ena-STUDY-MICHIGAN STATE UNIVERSITY-10-03-2015-18:29:34:129-82
Properties of Soil Pore Space Regulate Pathways of Plant Residue Decomposition and Community Structure of Associated Bacteria
Physical protection of soil carbon (C) is one of the important components of C storage. However, the exact mechanisms behind the interactions between spatial patterns in organic C and soil physical micro-environments enabling microbial access to C and influencing microbial activities are still not sufficiently lucid. The goal of this study was to explore the influence of soil structure, i.e. 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 bacterial communities. The study consisted of a series of 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, i.e., 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 the characteristics of soil pores and their air/water flow status determine the phylogenetic composition of the local microbial community and the direction and magnitude of soil C decomposition processes.
Physical protection of soil carbon (C) is one of the important components of C storage. However, the exact mechanisms behind the interactions between spatial patterns in organic C and soil physical micro-environments enabling microbial access to C and influencing microbial activities are still not sufficiently lucid. The goal of this study was to explore the influence of soil structure, i.e. 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 bacterial communities. The study consisted of a series of 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, i.e., 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 the characteristics of soil pores and their air/water flow status determine the phylogenetic composition of the local microbial community and the direction and magnitude of soil C decomposition processes.