Elevated atmospheric [CO2] from a natural soda spring affects the initial mineralization rates of naturally senesced C3 and C4 leaf litter

Naturally senesced leaves from the grasses Holcus lanatus (Yorkshire fog; C3 photosynthetic pathway) and Pennisetum clandestirum (Kikuyu; C4 photosynthetic pathway), grown in elevated atmospheric [CO2] surrounding a natural soda spring, were decomposed within respiratory chambers and the initial mineralization (0-30 days) of the litter measured. Significantly greater rates of initial mineralization of the C3 litters previously grown in elevated atmospheric [CO2] were detected compared to the C3 litters grown in ambient [CO2]. For example, within the first 15 days the rate of CO2 production from the litters grown in the elevated atmospheric [CO2] was two to five times greater than that seen from the litters grown in the ambient concentrations of CO2. The effect of elevated atmospheric [CO2] on the mineralization of the C4 litter was less pronounced, however rates of mineralization were still significantly greater from litters grown originally in elevated [CO2]. A significant decline in the C:N ratios and nitrogen content of the leaves of both the C3 and C4 grasses was observed, although analysing the relationship between the carbon and nitrogen content, or the C:N ratio, with the initial mineralization rate indicated that these litter quality parameters were not good indicators of the rate of mineralization of the litter from these grasses. (C) 2000 Elsevier Science Ltd. All rights reserved.