Soil ecology

[22][18] The majority of these organisms are aerobic, so the amount of porous space, pore-size distribution, surface area, and oxygen levels are crucial to their life cycles and activities.

Therefore, soil textural properties together with the depth of the water table are also important factors regulating their diversity, population sizes, and their vertical stratification.

In support of this, a small-scale field study revealed that the relationships between environmental heterogeneity and species richness might be a general property of ecological communities.

[23][18] The lack of distinct latitudinal gradients in soil biodiversity contrasts with those clear global patterns observed for plants above ground and has led to the assumption that they are indeed controlled by different factors.

[24] For example, in 2007 Lozupone and Knight found salinity was the major environmental determinant of bacterial diversity composition across the globe, rather than extremes of temperature, pH, or other physical and chemical factors.

[25] In another global scale study in 2014, Tedersoo et al. concluded fungal richness is causally unrelated to plant diversity and is better explained by climatic factors, followed by edaphic and spatial patterns.

However, the little evidence available appears to indicate that, at large scales, soil metazoans respond to altitudinal, latitudinal or area gradients in the same way as those described for above-ground organisms.

[31] Therefore, besides the difficulties in linking above and below ground diversities at different spatial scales, gaining a better understanding of the biotic effects on ecosystem processes might require incorporating a great number of components together with several multi-trophic levels [32] as well as the much less considered non-trophic interactions such as phoresy, passive consumption.

[46] Interactions between members of the soil microhabitat takes place via chemical signaling which is mediated by soluble metabolites and volatile organic compounds, in addition to extracellular polysaccharides.

[50] Microbes may also exchange metabolites to support each other's growth, e.g., the release of extracellular enzymes by ectomycorrhiza decomposes organic matter and releases nutrients which then benefits other members of the population, in exchange organic acids from bacteria stimulate fungal growth [51] These examples of trophic interactions especially metabolite dependencies drive species interactions and are important in the assembly of soil microbial communities.

They range in size from one-celled bacteria, algae, fungi, and protozoa, to more complex nematodes and micro-arthropods, to the visible earthworms, insects, small vertebrates, and plants.

Fundamentally, researchers are interested in understanding the interplay among microorganisms, fauna, and plants, the biogeochemical processes they carry out, and the physical environment in which their activities take place, and applying this knowledge to address environmental problems.