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Soil Aggregation and Organic Matter Mineralization in Forests and Grasslands: Plant Species Effects

Scott, Neal A.
Soil Science Society of America journal 1998 v.62 no.4 pp. 1081-1089
forest soils, grassland soils, prairie soils, Larix decidua, Quercus rubra, Pinus resinosa, Pinus strobus, Picea abies, Andropogon gerardii, Sorghastrum nutans, Calamovilfa longifolia, Panicum virgatum, Schizachyrium scoparium, Bouteloua curtipendula, soil organic matter, nitrogen, carbon, mineralization, biogeochemical cycles, vegetation types, correlation, soil aggregates, species differences
Plant-soil feedbacks can alter N cycling rates in terrestrial ecosystems, but the mechanistic relationship between species characteristics, soil properties, and N dynamics is unclear. Plant species may affect patterns of soil aggregation, which can affect soil C and net N mineralization. This mechanism was examined in two common garden experiments: one containing five tree species (European larch [ Miller], red oak [ L.], red pine [ Ait.], white pine [ L.], and Norway spruce [ (L.) Karst]) and one containing six grass species (big bluestem [ Vitm.], indiangrass [ (L.) Nash], prairie sandreed [ (Hook) Scrib.], switchgrass [ L.], little bluestem [ (Michx.) Nash.], and sideoats grama [ (Michx.) Torr.]). The grass monocultures are burned annually. Soils were wet sieved into four size classes (>2000, 250-2000, 53-250, and <53 µm). Unsieved soil was incubated aerobically for 30 and 387 d to examine C and net N mineralization. For tree species, aggregate weighted mean diameter (WMD) differed between species (= 0.01), and correlated positively with fungal biomass (= 0.56). Large macroaggregate (>2000 µm) C concentration ranged from 15 to 26 g kg, and was lowest for Norway spruce and red oak (= 0.07). Aggregate WMD correlated weakly (and negatively) with potentially mineralizable N (= −0.57) and in situ net N mineralization (= −0.67), but positively (again weakly) with potentially mineralizable C (= 0.49). Grass species had no effect on aggregate-size distribution or organic matter concentration in spite of twofold differences in root biomass and threefold differences in N cycling rates. Species-induced changes in soil aggregation explained little of the variation in whole-soil C and N cycling rates, and are therefore unlikely to be an important mechanism explaining species effects on ecosystem processes.