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 eith er 340 or 680 mu mol CO2 mol(-1) within controlled environment chamber s, 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 CO2 markedly increased growth, Differences between nutrient supply, but not atmospheric CO2 c oncentration, altered the allometric relations between root and shoot, Net photosynthesis of mature leaf blades and leaf N and P concentrati on were reduced in plants grown at the elevated CO, concentration, The question was asked: is it possible to ascribe all of these effects to elevated CO2 or are some due to nutrient deficiency caused by dilutio n 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, an d elevated CO2 concentration, was low leaf N concentration due to indu ced nutrient deficiency, The data are consistent with a model where th e 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 themse lves.