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Defoliation effects on mycorrhizal colonization, nitrogen fixation and photosynthesis in the Glycine‐Glomus‐Rhizobium symbiosis
Author(s) -
Bayne Henry G.,
Brown Milford S.,
Bethlenfalvay Gabor J.
Publication year - 1984
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1984.tb02802.x
Subject(s) - biology , photosynthesis , symbiosis , rhizobium , nitrogen fixation , fungus , glomus , mycorrhiza , botany , inoculation , colonization , endophyte , agronomy , horticulture , bacteria , microbiology and biotechnology , genetics
Soybean [ Glycine max (L.) Merr. cv. Wells] plants grown in a greenhouse were inoculated with Rhizobium japonicum strain 61A118 and the vesicular‐arbuscular mycorrhizal (VAM) fungus Glomus fasciculatum (Thaxt. sensu Gerd.) Gerd. & Trappe. Plants were defoliated (26, 48 and 66%) throughout the growth period and evaluated for VAM colonization, N 2 , fixation and photosynthesis at harvest (six weeks). Photosynthate stress as a result of defoliation affected nodulation and nodule activity most severely. Colonization of the roots by the VAM fungus was little affected in comparison, and the intensity of colonization increased with increasing stress. The CO 2 ‐exchange rate decreased less with defoliation than did leaf mass, and photosynthetic efficiency increased with the severity of defoliation. The increase in photosynthetic efficiency was significantly correlated with increases in leaf P (r = 0.91) and N (r = 0.97) concentrations. The results suggest that the VAM fungus should not be regarded as a simple P source and C sink in the tripartite legume association. Threeway source/sink relationships (VAM‐P, Rhizobium‐N, and host leaf‐C) are discussed.