The greater seedling high-light tolerance of Quercus robur over Fagus sylvatica is linked to a greater physiological plasticity

Abstract

The responses of Quercus robur (oak) and Fagus sylvatica (beech) seedlings to four different light environments (full, 50%, 40% and 15% sunlight) and to a rapid increase in irradiance were explored during the summer, after 2 years of growth in a forest nursery at Nancy (France). Significant differences between the two species were found for most variables. Phenotypic plasticity for morphological variables (root-shoot ratio, leaf size, leaf weight ratio) was higher in beech than in oak, while the reverse was true for anatomical (stomatal density, epidermis thickness, exchange surface area of the palisade parenchyma) and physiological (maximum photosynthetic rate, stomatal conductance, Rubisco activity) variables. Predawn photochemical efficiency (F v /F m ) was higher in oak than in beech in all light environments except in 15% sunlight. F v /F m was significantly lower in 100% sunlight than in the other light environments in beech but not in oak. Maximum photosynthetic rates (A max ) increased with increasing light availability in the two species but they were always higher in oak than in beech. Oak exhibited higher Rubisco activity than beech in full sunlight. The transfer of shade-adapted seedlings to the open caused a decrease of F v /F m , which was larger for beech than for oak. Transferred oak but not beech plants recovered gradually to the control F v /F m values. The decreased chlorophyll content and the increased nonphotochemical quenching observed in high-light beech seedlings were not enough to avoid photoinhibition. The results suggest that a greater tolerance of strong irradiance is linked to an enhanced physiological plasticity (variables related to photosynthesis), while shade tolerance relies on an enhanced plasticity in light-harvesting variables (crown morphology and chlorophyll content).

Fagus sylvatica L. recruitment across a fragmented Mediterranean Landscape, importance of long distance effective dispersal, abiotic conditions and biotic interactions

“…Growth and survival of Fagus have been reported to increase with light availability in pine forests, but they reach an asymptote at 5 -10% of light (Kunstler et al, 2005), which is included in the first class of light (0 -25%) of this study. Decrease in recruitment at higher light levels can be related to either an increase in the abundance of herbs correlated to light levels at the plot scale and thus higher herbaceous competition (Kunstler et al, 2006), or to light inhibition (Valladares et al, 2002). Similarly, shrub cover has a positive effect on recruitment and this effect is particularly important in grassland, in agreement with previous studies (Rousset & Lepart, 2000;Kunstler et al, 2006) that have shown shrub facilitation on recruitment of trees in grassland because of protection against herbivores and indirect facilitation through a limitation of herb competition.…”

Structural and physiological plasticity in response to light and nutrients in five temperate deciduous woody species of contrasting shade tolerance

“…The results of our study corroborate the previous evidence of greater physiological plasticity of shadeintolerant species (see Introduction). However, our results did not confirm a larger structural plasticity in shadetolerant species that has been hypothesized in some studies (Valladares et al 2002;Niinemets & Valladares 2004). In fact, the plasticity estimates based on the slopes of RGR vs. Ln(LAR) (structural plasticity) and RGR vs. Ln(NAR) (physiological variability) that merged both the light-and nutrient-dependent variation in LAR and NAR were positively associated (Fig.…”

“…The previous suggestions of greater morphological plasticity in shade-tolerant species have been based on limited data (Valladares et al 2002;Niinemets & Valladares 2004). In fact, Valladares et al (2002) comparing structural and physiological attributes of Q. robur and Fagus sylvatica found that the more tolerant species F. sylvatica was morphologically more plastic. However, the data provided by Welander & Ottosson (1998) for the same two species suggest that the plasticity is similar if not larger in Q. robur.…”

Quantitative estimation of phenotypic plasticity: bridging the gap between the evolutionary concept and its ecological applications

“…Many studies have used phenotypic plasticity indices to summarize the environmentally contingent trait expression of a given species, set of species or populations within a given species (Cheplick 1995;Poorter & Nagel 2000;Valladares et al 2000aValladares et al , 2002bValladares et al , 2005aBalaguer et al 2001;Gratani et al 2003) (see Table 1). Simple plasticity indices based on the mean phenotypes observed in each environment (e.g.…”