Nutrient relations in calcareous grassland under elevated CO2

摘要: Plant nutrient responses to 4 years of CO2 enrichment were investigated in situ calcareous grassland. Beginning year 2, plant aboveground C:N ratios increased by 9% 22% at elevated (P  98% community biomass), legume C/N was not reduced and N:P slightly increased. We attribute the less N concentration legumes fact that virtually all originated from symbiotic N2 fixation (%Ndfa ≈ 90%), thus growth limited soil N. While total affected CO2, microbial pools +18% under (P = 0.04) available decreased. Hence, there a net increase overall biotic pool, largely due increases pool. In order assess effects for ecosystem estimate degree which P-limited, two greenhouse experiments conducted, using firstly undisturbed grassland monoliths field site, secondly designed `microcosm' communities on natural soil. Half microcosms planted with half without. Both exposed P fertilization factored design. After seasons, both unfertilized microcosm unaffected enrichment, similar what found field. However, when added CO2. This community-level effect almost solely stimulation. The results suggest complex interaction between atmospheric concentrations, supply. Overall productivity is N-limited, whereas their are P.