Scale dependence in functional equivalence and difference in the soil microbiome

Climatic history can shape the functioning of soil microbial communities
and thus rates of ecosystem processes such as organic matter
decomposition. For example, broad spatial scale differences in climatic
history, such as contrasting precipitation regimes, have been shown to
generate unique microbial functional responses to contemporary moisture
conditions. Yet it is an open question as to whether local differences in
soil microclimate similarly influence the functional potential of
decomposer communities. Here, we use a multi-scale approach within and
among two temperate forest field sites to investigate this question. Soils
from fifty-four microsites, that vary in their soil moisture
climate-regimes, were used as inocula for a common leaf litter (Quercus
rubra) in a controlled, laboratory microcosm study. Microcosms were placed
under dry, mesic and wet lab-moisture conditions and the rate of carbon
(C) mineralization of the litter was measured over 202 days. Our results
reveal differences in decomposition rates under controlled conditions that
highlight broad-scale functional differences between the soil communities
at each site. Specifically, we found that C mineralization differed by as
much as two-fold for soil communities when compared between the sites. Our
results also show that functional differences of soil communities are
observable within one site but not the other. In the site where
local-scale functional legacies were apparent, the historical soil
moisture microclimate-regimes generated as much as an 89% change in C
mineralization rates of the leaf litter under the same contemporary,
lab-imposed moisture conditions. A similar pattern was not observable in
the other site; instead, laboratory moisture conditions explained almost
all variation in C mineralization. Our findings confirm those from prior
studies where regional-scale moisture-regime differences shape microbial
function, and extends this prior work by providing evidence that
pronounced local-scale differences in soil moisture microclimate-regimes
can generate microbial functional legacies.