Influence of mycorrhiza vs. soluble phosphate on growth,nodulation, and N2 fixation (15N) in alfalfa under different levels of water potential |
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Authors: | R. Azcón F. El-Atrach J. M. Barea |
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Affiliation: | (1) Departamento de Microbiologia, Estación Experimental del Zaidín, C.S.I.C., Prof. Albareda 1, E-18008 Granada, Spain |
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Abstract: | Summary The legume Medicago sativa (+Rhizobium melilott) was grown under controlled conditions to study the interactions between soluble P in soil (four levels), or a mycorrhizal inoculum, and the degree of water potential (four levels) in relation to plant development and N2 fixation. 15N-labelled ammonium sulphate was added to each pot for a qualitative estimate of N2 fixation, in order to rank the effects of the different treatments.Dry-matter yield, nutrient content and nodulation increased with the amount of plant-available P in the soil, and decreased as the water stress increased, for each P-level. The mycorrhizal effect on dry matter, N yield, and on nodulation was little affected by the water potential. Since P uptake was affected by the water content in mycorrhizal plants, additional mechanisms, other than those mediated by P, must be involved in the mycorrhizal activity.There was a positive correlation between N yield and nodulation for the different P levels and the mycorrhizal treatment at all water levels. A high correlation between plant unlabelled N content and atom% 15N excess was also found for all levels of P. In mycorrhizal plants, however, the correlation between unlabelled N yield and 15N was lower. This suggests that mycorrhiza supply plants with other N sources in addition to those derived from the improvement on N2 fixation. |
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Keywords: | Vesicular-arbuscular mycorrhiza N2 fixation 15N-labelled fertilizers Rhizobium Legume symbiosis Drought stress |
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