The spatial distribution of tree-tree interaction effects on soil
microbial biomass and respiration
Abstract
The capacity of forests to sequester carbon in both above- and
belowground compartments is a crucial tool to mitigate rising
atmospheric carbon concentrations. Belowground carbon storage in forests
is strongly linked to soil microbial communities that are the key
drivers of soil heterotrophic respiration, organic matter decomposition,
and thus nutrient cycling. However, the relationships between tree
diversity and soil microbial properties such as biomass and respiration
remain unclear with inconsistent findings among studies. It is unknown
so far how the spatial configuration and soil depth affects the
relationship of tree richness and microbial properties. Here, we studied
the spatial distribution of soil microbial properties in the context of
a tree diversity experiment by measuring soil microbial biomass and
respiration in subtropical forests (BEF-China experiment). We sampled
soil cores at two depths at five locations along a spatial transect
between the trees in mono- and heterospecific tree pairs of the native
deciduous species Liquidambar formosana and Sapindus saponaria. Our
analyses showed decreasing soil microbial biomass and respiration with
increasing soil depth and distance from the tree in monospecific tree
pairs. We calculated belowground overyielding of soil microbial biomass
and respiration - which is a higher microbial biomass or respiration
than expected from the monocultures - and analysed the distribution
patterns along the transect. We found no general overyielding across all
sampling positions and depths. Yet, we encountered a spatial pattern of
microbial overyielding with a significant microbial overyielding close
to L. formosana trees and microbial underyielding close to S. saponaria
trees. We found similar spatial patterns across microbial properties and
depths that only differed in their effect size. Our results highlight
the importance of small-scale variations of tree-tree interaction
effects on soil microbial communities and functions and are calling for
better integration of within-plot variability to understand
biodiversity-ecosystem functioning relationships.