Challenging the paradigm of nitrogen cycling: no evidence of in situ resource partitioning by coexisting plant species in grasslands of contrasting fertility.
Challenging the paradigm of nitrogen cycling: no evidence of in situ resource partitioning by coexisting plant species in grasslands of contrasting fertility.
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DOI：
10.1002/ece3.1244
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发表时间：
2015-01
影响因子：
2.6
通讯作者：
Bardgett, Richard D.
中科院分区：
文献类型：
--
作者：
Wilkinson, Anna;Hill, Paul W.;Vaieretti, Maria V.;Farrar, John F.;Jones, Davey L.;Bardgett, Richard D.
关键词：
在单一栽培中，某些植物物种能够优先利用不同的氮(N)形态，包括无机和有机的，包括氨基酸和肽，从而形成基于N的化学形态的基本生态位。然而，田间研究的结果是不一致的：一些表明共存的植物物种主要利用无机N，而另一些植物对不同的N形态表现出明显的种间偏好。因此，在自然界中，假设的利基地位在多大程度上实现仍不清楚。在这里，我们使用原位稳定同位素示踪技术在温带草原验证了基于化学形态的N的生态位分配与植物生产力以及有机和无机N的相对有效性有关的观点。我们还在现场测试了草地植物竞争和利用多肽的能力是否发生了变化，这些多肽最近被证明是高度N限制的生态系统中植物的氮源。我们推测，在无机氮有效性较高的高产草地上，植物优先利用硝态氮、−-N和NH4+-N，而不是溶解的有机氮。另一方面，在低生产力草地上，溶解无机氮的有效性较低，土壤中溶解有机氮的有效性较高，我们预测植物优先利用氨基酸和多肽中的氮，而不是微生物矿化。在两个生产力和土壤氮素有效性不同的典型草地上，原位注射15N标记的无机N(NO3-−和NH4+)和13C15N标记的氨基酸(L-丙氨酸)和多肽(L-三丙氨酸)的混合物。为了测量土壤微生物和植物对这些氮素形态的快速同化，在2.5小时内跟踪了这些底物在最丰富的植物物种的地上部以及根和土壤微生物生物量中的吸收。我们发现，与我们的假设相反，两个草原上的大多数植物都以NH4+的形式吸收了大部分N，这表明无机N是它们的主要氮源。然而，我们确实发现有机N是两个地点的植物都可以利用的N的来源，在低生产力的草地上，植物能够直接捕获一些三丙氨酸-N。虽然我们的发现不支持无机和有机氮有效性的差异促进草原资源分配的假设，但它们确实支持了新出现的观点，即多肽是陆地氮循环中一个重要的、但到目前为止被忽视的组成部分。
In monoculture, certain plant species are able to preferentially utilize different nitrogen (N) forms, both inorganic and organic, including amino acids and peptides, thus forming fundamental niches based on the chemical form of N. Results from field studies, however, are inconsistent: Some showing that coexisting plant species predominantly utilize inorganic N, while others reveal distinct interspecies preferences for different N forms. As a result, the extent to which hypothetical niches are realized in nature remains unclear. Here, we used in situ stable isotope tracer techniques to test the idea, in temperate grassland, that niche partitioning of N based on chemical form is related to plant productivity and the relative availability of organic and inorganic N. We also tested in situ whether grassland plants vary in their ability to compete for, and utilize peptides, which have recently been shown to act as an N source for plants in strongly N-limited ecosystems. We hypothesized that plants would preferentially use NO3−-N and NH4+-N over dissolved organic N in high-productivity grassland where inorganic N availability is high. On the other hand, in low-productivity grasslands, where the availability of dissolved inorganic N is low, and soil availability of dissolved organic N is greater, we predicted that plants would preferentially use N from amino acids and peptides, prior to microbial mineralization. Turves from two well-characterized grasslands of contrasting productivity and soil N availability were injected, in situ, with mixtures of 15N-labeled inorganic N (NO3− and NH4+) and 13C15N labeled amino acid (l-alanine) and peptide (l-tri-alanine). In order to measure rapid assimilation of these N forms by soil microbes and plants, the uptake of these substrates was traced within 2.5 hours into the shoots of the most abundant plant species, as well as roots and the soil microbial biomass. We found that, contrary to our hypothesis, the majority of plant species across both grasslands took up most N in the form of NH4+, suggesting that inorganic N is their predominant N source. However, we did find that organic N was a source of N which could be utilized by plant species at both sites, and in the low-productivity grassland, plants were able to capture some tri-alanine-N directly. Although our findings did not support the hypothesis that differences in the availability of inorganic and organic N facilitate resource partitioning in grassland, they do support the emerging view that peptides represent a significant, but until now neglected, component of the terrestrial N cycle.
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