Leaf morphology and chemistry in Fagus sylvatica L. (beech) trees as affected by site factors and ozone: results from Level II permanent monitoring plots in Italy

During the summer of 2001, leaf samples were collected from 7 beech stands that are part of the Italian network of permanent intensive monitoring plots (CON.ECO.FOR). In each plot, leaves from the upper crown (sun leaves) were collected from 5 trees. Measurements performed were of both chemical (foliar concentration of C and of macronutrients N, P, S, K, Ca, Mg) and morphological nature (leaf area, dry weight, leaf thickness and thickness of individual tissues). Based on these measurements, the following calculations were made: nutrient ratios (N/C, N/K, N/P, N/Ca, N/Mg, K/Ca, Mg/Ca), sclerophylly indices (Leaf Mass per Area, LMA; Leaf Density, LD) and nitrogen content per leaf area unit (N/LA). Stomatal density was also measured. Findings suggest that leaf area was smaller and sclerophylly (indicated as LMA) was greater in the southernmost plots and in conditions of drought. Reduced leaf area and increased LMA also appeared to be strongly related to ozone concentrations in the troposphere, whereas crown transparency was related mainly to site factors such as rainfall and temperature and, in a lesser extent, to ozone. The southernmost plots further displayed a lower N/C ratio than the more northern ones, suggesting that the apoplastic fraction of cells within the structure of the leaf played a greater role. In Northern Italy (especially in Lombardy and in Piedmont) ozone concentrations were very high, such as the levels of deposition of atmospheric ozone. In these plots, nutrient ratios were unbalanced and the high value of LMA appeared to be related primarily to the contribution of plasmatic components. Overall, leaf morphology displayed sensitivity to climate stress conditions in the southern plots and to environmental pollution conditions (nitrogen deposition and tropospheric ozone content) in some of the northern plots.