Efecto del aumento de la temperatura en la fotosíntesis de una especie alto-andina en dos altitudes

High-alpine environments have been proposed as particularly vulnerable to global warming. The interaction of variablessuch as water deficit and temperature conditions may restrict gas exchange in high-alpine areas. Due to different abioticconstraints that occur at different elevations in the Andes of central Chile we hypothesize that the temperature increases willpositively affect the photosynthesis of the high-Andean plant Phacelia secunda at high elevation but it will be negativelyaffected by warming at lower elevations. In this study we evaluated the effect of increased environmental temperature onthe gas exchange of P. secunda at two contrasting elevations: 2900 m and 3600 m a.s.l. At each elevation we exposed sixindividuals of P. secunda to a passive warming system with “Open Top Chamber” (OTC) that increased air temperature onca. 3ºC. Other six individuals we selected in open areas and maintained as control on each elevation. At both elevations,on each selected individual (i.e. within and outside OTCs) we measured gas exchange and xylem water potential. At bothelevations air temperature was on average 3.5°C higher inside the OTC. In contrast, OTC reduced 28% the soil and xylemwater potential only at 2900 m. The increased temperature inside the OTC reduced 40.7% gas exchange rates at 2900 m,but increased it 24.4% at 3600 m. These differential effects of warming on photosynthetic rates were accompanied bychanges in stomatal conductance. This suggests that the effects of global warming on the photosynthesis of P. secunda attwo contrasting altitudes are related with the concomitant changes on drought at each elevation.Se ha propuesto que los ambientes de alta montaña son especialmente vulnerables al calentamiento global. La interacciónde variables como déficit hídrico y las condiciones de temperatura ambiental puede restringir el intercambio gaseosoen zonas de alta-montaña. Debido a las distintas limitaciones abióticas que se encuentran en un gradiente altitudinal, sepropone que el aumento de la temperatura afectará positivamente la fotosíntesis de la planta alto-andina Phacelia secundaen elevadas altitudes y negativamente a las plantas de bajas altitudes. En el presente estudio se evaluó el efecto del aumentode la temperatura ambiental sobre el intercambio gaseoso de P. secunda en dos altitudes: 2900 m y 3600 m. En cada altitudse expusieron seis individuos de P. secunda a un sistema de calentamiento pasivo denominado “Open Top Chamber” (OTC)que aumenta la temperatura del aire en ca. 3ºC. Adicionalmente, en cada altitud se seleccionaron otros seis individuos enespacios abiertos para utilizarlos como control y que se encontraban a 2 m de la OTC más cercana. En cada individuo semidió el intercambio gaseoso y el potencial hídrico xilemático. La temperatura ambiental fue en promedio 3,5°C mayordentro de las OTC en ambas altitudes. En contraste, el potencial hídrico del suelo y de las plantas se redujo un 28% alinterior de las OTC, pero sólo a 2900 m. En esta altitud, las tasas de fotosíntesis al interior de las OTC se redujeronun 40,7%, mientras que a 3600 m las tasas aumentaron un 24,4%. Los efectos diferenciales en las tasas de fotosíntesisdebido a la temperatura fueron acompañados con cambios en la conductancia estomática. Esto sugiere que los efectosdel calentamiento global sobre la fotosíntesis de P. secunda son contrastantes entre ambas altitudes debido a los efectossecundarios que éste tiene sobre la disponibilidad hídrica en cada altitud

Efecto del aumento de la temperatura en la fotosíntesis de una especie alto-andina en dos altitudes Effect of the increase in temperature in the photosynthesis of a high-andean species at two elevations

Se ha propuesto que los ambientes de alta montaña son especialmente vulnerables al calentamiento global. La interacción de variables como déficit hídrico y las condiciones de temperatura ambiental puede restringir el intercambio gaseoso en zonas de alta-montaña. Debido a las distintas limitaciones abióticas que se encuentran en un gradiente altitudinal, se propone que el aumento de la temperatura afectará positivamente la fotosíntesis de la planta alto-andina Phacelia secunda en elevadas altitudes y negativamente a las plantas de bajas altitudes. En el presente estudio se evaluó el efecto del aumento de la temperatura ambiental sobre el intercambio gaseoso de P. secunda en dos altitudes: 2900 m y 3600 m. En cada altitud se expusieron seis individuos de P. secunda a un sistema de calentamiento pasivo denominado "Open Top Chamber" (OTC) que aumenta la temperatura del aire en ca. 3°C. Adicionalmente, en cada altitud se seleccionaron otros seis individuos en espacios abiertos para utilizarlos como control y que se encontraban a 2 m de la OTC más cercana. En cada individuo se midió el intercambio gaseoso y el potencial hídrico xilemático. La temperatura ambiental fue en promedio 3,5°C mayor dentro de las OTC en ambas altitudes. En contraste, el potencial hídrico del suelo y de las plantas se redujo un 28% al interior de las OTC, pero sólo a 2900 m. En esta altitud, las tasas de fotosíntesis al interior de las OTC se redujeron un 40,7%, mientras que a 3600 m las tasas aumentaron un 24,4%. Los efectos diferenciales en las tasas de fotosíntesis debido a la temperatura fueron acompañados con cambios en la conductancia estomática. Esto sugiere que los efectos del calentamiento global sobre la fotosíntesis de P. secunda son contrastantes entre ambas altitudes debido a los efectos secundarios que éste tiene sobre la disponibilidad hídrica en cada altitud.High-alpine environments have been proposed as particularly vulnerable to global warming. The interaction of variables such as water deficit and temperature conditions may restrict gas exchange in high-alpine areas. Due to different abiotic constraints that occur at different elevations in the Andes of central Chile we hypothesize that the temperature increases will positively affect the photosynthesis of the high-Andean plant Phacelia secunda at high elevation but it will be negatively affected by warming at lower elevations. In this study we evaluated the effect of increased environmental temperature on the gas exchange of P. secunda at two contrasting elevations: 2900 m and 3600 m a.s.l. At each elevation we exposed six individuals of P. secunda to a passive warming system with "Open Top Chamber" (OTC) that increased air temperature on ca. 3°C. Other six individuals we selected in open areas and maintained as control on each elevation. At both elevations, on each selected individual (i.e. within and outside OTCs) we measured gas exchange and xylem water potential. At both elevations air temperature was on average 3.5°C higher inside the OTC. In contrast, OTC reduced 28% the soil and xylem water potential only at 2900 m. The increased temperature inside the OTC reduced 40.7% gas exchange rates at 2900 m, but increased it 24.4% at 3600 m. These differential effects of warming on photosynthetic rates were accompanied by changes in stomatal conductance. This suggests that the effects of global warming on the photosynthesis of P. secunda at two contrasting altitudes are related with the concomitant changes on drought at each elevation

Does the life‑history strategy determine the freezing resistance of flowers and leaves of alpine herbaceous species?

In high-mountain habitats, summer frost events can have negative consequences for plant fitness. Despite this, most studies have evaluated the consequences of frosts for vegetative structures of perennial plants, and neither for leaves nor for flowers of annual plants. We hypothesize that the degree of freezing resistance of flowers and leaves of a species depends on its life-history strategy (LHS), and is probably the consequence of a trade-off between growth/reproduction and the cost of the freezing resistance. Specifically, flowers and leaves of short-lived annual species should be less freezing resistant than those of perennial plant species. We compared the freezing resistance of flowers and leaves of 10 annual and 12 perennial plant species from the Andes of central Chile using the electrolyte leakage method. Temperature damage for 50% tissue (LT50) of annual species was - 9.6 degrees C in flowers and - 11.9 degrees C in leaves. In perennial species, LT50 was similar in flowers (- 12.3 degrees C) and leaves (- 12.5 degrees C). Despite that, these differences were not significant (except the flowers of annual species), we found remarkable differences between LHS when freezing resistance was analyzed species by species. Like this, 58% and 83% of perennial species resist temperatures <= - 10 degrees C in their flowers and leaves, respectively, compared with only 30% and 40% of annual species. Additionally, in most of the species, the freezing resistance of leaves was greater than that of flowers, with this proportion being greater in annual (58%) than in perennial species (43%). Thus, we concluded that the degree of freezing resistance depends on the LHS, such that annual species, which are less freezing resistant than perennial species, have an infrequent occurrence and a distribution restricted to low elevation in high-mountain habitats.National Commission for Science and Technology (CONICYT) through the National Fund for Scientific and Technological Development FONDECYT 11150710 FONDECYT 1181688 CONICYT 2115106

Annual and perennial high‑Andes species have a contrasting freezing‑resistance mechanism to cope with summer frosts

In high-mountain habitats, summer frosts have negative consequences for plant fitness, therefore high-mountain plants have developed mechanisms of avoidance and tolerance to cope with freezing temperatures. Various hypotheses have been proposed to explain the prevalence of one freezing-resistance mechanism over another, focusing on thermal conditions without a consensus. We hypothesize that the prevalence of a freezing-resistance mechanism depends on the life-history strategy of the species, and is probably the consequence of a trade-off between growth/reproduction and the cost of the mechanism. Specifically, short-lived annual species should be freezing avoidant, whereas perennial long-lived species should be freezing tolerant. We used thermal analysis to determine the mechanism of freezing resistance of leaves and flowers for 10 annual and 14 perennial herb species from an alpine ecosystem in the Central Chilean Andes. We found that 70% of the annual species, their flowers and leaves were freezing avoidant, indicating that avoidance was their predominant freezing-resistance mechanism. In the case of perennial species, both mechanisms were almost equally represented in flowers and leaves. Overall, our results showed that a species freezing-resistance mechanism depends on its life-history strategy, and that leaves and flowers of single species exhibit the same freezing resistance mechanism, suggesting a common whole plant strategy. Further, freezing resistance strategies were not found to be mutually exclusive. In some cases, a specific combination of phenological, structural, and functional strategies may determine how freezing resistant vegetative and reproductive organs are to freezing during the growing season.National Commission for Science and Technology (CONICYT) through the National Fund for Scientific and Technological Development FONDECYT 11150710 Doctoral Scholarship CONICYT 2115106

Photosynthetic Light Responses May Explain Vertical Distribution of Hymenophyllaceae Species in a Temperate Rainforest of Southern Chile.

Some epiphytic Hymenophyllaceae are restricted to lower parts of the host ( 1000 μmol photons m(-2) s(-1)). Our aim was to study the photosynthetic light responses of two Hymenophyllaceae species in relation to their contrasting distribution. We determined light tolerance of Hymenoglossum cruentum and Hymenophyllum dentatum by measuring gas exchange, PSI and PSII light energy partitioning, NPQ components, and pigment contents. H. dentatum showed lower maximum photosynthesis rates (A max) than H. cruentum, but the former species kept its net rates (An) near Amax across a wide light range. In contrast, in the latter one, An declined at PPFDs > 60 μmol photons m(-2) s(-1). H. cruentum, the shadiest plant, showed higher chlorophyll contents than H. dentatum. Differences in energy partitioning at PSI and PSII were consistent with gas exchange results. H. dentatum exhibited a higher light compensation point of the partitioning of absorbed energy between photochemical Y(PSII) and non-photochemical Y(NPQ) processes. Hence, both species allocated energy mainly toward photochemistry instead of heat dissipation at their light saturation points. Above saturation, H. cruentum had higher heat dissipation than H. dentatum. PSI yield (YPSI) remained higher in H. dentatum than H. cruentum in a wider light range. In both species, the main cause of heat dissipation at PSI was a donor side limitation. An early dynamic photo-inhibition of PSII may have caused an over reduction of the Qa+ pool decreasing the efficiency of electron donation to PSI. In H. dentatum, a slight increase in heat dissipation due to acceptor side limitation of PSI was observed above 300 μmol photons m(-2)s(-1). Differences in photosynthetic responses to light suggest that light tolerance and species plasticity could explain their contrasting vertical distribution

Light response curves of PSII (ETR_II) and PSI (ETR_I) electron transport rates in fronds of <i>H</i>. <i>cruentum</i> and <i>H</i>. <i>dentatum</i>.

<p>Detached fronds were fully hydrated overnight and then dark adapted during 30 min. PPFD response curves were programmed using the scripting facility of the Dual-PAM 100 control software. Each frond was exposed to successively increasing actinic light levels (0 to 436 μmol photons m^-2 s^-1), with 3 min equilibration time at each light level before the application of saturating pulses. Values correspond to the mean ± SE (<i>n</i> = 4).</p

Light availability across a vertical gradient in the natural habitats of Hymenophyllaceae species in the Katalapi Park.

<p>Frequency of observed photosynthetic photon flux density (PPFD, μmol photons m^-2 s^-1) measured at three trunk heights: <1, 4.5 and 9 m using data collected by two different data-loggers from 01 October 2010 until 01 February 2011.</p

Changes in partitioning of absorbed excitation energy with increasing PPFD.

<p>This was measured at PSI (a, b) and PSII (c, d) level in fronds of <i>Hymenoglossum cruentum</i> and <i>Hymenophyllum dentatum</i>. A dashed line indicates the portion of the curve where comparisons between species were made. These points correspond to the light saturation points of <i>H</i>. <i>cruentum</i> at 24.6 μmol photons m^-2 s^-1 (Is_{<i>H</i>.<i>cru</i>}) and of <i>H</i>. <i>dentatum</i> at 40.5 μmol photons m^-2 s^-1 (Is_{<i>H</i>.<i>den</i>}), both obtained from gas exchange measurements. Values are shown as mean ± SE (<i>n</i> = 4).</p