Microclimatic conditions determined by stem density influence leaf anatomy and leaf physiology of beech (Fagus sylvatica L.) growing within stands that naturally regenerate from clear-cutting.

Abstract

Beech forests naturally regenerating from clear-cutting can exhibit different microclimates depending on size of saplings and stem density. When beech trees are young and stem density is low, the level of radiation inside the ecosystem reaching the soil surface is high; consequently, air and soil temperatures rise and the soil water content may decrease. These microclimatic parameters presumably will affect the anatomy, photosynthesis, and carbon metabolism of beech leaves. We studied the morphology and physiology of sun and shade leaves of beech trees differing in age and growing within clear-cut areas with distinct microclimate. Results were compared with those of adult trees in an unmanaged forest. We selected a stand clear-cut in 2001 (14,000 trees ha−1), another clear-cut in 1996 (44,000 trees ha−1) and an unmanaged forest (1,000 trees ha−1). Photosynthetic photon flux density (PPFD) incident on sun leaves, air temperature, soil moisture, and soil temperature within the forests affected water status and carbohydrate storage in all trees. As trees became older, PPFD also influenced pigment composition and Rubisco activity in sun leaves. On the other hand, shade leaves from the oldest trees were the most sensitive to PPFD, air temperature, and soil moisture and temperature inside the forest. Contrariwise, microclimatic parameters slightly affected the physiology of shade leaves of the beech in the stand with the highest light attenuation. Air and soil temperatures were the parameters that most affected the photosynthetic pigments and carbohydrate storage in shade leaves of the youngest trees.