Soil biota accelerate decomposition in high-elevation forests by specializing in the breakdown of litter produced by the plant species above them

P> There is mounting evidence that leaf litter typically decomposes more rapidly beneath the plant species it derived from than beneath the different plant species, which has been called home-field advantage (HFA). It has been suggested that this HFA results from the local adaptation of soil communities to decompose the litter that they encounter most often, which probably comes from the plant species above them. To test this hypothesis and to investigate how HFA varies over time and in relation to litter quality, we performed the first detailed assessment of HFA in relation to litter decomposition. We monitored decomposition over time in two reciprocal litter transplant experiments involving three high-elevation tree species that differ in litter quality. The three tree species used were trembling aspen (Populus tremuloides), lodgepole pine (Pinus contorta) and Engelmann spruce (Picea engelmannii). First, we incubated litter from each of these species with soil biota extracted from stands of each tree species in a laboratory experiment and observed greater cumulative respiration, a measure of decomposition, when litter was incubated with its home soil biota. Second, we performed a field experiment, which demonstrated that the decomposition HFA also occurred under field conditions. In addition, this experiment demonstrated that despite increased mass loss at home, litter also immobilized more nitrogen when in its home environment. In both experiments, the HFA was most pronounced for pine litter, which is consistent with the hypothesis that HFA increases with decreasing litter quality. Synthesis. As well as demonstrating conclusively that soil communities specialize in decomposing the litter produced by the plant species above them, our data challenge the widely held view that soil organisms are largely functionally redundant.