Soil microbial stability and function : the role of diversity, composition and soil resources

Abstract

Soil microbial function and stability may affect many other ecosystem functions, including soil carbon storage, nutrient cycling and plant productivity. However, the drivers of soil microbial stability itself are little understood. This thesis therefore aimed to develop a method and indices capable of quantifying soil microbial stability in terms of the resistance (amount of change caused by a disturbance), and resilience (rate of recovery) of the soil microbial community to a model disturbance, and to determine the role of three potential drivers of soil microbial function arid stability: diversity, composition and soil resources. Initially, soil microbial stability and soil resources were measured during three chronosequences to assess whether stability changes in a natural environment and whether resources are an important driver of these changes. Although soil resources were frequently related to resistance and resilience, the direction and strength of correlations depended on the response variable and chronosequence considered. This suggested a factor related to soil resources, which varied across chronosequences, was a stronger driver of soil microbial stability than resources themselves. Two potential factors were plant species composition and diversity. A glasshouse experiment that tested these factors was harvested at 4 times throughout a 16-month period. Plant species composition, but not diversity, proved to be a strong driver of soil microbial function and stability. As different plant species may alter soil microbial function and stability by depositing different carbon substrates, a further experiment manipulated the composition and diversity of carbon substrates added to a base soil. The composition, and sometimes the diversity, of added substrates affected the soil microbial community, its function and stability. Diversity effects saturated at low levels and depended on which substrates were added. The overall conclusion from this set of experiments was that the strongest drivers of soil microbial function and stability seemed to be the composition of plant and soil microbial communities as well as soil resources.