INTERNAL TRANSPORT OF NUTRIENTS IN CHESTN UT WOOD (CASTANEA-SATIVA MILLER) - DYNAMIC APPROACH OVER A CHRONOSEQUENCE OF STANDS .1. DISTRIBUTION OF MINERALS

Internal nutrient cycling from old to young organs is an efficient str ategy of perennial vegetation which can explain the relatively high pr oductivity of forest stands growing on poor soils. This work focused o n the internal nutrient cycling in chestnut coppice (Castanea sativa M iller) during a complete rotation. The objective of the paper was to c haracterize the distribution of major nutrients (N, P, K, Ca and Mg) i n stemwood. A series of stands of different ages was used (from 2 to 1 9 years old) to describe the variability of mineral content of stemwoo d. The stands were growing in Poitou-Charentes region in western Franc e in the same ecological context and managed identically (coppice with a 20-year rotation). The soil is a brown mesotrophic leached soil (ty pic Hapludalf, pH: 5, S/T of Al : 0.86) with a mean annual temperature = 11.5-degrees-C and an annual precipitation = 950 nun. Nutrient dist ribution in stemwood was investigated according to a vertical and a ra dial transect in the stem; tree increment ring groups were collected e very three meters along the stem and were gathered in 5 ring groups ([ 0-2], [3-5], [6-9], [10-15] and [16-19] (fig. 1 b). Five trees per sta nd were sampled according to their social status (they were classified according to the diameter at breast height, fig. 1 a). Each ring grou p sample at each level was analysed for nutrient content (N, P, K, Ca and Mg). Radial and vertical growth were determined by stem analysis w hich made it possible to reconstitute the ring width distribution insi de the tree. The variability of nutrient content of stemwood was inves tigated by analysis of variance: (i) age, width and vertical position of the ring group within the tree, and (ii) age of the stand are the m ost significant variables (table I). Mineral content of tree growth ri ngs varied mainly with the physiological age of the ring and its radia l position within the tree: concentration decreased slightly with the age of tree rings and with the distance from the bark, except in the c entral zone of the trunk (pith) where higher values were observed (fig . 5). Nutrient content decreased sharply from the apex to the base wit h a systematic increase in the stump zone (fig. 9 a). It was closely r elated to (i) the ring width (dilution effect) and (ii) to the current increment of the stand specially for the external ring group ([16-19] , fig. 7 b). Maximal values for ring mineral concentrations depended o n the age of the tree (fig. 7 a). Nutrient content was affected by the social status of tree: it seemed that the suppressed trees were chara cterized by higher concentrations (fig. 4 a). This paper underlines th e different ring and whole-tree parameters which control the mineral c omposition of tree rings. Special attention was paid to dynamics durin g stand development. These results will serve as data for a model desc ribed in a second paper.