Response of Potato Gas Exchange and Productivity to Phosphorus Deficiency and Carbon Dioxide Enrichment

The degree to which crops respond to atmospheric CO 2 enrichment may be influenced by nutrition. To determine the extent to which dry matter production, canopy and leaf photosynthesis, and transpiration are influenced by P and CO 2 , potatoes ( Solanum tuberosum L. cultivar Kennebec) were grown in outdoor soil–plant–atmosphere research (SPAR) chambers at two levels of CO 2 (400 or 800 μmol mol −1 ) and three levels of P fertilization. Total dry matter declined an average 42% between high and low P fertilizer and increased 13% in response to elevated CO 2 when averaged across the P treatments. This enhancement effect did not vary with level of P treatment. Leaf level photosynthetic rate was reduced 58% and stomatal conductance 43% between high and low P treatments. Biochemical model parameters for carboxylation rate, ribulose bisphosphate regeneration, and triose phosphate use were reduced by P deficiency but scarcely influenced by growth CO 2 . After tuber initiation, canopy assimilation rate increased under elevated CO 2 particularly at the middle levels of P fertilization, and diurnal canopy evapotranspiration showed a significant reduction in response to elevated CO 2 and declining P fertilizer. Lack of interactive effects between CO 2 and P on most measured responses suggests the effect of CO 2 enrichment on potato growth and assimilation is similar at each P‐treatment level; however, such effects may also be correlated with plant N status.