Elevated Atmospheric Carbon Dioxide and Leaf Litter Chemistry: Influences on Microbial Respiration and Net Nitrogen Mineralization

Abstract

AbstractElevated atmospheric CO2 has the potential to influence rates of C and N cycling in terrestrial ecosystems by altering plant litter chemistry and slowing rates of organic matter decomposition. We tested the hypothesis that the chemistry of leaf litter produced at elevated CO2 would slow C and N transformations in soil. Soils were amended with Populus leaf litter produced under two levels of atmo‐spheric CO2 (ambient and twice‐ambient) and soil N availability (low and high). Kinetic parameters for microbial respiration and net N mineralization were determined on soil with and without litter during a 32‐wk lab incubation. Product accumulation curves for CO2‐C and inorganic N were fit to a first order rate equation [y = A(1 − e−kt)] using nonlinear regression analyses. 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 availability but not by atmospheric CO2. Net N mineralization was a linear function of time and was not significantly different for leaves grown at ambient (50 mg N kg−1) and elevated CO2 (35 mg N kg−1). Consequently, we found no evidence for the hypothesis that leaf litter produced at elevated atmospheric CO2 will dampen the rates of C and N cycling in soil.