Harrison Kathryn A, Bol Roland, Bardgett Richard D
Institute of Environmental and Natural Sciences, Soil and Ecosystem Ecology Laboratory, Lancaster University, Lancaster LA1 4YQ, UK.
Ecology. 2007 Apr;88(4):989-99. doi: 10.1890/06-1018.
The growing awareness that plants might use a variety of nitrogen (N) forms, both organic and inorganic, has raised questions about the role of resource partitioning in plant communities. It has been proposed that coexisting plant species might be able to partition a limited N pool, thereby avoiding competition for resources, through the uptake of different chemical forms of N. In this study, we used in situ stable isotope labeling techniques to assess whether coexisting plant species of a temperate grassland (England, UK) display preferences for different chemical forms of N, including inorganic N and a range of amino acids of varying complexity. We also tested whether plants and soil microbes differ in their preference for different N forms, thereby relaxing competition for this limiting resource. We examined preferential uptake of a range of 13C15N-labeled amino acids (glycine, serine, and phenylalanine) and 15N-labeled inorganic N by coexisting grass species and soil microbes in the field. Our data show that while coexisting plant species simultaneously take up a variety of N forms, including inorganic N and amino acids, they all showed a preference for inorganic N over organic N and for simple over the more complex amino acids. Soil microbes outcompeted plants for added N after 50 hours, but in the long-term (33 days) the proportion of added 15N contained in the plant pool increased for all N forms except for phenylalanine, while the proportion in the microbial biomass declined relative to the first harvest. These findings suggest that in the longer-term plants become more effective competitors for added 15N. This might be due to microbial turnover releasing 15N back into the plant-soil system or to the mineralization and subsequent plant uptake of 15N transferred initially to the organic matter pool. We found no evidence that soil microbes preferentially utilize any of the N forms added, despite previous studies showing that microbial preferences for N forms vary over time. Our data suggest that coexisting plants can outcompete microbes for a variety of N forms, but that such plant species show similar preferences for inorganic over organic N.
人们越来越意识到植物可能会利用多种氮（N）形态，包括有机和无机形态，这引发了关于资源分配在植物群落中作用的问题。有人提出，共存的植物物种可能能够通过吸收不同化学形态的氮来分配有限的氮库，从而避免资源竞争。在本研究中，我们使用原位稳定同位素标记技术来评估温带草原（英国英格兰）共存的植物物种是否对不同化学形态的氮表现出偏好，包括无机氮和一系列复杂度不同的氨基酸。我们还测试了植物和土壤微生物对不同氮形态的偏好是否存在差异，从而缓解对这种有限资源的竞争。我们在田间研究了共存的禾本科植物和土壤微生物对一系列13C15N标记的氨基酸（甘氨酸、丝氨酸和苯丙氨酸）和15N标记的无机氮的优先吸收情况。我们的数据表明，虽然共存的植物物种同时吸收多种氮形态，包括无机氮和氨基酸，但它们都表现出对无机氮的偏好超过有机氮，对简单氨基酸的偏好超过更复杂的氨基酸。50小时后，土壤微生物在争夺添加氮方面胜过植物，但从长期（33天）来看，除苯丙氨酸外，所有氮形态在植物库中所含添加15N的比例都增加了，而微生物生物量中的比例相对于首次收获时下降了。这些发现表明，从长期来看，植物在争夺添加15N方面变得更具竞争力。这可能是由于微生物周转将15N释放回植物 - 土壤系统，或者是由于15N最初转移到有机质库后发生矿化并随后被植物吸收。我们没有发现证据表明土壤微生物优先利用添加的任何一种氮形态，尽管之前的研究表明微生物对氮形态的偏好会随时间变化。我们的数据表明，共存的植物在争夺多种氮形态方面可以胜过微生物，但这些植物物种对无机氮的偏好超过有机氮。
