RESUMEN
Responses to elevated CO2 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 CO2 concentration of 250µmol CO2 mol(-1) above ambient The interactive effects of high CO2 and nutrient supply (in plant growth and morphology were monitored throughout the growing season. A. capillaris exhibited positive growth responses to enhanced CO2 even at limiting supplies of N and P. Moreover, greater shoot mass at elevated CO2 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 CO2 , 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 CO2 enrichment.
RESUMEN
Responses to elevated CO2 have been studied using Agrostis capillaris L., an upland grass which is abundant on nutrient-poor soils. Plants were grown in sand culture with a wide range of nitrogen, phosphorus and potassium concentrations, and the impact of CO2 on the demand for nutrients was determined using isotopic root bioassays. Plants grown with the smallest concentrations of N and P showed typical foliar symptoms associated with deficiency of these elements. However, even when supplies of N and P were limiting to growth, additional CO2 (250 ppm above ambient) influenced neither total N nor total P in above-ground tissues, nor nutrient demands as indicated by the bioassay. The estimates of the demand of the plants for K from the 86 Rb bioassay indicated an appreciable increase when plants were raised in elevated CO2 . For plants of the same size with the same nutrient supply, those grown in elevated CO2 consistently displayed an increased internal demand for K. Uptake of K was not however, enhanced by elevated CO2 even in non-limiting conditions and it might therefore be limited by a factor other than K supply. The overall conclusion from the experiments is that when A. capillaris is grown in elevated CO2 , uptake of N, P and K fails to increase proportionally with dry mass. This was true even when nutrient supplies were adequate, and it appears that nutrient-use-efficiency might increase to enable the plants to maintain growth in elevated CO2 .