Microbes and microfauna associated with biological soil crusts
Biological Soil Crusts: Structure, Function, and Management
Microbial populations playa critical role in the regulation of nutrient cycling and energy flow in ecosystems, as they mediate decomposition and subsequent mineralization rates which, in turn, regulate nutrient availability and primary production (Zak and Freckman 1991). Even in regions where water is considered limiting, nutrient availability can restrict plant growth (Romney et al. 1978). Extreme temperatures and/or low soil moisture restrict soil food web development. As soil favorability increases, edaphic taxa generally appear in the following order: pigmented bacteria> actinomycetes > algae and cyanobacteria> fungi, protozoa, other bacteria> lichens> mosses and microarthropods (Cameron et al. 1970).
The trophic structure of soil food webs is very important in soil nutrient cycles. Soil primary producers are lichens, mosses, green algae, and cyanobacteria. These organisms, along with plant material, are both grazed directly and decomposed by soil biota. During decomposition, early-colonizing yeast and bacteria are grazed by nematodes and protozoans, while mites control nematode numbers. Later stages of decomposition are dominated by fungi, which are grazed by nematodes, collembola, and mites. Thus, trophic relationships among soil biota become major regulators of decomposition and mineralization in soils (Ingham et al. 1985).
There is also a synergy between bacteria, fungi, protozoa, and cyanobacteria. Grazing by protozoa stimulate cyanobacterial nitrogen fixation (Ghabbour et al. 1980). Addition of heterotrophic bacteria and fungi to soils significantly increases cyanobacterial biomass (Schiefer and Caldwell 1982 ). Bacteria and fungi release nutrients and scavenge cyanobacterial "wastes", including 02' enhancing cyanobacterial N fixation (see Chap. 19). Nitrogen provided by the cyanobacteria, in turn, increases microbial decomposition activity (Lynch and Harper 1983). The objective of this chapter is to discuss the relationship between biological soil crusts and other heterotrophic components of the soil food web, such as bacteria, fungi, protista, nematodes, and soil invertebrates.
Belnap, J., 2003, Microbes and microfauna associated with biological soil crusts, in Belnap, J., and Lange, O. L., eds., Biological Soil Crusts: Structure, Function, and Management: Berlin, Springer-Verlag, p. 167-174.