Protists in soil ecology and forest nutrient cycling

Abstract

Recent progress in protistology has shown that these organisms (protists) are far more diverse than traditionally assumed by soil ecologists. Most studies have grouped these into motility groups, as amoebae, flagellates, and ciliates. Unfortunately, these do not represent functionally useful groups and do not have any ecological relevance to food web processes and community structure. Typically, abundance values have relied on the most probable number estimate based on bacterivore cultures. In fact, there are many functional groups of protists besides the bacterivores. These other functional groups are very much part of the forest soil decomposition food web, but they remain unaccounted for in models. Modelling studies have shown repeatedly that protozoan bacterivores are responsible for much of the nutrient turnover and flux through the soil food web, as they are in the aquatic microbial loop. The contribution of other protist functional groups to this nutrient cycling remains to be quantified. To this end, new sampling strategies are required, and functional diversity needs to be considered in future studies. We consider both temporal and spatial stratification as contributing factors, to explain the apparent redundancy of function. Finally, drawing on data from agricultural fields, we consider new ideas on rates of recovery after disturbance.