EFFECT OF GRAZING ON GROWTH, CARBOHYDRATE POOLS, AND MYCORRHIZAE IN WINTER WHEAT

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Abstract
Winter wheat (Triticum aestivum L.) was either subjected to fall grazing or left ungrazed and was examined the following spring for above and below ground growth, carbohydrate pools, and root length colonized by vesicular-arbuscular mycorrhizae (VAM). Root colonization by VAM occurred in both grazed and ungrazed winter wheat during reproductive growth (late spring). Prior to May, low soil temperatures apparently inhibited VAM colonization. Percent VAM colonization did not differ between treatments during reproductive growth, but root length per unit of soil volume was reduced by grazing, resulting in a greater colonized root length for ungrazed plants. Grazing reduced total carbohydrate pools. Although grazing and VAM colonization were separated in time, a grazing effect on colonization was evident. Colonization may be governed by the wheat plant’s ability to recover from grazing during the period prior to VAM spore germination. Although grazed plants gained more carbon during reproductive growth, the gain was not sufficient to overcome the grazing induced carbon limitation, as grain yields and VAM root length density were reduced by 16 and 38%, respectively.Key words: Wheat (winter), grazing, mycorrhizae, carbohydrates