Leaf nitrogen concentration of wheat subjected to elevated [CO2] and either water or N deficits

Leaf N concentration is important because it is associated with the CO2 ass imilatory capacity of crops, and in grasslands, it is an important determin ant of forage nutritive value. Consequently, the productivity of both domes tic and native animals in future global environments may be closely linked to possible changes in leaf N concentration of grasses. Since grasslands ar e frequently subjected to water-deficit or N-deficit conditions, it is impo rtant to investigate the interactive responses between elevated [CO2] and t hese stress conditions. Therefore, this 4-year research program was underta ken with wheat (Triticum aestivum L.) as a model system for forage grasses, to document the potential changes in leaf N concentration in response to g lobal environment changes. Wheat crops grown under field conditions near Ph oenix, AZ, USA, were subjected to elevated [CO2] and either water-deficit o r N-deficit treatments using large Free Air Carbon dioxide Enrichment (FACE ) arrays. Surprisingly, the elevated [CO2] treatment under optimum conditio ns resulted in little change in leaf N concentration. Therefore, no change in the nutritive value of forage from highly managed pastures would be expe cted. Further, water-deficit treatment had Little influence on leaf N conce ntration. To some extent, the lack of response to the water-deficit treatme nt resulted because severe deficits did not develop until late in the growi ng seasons. Only on one date late in the season was the water-deficit treat ment found to result in decreased leaf N concentration. The low N treatment in combination with elevated [CO2], however, had a large influence on leaf N concentration. Low levels of applied N resulted in decreased leaf N conc entration under both [CO2] treatments, but the lowest levels of leaf N conc entration were obtained under elevated [CO2] through much of the growing se ason. These results point to a potential problem with grasslands in that th e nutritive value of the forage consumed by animals will be decreased under future global environment changes. (C) Published by Elsevier Science B.V.