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They are the most abundant microorganisms in the soil, and serve many important purposes, including nitrogen fixation. [9] Some bacteria can colonize minerals in the soil and help influence weathering and the breaking down of these minerals. The overall composition of the soil can determine the amount of bacteria growing in the soil.
Soil microbial communities are characterized in many different ways. The activity of microbes can be measured by their respiration and carbon dioxide release. The cellular components of microbes can be extracted from soil and genetically profiled, or microbial biomass can be calculated by weighing the soil before and after fumigation.
Another common farming practice, tillage, can have the immediate effect of decreasing carbon and nitrogen originating from microbial biomass. [12] Conversely, no-till practices have been shown to be able to increase soil health, increase microbial growth, and increase microbial community functionality. [12]
Soil biology is the study of microbial and faunal activity and ecology in soil. Soil life , soil biota , soil fauna , or edaphon is a collective term that encompasses all organisms that spend a significant portion of their life cycle within a soil profile, or at the soil- litter interface.
In young plants, growth allocation is often quite similar to the actual biomass allocation. But especially in trees, there may be a high yearly turnover in leaves and fine roots, and a low turnover in stems, branches and thick roots. In those cases, the allocation of growth and the final biomass allocation may diverge quite strongly over the years.
Soil respiration refers to the production of carbon dioxide when soil organisms respire. This includes respiration of plant roots, the rhizosphere, microbes and fauna.. Soil respiration is a key ecosystem process that releases carbon from the soil in the form of CO 2.
Finally the tertiary consumers, large cats and wolves. The biomass pyramid decreases markedly at each higher level. Changes in plant species in the terrestrial ecosystem can result in changes in the biomass of soil decomposer communities. [13] Biomass in C 3 and C 4 plant species can change in response to altered concentrations of CO 2. [14]
Biological soil crusts cover about 12% of the earth's landmass. [8] They are found on almost all soil types, but are more commonly found in arid regions of the world where plant cover is low and plants are more widely spaced. This is because crust organisms have a limited ability to grow upwards and cannot compete for light with vascular plants.