Long‐term effects of elevated CO₂ and nutrients on photosynthesis and rubisco in loblolly pine seedlings

Abstract

ABSTRACT The effects of long‐term CO 2 enhancement and varying nutrient availability on photosynthesis and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (rubisco) were studied on loblolly pine ( Pinus taeda L.) seedlings grown in two atmospheric CO 2 partial pressures (35 and 65 Pa) and three nutrient treatments (low N, low P, and high N and P). Measurements taken in late autumn (November) after 2 years of CO 2 enrichment and nutrient addition showed that photosynthetic rates were higher for plants grown at elevated CO 2 only when they received supplemental N. Total rubisco activity and rubisco content decreased at elevated CO 2 , but there was an increase in activation state. At elevated CO 2 , proportionately less N was found in rubisco and more N was found in the light reaction components. These results demonstrate acclimation of photosynthetic processes to elevated CO 2 through reallocation of N. Loblolly pine grown in nutrient conditions similar to native soils (low N availability) had lower needle N and chlorophyll content, lower total rubisco activity and content, and lower photosynthetic rates than plants grown at high N and P. This suggests that the magnitude of the photosynthetic response to a future, high‐CO 2 environment will be dependent on soil fertility in the system.