Does photosynthetic acclimation to elevated CO2 increase photosynthetic nitrogen-use efficiency? A study of three native UK grassland species in opentop chambers.

摘要

Photosynthetic response to elevated CO2 and nutrient stress was investigated in Agrostis capillaris, Lolium perenne and Trifolium repens grown in an open-top chamber facility for 2 years under two nutrient regimes. Acclimatization was evaluated by measuring the response of light-saturated photosynthesis to changes in the substomatal CO2 concentration. Growth at elevated CO2 resulted in reductions in apparent Rubisco [ribulose-bisphosphate carboxylase] activity in vivo in all three species, which were associated with reductions of total leaf nitrogen content on a unit area basis for A. capillaris and L. perenne. Despite this acclimatization, photosynthesis was significantly higher at elevated CO2 for T. repens and A. capillaris, the latter exhibiting the greatest increase of carbon uptake at the lowest nutrient supply. Photosynthetic nitrogen-use efficiency (the rate of carbon assimilation per unit leaf nitrogen) increased at elevated CO2, not only because of higher rates of photosynthesis at elevated CO2, but also as a result of lower leaf nitrogen contents. Contrary to most previous studies, this investigation indicated that elevated CO2 can stimulate photosynthesis under a severely limited nutrient supply. It is suggested that changes in photosynthetic nitrogen-use efficiency may be a critical determinant of plant competition within low nutrient ecosystems and low input agricultural systems.