Effect of elevated CO2 and nutrient status on growth, dry matter partitioning and nutrient content of Poa alpina var. vivipara L.

Poa alpina var. vivipara L. was grown in an atmosphere containing either 340 or 680 μmol CO 2 mol -1 within controlled environment chambers. The available nutrient regime was varied by altering the supply of nitrogen and phosphorus within a complete nutrient solution. At a high, but not low, N and P supply regime, elevated CO 2 markedly increased growth. Differences between nutrient supply, but not atmospheric CO 2 concentration, altered the allometric relations between root and shoot. Net photosynthesis of mature leaf blades and leaf N and P concentration were reduced in plants grown at the elevated CO 2 concentration. The question was asked: is it possible to ascribe all of these effects to elevated CO 2 or are some due to nutrient deficiency caused by dilution with excess carbon? Several criteria, including the nutrient content of sink tissue, root:shoot allometry and the use of divalent cations to estimate integrated water flows are suggested in order to make this distinction. It is concluded that only at a low supply of N and P, and elevated CO 2 concentration, was low leaf N concentration due to induced nutrient deficiency. The data are consistent with a model where the capacity of sinks to use photosynthetically assimilated carbon sets both the rate of import into those sinks (and thus rate of export from source leaves) and the rate of photosynthesis of source leaves themselves.