¿ Cómo responden dos especies de Lupinus a la temperatura en un gradiente altitudinal en los Andes venezolanos? (original) (raw)
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Revista chilena de historia natural, 2008
Temperature determines plant formations and species distribution along altitudinal gradients. Plants in the tropical high Andes, through different physiological and morphological characteristics, respond to freezing night temperatures and high daytime energy inputs which occur anytime of the year. The main objective of this study was to characterize day and night temperature related responses of two Lupinus species with different altitudinal ranges (L. meridanus, 1,800-3,600 and L. eromonomos, 3,700-4,300 m of altitude). Are there differences in night low temperature resistance mechanisms between the species along the gradient? How do these species respond, in terms of optimum temperature for photosynthesis, to increasing altitude? Lupinus meridanus shows frost avoidance, in contrast to L. eromonomos, which tolerates freezing at higher altitudes. Optimum temperature for photosynthesis decreases along the gradient for both species. Maximum CO 2 assimilation rates were higher in L. meridanus, while L. eromonomos showed decreasing CO 2 assimilation rates at the higher altitude. In most cases, measured daily leaf temperature is always within the 80 % of optimum for photosynthesis. L. meridanus' upper distribution limit seems to be restricted by cold resistance mechanisms, while L. eromonomos' to a combination of both cold resistance and to CO 2 assimilation responses at higher altitudes.
Oecologia, 1998
The eects of temperature on photosynthesis of a rosette plant growing at ground level, Acaena cylindrostachya R. et P., and an herb that grows 20±50 cm above ground level, Senecio formosus H.B.K., were studied along an altitudinal gradient in the Venezuelan Andes. These species were chosen in order to determine ± in the ®eld and in the laboratory ± how dierences in leaf temperature, determined by plant form and microenvironmental conditions, aect their photosynthetic capacity. CO 2 assimilation rates (A) for both species decreased with increasing altitude. For Acaena leaves at 2900 m, A reached maximum values above 9 lmol m A2 s A1 , nearly twice as high as maximum A found at 3550 m (5.2) or at 4200 m (3.9). For Senecio leaves, maximum rates of CO 2 uptake were 7.5, 5.8 and 3.6 lmol m A2 s A1 for plants at 2900, 3550 and 4200 m, respectively. Net photosynthesis-leaf temperature relations showed differences in optimum temperature for photosynthesis (A o.t. ) for both species along the altitudinal gradient. Acaena showed similar A o.t. for the two lower altitudes, with 19.1°C at 2900 m and 19.6°C at 3550 m, while it increased to 21.7°C at 4200 m. Maximum A for this species at each altitude was similar, between 5.5 and 6.0 lmol m A2 s A1 . For the taller Senecio, A o.t. was more closely related to air temperatures and decreased from 21.7°C at 2900 m, to 19.7°C at 3550 m and 15.5°C at 4200 m. In this species, maximum A was lower with increasing altitude (from 6.0 at 2900 m to 3.5 lmol m A2 s A1 at 4200 m). High temperature compensation points for Acaena were similar at the three altitudes, c. 35°C, but varied in Senecio from 37°C at 2900 m, to 39°C at 3550 m and 28°C at 4200 m. Our results show how photosynthetic characteristics change along the altitudinal gradient for two morphologically contrasting species in¯uenced by soil or air temperatures.
The Thermal Tolerances, Distributions, and Performances of Tropical Montane Tree Species
Frontiers in Forests and Global Change, 2020
Due to global warming, many species will face greater risks of thermal stress, which can lead to changes in performance, abundance, and/or geographic distributions. In plants, high temperatures above a species-specific critical thermal maximum will permanently damage photosystem II, leading to decreased electron transport rates, photosynthetic failure, and eventual leaf and plant death. Previous studies have shown that plant thermal tolerances vary with latitude, but little is known about how they change across smaller-scale thermal gradients (i.e., with elevation) or about how these thermal tolerances relate to species' local performances and geographic distributions. In this study, we assess the maximum photosynthetic thermal tolerances (T 50) of nearly 200 tropical tree species growing in 10 forest plots distributed across a >2,500 m elevation gradient (corresponding to a 17 • C temperature gradient) in the northern Andes Mountains of Colombia. Using these data, we test the relationships between species' thermal tolerances and (1) plot elevations and temperatures, (2) species' largescale geographic distributions, and (3) changes in species' abundances through time within the plots. We found that species' T 50 do in fact decrease with plot elevation but significantly slower than the corresponding adiabatic lapse rate (−0.4 vs. −5.7 • C km −1) and that there remains a large amount of unexplained variation in the thermal tolerances of co-occurring tree species. There was only a very weak association between species' thermal tolerances and their large-scale geographic distributions and no significant relationships between species' thermal tolerances and their changes in relative abundance through time. A potential explanation for these results is that thermal tolerances are adaptations to extreme leaf temperatures that can be decoupled from regional air temperatures due to microclimatic variations and differences in the species' leaf thermoregulatory properties.
Variabilidad de la temperatura local en bosques de coníferas por efectos de la deforestación
Revista Mexicana de Ciencias Forestales, 2018
Ante lo prioritario que resulta la evaluación de los impactos de la deforestación sobre las variaciones del clima local en los bosques mexicanos, se planteó el estudio que se describe a continuación con el propósito de precisar la variabilidad de la temperatura (máxima, mínima y media) en algunas asociaciones de coníferas y áreas vecinas deforestadas en México, así como sus diferencias diurnas y nocturnas. Se ubicaron seis sitios en pinares, oyametales y en zonas sin arbolado próximas a los mismos en los estados de Tlaxcala, Coahuila, Michoacán, Jalisco y Durango, donde se colocaron Estaciones Meteorológicas Automáticas (EMA). Los resultados indican que las zonas deforestadas presentan mayor temperatura que las arboladas (de 0. 43 °C a 0. 69 °C). En el bosque de Pinus michoacana se registraron los valores más altos de temperatura, mientras que en el de Abies vejarii los menores. Entre las temperaturas diurnas y nocturnas se observó una diferencia media de 3 °C y predominó una temperatura superior en las territorios deforestados con 1. 4 %, respecto a los cubiertos por árboles. Finalmente, las áreas con Pinus durangensis tuvieron la mayor oscilación de temperatura entre el día y la noche (arriba de 4 °C) y las de Abies religiosa, la más baja, con valores inferiores a 1.5 °C.
Diurnal temperature variation in the major growth forms of an Ecuadorian páramo plant community
2001
Tropical alpine areas are characterised by a climate of warm days and cold nights, and frosts can occur on any night of the year. The extent to which six typical growth forms were decoupled from ambient air and soil temperatures was investigated in the páramo of Volcán Chiles, on the Ecuador-Colombia border. A giant stem rosette species (Espeletia pycnophylla subsp. angelensis) maintained higher than expected leaf and stem temperatures at night by means of pubescence and an insulating jacket of dead leaves. Plant height affected the temperatures experienced by the leaf rosette. Tussock plants (Calamagrostis intermedia and Cortaderia sericantha) benefited from trapped air between the leaves, which cooled slowly after dark. Sessile rosettes (Valeriana bracteata, Senecio hypsobates, and Oritrophium peruvianum), at the soilair interface, remained warmer than air at night, perhaps as a result of heat output from the ground. The surface rosettes of cushion plants (Xenophyllum humile, Oreobolus obtusangulus, and Plantago rigida) followed a similar pattern, but the internal temperature of the cushion was remarkably stable. Erect shrubs (Loricaria ilinissae, Pentacalia stuebelii, Pentacalia andicola, and Hypericum sprucei) and herbs (Jamesonia goudotii, Huperzia crassa, Perezia pungens, Castilleja fissifolia, and Lasiocephalus ovatus) mirrored ambient air temperatures by night and were warmed by direct sunlight by day. In some cases, physiological and morphological tolerance mechanisms mitigate the need for avoidance strategies. Nevertheless, avoidance of low night-time temperatures has evolved in a number of plants: shielding sensitive plant parts with dead, hardy or expendable parts; using pubescence to increase the boundary layer of still air and reduce convective heat transfer from leaf to air; and occupying the soil-air interface where low temperatures are moderated by the warmer soil.
Plant Ecology & Diversity
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Low temperature resistance in saplings and ramets of Polylepis sericea in the Venezuelan Andes
Acta Oecologica, 2009
The frequent occurrence of all year-round below zero temperatures in tropical high mountains constitutes a most stressful climatic factor that plants have to confront. Polylepis forests are found well above the continuous forest line and are distributed throughout the Andean range. These trees require particular traits to overcome functional limitations imposed on them at such altitudes. Considering seedling and sapling stages as filter phases in stressful environments, some functional aspects of the regeneration of Polylepis sericea, a species associated to rock outcrops in the Venezuelan Andes, were studied. We characterized microclimatic conditions within a forest, in a forest gap and surrounding open pá ramo and determined low temperature resistance mechanisms in seedlings, saplings and ramets. Conditions in the forest understory were more stable compared to the forest gaps and open surrounding pá ramo. Minimum temperatures close to the ground were 3.6 C lower in the open pá ramo compared to the forest understory. Maximum temperatures were 9.0 C higher in the open pá ramo. Ice nucleation and injury temperatures occurred between À6 and À8 C for both ramets and saplings, an evidence of frost avoidance to low nighttime temperatures. In this particular forest, this resistance ability is determinant in their island-like distribution in very specific less severe temperature habitats.
Facilitative interactions do not wane with warming at high elevations in the Andes
Oecologia, 2012
Positive interactions between species are known to play an important role in the structure and dynamics of alpine plant communities. The balance between negative and positive interactions is known to shift along spatial and temporal gradients, with positive effects prevailing over negative ones as the environmental stress increases. Thus, this balance is likely to be affected by climate change. We hypothesized that increases in temperature (a global warming scenario) should decrease the importance of positive interactions for the survival and growth of alpine plant species. To test this hypothesis, we selected individuals of the native grass species Hordeum comosum growing within the nurse cushion species Azorella madreporica at 3,600 m.a.s.l. in Los Andes (Chile), and performed nurse removal and seedling survival experiments under natural and warmer conditions. For warmer conditions, we used open-top chambers, which increased the temperature by 4 °C. After two growing seasons, we compared the effect of nurse removal on the survival, biomass, and photochemical efficiency of H. comosum individuals under warmer and natural conditions. Nurse removal significantly decreased the survival, biomass, and photochemical efficiency of H. comosum, demonstrating the facilitative effects of nurse cushions. Seedling survival was also enhanced by cushions, even under warmer conditions. However, warmer conditions only partially mitigated the negative effects of nurse removal, suggesting that facilitative effects of cushions do not wane under warmer conditions. Thus, facilitative interactions are vital to the performance and survival of alpine species, and these positive interactions will continue to be important in the warmer conditions of the future in high-alpine habitats.