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 approximate to 359 & approximate to 719 mu L L- 1 at three mineral N supply rates (2.2, 6.7 & 19.8 g m(-2) y(-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.