References

Microorganisms of Biological Crusts on Soil Surfaces 319
organic matter in soil particles; (2) bryophillous/herbicolous, saprotrophic
on mosses and plants; (3) fungicolous/lichenicolous, parasites, parasymbionts
or saprobes on lichens and on other fungi and (4) mycorrhizaforming,
with vascular plant roots. However, what really becomes clear
from the literature on the diversity and role of fungi in biological soil
crusts, is our rather limited knowledge. Future systematic and more standardized
studies are badly needed in order to understand the true diversity
and function of fungi in soil crust dynamics.
3.3
Heterotrophic Protists and Invertebrate Animals
During decomposition, early-colonizing yeast and bacteria are grazed by
protozoans and nematodes, while mites control nematode number. Later
stages of decomposition are dominated by fungi, which are grazed by
nematodes, collembola, and mites (Ingham et al. 1985). In Bamforth’s study
(1984), a total of 49 protozoan taxa were found in the soil crusts of deserts
andsemiaridwoodlandsofArizona.Thisnumberincluded13flagellates,
23 ciliates and 13 testate amoebae. Feeding of protists on cyanobacteria
and algae has been observed several times (e.g., Tchan and Whitehouse
1953; Whitford 1996). The amoebae feeding on unicellular cyanobacteria
from rocks and soils have been regularly observed in crust formations of
southern Africa and Arizona (own observations, unpubl.).
Grazing of nematodes on coccoid algae has been observed in moistened
biological soil crusts (Evans and Johansen 1999), but is also known
from soils of Antarctica (Powers et al. 1998). Arthropod taxa, feeding on
Table 5. Soil arthropods feeding on cyanobacteria, algae, and fungi from the Chihuahuan
Desert. (Adapted from Belnap 2001)
Coleoptera Anotylus sp. –
Collembola Folsomia elongata Hypogastura scotti
Oribatida Ceratozetes sp. Haplozetes sp.
Oppia sp. Peloribates sp. Pergalumna sp.
Pilogalumna sp. – –
Astigmata Tryophagus similis Tryophagus zachvakini
Endeostigmata Alicorhagia fragilis Alicorhagia usitata
Prostigmata Eupodes spp. Linopodes sp.
Paratydeus sp. – –
Tardigrada Not specified –