Leaf gas exchange of beech (Fagus sylvatica L.) seedlings in lightflecks: effects of fleck length and leaf temperature in leaves grown in deep and partial shade

Abstract

Summary. Responses of leaf gas exchange in shade and half-shade grown seedlings of the European beech, Fagus sylvatica L., to constant light conditions indicate different phases of photosynthetic induction: an immediate, a fast and a subsequent slow phase. The slow phase has both biochemical and stomatal components. The higher the induction, the higher the lightfleck utilization efficiency (LUE) attributable to a lightfleck. LUE can be higher than 100% compared to a theoretical instantaneous response. Lightfleck quantum yield (total carbon gain attributable to a lightfleck per incident quantum density in the fleck) is highest in short pulses of light. Post-illumination carbon gain initially increases with fleck length, levelling off above 20 s. The lower the induction, the longer carbon is fixed post-illuminatively (up to 84 s) but the less carbon is gained. Shade leaves are induced much faster than partial shade leaves. They utilize series of lightflecks to become fully induced, while half-shade (and sun) leaves depend on continuous high light. Half-shade leaves lose induction faster in low light between lightflecks. High as well as low temperatures strongly delay induction in half-shade but not in shade leaves. In general, shade leaves are much better adapted to the dynamic light environment of the forest understorey; however, their water-use efficiency during induction is lower.

Effects of elevated CO2 on leaf gas exchange in beech and oak at two levels of nutrient supply: consequences for sensitivity to drought in beech

“…Juvenile beech plants in their natural habitat depend strongly on short light flecks for their assimilation (Kuppers & Schneider 1993). Understorey plants typically maintain a relatively high conductance between light flecks (Pearcy & Calkin 1983;Pearcy 1987).…”

A interação ecofisiológica planta-ambiente

“…In fact, some studies of lightfleck utilization have suggested that shade leaves may be capable of using sunflecks more efficiently than sun leaves (CHAZDON & PEARCY, 1986b;KÜPPERS & SCHNEIDER, 1993; TANG et al, 1994). This capacity could be related to a significant efficiency in increasing photosynthetic capacity exhibited by shade species in response to increasing light availability (CHOW et al, 1988; TURNBULL, 1991; THOMPSON et al, 1992).…”

“…Rubisco, stomatal opening and their maintenance under low-light (CHAZDON, 1988;PEARCY et al, 1994). Previous studies have suggested that shade-tolerant species are more efficient in sunfleck utilization due to the ability to achieve and maintain a high photosynthetic induction state when compared to shade-intolerant species (SCHNEIDER et al, 1993;KÜPPERS et al, 1996). It is a crucial trait since sunflecks contribute with 10-80% of total diurnal photosynthetically active radiation (CHAZDON et al, 1996), being determinant to the carbon gain of plants in understory environments (SIMS & PEARCY, 1993; PEARCY & YANG, 1998).…”

“…These periods of high irradiance can last for a few seconds to several minutes, and can contribute from 10−80 % of daily photon flux density (PFD) received by a plant (CHAZDON, 1988). Photosynthesis during sunflecks may contribute to 30−60 % of the daily carbon gain, indicating that plants depend on sunflecks to maintain a positive carbon balance (CHAZDON, 1988).Previous works have shown that understorey plants typically exhibit photosynthetic adaptation and acclimation that allows maximization of carbon gain under such dynamic irradiance regimes (CHAZDON & PEARCY, 1986a,b;ÖGREN & SUNDIN, 1996; VALLADARES et al, 1997).Plant growth is not determined only by photosynthesis, but the photosynthetic utilization of photon energy plays a major role in the rain forest understorey where irradiance is frequently the most limiting environmental factor (KÖRNER, 1991;KÜPPERS & SCHNEIDER, 1993; FETCHER et al, 1994). Differences in photosynthetic characteristics between shade tolerant and irradiance demanding species may allow for differential utilization of the patchy radiation resource in rain forest environments (PRESS et al, 1996).…”

“…Plant growth is not determined only by photosynthesis, but the photosynthetic utilization of photon energy plays a major role in the rain forest understorey where irradiance is frequently the most limiting environmental factor (KÖRNER, 1991;KÜPPERS & SCHNEIDER, 1993; FETCHER et al, 1994). Differences in photosynthetic characteristics between shade tolerant and irradiance demanding species may allow for differential utilization of the patchy radiation resource in rain forest environments (PRESS et al, 1996).…”