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Soybean Nodule Size and Relationship to Nitrogen Fixation Response to Water Deficit
Author(s) -
King C. Andy,
Purcell Larry C.
Publication year - 2001
Publication title -
crop science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.76
H-Index - 147
eISSN - 1435-0653
pISSN - 0011-183X
DOI - 10.2135/cropsci2001.4141099x
Subject(s) - biology , cultivar , nodule (geology) , nitrogen fixation , root nodule , agronomy , drought tolerance , greenhouse , horticulture , botany , paleontology , genetics , bacteria
Decreased N 2 fixation in response to drought in soybean [ Glycine max (L.) Merr.] constrains grain and protein production, but differences exist among cultivars in sensitivity of N 2 fixation to drought. We tested the hypothesis that large nodules may help confer drought tolerance because the fraction of N 2 ‐fixing tissue (i.e., noncortical) is greater in large than small nodules. Consequently, the high energy demand of N 2 fixation may create a greater sink demand by large nodules than small nodules during water deficit, increase phloem water supply to nodules, maintain nodule permeability to O 2 , provide sugars to support nodule activity, and supply water for the export of ureides from nodules. This hypothesis was evaluated for the cultivars Jackson (drought tolerant) and KS4895 (drought sensitive) in greenhouse and growth chamber experiments. Individual nodule mass and permeability to O 2 were 0.65 to 0.70 times greater in Jackson than in KS4895 under well‐watered and water‐deficit conditions. For both cultivars, large nodules maintained a higher relative water content than small nodules across a range of soil‐water deficits. One day after labeling leaves of well‐watered plants with 14 CO 2 , nodules ≤2 mm diam. had approximately 3.5 times the 14 C concentration of nodules ≥4 mm diam. For plants of the water‐deficit treatment, 14 C concentration of nodules ≤2 mm diam. was only 1.6 times that of nodules ≥4 mm diam. Nodules from the plants of the water‐deficit treatment had a greater 14 C concentration than nodules from the well‐watered treatment for all nodule size classes >2 mm diam. Additionally, 14 C concentration for all nodule size classes was greater for Jackson than for KS4895. We conclude that drought tolerance of Jackson is partially due to the advantages of large nodules, but that drought tolerance in Jackson also results from an inherently greater supply of photosynthates to nodules.