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ARS Home » Northeast Area » University Park, Pennsylvania » Pasture Systems & Watershed Management Research » Research » Publications at this Location » Publication #180124
Title: EUBACTERIAL COMMUNITIES IN DIFFERENT SOIL MACROAGGREGATE ENVIRONMENTS AND CROPPING SYSTEMS

Author
item BLACKWOOD, C - UNIV OF MICHIGAN
item Dell, Curtis
item SMUCKER, A J - MICHIGAN STATE UNIV
item PAUL, E - COLORADO STATE UNIV

Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2005
Publication Date: 4/20/2006
Citation: Blackwood, C.B., Dell, C.J., Smucker, A.M., Paul, E.A. 2006. Eubacterial communities in different soil macroaggregate environments and cropping systems. Soil Biology and Biochemistry. 38:720-728.

Interpretive Summary: Soil microbial communities and the physical structure of soils are interlinked. The geometric configuration of soil components and number and size of soil pores influences moisture content and oxygen concentration, thus influencing the size and species composition of the microbial community. The distance to the outer surface of soil aggregates can create changes in the environment which may be causing differences in structure of the microbial community within the soil aggregates. Not only is the microbial community influenced the physical structure of soil, but microbes influence the their environment because metabolic by-products act as glues which help to bind soil particles and create desirable soil structure. In this study, the molecular diversity of the bacterial communities in soil aggregates from three management systems in Michigan and Ohio were assessed. Soil aggregates were segmented into concentric layers, and the microbial communities from near the outer surfaces were compared to those residing at the central core of the aggregates. Terminal restriction fragment length polymorphism (T-RFLP) showed only limited differences in microbial community structure between intra-aggregates regions. However, T-RFLP profiles varied greatly among individual aggregates from each of the three management regimes. The results of the study indicate the proximity of the aggregate to macropores or plant residues may have a larger influence of the type on microbial community present than does the location within the aggregate.

Technical Abstract: Different positions within soil macroaggregates, and macroaggregates of different sizes, have different chemical and physical properties which could affect microbial growth and interactions among taxa. The hypothesis that these soil aggregate fractions contain different eubacterial communities was tested using terminal restriction fragment length polymorphism (T-RFLP) of the 16S ribosomal gene. Communities were characterized from two field experiments, located at the Kellogg Biological Station (KBS), MI, USA and the Ohio Agricultural Research and Development Center (OARDC), Wooster, OH, USA. Three soil management regimes at each site were sampled and management was found to significantly affect T-RFLP profiles. The soil aggregate erosion (SAE) method was used to isolate aggregate regions (external and internal regions). Differences between eubacterial T-RFLP profiles of aggregate exteriors and interiors were marginally significant at KBS (accounting for 12.5% of total profile variance), and not significant at OARDC. There were no significant differences among macroaggregate size classes at either site. These results are in general agreement with previous studies using molecular methods to examine microbial communities among different soil macroaggregate size fractions, although further study of communities within different aggregate regions is warranted. Analysis of individual macroaggregates revealed large inter-aggregate variability in community structure. Hence the tertiary components of soil structure, eg. arrangement of aggregates in relation to shoot residue, roots, macropores, etc., may be more important than aggregate size or intra-aggregate regions, in the determination of the types of microbial communities present in aggregates. Direct microscopic counts were also used to examine the bacterial population size in aggregate regions at KBS. The proportion of bacterial cells with biovolumes >0.18 'm3 was higher in aggregate interiors than in exteriors, indicating potentially higher activity in that environment. This proportion was significantly related to percent C of the samples, while total bacterial cell counts were not.