Desacople térmico y resistencia al calor en plantas altoandinas con distintas formas de crecimiento de Nevados de Chillán
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Date
2024
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Universidad de Concepción
Abstract
Las plantas de alta montaña pueden experimentar elevadas temperaturas durante el día, es por esto que cuentan con estrategias que les permiten atenuar la exposición y/o los efectos de las altas temperaturas. Una de ellas es la forma de crecimiento, la cual combina la estatura y disposición de los órganos vegetativos y reproductivos resultando en una estrategia de resistencia térmica integrada. Las formas de crecimiento que predominan en la alta montaña son los arbustos achaparrados, hierbas en rosetas, plantas en cojín y graminoides. Aunque estas formas de crecimiento son en general de baja estatura (<100 cm), hay variaciones entre ellas. Por ejemplo, en las hierbas en roseta las hojas están muy cercanas al suelo, exponiéndolas a mayores fluctuaciones térmicas entre el día y la noche. Por ello, sus hojas podrían registrar temperaturas muy distintas a la del aire circundante, fenómeno denominado desacople térmico (TD). En contraste, las hojas de los arbustos tienden a disponerse más alejadas del suelo, presentando temperaturas más similares a la del aire, lo que resultaría en un menor TD. Aunque las altas temperaturas se han considerado menos frecuentes en la alta montaña, sí lo son y las plantas de estos sistemas son capaces de resistir temperaturas superiores a los 45°C. Las altas temperaturas son más frecuentes en sustratos oscuros y en las cercanías del suelo, producto de la radiación incidente, alcanzando temperaturas sobre 60ºC. Pese a que algunos estudios han demostrado que algunas especies de alta montaña poseen una elevada resistencia al calor, se espera que las altas temperaturas excedan los límites de tolerancia térmica de muchas especies durante las temporadas de crecimiento poniendo en riesgo su supervivencia. El complejo volcánico Nevados de Chillán (Ñuble) alberga una gran cantidad de especies en la zona altoandina, las cuales presentan distintas formas de crecimiento, dominando las formas arbustivas y rosetas herbáceas. Además, en este lugar se han registrado temperaturas máximas del aire sobre 40°C durante la temporada de crecimiento. Es por esto, que esta zona es un lugar propicio para estudiar la capacidad de desacople térmico y la resistencia al calor en especies con distintas formas de crecimiento. En esta propuesta de investigación caracterizamos la respuesta al calor en especies de plantas con distintas formas de crecimiento en Nevados de Chillán. Siendo más específicos buscamos: 1) Caracterizar el desacople térmico en plantas con distinta forma de crecimiento y 2) Comparar la resistencia al calor entre rosetas y arbustos y su relación con el desacople térmico. Para ello, seleccionamos 3 especies arbustivas y 3 especies en roseta, conocidas por ser abundantes en la zona altoandina. Por cada especie se seleccionaron 7 individuos, los cuales fueron fotografiados con una cámara termográfica abarcando toda la planta. En paralelo registramos la temperatura del aire circundante, estimando la diferencia entre la temperatura de la planta (PT) y la del aire (AT) para determinar el desacople térmico (TD). Las mediciones se hicieron durante el medio día solar, cuando se registran las temperaturas más cálidas. Para medir la resistencia al calor se colectaron 10 hojas de 7 individuos por cada especie de estudio. Estas hojas fueron expuestas a 5 temperaturas diferentes (25°C, 35°C, 45°C, 55°C, 60°C) dentro de baños termorregulados. Además, se consideró un grupo control que se mantuvo a temperatura ambiente. Una vez terminadas las exposiciones a las distintas temperaturas, evaluamos la temperatura que produjo un 50% (LT50) en las hojas, utilizando como criterio de daño la fotoinactivación. Las imágenes termográficas evidenciaron que todas las especies experimentaron diferentes temperaturas en relación con la temperatura del aire. Las especies Viola aizoon(roseta) y Senecio pachyphyllos(arbusto) exhibieron los mayores grados de TD, con temperaturas de sus hojas siempre inferiores a la temperatura del aire (TD = -6°C). Por el contrario, la especie arbustiva Berberis empetrifolia se mostró temperaturas foliares similares a la temperatura del aire. Al contrario de lo esperado, el TD fue similar entre arbustos y rosetas. Las especies estudiadas difieren en su grado de resistencia al calor (TL50). Por otro lado, estas diferencias en el grado de resistencia al calor (TL50) se mantuvieron al agrupar las especies en arbustos y rosetas, con los arbustos mostrando una variabilidad significativa en TL50, que abarcó desde los 36 hasta los 54°C. En contraste, las rosetas presentaron valores de TL50 entre los 47 y 48°C. B. empetrifolia fue la especie con mayor TL50, con un promedio de 54°C, mientras que S. pachyphyllos mostró los menores TL50 con 35°C. Al contrario de lo propuesto, No se encontró una relación clara entre el desacople térmico y la resistencia al calor entre las formas de crecimiento. Nuestros resultados revelan patrones inesperados en el desacople térmico, destacando la importancia de los mecanismos de termorregulación (e.g. enfriamiento por transpiración) y sugieren la integración de otros elementos para futuras investigaciones sobre la resistencia térmica en plantas de alta montaña.
The plants of high-mountain can experience heat temperatures during the day, which is why they have strategies that allow them to mitigate the exposure and/or effects of high temperatures. One of these strategies is the growth form, which combines the stature and arrangement of vegetative and reproductive organs, resulting in an integrated thermal resistance strategy. The predominant growth forms in high mountains include low shrubs, rosette herbs, cushion plants, and graminoids. Although these growth forms are generally of low stature (<100 cm), there are variations among them. For instance, in rosette herbs, the leaves are very close to the ground, exposing them to greater thermal fluctuations between day and night. Therefore, their leaves may register temperatures very different from the surrounding air, a phenomenon known as thermal decoupling (TD). In contrast, the leaves of shrubs tend to be more distant from the ground, showing temperatures more similar to the air, resulting in a lower TD. Even though high temperatures have been considered less frequent in high mountains, they do occur, and plants in these systems can withstand temperatures exceeding 45°C. High temperatures are more common in dark substrates and near the ground, a result of incident radiation, reaching temperatures above 60°C. Although some studies have demonstrated that certain high-mountain species possess high heat resistance, it is expected that high temperatures will exceed the thermal tolerance limits of many species during the growing seasons, putting their survival at risk. The Nevados de Chillán volcanic complex (Ñuble) harbors many species in the high Andean zone, which exhibit different growth forms, with shrubby and rosette herbaceous forms dominating. Additionally, maximum air temperatures above 40°C have been recorded in this area during the growing season. Therefore, this area is a suitable location to study thermal decoupling capacity and heat resistance in species with different growth forms. In this research proposal, we characterize the heat response in plant species with different growth forms in Nevados de Chillán. More specifically, we aim to 1) Characterize thermal decoupling in plants with different growth forms, and 2) Compare heat resistance between rosettes and shrubs and its relationship with thermal decoupling. For this purpose, we selected 3 shrub species and 3 rosette species known to be abundant in the high Andean zone. For each species, 7 individuals were selected and photographed with a thermal camera covering the entire plant. Simultaneously, we recorded the temperature of the surrounding air, estimating the difference between the plant temperature (PT) and the air temperature (AT) to determine thermal decoupling (TD). Measurements were taken during solar noon, when the warmest temperatures are recorded. To measure heat resistance, 10 leaves from 7 individuals per species were collected. These leaves were exposed to 5 different temperatures (25°C, 35°C, 45°C, 55°C, 60°C) within thermo-regulated baths. Additionally, a control group was kept at room temperature. After the exposures to different temperatures were completed, we assessed the temperature that caused 50% damage (LT50) in the leaves, using photoinactivation as the damage criterion. Thermographic images revealed that all species experienced different temperatures in relation to the air temperature. The species Viola aizoon (rosette) and Senecio pachyphyllos (shrub) exhibited the highest degrees of TD, with leaf temperatures always lower than the air temperature (TD = -6°C). In contrast to expectations, TD was similar between shrubs and rosettes. The studied species differed in their degree of heat resistance (LT50). Furthermore, these differences in heat resistance (LT50) were maintained when grouping the species into shrubs and rosettes, with shrubs showing significant variability in LT50, ranging from 36 to 54°C. In contrast, rosettes presented LT50 values between 47 and 48°C. B. empetrifolia was the species with the highest LT50, with an average of 54°C, while S. pachyphyllos showed the lowest LT50 at 35°C. Contrary to the proposed hypothesis, no clear relationship was found between thermal decoupling and heat resistance among growth forms. Our results reveal unexpected patterns in thermal decoupling, highlighting the importance of thermoregulation mechanisms (e.g. transpiration cooling) and suggest the integration of other elements for future research on thermal resistance in high-mountain plants.
The plants of high-mountain can experience heat temperatures during the day, which is why they have strategies that allow them to mitigate the exposure and/or effects of high temperatures. One of these strategies is the growth form, which combines the stature and arrangement of vegetative and reproductive organs, resulting in an integrated thermal resistance strategy. The predominant growth forms in high mountains include low shrubs, rosette herbs, cushion plants, and graminoids. Although these growth forms are generally of low stature (<100 cm), there are variations among them. For instance, in rosette herbs, the leaves are very close to the ground, exposing them to greater thermal fluctuations between day and night. Therefore, their leaves may register temperatures very different from the surrounding air, a phenomenon known as thermal decoupling (TD). In contrast, the leaves of shrubs tend to be more distant from the ground, showing temperatures more similar to the air, resulting in a lower TD. Even though high temperatures have been considered less frequent in high mountains, they do occur, and plants in these systems can withstand temperatures exceeding 45°C. High temperatures are more common in dark substrates and near the ground, a result of incident radiation, reaching temperatures above 60°C. Although some studies have demonstrated that certain high-mountain species possess high heat resistance, it is expected that high temperatures will exceed the thermal tolerance limits of many species during the growing seasons, putting their survival at risk. The Nevados de Chillán volcanic complex (Ñuble) harbors many species in the high Andean zone, which exhibit different growth forms, with shrubby and rosette herbaceous forms dominating. Additionally, maximum air temperatures above 40°C have been recorded in this area during the growing season. Therefore, this area is a suitable location to study thermal decoupling capacity and heat resistance in species with different growth forms. In this research proposal, we characterize the heat response in plant species with different growth forms in Nevados de Chillán. More specifically, we aim to 1) Characterize thermal decoupling in plants with different growth forms, and 2) Compare heat resistance between rosettes and shrubs and its relationship with thermal decoupling. For this purpose, we selected 3 shrub species and 3 rosette species known to be abundant in the high Andean zone. For each species, 7 individuals were selected and photographed with a thermal camera covering the entire plant. Simultaneously, we recorded the temperature of the surrounding air, estimating the difference between the plant temperature (PT) and the air temperature (AT) to determine thermal decoupling (TD). Measurements were taken during solar noon, when the warmest temperatures are recorded. To measure heat resistance, 10 leaves from 7 individuals per species were collected. These leaves were exposed to 5 different temperatures (25°C, 35°C, 45°C, 55°C, 60°C) within thermo-regulated baths. Additionally, a control group was kept at room temperature. After the exposures to different temperatures were completed, we assessed the temperature that caused 50% damage (LT50) in the leaves, using photoinactivation as the damage criterion. Thermographic images revealed that all species experienced different temperatures in relation to the air temperature. The species Viola aizoon (rosette) and Senecio pachyphyllos (shrub) exhibited the highest degrees of TD, with leaf temperatures always lower than the air temperature (TD = -6°C). In contrast to expectations, TD was similar between shrubs and rosettes. The studied species differed in their degree of heat resistance (LT50). Furthermore, these differences in heat resistance (LT50) were maintained when grouping the species into shrubs and rosettes, with shrubs showing significant variability in LT50, ranging from 36 to 54°C. In contrast, rosettes presented LT50 values between 47 and 48°C. B. empetrifolia was the species with the highest LT50, with an average of 54°C, while S. pachyphyllos showed the lowest LT50 at 35°C. Contrary to the proposed hypothesis, no clear relationship was found between thermal decoupling and heat resistance among growth forms. Our results reveal unexpected patterns in thermal decoupling, highlighting the importance of thermoregulation mechanisms (e.g. transpiration cooling) and suggest the integration of other elements for future research on thermal resistance in high-mountain plants.
Description
Seminario de título presentado para optar al título profesional de Biólogo/a
Keywords
Plantas, Crecimiento (Plantas), Montañas - ecología