INTERACTIONS BETWEEN VESICULAR-ARBUSCULAR MYCORRHIZA AND Rhizobium AND THEIR EFFECT ON SWEETVETCH GROWTH

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Abstract
Sweetvetch (Hedysarum boreale Nutt.) is a legume native to the intermountain West that grows on foothills and intermediate mountain elevations. It has many attributes that are desirable in plant species used in revegetating disturbed lands and improving deteriorated rangelands in the West. We studied the effect and interactions of Glomus fasciculatus (Thaxter sensu Gerdemann) Gerdemann and Trappe and Rhizobium sp. on sweetvetch growth to determine the dependence of sweetvetch on these symbionts. Plants were grown under controlled conditions in sterilized soil or sterilized soil infested with G. fasciculatus, Rhizobium, or a combination of the symbionts. Following a 12-week growth period, above- and belowground plant production, percent mycorrhizal infection, nitrogen and phosphorus content, and rate of nitrogen fixation were quantified. Plants inoculated with either a combination of mycorrhizal fungi and rhizobia or mycorrhizal fungi alone grew taller and produced more aboveground plant material than plants infected with rhizobia alone or control plants. The presence of rhizobia increased the nitrogen content of the aboveground foliage, and inoculation with mycorrhizal fungi increased the phosphorus content. Mycorrhizal fungi and rhizobia also were found to be synergistic with respect to nitrogen fixation rates and mycorrhizal infection levels. The results point to a need for having appropriate inocula for normal plant growth and nitrogen fixation when growing sweetvetch on disturbed lands. Sweetvetch (Hedysarum boreale Nutt.) is a legume native to the intermountain West that grows on foothills and intermediate mountain elevations. It has many attributes that are desirable in plant species used in revegetating disturbed lands and improving deteriorated rangelands in the West. We studied the effect and interactions of Glomus fasciculatus (Thaxter sensu Gerdemann) Gerdemann and Trappe and Rhizobium sp. on sweetvetch growth to determine the dependence of sweetvetch on these symbionts. Plants were grown under controlled conditions in sterilized soil or sterilized soil infested with G. fasciculatus, Rhizobium, or a combination of the symbionts. Following a 12-week growth period, above- and belowground plant production, percent mycorrhizal infection, nitrogen and phosphorus content, and rate of nitrogen fixation were quantified. Plants inoculated with either a combination of mycorrhizal fungi and rhizobia or mycorrhizal fungi alone grew taller and produced more aboveground plant material than plants infected with rhizobia alone or control plants. The presence of rhizobia increased the nitrogen content of the aboveground foliage, and inoculation with mycorrhizal fungi increased the phosphorus content. Mycorrhizal fungi and rhizobia also were found to be synergistic with respect to nitrogen fixation rates and mycorrhizal infection levels. The results point to a need for having appropriate inocula for normal plant growth and nitrogen fixation when growing sweetvetch on disturbed lands. © Williams & Wilkins 1981. All Rights Reserved.