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 mu mol mol(-1) CO2 , under sufficient (0.25 mm P) and deficient (0.69 mu m 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.