Habitable Pore Space and Microbial Trophic Interactions

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Abstract
Microbial trophic structure and available soil pore space influence rates of decomposition and mineralization. The nematode (Mesodiplogaster) used feeds on bacteria (Pseudomonas) and amoebae (Acanthamoeba) but grows best in the presence of amoebae. Respiration rates were higher when both grazers were grown with bacteria (food web) than when grazers were grown singly with bacteria (simple food chain). One reason for increased nematode growth in the presence of amoebae may be that protozoa make food more available to nematodes by entering soil pores inaccessible to nematodes, feeding on bacteria within the pores and emerging as food otherwise unavailable to nematodes. To test this possibility, an experiment was designed using a fine-textured (with fewer habitable pores for nematodes) and a coarse-textured soil. There was a greater proportional increase in nematode growth with amoebae in the fine than in the coarse soil. Microbial trophic structure in relation to soil texture and habitable pore space may be an important influencing energy flow in terrestrial ecosystems.

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