Microbial Communities and Carbon Dynamics Across a Depth Profile in an Organic and Conventionally Managed Agricultural Soil.

It is firmly established that soil carbon stocks in agricultural soil must be measured to at least 40 cm to assess true rates of C storage; however, microbial studies of agricultural soils rarely sample deeper than 10 or 20 cm at most. In this study, we analyzed soils under organic, no-till, and chisel-till management regimes to observe interactions between edaphic factors, microbial community size and structure, and carbon chemistry in these systems. Meter-deep sample cores were separated into six depth fractions; three above and three below the plow layer. We extracted DNA from each of these fractions and measured archaeal, bacterial, and fungal populations and community structures through Q-PCR and Illumina sequencing of 16S and ITS rRNA genes. Additionally, we studied the mass and chemistry of particulate organic matter (POM) to observe fine-scale effects of management regime on soil carbon. We found large significant differences in microbial community structure above and below the plow layer, correlated with soil texture and total carbon content. Preliminary results also suggest that no-till management resulted in greater total carbon and 53-250 um POM mass than other treatments in the 0-5 cm depth increment. However, when all increments above the plow layer were considered, organic management resulted in an equal or greater mass of POM and total stored carbon. This work shows the importance of depth in considering the effects of management regime on agricultural soil biochemistry and microbiology, especially considering the position of the plow layer in currently (or previously) tilled soils.