Nitrogen, phosphorus and potassium uptake and demand in Agrostis capillaris: the influence of elevated CO 2 and nutrient supply.

Responses to elevated CO ₂ 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 CO ₂ 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 CO ₂ (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 CO ₂ . For plants of the same size with the same nutrient supply, those grown in elevated CO ₂ consistently displayed an increased internal demand for K. Uptake of K was not however, enhanced by elevated CO ₂ 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 CO ₂ , 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 CO ₂ .