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

During summer 2001, leaf samples were collected from seven beech stands that are part of the Italian network of permanent monitoring plots (CONECOFOR). In each plot, sun leaves from the upper crown were collected from five trees and subjected to chemical analysis (C, N, P, S, K, Ca and Mg) and morphological analysis (area, dry mass, thickness and thickness of individual tissues). Based on the measurements, nutrient ratios (N/C, N/K, N/P, N/Ca, N/Mg, K/Ca, Mg/Ca), sclerophylly indices (leaf mass per area (LMA) and leaf density (LD)) and nitrogen content per leaf area unit (NLA) were determined. Stomatal density was also measured. Among stands, leaf area was smallest and sclerophylly (indicated as LMA) was greatest in the southernmost stands and under drought conditions. Reduced leaf area and increased LMA also appeared to be strongly related to tropospheric ozone concentrations, whereas crown transparency was related mainly to site factors such as rainfall and temperature and, to a lesser extent, ozone concentration. The southernmost stands had a lower N/C ratio than the more northern stands, suggesting that the apoplastic fraction of cells within the leaf played a greater role. In the northern stands (especially at Lombardy and in Piedmont) where ozone concentrations were high, nutrient ratios were unbalanced and the high value of LMA appeared to be related primarily to the contribution of plasmatic components. Overall, leaf morphology was most sensitive to climate stress at the southern plots and to environmental pollution (nitrogen deposition and tropospheric ozone concentration) at some of the northern plots.