Low leaf‐level response to light and nutrients in Mediterranean evergreen oaks: a conservative resource‐use strategy?

Abstract

We have explored leaf-level plastic response to light and nutrients of Quercus ilex and Q. coccifera, two closely related Mediterranean evergreen sclerophylls, in a factorial experiment with seedlings. Leaf phenotypic plasticity, assessed by a relative index (PI l (maximum value -minimum)\maximum) in combination with the significance of the difference among means, was studied in 37 morphological and physiological variables. Light had significant effects on most variables relating to photosynthetic pigments, chlorophyll fluorescence and gas exchange, whereas nutrient treatment had a significant effect in only 10% of the variables. Chlorophyll content was higher in the shade whereas carotenoid content and nonphotochemical quenching increased with light. Nutrient limitations increased the xanthophyll-cycle pool but only at high light intensities, and the same interaction between light and nutrients was observed for lutein. Predawn photochemical efficiency of PSII was not affected by either light or nutrients, although midday photochemical efficiency of PSII was lower at high light intensities. Photosynthetic light compensation point and dark respiration on an area basis decreased with light, but photosynthetic capacity on a dry mass basis and photochemical quenching were higher in low light, which translated into a higher nitrogen use efficiency in the shade. We expected Q. ilex, the species of the widest ecological distribution, to be more plastic than Q. coccifera, but differences were minor : Q. ilex exhibited a significant response to light in 13% more of the variables than Q. coccifera, but mean PI was very similar in the two species. Both species tolerated full sunlight and moderate shade, but exhibited a reduced capacity to enhance photosynthetic utilization of high irradiance. When compared with evergreen shrubs from the tropical rainforest, leaf responsiveness of the two evergreen oaks was low. We suggest that the low leaf-level responsiveness found here is part of a conservative resource use strategy, which seems to be adaptive for evergreen woody plants in Mediterranean-type ecosystems

Interspecific variation in leaf pigments and nutrients of five tree species from a subtropical forest in southern Brazil

“…In addition, as different units are increasingly used to express concentration, different study results should be interpreted with caution. For instance, sun leaves presented higher Car tot than shade leaves when the calculation was based on leaf area; however, the contrary was shown based on dry leaf weight (Valladares et al 2000).…”

Growth responses and accumulation of soluble sugars in Inga marginata Wild. (Fabaceae) subjected to flooding under contrasting light conditions

“…Valladares et al (2000b) suggest that pioneer species in the succession process exhibit greater phenotypic plasticity and ability to adapt to environments with high light than secondary species (Valladares et al, 2002). The lowest phenotypic plasticity in secondary species can also be associated with a conservative strategy in resource use (Valladares et al, 2000a). Inga marginata is classified as an early successional species in the forest succession process, indicating that plants acclimated to sun and under unfavorable water conditions are often more sensitive to the effects of soil waterlogging compared to shade plants.…”

Direct sowing of holm oak acorns: effects of acorn size and soil treatment

“…ballota) and the cork oak (Q. suber). These studies have centred fundamentally on enhancing the quality of nursery seedlings [11,47], improving planting techniques [2,37,44], and finding effective post-planting treatments [17,26,34,41,42].…”