EFFECTS OF ELEVATED CO2 AND NITROGEN-FERTILIZATION PRETREATMENTS ON DECOMPOSITION ON TALLGRASS PRAIRIE LEAF-LITTER

Standing dead and green foliage litter was collected in early November 1990 from Andropogon gerardii (C-4), Sorghastrum nutans (C-4), and Po a pratensis (C-3) plants that were grown in large open-top chambers un der ambient or twice ambient CO2 and with or without nitrogen fertiliz ation (45 kg N ha(-1)). The litter was placed in mesh bags on the soil surface of pristine prairie adjacent to the growth treatment plots an d allowed to decay under natural conditions. Litter bags were retrieve d at fixed intervals and litter was analyzed for mass loss, carbon che mistry, and total Kjeldahl nitrogen and phosphorus. The results indica te that growth treatments had a relatively minor effect on the initial chemical composition of the litter and its subsequent rate of decay o r chemical composition. This suggests that a large indirect effect of CO2 on surface litter decomposition in the tallgrass prairie would not occur by way of changes in chemistry of leaf litter However, there wa s a large difference in characteristics of leaf Litter decomposition a mong the species. Paa leaf fitter had a different initial chemistry an d decayed more rapidly than C-4 grasses. We conclude that an indirect effect of CO2 on decomposition and nutrient cycling could occur if CO2 induces changes in the relative aboveground biomass of the prairie sp ecies.