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 rec ently developed and it is here briefly described. Such a MiniFACE syst em allowed the elevation of CO2 concentration of small field plots avo iding 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 d esign was used with the treatment combination CO2 x soil N, replicated twice. Gas exchange measurements showed that photosynthetic capacity was significantly decreased in plants exposed to elevated CO2 and grow n under nitrogen deficiency. Photosynthetic acclimation was, in this c ase, due to the occurrence of reduced rates of rubP saturated and rubP regeneration limited photosynthesis. Gas exchange measurements did no t instead reveal any significant effect of elevated CO2 on the photosy nthetic capacity of leaves of plants well fertilized with nitrogen, in spite of a transitory negative effect on rubP regeneration limited ph otosynthesis that was detected to occur in the central part of a day w ith high irradiance. It is concluded that the levels of nitrogen ferti lization will play a substantial role in modulating CO2 fertilization effects on growth and yields of wheat crops under the scenario of futu re climate change.