Elevated CO₂ and nitrogen supply alter leaf longevity of grassland species

The longevity of green leaf area for 10 grassland species was measured to establish whether elevated CO₂ and N fertilization alter leaf longevity, an important determinant of ecosystem leaf area and ecosystem carbon gain. Plants were selected from monocultures in their second year of growth in a field experiment that directly manipulated atmospheric CO₂ (550 ppm and ambient) and nitrogen fertilization (4 g N m^-2 and ambient). Leaves were censused biweekly over a 4-month period. Leaf longevity increased under elevated CO₂ (+3.4 d, P = 0.03) and decreased under elevated N (-4.2 d, P = 0.03). Leaf longevity increased under elevated CO₂ for C₃ species only; there was no change in leaf longevity of C₄ species under elevated CO₂. For both CO₂ and N, changes in leaf longevity were congruent with expectations based on observed changes in N cycling. In addition to supplies of resources such as CO₂ and N, site fertility and the development of ecosystem feedbacks appear to be important in determining leaf longevity.