The biogeochemistry of five wetland-upland landscapes

Links between vegetation patterns and biogeochemical processes were measured along four Minnesota upland-wetland toposequences at the Cedar Creek Natural History Area and one toposequence at the Marcell Experimental forest. Marked changes in vegetation occur along the transects, and sampling occurred in each plant community along each toposequence. Upland, margin, lagg, and central wetland community types were identified, based upon species composition, nitrogen mineralization rates, litter and cellulose decomposition rates, and C and N pools.; Soil cores were collected down to mineral soil in each community. The largest C and N accumulations occurred in central communities and the smallest occurred in upland communities. Rapid changes in soil organic matter, soil C and N, and soil moisture occurred between upland and margin communities. Depth to mineral soil was the most useful physical measure for predicting pool size of soil C and soil moisture was the most significant microclimatic variable. Within the upper 20 cm of soil, the largest C and N pools were in the margin.; Bags of plant litter and cellulose strips were used to measure decomposition rates in peat and soil over a two year period. Decomposition was greatest in upland communities and lowest in central wetland communities. Mass-loss in margin and lagg communities was not necessarily intermediate. Among central wetland communities, soil moisture and pH best predicted litter mass-loss, and pH alone was the best predictor of cellulose mass-loss. For the upland, margin, and lagg communities soil moisture best explained variability in litter mass-loss, whereas soil organic matter best explained variability in cellulose mass-loss.; Ammonification and nitrification rates were measured from June 1992 to July 1993. Lowest rates of total N-mineralization occurred over winter and highest rates from mid-May to July. In all sites total mineralization was highest in upland and margin communities. Soil moisture was the dominant variable accounting for differences in nitrogen mineralization along the toposequence. Warmer soil temperatures and decreased soil moisture from global climate change would likely cause increased C and N mineralization with a release of nutrients favoring nutrient-loving species. Margin, lagg, and central communities may experience community changes as nutrients become available.