Phillips, C. L., Kluber, L. A., Martin, J. P., Caldwell, B. A., and Bond, B. J. 2012. Contributions of ectomycorrhizal fungal mats to forest soil respiration, Biogeosciences, 9, 2099-2110, doi:https://doi.org/10.5194/bg-9-2099-2012.
Distinct aggregations of fungal hyphae and rhizomorphs,
or “mats”, formed by some genera of ectomycorrhizal
(EcM) fungi are common features of soils in coniferous
forests of the Pacific Northwest. We measured in situ
respiration rates of Piloderma mats and neighboring non-mat
soils in an old-growth Douglas-fir forest in western Oregon to
investigate whether there was higher respiration from mats,
and to estimate mat contributions to total soil respiration.
We found that areas where Piloderma mats colonized the organic
horizon often had higher soil surface flux than nonmats,
with the relative increase in respiration averaging 16%
across two growing seasons. Both soil physical factors and
biochemistry were related to the higher surface flux of mat
soils. When soil moisture was high, soil CO2 production was
concentrated into near-surface soil horizons where mats tend
to colonize, resulting in greater apparent differences in respiration
between mat and non-mat soils. Respiration rates were
also correlated with the activity of chitin-degrading soil enzymes.
This finding supports the notion that the abundance of
fungal biomass in EcM mats is an important driver of C and
N cycling. We found Piloderma mats present across 57%
of the exposed soil, and use this value to estimate a respiratory
contribution from mats at the stand-scale of about 9%
of total soil respiration. The activity of EcM mats, which includes
both EcM fungi and microbial associates, appeared to
constitute a substantial portion of total soil respiration in this
old-growth Douglas-fir forest.