Interactions between atmospheric CO2 concentration and phosphorus nutrition on the formation of proteoid roots in white lupin (Lupinus albus L.)

Atmospheric CO₂] affects photosynthesis and therefore should affect the supply of carbon to roots. To evaluate interactions between carbon supply and nutrient acquisition, the CO₂] effects on root growth, proteoid root formation and phosphorus (P) uptake capacity were studied in white lupin (Lupinus albus L.) grown hydroponically at 200, 410 and 750 µmol mol^?1 CO₂, under sufficient (0·25 mm P) and deficient (0·69 µm P) phosphorus. Plant size increased with increasing CO₂] only at high P. Both P deficiency and increasing CO₂] increased the production of proteoid clusters; the increase in response to increased CO₂] was proportionally greater from low to ambient CO₂] than from ambient to high. The activity of phosphoenol pyruvate carboxylase in the proteoid root, the exudation of organic acids from the roots, and the specific uptake of P increased with P deficiency, but were unaffected by CO₂]. Increasing CO₂] from Pleistocene levels to those predicted for the next century increased plant size and allocation to proteoid roots, but did not change the specific P uptake capacity per unit root mass. Hence, rising CO₂] should promote nutrient uptake by allowing lupins to mine greater volumes of soil.