaches that allow us to track the turnover and fate of components of DON in these ecosystems. We believe that our data will provide new insights into terrestrial N cycling and the role of DON in plant nutrition and resource partitioning, which is the basis for plant diversity.