The role of the soil microbial comunity in decomposition in a raised mire system

Abstract

Peatlands make up 3% of the earth's land surface and contain about one third of the C contained in soils globally. The role of peatlands in the C cycle is as a net sink. Organic matter accumulates in these areas because the rate of net primary productivity (NPP) exceeds the rate of decay. Peatlands are often harsh environments, characterized by cold, wet and anoxic conditions, therefore it is not accelerated NPP which exerts the main control over the accumulation of peat, but the slow rate of decomposition. During the decomposition process, nearly all organic matter passes through the soil microbial pool, and so the soil microbial community is an important factor in the decomposition process. Despite the obvious importance of the soil microbial community in decomposition in peatlands, our knowledge of their role in peatland C cycling is still largely limited. This thesis addresses some aspects of the soil microbial community and investigates their role in decomposition in a raised mire. The soils in a raised mire system may be categorized according to their nutrient input into nutrient rich, mineral soils and soils of the lagg fen, and nutrient poor, soils of the mire expanse. The soil microbial community in the three soils was characterized in terms of size, activity and composition. The size of the soil microbial community in the soils of the mire expanse was small in comparison with that of the mineral soils and soils of the lagg fen, however it was very active. The hypothesis that nutrients restrict the size of the soil microbial community in the soils of the mire expanse was tested. The data showed that nutrients did not significantly effect the size of the soil microbial community. Litterbags were used to investigate the decomposition of a range of plant species found on the different soils and mass loss and C02 production were used as indicators of decomposition. C02 production was a more sensitive and reliable measure of decomposition than mass loss. The size of the soil microbial community was an important factor in decomposition rate. Litter quality of the above ground biomass was not related to decomposition rate. The relationship between the size of the microbial community in contact with decaying plant material and decomposition was investigated. In this study, microbial colonization of decaying litter was not correlated with the measure of litter quality used. This work has provided baseline information the environmental factors that influence decomposition and future work should focus on investigating the changes in the soil microbial community during the decomposition process.