ROLE OF NITROGEN IN WOOD DETERIORATION: AMOUNTS AND DISTRIBUTION OF NITROGEN IN TREE STEMS

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Abstract
Radial gradients in nitrogen content across stems of three hardwoods and two softwoods followed similar patterns. Sapwood and inner bark contained a higher proportion of the total nitrogen in cross sections than heartwood and outer bark, respectively. Nitrogen content of individual annual increments decreased progressively from the cambium to the transition zone between sapwood and heartwood, or, in species without heartwood, to the increments nearest the pith. In some cases, an abrupt decrease in nitrogen content was observed across the sapwood–heartwood boundary. The diminution of nitrogen content across the sapwood was associated with death of parenchyma cells. As the cells die, nitrogen in their cytoplasm apparently is retrieved for possible reuse elsewhere in the tree. Pith contained more nitrogen by weight than heartwood and in some cases more than sapwood. Nitrogen content was correlated directly with parenchyma volume for sapwood but not for heartwood of 16 species of angiosperms.Nitrogen extractable from sapwood with neutral solvents consisted in part of free amino acids but only traces of these acids were detected in heartwood. Hydrolysates of sapwood and heartwood prepared with 6 N HCl contained many typical protein amino acids.