Effects of elevated CO 2 and nutrient supply on the seasonal growth and morphology of Agrostis capillaris

summary Responses to elevated CO 2 have been studied using an upland grass species, Agrostis capillaris L. The plants were grown in sand culture with a range of N, P and K concentrations, in ‘Solardome’ growth chambers with either ambient air or a CO 2 concentration of 250μmol CO 2 mol −1 above ambient The interactive effects of high CO 2 and nutrient supply (in plant growth and morphology were monitored throughout the growing season. A. capillaris exhibited positive growth responses to enhanced CO 2 even at limiting supplies of N and P. Moreover, greater shoot mass at elevated CO 2 was attributed to disproportionate increases in leaf and tiller number, resulting in an increase in the average leaf number per tiller. However, total leaf area remained unaffected, indicating that leaf size was reduced. There was no evidence of any acclimation in the growth response of A. capillaris to additional CO 2 , even in N and P‐stressed plants. On the contrary, a stimulation in leaf production was observed later in the growing season. A consistent interaction was observed between N and P concentrations, whereby the response to one element was greater at higher concentrations of the other. In addition, there were indications of competition among the three elements for uptake at the root. These findings indicate the importance of multifactorial nutrient experiments in developing an understanding of the complex relationships during CO 2 enrichment.