Prolonged elevated atmospheric CO₂ does not affect decomposition of plant material

Prolonged elevated atmospheric CO₂ might alter decomposition. In a 90-day incubation study, we determined the long-term (9 years) impact of elevated CO₂ on N mineralization of Lolium perenne and Trifolium repens plant material grown at ambient and elevated CO₂ and low- and high-¹⁵N fertilizer additions. No significant differences were observed in N15-NO3- recovery rates between any of the treatments, except an N addition effect was observed for L. perenne (0.4 versus 0.5% N15-NO3- day ^-1 in high versus low N). The results suggest that elevated CO ₂ did not change plant N mineralization in any of the soils, because of a surplus of available N in the fertilized and leguminous systems, and because of insignificant plant responses to elevated CO₂ in the low soil N availability systems.