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 containingeither 340 or 680 µmol CO₂ mol^–1 within controlledenvironment chambers. The available nutrient regime was variedby altering the supply of nitrogen and phosphorus within a completenutrient solution. At a high, but not low, N and P supply regime,elevated CO₂ markedly increased growth. Differences betweennutrient supply, but not atmospheric CO₂ concentration, alteredthe allometric relations between root and shoot. Net photosynthesisof mature leaf blades and leaf N and P concentration were reducedin plants grown at the elevated CO₂ concentration. The question was asked: is it possible to ascribe all of theseeffects to elevated CO₂ or are some due to nutrient deficiencycaused by dilution with excess carbon? Several criteria, includingthe nutrient content of sink tissue, root:shoot allometry andthe use of divalent cations to estimate integrated water flowsare suggested in order to make this distinction. It is concludedthat only at a low supply of N and P₁ and elevated CO₂ concentration,was low leaf N concentration due to induced nutrient deficiency.The data are consistent with a model where the capacity of sinksto use photosynthetically assimilated carbon sets both the rateof import into those sinks (and thus rate of export from sourceleaves) and the rate of photosynthesis of source leaves themselves. Key words: Poa alpina L., growth, photosynthesis, carbohydrate, export, nitrogen, phosphorus