Microbial substrate stoichiometry governs nutrient effects on nitrogen cycling in grassland soils
Microbial substrate stoichiometry governs nutrient effects on nitrogen cycling in grassland soils
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DOI：
10.1016/j.soilbio.2021.108168
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发表时间：
2021-04
影响因子：
9.7
通讯作者：
P. Schleuss;M. Widdig;L. Biederman;E. Borer;M. Crawley;K. Kirkman;E. Seabloom;P. D. Wragg;M. Spohn
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文献类型：
--
作者：
P. Schleuss;M. Widdig;L. Biederman;E. Borer;M. Crawley;K. Kirkman;E. Seabloom;P. D. Wragg;M. Spohn
人类活动增加了陆地生态系统中氮（N）和磷（P）的输入，改变了碳（C）的可用性，改变了土壤中微生物基质的化学计量，例如溶解有机物库的C：N：P比率。微生物生物量与其基质之间的化学计量偏差可能控制着微生物的氮循环过程。我们研究了这种化学计量不匹配的影响，在南非，美国和英国的6个草地生态系统中复制的全因子N和P添加实验。结果表明，氮、磷的添加改变了土壤溶解性有机质的碳氮比，但对土壤微生物生物量的碳氮比没有影响。与磷添加相比，氮添加使微生物通过非共生固氮获得的氮减少了-55%，并使微生物通过净氮矿化释放的氮增加了+134%。一个可能的解释是，溶解的元素，例如，溶解有机碳（DOC）和溶解总氮（DN）作为主要的微生物基质，其C：N比决定了微生物对氮的需求是丰富还是缺乏。如果相对于微生物的需求，氮是过量的，净氮矿化增加。相反，当氮是稀缺的，固定超过释放减少净氮矿化。然而，亮氨酸氨肽酶的活性，分解肽，不受营养添加。此外，C，而不是P的可用性可能会控制非共生固氮率在6个研究草地网站。总之，全球范围内不断增加的养分投入改变了草地生态系统微生物氮的获取和释放过程，这些变化在很大程度上是由基质化学计量的变化所驱动的。
Human activities have increased nitrogen (N) and phosphorus (P) inputs in terrestrial ecosystems and altered carbon (C) availability, shifting the stoichiometry of microbial substrates in soils, such as the C:N:P ratios of the dissolved organic matter pool. These stoichiometric deviations between microbial biomass and its substrate may control microbial processes of N cycling. We studied the effects of this stoichiometric mismatch using a full factorial N and P addition experiment replicated in six grassland ecosystems in South Africa, the USA, and the UK. We found that N and P addition changed the dissolved organic matter C:N ratio, but not the C:N ratio of the soil microbial biomass. Compared to P addition, N addition decreased microbial N acquisition via non-symbiotic N2fixation by −55% and increased microbial N release via net N mineralization by +134%. A possible explanation is that the dissolved elements, e.g., dissolved organic C (DOC) and dissolved total N (DN), serve as the main microbial substrate and its C:N ratio defines whether N is scarce or abundant with respect to microbial demands. If N is available in excess relative to microbial demands, net N mineralization increases. In contrast, when N is scarce, immobilization outweighs release decreasing net N mineralization. However, the activity of leucine aminopeptidases, which decompose peptides, was not affected by nutrient additions. Further, C rather than P availability may control the rates of non-symbiotic N2fixation in the six studied grassland sites. In conclusion, globally increasing nutrient inputs change processes of microbial N acquisition and release in grassland ecosystems and these changes are largely driven by shifts in substrate stoichiometry.