Litter quality and decomposition in Danthonia richardsonii swards in response to CO₂ and nitrogen supply over four years of growth

Litter quality parameters of Danthonia richardsonii grown under CO₂ concentrations of ~359 and ~719 μL L^-1 at three mineral N supply rates (2.2, 6.7 and 19.8 gm^-2y^-1) were determined. C:N ratio was increased in senesced leaf (enhancement ratios, R(e/c), of 1.25-1.67), surface litter (1.34-1.64) and root (1.13-1.30) by CO₂ enrichment. After 3 years of growth, nonstructural carbohydrate concentrations were reduced in senesced leaf lamina (avg. R(e/c) = 0.84) but not in root in response to CO₂ enrichment. Cellulose concentrations increased slightly in senesced leaf (avg. R(e/c) = 1.07) but not in root in response to CO₂ enrichment. Lignin and polyphenolic concentrations in senesced leaf and root were not changed by CO₂ enrichment. Decomposition, measured as cumulative respiration in standard conditions in vitro, was reduced in leaf litter grown under CO₂ enrichment. Root decomposition in vitro was lower in the material produced under CO₂ enrichment at the two higher rates of mineral N supply. Significant correlations between decomposition of leaf litter and initial %N, C:N ratio and lignin:N ratio were found. Decomposition in vivo, measured as carbon disappearance from the surface litter was not affected by CO₂ concentration. Arbuscular mycorrhizal infection was not changed by CO₂ enrichment. Microbial carbon was higher under CO₂ enrichment at the two higher rates of mineral N supply. Possible reasons for the lack of effect of changes in litter quality on in-sward decomposition rates are discussed.