ELEVATED ATMOSPHERIC CARBON-DIOXIDE AND LEAF-LITTER CHEMISTRY - INFLUENCES ON MICROBIAL RESPIRATION AND NET NITROGEN MINERALIZATION

Elevated atmospheric CO2 has the potential to influence rates of C and N cycling in terrestrial ecosystems by altering plant litter chemistr y and slowing rates of organic matter decomposition, We tested the hyp othesis that the chemistry of leaf litter produced at elevated CO2 wou ld slow C and N transformations in soil. Soils were amended with Popul us leaf litter produced under two levels of atmospheric CO2 (ambient a nd twice-ambient) and soil N availability (low and high). Kinetic para meters for microbial respiration and net N mineralization were determi ned on soil with and without litter during a 32-wk lab incubation, Pro duct accumulation curves for CO2-C and inorganic N were fit to a first order rate equation [y = A(1 - e(-kt))] using nonlinear regression an alyses, Although CO2 treatment affected soluble sugar concentration in leaf litter (ambient = 120 g kg(-1), elevated = 130 g kg(-1)), it did not affect starch concentration or C/N ratio, Microbial respiration, microbial biomass, and leaf litter C/N ratio were affected by soil N a vailability but not by atmospheric CO2, Net N mineralization was a lin ear function of time and was not significantly different for leaves gr own at ambient (50 mg N kg(-1)) and elevated CO2 (35 mg N kg(-1)). Con sequently, we found no evidence for the hypothesis that leaf litter pr oduced at elevated atmospheric CO2 will dampen the rates of C and N cy cling in soil.