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中对植物营养的重要性一直占据着中心地位。然而，最近的研究已经开始挑战这一点，表明植物也可以利用氨基酸形式的溶解有机氮(DON)。人们越来越意识到植物利用DON的能力，并与土壤中的微生物竞争这一氮库，这促使人们对陆地N循环和控制植物获得N的过程进行了彻底的反思。这种新思维的另一个令人惊讶的结果是，它重新引发了关于资源划分在植物群落中物种共存中所扮演的角色的辩论。事实上，已有研究表明，一些植物物种吸收不同化学形态的无机和有机氮的能力不同，因此它们可以避免与邻居竞争土壤氮。如果植物在田间这样做，它将提供一种机制，使它们能够在自然群落中共存，从而有助于维持植物多样性。尽管人们越来越意识到DON在陆地生态系统中的作用，但最近的研究表明，DON对植物营养和资源分配的重要性在不同的生态系统中差异很大。这种变异性导致了一种观点，即在低生产力生态系统中，由于DON池的微生物周转率较低，DON相对于无机N(DIN)的相对有效性很高，因此植物对DON的使用对于植物营养和物种共存(即通过基于化学形态的资源分配)是最重要的。这就是我们希望在这项研究中检验的，我们的总体假设是，DON对植物的有效性，以及共存植物物种根据N的化学形态划分土壤N库的能力，在DON主导土壤N库的低生产力生态系统中最大。我们将采取全面的、基于田间的方法来验证这一假设，使用具有良好特征的无处不在的草原生产力梯度，再加上非破坏性的稳定和放射性同位素示踪方法，使我们能够跟踪DON在这些生态系统中的周转和命运。我们相信，我们的数据将为陆地N循环以及DON在植物营养和资源分配中的作用提供新的见解，这是植物多样性的基础。

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.