ECOPHYSIOLOGICAL RESPONSES OF FAGUS-SYLVATICA SEEDLINGS TO CHANGING LIGHT CONDITIONS .2. THE INTERACTION OF LIGHT ENVIRONMENT AND SOIL FERTILITY ON SEEDLING PHYSIOLOGY

The survival and growth of natural beech regeneration after canopy rem oval is variable and little is known about ecophysiological mechanisms of these responses. Biomass, nonstructural carbohydrate levels and ni trogen concentrations were measured in an Italian population of Europe an beech seedlings. Seedlings were container-grown in two types of soi l, organic and mineral, collected at the study site, The seedlings wer e grown under three light treatments: under full beech canopy (underst ory), exposed to full sun only during midday (gap) and under full sun (clearing). Leaf gas exchange and chlorophyll a fluorescence parameter s were measured and then foliar analyses were conducted for chlorophyl l, phenolic and tannin levels, Biomass and allocation were significant ly affected by light and soil treatments, The clearing seedlings and t hose in organic soil were larger than seedlings in the other light tre atments or soil type. Total nonstructural carbohydrate concentrations were lower in the understory seedlings acid significant differences be tween soil types were present in the gap and clearing seedlings. Nitro gen concentrations were higher in the understory seedlings and those g rowing in the organic soil compared to the other treatments. Gas excha nge rates were highest in clearing and the organic soil seedlings. Gap seedlings exhibited photosynthetic acclimation that allowed them to u tilize high light of midday and any sunflecks during the morning and a fternoon. Relative fluorescence was significantly influenced by both l ight treatment and soil type, with the highest values observed in the gap seedlings. Light response curves showed decreasing apparent maximu m quantum efficiency from the understory to clearing, while maximum ph otosynthetic rate was highest in the gap seedlings. Chlorophyll concen tration was highest in understory seedlings and those growing in organ ic soil and higher in seedlings growing in organic than in mineral soi l. Both foliar tannin and phenolic levels were highest in clearing see dlings, and only tannin concentrations were affected by soil type. Und erstory seedlings had the highest mortality and insect herbivory; the latter was found to be inversely related to tannin concentration. Over all, growth and photosynthesis in beech seedlings responded positively to high light associated with small canopy gaps. Organic soil increas ed seedling size, particularly in the gap and clearing environments, W e conclude that forest gaps are favorable for photosynthesis and growt h of European beech seedlings.