No abstract

Great variation in shape and size between primary (juvenile) and secondary (adult) needles, so-called leaf-heteroblasty, occurs in several Pinus species. Most of them loss primary needles during the juvenile-to-adult transition of the tree. An exception to this is Pinus canariensis (a Canary Islands endemism) in which basal resprouting twigs of adult trees frequently wear both primary and secondary needles. Taking advantage of this extraordinary study-case-species, we conducted an exhaustive comparison of both needle types through quantitative analyses of needle anatomy, photochemical performance, gas exchange, and resistance to extreme dehydration and to extreme needle temperature. We hypothesized that primary needles would show lower investment to leaf structure but higher photosynthetical efficiency. Primary needles had less stomatal density and thicker and less wettable cuticles. In cross section, primary needles showed smaller structural fraction (e.g., percent of hypodermis, endodermis and vascular tissue) and higher fraction of photosynthetic parenchyma. Significant differences between primary and secondary needles were not found in net carbon assimilation not in their leaf mass area values. Interestingly, secondary needles showed higher electron transport rate, and they were additionally much more efficient in retaining water under severe and controlled desiccant conditions. When subjected to extreme temperatures (−10° to +50 °C), primary needles recovered better their photochemical efficiency than secondary needles, after +46° and +48 °C heat-shock treatments. Our results indicate that both needle types broaden the diversity of physiological responses against environmental constrains in basal twigs of adult P. canariensis trees. Considering that this is a fire-resistant and resprouting species, this advantage could be particularly useful after a drastic environmental change such a fire or a gap opening in the forest.

Populations inhabiting the periphery of a species’ distribution suffer the immediate pressure of the environmental changes. Studying their physiology under stressful conditions is essential in the context of climate change. We characterized two morphotypes with measurements of length, thickness and width of the thallus of the macroalga Fucus guiryi in two localities (north and south) in Tenerife (Canary Islands), the southern limit of distribution of the species. We hypothesized that the individuals from the north locality, especially the large morphotype, would be more vulnerable to desiccation and high temperatures than those from the south. Tolerance to desiccation was tested through two long desiccation experiments and by comparing the vegetative and reproductive blades. Tolerance to high temperatures was tested by keeping the individuals in seawater (26–32 °C) for 24 h. The recovery of physiological functions after the stressful conditions was estimated through maximal photochemical efficiency of PSII. Results indicate that both of the two morphometrically differentiated morphotypes were tolerant to prolonged desiccation; however, the small one was more affected, particularly in the northern locality. The reproductive blades were hardly affected, indicating greater tolerance to desiccation than the vegetative blades. Fucus guiryi showed tolerance to high temperatures (32 °C) suggesting plasticity to future warming scenarios.

The brown macroalgae in the order Fucales include foundation species on rocky habitats of temperate regions. This work focused on Fucus guiryi, a recently described species segregated from F. spiralis in a molecular basis. It inhabits the upper intertidal zone from the eastern North Atlantic to the subtropical Canary Islands, where is considered its southern limit. We examined morphology and anatomy of vegetative and reproductive structures of F. guiryi from the Canary Islands. Several distinctive characteristics in habit existed between F. guiryi and other species of the genus distributed northwards, such as length and width of stipe and branches, number of branches, and morphology and number of receptacles. Anatomical features reported here for the first time exhibited subtle differences with temperate F. vesiculosus, F. spiralis and F. serratus. The morphology and arrangement of medulla, cortex and meristoderm were also distinctive for F. guiryi. Mucilage in cellular interstitial spaces constitutes good evidence that explains the presence of F. guiryi at its warmest distribution limit in the Canary Islands.