Forest biogeochemical cycles are shaped by effects of dominant tree species on soils, but the underlying mechanisms are not well understood. We investigated effects of temperate tree species on interactions among carbon (C), nitrogen (N), and acidity in mineral soils from an experiment with replicated monocultures of 14 tree species. To identify how trees affected these soil properties, we evaluated correlations among species-level characteristics (e. g. nutrient concentrations in leaf litter, wood, and roots), stand-level properties (e. g. nutrient fluxes through leaf litterfall, nutrient pools in stemwood), and components of soil C, N, and cation cycles. Total extractable acidity (aciditytot) was correlated positively with mineral soil C stocks (R2 = 0. 72, P < 0. 001), such that a nearly two-fold increase in aciditytot was associated with a more than two-fold increase of organic C. We attribute this correlation to effects of tree species on soil acidification and subsequent mineral weathering reactions, which make hydrolyzing cations available for stabilization of soil organic matter. The effects of tree species on soil acidity were better understood by measuring multiple components of soil acidity, including pH, the abundance of hydrolyzing cations in soil solutions and on cation exchange sites, and aciditytot. Soil pH and aciditytot were correlated with proton-producing components of the soil N cycle (e. g. nitrification), which were positively correlated with species-level variability in fine root N concentrations. Soluble components of soil acidity, such as aluminum in saturated paste extracts, were more strongly related to plant traits associated with calcium cycling, including leaf and root calcium concentrations. Our results suggest conceptual models of plant impacts on soil biogeochemistry should be revised to account for underappreciated plant traits and biogeochemical processes.
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Acknowledgments We thank Burt Thomas, Katherine Freeman, Jörg Prietzl, Michael Castellano, and Jason Kaye for helpful discussion. DME and KEM acknowledge National Science Foundation (NSF) awards DEB-0816935 and OISE-0754731. OAC, JC, DME, SEH, JO, and PBR were also supported by NSF DEB-0128958. KEM received a US Department of Energy Graduate Research Environmental Fellowship and a European Association of Organic Geochemists travel award.
- Plant traits
- Soil organic matter