Negassa Wakene C, Guber Andrey K, Kravchenko Alexandra N, Marsh Terence L, Hildebrandt Britton, Rivers Mark L
IASS-Global Soil Forum, Institute for Advanced Sustainability Studies, Potsdam, Germany.
Department of Plant, Soil and Microbial Sciences, Michigan State University, East Lansing, Michigan, United States of America.
PLoS One. 2015 Apr 24;10(4):e0123999. doi: 10.1371/journal.pone.0123999. eCollection 2015.
Physical protection of soil carbon (C) is one of the important components of C storage. However, its exact mechanisms are still not sufficiently lucid. The goal of this study was to explore the influence of soil structure, that is, soil pore spatial arrangements, with and without presence of plant residue on (i) decomposition of added plant residue, (ii) CO2 emission from soil, and (iii) structure of soil bacterial communities. The study consisted of several soil incubation experiments with samples of contrasting pore characteristics with/without plant residue, accompanied by X-ray micro-tomographic analyses of soil pores and by microbial community analysis of amplified 16S-18S rRNA genes via pyrosequencing. We observed that in the samples with substantial presence of air-filled well-connected large (>30 µm) pores, 75-80% of the added plant residue was decomposed, cumulative CO2 emission constituted 1,200 µm C g(-1) soil, and movement of C from decomposing plant residue into adjacent soil was insignificant. In the samples with greater abundance of water-filled small pores, 60% of the added plant residue was decomposed, cumulative CO2 emission constituted 2,000 µm C g(-1) soil, and the movement of residue C into adjacent soil was substantial. In the absence of plant residue the influence of pore characteristics on CO2 emission, that is on decomposition of the native soil organic C, was negligible. The microbial communities on the plant residue in the samples with large pores had more microbial groups known to be cellulose decomposers, that is, Bacteroidetes, Proteobacteria, Actinobacteria, and Firmicutes, while a number of oligotrophic Acidobacteria groups were more abundant on the plant residue from the samples with small pores. This study provides the first experimental evidence that characteristics of soil pores and their air/water flow status determine the phylogenetic composition of the local microbial community and directions and magnitudes of soil C decomposition processes.
土壤碳（C）的物理保护是碳储存的重要组成部分之一。然而，其确切机制仍不够清晰。本研究的目的是探讨土壤结构，即土壤孔隙空间排列，在有和没有植物残体的情况下对（i）添加植物残体的分解、（ii）土壤CO2排放以及（iii）土壤细菌群落结构的影响。该研究包括几个土壤培养实验，使用具有对比孔隙特征的样品，有/无植物残体，并伴有土壤孔隙的X射线显微断层分析以及通过焦磷酸测序对扩增的16S - 18S rRNA基因进行微生物群落分析。我们观察到，在大量存在通气良好的大孔隙（>30 µm）的样品中，75 - 80%的添加植物残体被分解，累积CO2排放为1200 µm C g(-1)土壤，并且分解的植物残体中的碳向相邻土壤的迁移不显著。在充满水的小孔隙更丰富的样品中，60%的添加植物残体被分解，累积CO2排放为2000 µm C g(-1)土壤，并且残体碳向相邻土壤的迁移显著。在没有植物残体的情况下，孔隙特征对CO2排放，即对天然土壤有机碳分解的影响可以忽略不计。大孔隙样品中植物残体上的微生物群落有更多已知的纤维素分解菌微生物类群，即拟杆菌门、变形菌门、放线菌门和厚壁菌门，而一些贫营养酸杆菌类群在小孔隙样品的植物残体上更为丰富。本研究提供了首个实验证据，表明土壤孔隙特征及其空气/水流状态决定了当地微生物群落的系统发育组成以及土壤碳分解过程的方向和幅度。
