Is there a home-field advantage for bark decomposition in temperate forest soils?

Bark decomposition is an underexamined component of soil carbon cycling and soil community assembly. Numerous studies have shown preferential decomposition of leaf litter in “home” environments (i.e. within soil adjacent to the plant that produced the leaves), suggesting potential legacy effects from previous deposition of similar litter. This is expected to occur through, in part, accumulation of microorganisms that metabolize substrates the litter provides. Whether a similar “home-field advantage” exists for bark decomposition is unknown, but this dynamic may differ since annual bark deposits to soil are minimal relative to leaf deposits. Irrespective of a home-field advantage, we expected that the deposition of bark would alter the surrounding soil community, due to the liberation, solubilization, and dispersal of bark compounds into soil during decomposition. We hypothesized that 1) as with leaf litter, bark will be preferentially decomposed near to the tree from which it was collected, and 2) that different bark types will differentially shape microbial composition in surrounding soils. To test this hypothesis, we used a full factorial design that included two bark types (collected from eastern hemlock, Tsuga canadensis, and white oak, Quercus alba) and two soil types (‘home’ and ‘away’) within a temperate mixed hardwood forest at the Shale Hills Catchment in central Pennsylvania, USA. Bark was excised from 25 replicates of each tree type, buried in either home or away soil, and incubated belowground from July 2017 to June 2018. Decomposition was assessed through proportionate mass loss over time, while microbial composition in the bark and adjacent soil was assessed through high-throughput sequencing of 16S rRNA gene and fungal ITS fragments. Bark decomposition varied at the local scale, as decomposition was suppressed in soil beneath the canopy of Eastern hemlock, but enhanced in soil beneath the canopy of white oak. This effect was irrespective of bark type, suggesting no obvious home field advantage in this study. We also observed that bark-adjacent soil microbial assemblages sorted according to bark type rather than soil type, suggesting that bark creates a strong filter on the composition of nearby microorganisms. Taken together, these findings suggest that recalcitrant litter can shift microbial assemblages, but, likely due to infrequent deposition, it is not indicated as a primary driver of soil community composition across landscapes.