The effect of free air carbon dioxide enrichment (FACE) and soil nitrogen availability on the photosynthetic capacity of wheat.

A simple system for free air carbon dioxide enrichment (FACE) was recently developed and it is here briefly described. Such a MiniFACE system allowed the elevation of CO2 concentration of small field plots avoiding the occurrence of large spatial and temporal fluctuations. A CO2 enrichment field experiment was conducted in Italy in the season 1993-1994 with wheat (cv. Super-dwarf Mercia). A randomized experimental design was used with the treatment combination CO2 × soil N, replicated twice. Gas exchange measurements showed that photosynthetic capacity was significantly decreased in plants exposed to elevated CO2 and grown under nitrogen deficiency. Photosynthetic acclimation was, in this case, due to the occurrence of reduced rates of rubP saturated and rubP regeneration limited photosynthesis. Gas exchange measurements did not instead reveal any significant effect of elevated CO2 on the photosynthetic capacity of leaves of plants well fertilized with nitrogen, in spite of a transitory negative effect on rubP regeneration limited photosynthesis that was detected to occur in the central part of a day with high irradiance. It is concluded that the levels of nitrogen fertilization will play a substantial role in modulating CO2 fertilization effects on growth and yields of wheat crops under the scenario of future climate change.