School of Natural Resources & Environment, University of Michigan, Ann Arbor, MI, USA.
Department of Ecology & Evolutionary Biology, University of Michigan, Ann Arbor, MI, USA.
Glob Chang Biol. 2017 Feb;23(2):933-944. doi: 10.1111/gcb.13480. Epub 2016 Oct 11.
Accumulating evidence indicates that future rates of atmospheric N deposition have the potential to increase soil C storage by reducing the decay of plant litter and soil organic matter (SOM). Although the microbial mechanism underlying this response is not well understood, a decline in decay could alter the amount, as well as biochemical composition of SOM. Here, we used size-density fractionation and solid-state C-NMR spectroscopy to explore the extent to which declines in microbial decay in a long-term (ca. 20 yrs.) N deposition experiment have altered the biochemical composition of forest floor, bulk mineral soil, as well as free and occluded particulate organic matter. Significant amounts of organic matter have accumulated in occluded particulate organic matter (~20%; oPOM); however, experimental N deposition had not altered the abundance of carboxyl, aryl, alkyl, or O/N-alkyl C in forest floor, bulk mineral soil, or any soil fraction. These observations suggest that biochemically equivalent organic matter has accumulated in oPOM at a greater rate under experimental N deposition, relative to the ambient treatment. Although we do not understand the process by which experimental N deposition has fostered the occlusion of organic matter by mineral soil particles, our results highlight the importance of interactions among the products of microbial decay and the chemical and physical properties of silt and clay particles that occlude organic matter from microbial attack. Because oPOM can reside in soils for decades to centuries, organic matter accumulating under future rates of anthropogenic N deposition could remain in soil for long periods of time. If temperate forest soils in the Northern Hemisphere respond like those in our experiment, then unabated deposition of anthropogenic N from the atmosphere has the potential to foster greater soil C storage, especially in fine-texture forest soils.
越来越多的证据表明，未来大气氮沉降的速率有可能通过减少植物凋落物和土壤有机质（SOM）的分解来增加土壤碳储存。尽管这种反应的微生物机制尚未得到很好的理解，但分解的减少可能会改变 SOM 的数量和生物化学组成。在这里，我们使用大小密度分级和固态 13C-NMR 光谱法来探索在长期（约 20 年）氮沉降实验中微生物分解减少的程度，以及它如何改变林地表层、矿质土壤以及自由和包裹的颗粒有机物质的生物化学组成。大量的有机物质已经在包裹的颗粒有机物质（oPOM）中积累（约 20%）；然而，实验性氮沉降并没有改变林地表层、矿质土壤或任何土壤层中羧基、芳基、烷基或 O/N-烷基 C 的丰度。这些观察结果表明，在实验性氮沉降下，生物化学上等同的有机物质以比环境处理更高的速率积累在 oPOM 中。虽然我们不理解实验性氮沉降促进有机物质被矿物土壤颗粒包裹的过程，但我们的结果强调了微生物分解产物与阻碍有机物质免受微生物攻击的粉砂和粘土颗粒的化学和物理性质之间相互作用的重要性。由于 oPOM 可以在土壤中存在数十年到数百年，因此在未来人为氮沉降速率下积累的有机物质可能会在土壤中长时间存在。如果北半球的温带森林土壤像我们的实验一样做出反应，那么大气中人为氮的无节制沉积有可能促进更大的土壤碳储存，特别是在细质地森林土壤中。
