Phenolics and condensed tannins in relation to altitude in neotropical Pteridium spp

Abstract

Two species of neotropical bracken, Pteridium caudatum (L.) Maxon (P.c.) and P. arachnoideum (Kaulf.) (P.a.), thrive dominantly in habitats extending from near the sea level to the Andean alpine zone around 3000 m altitude. The scope of sources of stress associated with elevation has three main components: plant competition for resources, activity of herbivores/pathogens, and climate. The contribution of each component varies greatly from place to place and bracken must respond with considerable physiological/genetic plasticity to maintain its dominant status in all these habitats. Phenolic compounds have a number of properties for plant adaptation to evolutionary selective forces of biotic and climatic nature, in particular with reference to their protective role against excessive solar radiation. We have examined the second of these properties by studying the dynamics of low (LMP) and high (HMP) molecular weight phenolics in neotropical bracken ferns in two groups of field experiments: (1) their variation during the phenologic development of blades in sympatric populations of both bracken species to examine the synthesis and allocation of these materials under similar conditions of competition, predation and solar UV-B radiation; (2) the contents of LMP and HMP in six bracken populations of P.c. along its typical altitudinal range [1180-2140 m above sea level (asl)] and six additional populations of P.a. (1880-3190 m asl), which grows at higher elevations in the western Andes of Venezuela, to investigate the phenolics' response to the ecological gradients associated with elevation in these plants. From series (1), we recorded the progressive accumulation of both types of phenolics with frond expansion, and hence increased surface of lamina exposed to sunlight, in P.c. and P.a. However, phenolics in mature blades of P.a. were 1.6 (LMP) and 3.26 (HMP) greater in amount than in P.c. From series (2), synthesis and accumulation of LMP was found to be à Corresponding author. independent of altitude, except for the subalpine population of P.a. at 3190 m asl, where a 167% increment of the average contents was recorded. By contrast, the levels of HMP correlated positively with elevation in both bracken species. The independent response of both types of phenolics to solar radiation may be interpreted as either more effective and metabolically cost-effective protection of HMP against UV-B light than LMP or differential light activation of key steps in the biosynthesis of HMP and LMP in bracken. #

Phenolics and condensed tannins of high altitude Pteridium arachnoideum in relation to sunlight exposure, elevation, and rain regime

“…We had observed earlier that a direct correlation exists between total phenolics accumulation in aerial parts of P. arachnoideum and frond ontogeny (Alonso-Amelot et al, 2004). Although this might imply a reduced chemical defense at the fragile young stage of the frond, other compensatory mechanisms are present in the growing blade to protect it.…”

“…Volatile solvents were removed from each fraction and their volume was corrected to 100.0 ml. Aliquots (1 ml) were destined for analysis using the reported method (Alonso-Amelot et al, 2004) and employing Sephadex LH-20-purified quebracho (Schinopsis quebracho-colorado (Schltdl.) F.A.…”

“…responded to altitude during the rainy season by increasing its content of high molecular weight phenolics (HMP) only at elevations greater than 2600 m above sea level (Alonso-Amelot et al, 2004). In a continued effort to understand the various biological and chemical traits that make Pteridium ferns among the most dominant plants in the world (Alonso-Amelot et al, 2001;Alonso-Amelot, 2002), we pursued further dynamics of their LMPeHMP load in order to evaluate the effects of season (rain regime and cloudiness), altitude in exposed and self shaded pinnae, and the position of each pinnae relative to the axis of the blade (rachis) in dense high altitude thickets of tropical P. arachnoideum, under field conditions.…”

Environmental trends in the variation of biologically active phenolic compounds in Labrador tea, Rhododendron groenlandicum, from northern Quebec, Canada

“…Positive relationships with altitude were observed in Andean alpine species of Dennstaedtiaceae, Pteridium caudatum (L.) Maxon and Pteridium arachnoideum (Kaulf.) Maxon (Alonso-Amelot et al 2004, as well as a species of Jungermanniaceae, Jungermannia exsertifolia Steph. subsp.…”

Herbivory on bracken (Pteridium spp.) by Bolax palliata Burmeister (Coleoptera: Scarabaeidae), a poliphagous beetle of the Venezuelan Andes

“…A recent comparative analysis of the chemistry of the two bracken species (Alonso-Amelot et al 2004) revealed important differences in content of condensed tannins in the fronds. Concentration in P. arachnoideum is nearly three times that of P. caudatum, suggesting a possible phytochemical base for the preference of B. palliata for the fi rst of the two species.…”