SOM density fractions beneath trees of different mycorrhizal types in New England forests

Recent work suggests mycorrhizal fungi are important drivers of soil
organic matter dynamics; however, whether this is a result of the
fungi themselves or related traits of their host trees remains
unclear. We evaluated how tree mycorrhizal associations and foliar
chemistry influence mineral-associated organic matter (MAOM) and
particulate organic matter (POM) in temperate forests of northern New
England, USA. We measured carbon (C) and nitrogen (N) concentrations
and C:N of three soil density fractions beneath six tree species that
vary in both mycorrhizal association and foliar chemistry. We found a
significant decline in the concentration of MAOM C and N with
increasing foliar C:N in soil beneath tree species with arbuscular
mycorrhizal (AM), but not ectomycorrhizal (ECM) fungi. The C:N of POM
and MAOM was positively associated with the foliar C:N of the dominant
tree species in a forest, and MAOM C:N was also higher beneath ECM-
rather than AM-associated tree species. These results add to the
growing body of support for mycorrhizal fungi as predictors of soil C
and N dynamics, and suggest that C concentration in the MAOM fraction
is more sensitive to organic matter chemistry beneath AM-associated
tree species. Because MAOM decomposition is thought to be less
responsive than POM decomposition to changes in soil temperature and
moisture, differences in the tendency of AM- vs. ECM-dominated forests
to support MAOM formation and persistence may lead to systematic
differences in the response of these forest types to ongoing climate
change.

These data were gathered as part of the Hubbard Brook Ecosystem Study
(HBES). The HBES is a collaborative effort at the Hubbard Brook
Experimental Forest, which is operated and maintained by the USDA
Forest Service, Northern Research Station.