Mahaney, W.M., K.A. Smemo, and K.L. Gross
Presented at the All Scientist Poster Reception (2006-05-09 )
Humans are altering biodiversity and species distributions around the world, but the ecological implications of these changes are poorly understood. A mechanistic understanding of how plant species impact soil processes is needed to improve our ability to predict how future species shifts may affect ecosystem function. Agriculture in southwestern Michigan has reduced soil carbon © and nitrogen (N) levels dramatically and, following abandonment, old-fields that were once dominated by C4 grasses typically contain mainly non-native C3 species. We examined whether the reintroduction of C4 grasses into old-fields has altered soil C and N cycling, over what timescale these impacts are measurable, and whether specific plant traits can predict those impacts. C4 species typically have higher biomass and more recalcitrant tissue than C3 grasses, and these differences in litter quality and quantity may affect C and N cycling. To examine decadal scale impacts, we measured plant and soil properties under monocultures of a C4 species (Andropogon gerardii) established in 1994 in two old-fields and compared this to samples from adjacent C3 grass-dominated plots. Andropogon had greater biomass and more recalcitrant tissue than the C3 grass plots, and soils under Andropogon had significantly less inorganic N than under the C3 species. We are using stable isotope analysis to determine if species differences are affecting total, labile and recalcitrant soil C pools. We are also investigating if these differences are related to species’ N uptake/utilization or plant-soil feedbacks mediated through the microbial community. These preliminary findings have implications for our ability to predict how species invasions, extinctions, or shifts in relative abundance may alter soil processes.
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