Nitrogen dynamics under elevated carbon dioxide

It is known that N demand is lower under eCO2 and this reduces the rate at which N is cycled through the soil/plant system. The low availability of N progressively suppresses the positive response of the biomass of species to elevated CO2 (Reich et al., 2006), but generally stimulates crop biomass to a greater extent (Ma et al., 2007). In comparison, elevated CO2 concentration increases symbiotic and non-symbiotic N2 fixation, resulting in more N being gained and less lost. The additional C fixed in elevated CO2 also retains more N (Thornley and Cannell, 2000). It is therefore interesting to investigate the effect of N supply to both legumes and non-legumes under elevated CO2 concentration.
Several research groups have identified that under elevated CO2, nitrogen become less available over time as a result of changing C:N inputs, rhizosphere biology and N demands. Termed Progressive Nitrogen Limitation, this research aims to assess if PNL is likely to affect the management of rainfed cropping systems. Within the Australian Grains Free Air Carbon Dioxide Enrichment facility at Horsham, a series of experiments are being undertaken to evaluate the effects of high CO2 on N fixation, N2O production, N uptake by crops, N access to fertilizer sources and N/C dynamics in the soil. These data will be incorporated into existing N dynamics models to assess the impact of climate change on N demand and supply for cropping systems.