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Character and Significance of Forest Tree Root Exudates

Smith, William H.
Ecology 1976 v.57 no.2 pp. 324-331
Acer saccharum, Betula alleghaniensis, Fagus grandifolia, amides, amino acids, biogeochemical cycles, calcium, carbohydrates, forest trees, hardwood forests, inorganic ions, interspecific variation, organic acids and salts, potassium, root exudates, root tips, sodium, sulfates
Root exudates from the unsuberized tips of new woody roots were collected from mature Betula alleghaniensis, Fagus grandifolia, and Acer saccharum in a northern hardwood forest. Numbers of new woody root tips were also determined for these three species. Exudates were fractioned into carbohydrates, amino acids/amides, organic acids, and 9 inorganic ions. Considerable species variation characterized the quantitative and qualitative nature of the organic fraction. Organic acids were the most abundant component. Fagus grandifolia released the largest amount of amino and organic acids per hectare, while B. alleghaniensis exuded the largest amount of carbohydrates. Sodium (possibly anomalous), K, and Ca dominated the cationic fraction, while the anionic fraction was chiefly SO₄ and Cl. Betula alleghaniensis and F. grandifolia released considerably greater quantities of inorganic ions than A. saccharum, but the inorganic root exudate patterns of the three species were relatively uniform. These results indicate root exudates have some role in intrasystem nutrient cycling.