Impacts des milieux pedologiques en bosses et creux sur les teneurs en composes phenoliques et en elements mineraux dans les feuilles d'erables a sucre (Acer saccharum) en deperissement du Quebec | Impact of soils with lumps and hollows on the contents of phenolic compounds and mineral elements in the leaves of the sugar maple (Acer saccharum) affected by decline in Quebec

We conducted a study on the influence of microrelief on the content of phenolic compounds and mineral elements in leaves of sugar maple (Acer saccharum Marsh.) at various stages of decline. The stand of origin was located in the Appalachian Highlands of Quebec, on acidic material with a microrelief constituted of hollows and bumps, the height of the latter varying between 30 and 60 cm. Well aerated podzols developed on bumps, while gleysols developed in hollows. Trees generally grew on bumps and their roots could extend as far as 5 m away from the tree. Microrelief and soils were described within a 5-m radius around every sugar maple under study. Pedological sites were classified into three categories according to their microrelief (percent surface area covered by bumps): (i) less than 30% of surface (dominance of poorly drained soils). (ii) between 30 and 50% of surface (dominance of imperfectly drained soils), and (iii) more than 50% of surface (dominance of well drained soils). A principal component analysis on site distribution and a chemical analysis of soils showed an increase in total N and in K, Ca, and Mg availability with an increase in soil humidity. The principal component analysis and chemical analysis of leaves indicated that the content of phenolic compounds was highest, and those of N and K lowest, in moistest soils. The decline was also greatest on those sites. There was a strong correlation between synthesis of phenolic compounds and foliar N contents, and between decline intensity and foliar N content. The high humidity of some soils of the study sites reduces the availability of N, causing a stress to sugar maples. This phenomenon would result in an increased synthesis of phenolic compounds and a decline in less resistant trees. Phenolic compounds could then be utilized as a physiological indicator of stress. Those results explain why healthy trees can grow next to declining trees.