Habitable Pore Space and Microbial Trophic Interactions

Abstract

Microbial trophic structure and available soil pore space influence rates of decomposition and mineralization. The nematode (Mesodiplogaster) used feeds on bacteria (Pseudomonas) as well as 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). We hypothesized that one reason for increased nematode growth in the presence of amoebae is 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, we designed an experiment 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. We conclude that microbial trophic structure in relation to soil texture and habitable pore space is an important factor influencing energy flow in terrestrial ecosystems.