Analysis of edaphic and ecophysiological parameters in relation to nutrient levels and growth of " Pinus pinaster " in acidic soils

Abstract

The main aim of this doctoral research was to improve the understanding of the relationships between the ecophysiological and edaphic parameters that determine the growth of Pinus pinaster and its ability to adapt to different environments, in order to facilitate the decision-making involved in wood and biomass production and other forest products. For this purpose, five specific studies were carried out. The relationships between soil properties, foliar nutrients and growth were studied in 128 plots of Pinus pinaster established in soil over different types of bedrock (granitic rocks, sediments, sandstone and quartzite, slates and phyllites, mica schist, biotitic schist, gneiss and migmatites). Good adaptation of Pinus pinaster was observed in soils developed over biotitic schist, granitic rocks, gneiss and migmatites, in which growth of the species was highest and foliar nutrients, particularly K, were also generally higher than in the other types of soil. Two regression models were developed for predicting site index. In a complete model considering all geological materials, foliar Ca and K, soil depth and average annual temperature explained around 52% of the variability in site index. In another model considering granitic rocks, all of the previous parameters, except foliar Ca, explained 53% of the variability in site index. Needle size, leaf traits and site parameters were studied in 31 plots. Needle length, width and thickness were closely related to climate conditions, year of formation and also foliar concentrations of N and Mg. Needle age class is the main factor leading to variation in needle dimensions. The specific leaf area was positively affected by concentrations of foliar nutrients, particularly K. The variability in needle lifespan, foliar biomass and leaf area index was analysed in the 31 plots. Needle longevity was closely related to site index and foliar concentrations of Mg and K. Foliage biomass and leaf area index were negatively correlated with needle age and positively correlated with site index and foliar nutrients. Growth efficiency (the annual above-ground biomass increment per unit leaf area) increased as foliar K and particularly the K:N ratio increased. The influence of the parent rock on Al fractionation, speciation and toxicity was studied in 4 of 31 plots developed over biotitic schist, mica schist, granite and slate. In the soil over biotitic schist, the concentrations of oxalate and pyrophosphate Al were higher than in other soils and tended to form highly stable organic–aluminium complexes. In the soil developed from slate, the more labile forms of Al predominated and were more liable to move to the liquid phase and be absorbed by the plant. The highest concentrations of the Al forms considered most toxic (Al3+ and Al-OH) were found in the soils over slate and mica schist, in accordance with the lower site index in these plots. All toxicity indices considered indicated a higher risk of Al toxicity in the plots developed over slate and mica schist, but no risk of Al toxicity in the plots on biotitic schist. The indices obtained considering labile Al and Al3+ + Al-OH in the soil solution indicated no risk of Al toxicity in plots over granite, according to productivity and biomass variables. Application of the other indices indicated risk of toxicity by this element.