Sunflecks in forest communities and their importance for plant life in a forest understorey

Plant life in forest understorey is limited by several environmental factors, esp. by limited light resources (solar radiation). Various adaptations (life strategies) help plants to use heterogeneity of the environment, including moving shortterm sunflecks of direct solar radiaton, which penetrates throught openings between crowns of tall trees to the soil surface. Size, frequency and duration of sunflecks change, depending on stand structure and position of sun on the ski. Sunflecks occurrence and effects on stomatal conductance, water relations and photosynthesis were studied during sunny days in understories of deciduous forests at Bab and Bratislava - Patronka (both in Western Slovakia, Central Europe), as well as in laboratory conditions. Suden increasing of solar radiation (from ca 6 W m(-2) to 50 and more) caused by natural sunflecks natural sunflecks increased stomatal stomatal conductance, transpiration rate and net photosynthetic rate ca 50-90%. Responses of spring and summer herbs were similar. In an annual Impatiens parviflora, rapid increasing of radiation in laboratoty conditions increased stomatal conductance and photosynthesis by 25-70%. In all cases plant responses were immediate and steday state was reached up to 400 sec. Long-term sunflecks (more than 30 min.) on a plant can caused water stress and temporal wilting of leaves andor plants. In sensible plants we can observed damage by light (photoinhibition). Plants growing in the forest understory can improve their energy balance by utilizing sunflecks and gaps. And by higher photosynthetic rate large portion of daily carbon gain which is important for carbon balance of a plant (in long period the gain can be up to 60%).