Microbial grazing
Microbial grazing is primarily performed by soil meso-fauna, such as soil mites, springtails, and micro-fauna like nematodes and larger protozoa; such as ciliates and also some testate amoeba which feed on the small bacteria, fungi and small protozoan species. In doing so, these meso and micro-fauna recycle the carbon and nutrients locked-up in the microbial biomass and control their numbers.
Microbial grazing supports three out of four soil functions in a number of different ways. During the feeding process, carbon is respired and the act of grazing influences the amount of the microbial biomass (the number of micro-organisms in the soil) and how efficient the microbes are in decomposing organic matter. This is why microbial grazing supports decomposition in the Carbon and Climate Regulation function, and is also important for the Disease and Pest Management function. By grazing, the meso-fauna influence the flow of carbon and nutrients through the food chain, and it is therefore included as a sub-process (renamed “bacterial and fungal feeding”) influencing food web assimilation in the Nutrient Cycling and (again) Carbon and Climate Regulation functions.
Measuring microbial grazing can be challenging, depending on its purpose. In the context of decomposition, microbial grazing can be measured using litter bag[1] or bait lamina[2] tests, whereby coarse plant remains or powdered plant material are placed in the soil and retrieved at a later moment to measure the feeding activity of the meso-fauna alongside the microbial activity. Microbial grazing in the context of food web assimilation can be quantified using food web models[3], or by tracing the carbon and nitrogen flows through the food web[4].
[1] Crossley DA & Hoglund MP. 1962. A Litter-Bag Method for the Study of Microarthropods Inhabiting Leaf Litter. Ecology 43: 571–573.
[2] Kratz W. 1998. The bait-lamina test. Environmental Science and Pollution Research 5: 94–96.
[3] Holtkamp R. 2011. Modelling C and N mineralisation in soil food webs during secondary succession on ex-arable land. Soil Biology and Biochemistry 43: 251–260.
[4] Morriën E et al. 2017. Soil networks become more connected and take up more carbon as nature restoration progresses. Nature Communications 8: 14349.