Spatial and temporal variability of foliar mineral concentration in beech (Fagus sylvatica) stands in northeastern France

Foliar mineral concentration may provide a basis for monitoring the consequ ences of long-term environmental changes, such as eutrophication and acidif ication of soils, or increase in atmospheric CO2 concentration. However, an alytical drifts and inter-tree and year-to-year variations may confound env ironmental effects on long-term changes in foliar mineral concentration. We have characterized the relative effects of these potentially confounding f actors on foliar carbon, nitrogen, phosphorus, calcium, potassium, magnesiu m and manganese concentrations in 118 pure beech (Fagus sylvatica L.) stand s, sampled in 1969-71 and 1996-97. Interannual fluctuations of these elemen ts were quantified in a subset of six beech stands monitored for 5 years. Intercalibration between the methods used at each sampling period for nitro gen and phosphorus analyses showed significant, but low, relative differenc es (0.8 and 3.3% for N and P, respectively). Based on inter-tree variabilit y, elements could be arranged in four groups: C (constant), N and P (low va riability), K and Ca (medium variability), Mn and Mg (high variability). In ter-tree coefficients of variation were 2, 6, 8, 15, 18, 22 and 27%, respec tively. Year-to-year fluctuations increased in the order N, P, Mg, K, Ca, a nd Mn (coefficients of variation of 4, 4, 7, 9, 11, 15 and 29%, respectivel y). Between the two sampling periods, foliar N concentration increased 12%, whe reas decreases were observed for P (-23%), Mg (-38%) and Ca (-16%). Ratios of N/P, N/K and N/Mg increased by 42, 19 and 77%, respectively. These chang es were larger than the interannual variations for P, Mg, N/P, N/Mg and Mg/ Ca. Decreasing concentrations of P and cations were particularly marked for trees growing on acidic soils, whereas the positive N trend did not depend on soil type. Both increasing atmospheric CO2 concentrations and acidifica tion of forest soils could contribute to decreasing P and cation concentrat ions in foliage. The increase in foliar N concentration with time suggests a nitrogen deposition effect. Whatever the causes of these changes, the lar ge shift in element ratios indicates an accelerating imbalance between nitr ogen and cation status.