Ecophysiological responses of Fagus sylvatica seedlings to changing light conditions. II. The interaction of light environment and soil fertility on seedling physiology

Abstract

M. 1997. Ecophysiological responses of Eagus sylvatica seedlings to changing light conditions. II. The interaction of light environment and soil fertility on seedling physiology. -Physiol. Plant. 101: 124-134.The survival and growth of natural beech regeneration after canopy removal is variable and little is known about ecophysiological mechanisms of these responses. Biomass, nonstructural carbohydrate levels and nitrogen concentrations were measured in an Italian population of European beech seedlings. Seedlings were container-grown in two types of soil, organic and mineral, collected at the study site. The seedlings were grown under three light treatments: under full beech canopy (understory), exposed to full sun only during midday (gap) and under full sun (clearing). Leaf gas exchange and chlorophyll a fluorescence parameters were measured and then foliar analyses were conducted for chlorophyll, phenolic and tannin levels. Biomass and allocation were significantly affected by light and soil treatments. The clearing seedlings and those in organic soil were larger than seedlings in the other light treatments or soil type. Total nonstructural carbohydrate concentrations were lower in the understory seedlings and significant differences between soil types were present in the gap and clearing seedlings. Nitrogen concentrations were higher in the understory seedlings and those growing in the organic soil compared to the other treatments. Gas exchange rates were highest in clearing and the organic soil seedlings. Gap seedlings exhibited photosynthetic acclimation that allowed them to utilize high light of midday and any sunflecks during the moming and afternoon. Relative fluorescence was significantly influenced by both light treatment and soil type, with the highest values observed in the gap seedlings. Light response curves showed decreasing apparent maximum quantum efficiency from the understory to clearing, while maximum photosynthetic rate was highest in the gap seedlings. Chlorophyll concentration was highest in understory seedlings and those growing in organic soil and higher in seedlings growing in organic than in mineral soil. Both foliar tannin and phenolic levels were highest in clearing seedlings, and only tannin concentrations were affected by soil type. Understory seedlings had the highest mortality and insect herbivory: the latter was found to be inversely related to tannin concentration. Overall, growth and photosynthesis in beech seedlings responded positively to high hght associated with small canopy gaps. Organic soil increased seedling size, particularly in the gap and clearing environments. We conclude that forest gaps are favorable for photosynthesis and growth of European beech seedlings.

The influence of microclimate and tree age on the defense capacity of European beech (Fagus sylvatica L.) against oxidative stress

“…Consequently, area based values of antioxidants and photoprotective pigments are of potential importance, to relate defense capacity to environmental impacts [46], especially when tree ageing coincides with alterations in leaf morphology [39,46,47]. In coincidence with previous studies in seedling and adult Fagus sylvatica trees [12,15,20,22,26,29,30,41] there were clear differences in antioxidant and pigment contents with respect to crown position. The higher dry weight and area based contents of ascorbate and a-tocopherol in sun exposed leaves are consistent with their greater need for antioxidant protection [10].…”

Water relations of cork oak (Quercus suber L.) seedlings in response to shading and moderate drought

“…For both water treatments, seedlings grown at high irradiances showed a higher soluble sugar concentration than seedlings grown under low irradiances. Similar results have been reported by Niinemets [36] in three temperate woody species and by Johnson et al [24] in Fagus sylvatica, but contrast to those presented by Meletiou-Christou et al [30] in four Mediterranean evergreen sclerophylls, which showed no substantial differences on soluble sugars when comparing sun and shade leaves. Changes on water availability through the growing season did not affect either soluble sugar concentration in twoyear-old cork oak seedlings grown outdoors in Portugal, although mean values are higher than ours (between 1.0 and 1.7 mg glucose·cm -2 ), probably related to seedling age [12].…”

“…Acclimation to different light environments occurs at both whole-plant and leaf levels [24]; leaf acclimation being associated with morphological, anatomical and physiological changes [31]. It is suggested that plants genotipically adapted to open sunny habitats have the ability to acclimate and grow under shaded conditions [42].…”

Multiple environmental control of leaf area and its significance for productivity in beech saplings

“…However, when both parameters were changed synchronously in the 24°C/500 Pa treatment, productivity was about 150% higher than in the 18°C/ 1,000 Pa treatment, which is substantially more than the added temperature and air humidity effects. In European beech, synergy effects were also observed for the combination of temperature and [CO 2 ] (Saxe and Kerstiens 2005;Bruhn et al 2000), temperature and light (Fotelli et al 2005) as well as for the light/soil fertility interaction (Johnson et al 1997). These results underline the importance of multi-factor studies when attempting to predict the response of trees to climatic changes.…”