Soil management modifications of bacterial morphotypediversity in soil aggregates

Dopp, H.A., E.J. Park, F.B. Dazzo, A.J.M. Smucker

Presented at the All Scientist Meeting (2004-10-08 )

Soil aggregation processes and wetting-drying cycles modify micro-habitats by changing pore networks and sequestering carbon © within newly formed microsites within interiors of aggregates.  Morphotype analyses of bacterial communities within concentric layers of soil aggregates can be used to estimate bacterial populations associated with these micro-habitats located on surfaces and within the central regions of macroaggregates.  Bacterial morphotypes were identified by computer image processing software developed by the Center for Microbial Ecology Image Analysis System (CMEIAS) at Michigan State University.  Bacteria were extracted from exterior and interior regions of soil aggregates by mechanical soil aggregation erosion (SAE) chambers and stained with DTAF (5-(4,6-dichlorotriazin-2-yl) aminofluorescein).  Diversity and the number of bacteria were compared with C concentrations.  Soil C contents identified on aggregate exteriors were 12% and 3% greater than interior regions of macro-aggregates sampled from native forest (NF) and conventionally tilled (CT) agroecological soils at the Kellogg Biological Station (KBS) LTER site and the Upper Peninsula (UP) research sites.  Increased numbers of bacteria per gram of soil were observed in the exterior regions of soil aggregates from the KBS loam (6.24E10 in exterior, 5.25E10 in interior) and UP sandy loam soils (4.98E10 in exterior, 4.66E10 in interior).  Although extraction and staining protocols for identifying soil bacteria have been developed, the anticipated greater quantities of bacterial morphotypes located within exterior regions of soil aggregates could not be observed by the CEMIAS evaluations of stained soil layers extracted from aggregates.  However, direct relationships between C concentrations and extracted bacteria per gram of soil were observed.

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