Role of Nitrogen in Wood Deterioration: Amounts and Distribution of Nitrogen in Tree Stems

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.

Mineral nutrient concentrations in sapwood and heartwood: a literature review

“…The similarity, from a functional point of view, between heartwood formation and leaf senescence has often been postulated [7, 9, 37-39, 71, 72, 74]. Since the pioneering works of Merrill and Cowling [50] and Ziegler [76], it is generally assumed that N-and P-compounds are actively hydrolysed and retrieved from senescing sapwood rings. However, the observation of differences in mineral nutrient concentrations between heartwood and sapwood does not in itself prove that translocations are involved.…”

“…Secondly, the differences among elements and the correlation pattern among them (N-P on the one hand and Ca-Mg on the other hand) are consistent with the well-known differences in mobility and chemical form of these elements in the xylem. Thus, a high proportion of N, P and K is located in the symplast of parenchyma ray cells [50,64,72] which is thought to be withdrawn during sapwood senescence [27,66,76]. In contrast, a substantial proportion of Ca and Mg in wood is located in the cell wall either adsorbed on negatively charged exchange sites or incorporated in the form of pectates or in the lignin matrix [17,44,48].…”

“…[70]). The lower mineral element concentrations in Gymnosperm sapwood may well be constitutive, since N concentration in wood is correlated to the proportion of living parenchyma cells [50], which is lower in Gymnosperm sapwood compared to Angiosperms [32]. It is well known that evergreen species, including Conifers, have intrinsically lower concentrations of N in leaves (on a mass basis) compared to deciduous species and such low foliar concentrations are regarded as a key component of the nutrient conservation strategy of evergreens [1][2][3]37].…”

“…During the conversion of sapwood into heartwood, extensive translocation of chemical compounds occurs. Secondary compounds tend to accumulate in heartwood, while storage products (starch), soluble sugars, amino-acids and mineral elements are removed from senescing sapwood rings [9,10,15,16,32,50,76].…”

Reconstructing terrestrial nutrient cycling using stable nitrogen isotopes in wood

“…In some cases, the sharp increase at the heartwood/sapwood boundary is lessened, and rings show a constant increase in [N] through both the heartwood and the sapwood (Poulson et al 1995;McLauchlan and Craine 2012). When the pith is present, it may also exhibit a spike in [N] comparable to, and sometimes exceeding, the spike in the most recent ring (Merrill and Cowling 1966). These general trends have been reported across numerous taxa, disparate environmental growing conditions, different preparation techniques (see extraction section below), and different levels of ecosystem N availability.…”