<P> Rhizodeposition allows for the growth of communities of microorganisms directly surrounding and inside plant roots . This leads to complex interactions between species including mutualism, predation / parasitism, and competition . </P> <P> Predation is considered to be top - down because these interactions decrease the population, but the closeness of the interactions of species directly effects the availability of resources causing the population to also be affected by bottom - up controls . Without soil fauna, microbes that directly prey upon competitors of plants and plant mutualists, interactions within the rhizosphere would be antagonistic toward the plants . Soil fauna provide the top - down component of the rhizosphere while also allowing for the bottom - up increase in nutrients from rhizodeposition and inorganic nitrogen . The complexity of these interactions have also been shown through experiments with common soil fauna, such as nematodes and protists . Predation by bacterial - feeding nematodes was shown to influence nitrogen availability and plant growth . There was also an increase in the populations of bacteria in which nematodes were added . Predation upon Pseduomonas by amoeba shows predators are able to upregulate toxins produced by prey without direct interaction using supernatant . The ability of predators to control the expression and production of biocontrol agents in prey without direct contact is related to the evolution of prey species to signals of high predator density and nutrient availability . </P> <P> The food web in the rhizosphere can be considered as three different channels with two different sources of energy; the detritus - dependent channels are fungi and bacterial species and the root energy dependent channel consists of nematodes, symbiotic species, and some arthropods . This food web is constantly in flux as the amount of detrius available and the rate of root sloughing changes as roots grow and age . This bacterial channel is considered to be a faster channel because of the ability of species to focus on more accessible resources in the rhizosphere and have faster regeneration times compared with the fungal channel . All three of these channels are also interrelated to the roots that form the base of the rhizosphere ecosystem and the predators, such as the nematodes and protists, that prey upon many of the same species of mircroflora . </P> <P> Allelopathy and autotoxicity and negative root - root communications </P>

What supplies the energy for most of the microorganisms in the rhizosphere