Effects of light intensity and CO2concentration on the kinetics of 1st month growth and nitrogen fixation of alfalfa

摘要

Medicago sativaL. cv. Algonquin seedlings were grown for 28 days in growth rooms at several intensities of light and concentrations of CO2. Optimal or deficient NO3minus;concentrations were provided, the latter with or without inoculation and nodulation byRhizobium melilotistr. 102F70 (Burton). All growth coefficients (k1prime;) were hyperbolically dependent on the intensity of light. Light saturation of plantk1prime; was achieved, but thek1prime; for nitrogenase development the highest in value, was not light saturated at high CO2by the highest light intensity (555ensp;mu;E∙mminus;2∙sminus;1). That intensity also did not saturate the photosynthesis of plants grown at that intensity nor the amount (yield) and absolute rate of plant growth. The latter were very much reduced at intensities below the compensation point (100ensp;mu;E∙mminus;2∙sminus;1) of net photosynthesis. The data fork1prime; at low light intensity indicated that photosynthate was utilized with equal efficiency for N2and NO3minus;reduction. Fourfold enrichment of CO2concentration did not influence thek1prime; of plant growth in optimum NO3minus;and high light intensity but increased the yield by 78. In the absence of high NO3minus;concentration, however, it nearly doubled the nitrogenase growthk1prime;, to a doubling time of 1.4 days, increased the nodule yield fourfold, the plant (symbiotic) yield threefold, and N content twofold. Sevenfold enrichment of CO2was inhibitory to yields of N-deficient plants and nodules. The previous conclusion that added (combined) N chiefly limited seedling growth was supported by the lack of effect on plantk1prime; of the stimulation of photosynthesis by high light intensity and CO2concentration. A limitation on the value of thek1prime; for shoot elongation in deficient combined N raised CO2and high light was relieved symbio