Desert Nematodes and Biological Soil Crusts
Biological Soil Crusts
Biological soil crusts can represent up to 70% of the living vegetative soil cover in arid lands. Early-colonizing fungi and cyanobacteria stabilize the soil surface and facilitate colonization by lichens, green algae, and mosses. Biological soil crusts increase the physical surface stability and soil fertility through dust entrapment, photosynthesis, nitrogen fixation, and mineral chelation (reviewed in Belnap, 2003).
We first sought to characterize the microfauna associated with biological soil crusts. In general, a greater abundance and diversity of microfauna inhabitat well-developed biological soil crusts than soils with absent or less well-developed crusts. The magnitude in difference is comparable to the difference in nematode abundance between soil adjacent to plant and that in plant interspaces. Some microfauna are known to feed directly on various components of the crust microflora, but the exact feeding habits of most species have yet to be worked out.
This species of Acrobeles mostly feeds on bacteria, but may also pick up some fungal spores or other small particulates.
This species of Aphelenchoides is generally thought to feed mostly on fungal hyphae, but here is an image of an isolate that was being successfully cultured on cyanobacteria (Microcoleus vaginatus) for several generations.
In addition to finding more individuals, and more species, associated with well developed, late-successional crusts than early successional crusts, we also found that a larger proportion of the species in well-developed crusts were longer lived species that tend to have fewer total progeny. This Dorylaimida (above), which is an example of the longer-lived type of species that tend to be more abundant in late-successional stage crusts than early, is imaged here with dark green/cyan intestinal contents. These species are sometimes predaceous, but mostly feed on fungi, algae, or cyanobacteria. In this case, this individual was likely feeding on some sort of primary producer, likely cyanobacteria, just before being sampled from the field.
The autotrophic components of crusts are highly sensitive to surface disturbances and climate changes, such as altered temperature and precipitation (Belnap, 2003). We also asked how altered temperature and summer precipitation affected soil microfauna. Here is the field site; note the plots set up with infrared heating lamps (to achieve 2-3 °C warming).
Darby, B.J., Neher, D.A., Housman, D.C, and Belnap, J. 2011. Few apparent short-term effects of elevated soil temperature and increased frequency of summer precipitation on the abundance and taxonomic diversity of desert soil micro- and meso-fauna. Soil Biology and Biochemistry. 43:1474-1481.
Darby, B.J., Neher, D.A., and Belnap, J. 2010. Impact of biological soil crusts and desert plants on soil microfaunal community composition. Plant and Soil 328:421-431.
Neher, D.A., Lewins, S.A., Weicht, T.R., and Darby, B.J. 2009. Microarthropod communitites associated with biological soil crusts in the Colorado Plateau and Chihuahuan deserts. Journal of Arid Environments 73:672-677.
Darby, B.J., Neher, D.A., and Belnap, J. 2007. Soil nematode communities are ecologically more mature beneath late-than early-successional stage biological soil crusts. Applied Soil Ecology 35:203-212.
Housman, D.C, Yeager, C.M., Darby, B.J., Sanford, B., Kuske, C.R., Neher, D.A., Belnap, J. 2007. Heterogeneity of soil nutrients and subsurface biota in dryland ecosystems. Soil Biology and Biochemistry 39:2138-2149.
Darby, B.J., Housman, D.C., Zaki, A.M., Shamout, Y., Adl, S., Belnap, J., and Neher, D.A. 2006. Effects of altered temperature and precipitation on desert protozoa associated with biological soil crusts. Journal of Eukaryotic Microbiology 53(6): 507-514.