Spatial location of active soil bacteria and their association with soil organic matter fractions

• Main Author: McCabe, Darren P. M.
• Published: University of Reading 2011
• Subjects: 578.757
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.559246

The heterogeneous maze of water and gas filled pores within the soil forms the habitat for the diverse bacterial component of the soil biota. These microorganisms play an essential role in soil processes, but the specificity of their location and that of their associated substrates within these pores remains to be revealed. This research tested a novel approach to assess the contribution of pore neck size to bacterial diversity in soil, using soil aggregates obtained at increasing depths from a rhizotron under the perennial bioenergy crop Miscanthus x giganteus. The nucleotide analogue bromodeoxyuridine (BrdU) was added to soil aggregates using a model that relates the neck diameter of water-filled pores to the soil water matric potential. The BrdU labels the DNA of actively dividing cells within contrasting pore size ranges which can then be isolated through an optimised procedure. A second experiment assayed for soil- and plant-derived enzymes as indicators for root/rhizosphere activity and substrates present across the course of a growing season. Thirdly, the soil carbon was physically fractionated to investigate soil organic matter dynamics on a seasonal scale, and the potential for Miscanthus to accumulate soil carbon on an annual scale. The results provide the first direct evidence that distinct active bacterial communities form within soil pore classes. Further, communities within small pores (-1 - 30 urn) were more diverse than in large pores (30 - 3000 urn). There was marked seasonal variation in both soil enzyme activities and soil light fractions. The soil under Miscanthus was found to be more porous with more accumulated carbon then a comparable arable soil. In summary, the project emphasises the importance of using an integrated multidisciplinary approach to advance our understanding of soil processes on a micro scale so that we can understand and potentially improve soil functioning at the field scale.