Role of microorganisms in the nutrient cycling of subtropical savannah soilsThe

Abstract

The identification of environmental factors controlling and influencing the soil microbial community and hence the nutrient cycling were investigated in the present study. The breakdown of soil organic matter is initialized by exoenzymes. The activities of the glucosidase, xylosidase, phosphatase and aminopeptidase varied with the soil type, the land use type and the water availability. Moreover, the land use type and the water availability influenced the liberation of nitrogen from complex amino compounds by ammonification and nitrification as well. In sandy Subsaharan savannah soils the decreased nutrient and water availability, the lower aggregate stability reduced total bacterial cell numbers and therefore activity values. But the soil microbial community benefit from stable soil aggregates, nutrients and water provided by soil organic matter in nutrient rich dark loamy pristine soils, pristine woodland and bushveld savannah soils and in the peatland soils. Both land use type and water availability effected the active microbial community composition as well. Predominantly bacterial phyla and species adapted to the nutrient limitation, water stress and heat survived the conditions in the sandy soils. Proteobacteria and Actinobacteria as typical soil phyla dominated the riparian woodland and bushveld savannah soils whereas Firmicutes and some Actinobacteria benefit from the drought in the bushveld soils and from the conditions in the agriculturally used soils. Anthropogenic impact as the addition of fertilizers decreased microbial abundances of the Proteobacteria and Actinobacteria and provided growth advantage of the Firmicutes. After the dry season and rewetting of the soils during a stimulation experiment fast growing Gammaproteobacteria dominated the active microbial community in the riparian woodland and bushveld savannah soils. High abundances of nitrogen fixing microorganisms and microorganisms well adapted to phosphorus limitation in soils confirmed nitrogen and phosphorus limitation in the subtropical savannah soils. In the present study two new representatives were isolated from Namibian soil samples and characterized. Due to morphological, physiological, phylogenetic and molecular characteristics the new isolates A22_HD_4H and Ac_23_E3 were proposed as the new genus Aridibacter with the new species A. famidurans and A. kavangonensis, respectively.