Elevated CO2 and temperature effects on soil carbon and nitrogen cycling in ryegrass/white clover turves of an Endoaquept soil

Abstract

Effects of elevated CO2 (700/.tL L -l) and a control (350/tL L -I CO2) on the productivity of a 3-year-old ryegrass/white clover pasture, and on soil biochemical properties, were investigated with turves of a Typic Endoaquept soil in growth chambers. Temperature treatments corresponding to average winter, spring, and summer conditions in the field were applied consecutively to all of the turves. An additional treatment, at 700/IL L-i CO2 and a temperature 6°C higher throughout than in the other treatments, was included.Under the same temperature conditions, overall herbage yields in the '700 #L L-l CO2' treatment were ca. 7% greater than in the control at the end of the 'summer' period. Root mass (to ca 25 cm depth) in the '700 juL L-CO2' treatment was then about 50% greater than in the control, but in the '700 ~L L -1 CO2 + 6°C ' treatment it was 6% lower than in the control. Based on decomposition results, herbage from the '700 ~tL L-l + 6oc , treatment probably contained the highest proportion of readily decomposable components.Elevated CO2 had no consistent effect on soil total C and N, microbial C and N, or extractable C concentrations in any of the treatments. Under the same temperature conditions, it did, however, enhance soil respiration (CO2-C production) and invertase activity. The effects of elevated CO2 on rates of net N mineralization were less distinct, and the apparent availability of N for the sward was not affected. Under elevated CO2, soil in the higher-temperature treatment had a higher microbial C:N ratio; it also had a greater potential to degrade plant materials.Data interpretation was complicated by soil spatial variability and the moderately high background levels of organic matter and biochemical properties that are typical of New Zealand pasture soils. More rapid cycling of C under CO2 enrichment is, nevertheless, indicated. Futher long-term experiments are required to determine the overall effect of elevated CO2 on the soil C balance.

Elevated CO2 evokes quantitative and qualitative changes in carbon dynamics in a plant/soil system: mechanisms and implications

“…This effect was similar to results reported by Billes et al (1993), dry weight was stimulated more (in a range of + 44 to + 143%) than shoot dry weight (a range of -2 to + 23%). A similar observation in ryegrass was reported by Ross et al (1995), who found an increase of about 7% and 50% of herbage yield and roots, respectively and by Schapendonk et al (1996) who found increases of 23% and 86%, respectively, in ryegrass swards. For trees, Rouhier et al (1994) found a nonsignificant increase in the fine roots of sweet chestnuts, but not in the aboveground parts.…”

Effects of elevated [CO2] at the community level mediated by root symbionts

“…Newton et al (1994) and Ross et al (1995), working with turves ofTrifolium repens and Lolium perenne, found that elevated [CO2] differentially promoted the growth of nodulating T. repens. On the other hand, preliminary results reported by Rrtzel et al (1995) suggest no differential responses of nodulating legumes to elevated [CO2] in calcareous grasslands, as compared with non-nodulating plants.…”

Belowground responses of Picea asperata seedlings to warming and nitrogen fertilization in the eastern Tibetan Plateau

“…Root biomass is often reported to be enhanced by elevated temperature, for example, increased up to 65% in Bouteloua gracilis (Morgan et al 1994) and 50% in a grass/clover mixture (Ross et al 1995). Experimental warming significantly increased green aboveground biomass in a tallgrass prairie.…”