Soil ecological interactions: comparisons between tropical and subalpine forests

Soil fauna can influence soil processes through interactions with the micro bial community. Due to the complexity of the functional roles of fauna and their effects on microbes, little consensus has been reached on the extent to which soil fauna can regulate microbial activities. We quantified soil m icrobial biomass and maximum growth rates in control and fauna-excluded tre atments in dry and wet tropical forests and north- and south-facing subalpi ne forests to test whether soil fauna effects on microbes are different in tropical and subalpine forests. Exclusion of fauna was established by physi cally removing the soil macrofauna and applying naphthalene. The effect of naphthalene application on the biomass of microbes that mineralize salicyla te was quantified using the substrate induced growth response method. We fo und that: (1) the exclusion of soil fauna resulted in a higher total microb ial biomass and lower maximum growth rate in the subalpine forests, (2) soi l fauna exclusion did not affect the microbial biomass and growth rate in t he tropical forests, and (3) the microbial biomass of salicylate mineralize rs was significantly enhanced in the fauna-exclusion treatment in the tropi cal wet and the south-facing subalpine forests. We conclude that non-target effects of naphthalene on the microbial community alone cannot explain the large differences in total microbial biomass found between control and fau na-excluded treatments in the subalpine forests. Soil fauna have relatively larger effects on the microbial activities in the subalpine forests than i n tropical dry and wet forests.