Application of heat stress in situ demonstrates a protective role of irradiation on photosynthetic performance in alpine plants

Abstract

The impact of sublethal heat on photosynthetic performance, photosynthetic pigments and free radical scavenging activity was examined in three high mountain species, Rhododendron ferrugineum, Senecio incanus and Ranunculus glacialis using controlled in situ applications of heat stress, both in darkness and under natural solar irradiation. Heat treatments applied in the dark reversibly reduced photosynthetic performance and the maximum quantum efficiency of photosystem II (Fv/Fm), which remained impeded for several days when plants were exposed to natural light conditions subsequently to the heat treatment. In contrast, plants exposed to heat stress under natural irradiation were able to tolerate and recover from heat stress more readily. The critical temperature threshold for chlorophyll fluorescence was higher under illumination (Tc′) than in the dark (Tc). Heat stress caused a significant de-epoxidation of the xanthophyll cycle pigments both in the light and in the dark conditions. Total free radical scavenging activity was highest when heat stress was applied in the dark. This study demonstrates that, in the European Alps, heat waves can temporarily have a negative impact on photosynthesis and, importantly, that results obtained from experiments performed in darkness and/or on detached plant material may not reliably predict the impact of heat stress under field conditions.

Metabolic and physiological responses of Mediterranean high‐mountain and alpine plants to combined abiotic stresses

“…ferrugineum . Nonetheless, complete F v / F m recovery was observed for all species by the end of the warming treatment (Buchner et al ). These results are in agreement with the one reported by Shi et al () and allow inferring that the increase in Chl content because under warmer climate could translate into an enhancement of photosynthetic activity, plant growth and carbon assimilation in alpine species if there is no water limitation.…”

“…This indicates a higher adaptation capacity of perennial herbs to shifts in temperature, in comparison to non‐perennial species (Shi et al ). Furthermore, Buchner et al () have reported the significant effect of rising temperatures on photosynthetic parameters in Senecio incanus, Ranunculus glacialis and Rhododendron ferrugineum . The F v / F m showed no significant decrease under high temperature in the two species, although a considerable reduction of the values for this parameter was observed in Rh.…”

“…Studies in alpine plants have depicted a highly efficient ROS scavenging capacity under combined drought and heat stress, suggesting their great adaptive response to warming. The significant increases in de‐epoxidation of the xanthophyll cycle in alpine species under heat stress indicate its important role as a photoprotection strategy, enhancing the stability of the photosynthetic apparatus under elevated temperatures through NPQ and the stabilization of the thylakoid membrane and PSII reaction centers (Buchner et al ).…”

Solar irradiation levels during simulated long‐ and short‐term heat waves significantly influence heat survival, pigment and ascorbate composition, and free radical scavenging activity in alpine Vaccinium gaultherioides

“…A purpose‐built ‘heat tolerance testing system’ (HTTS) was recently developed that allows for the measurement of responses in intact plants in situ under controlled conditions in the field, without removing plants from their natural habitat (Buchner et al ). Using the HTTS, it was shown that light during short‐term heat exposure may have a positive effect on heat tolerance and photosynthetic performance (Buchner et al , ).…”

Exogenous application of brassinolide can alter morphological and physiological traits of Leymus chinensis (Trin.) Tzvelev under room and high temperatures

“…High temperature is an important abiotic stress which is becoming most limiting factor for normal plant growth and development, especially under climate change scenario which is projected to the average temperature be increased 1.1 °C in the last 50 yr (Ding et al, 2007). High temperature imparts its injurious effects on photosynthesis (Buchner et al, 2015), disrupts the overall balance of the metabolic processes, leading to the over production of reactive oxygen species (ROS) which ultimately causes oxidative damage to the plant cells (Larkindale et al, 2005). The enhanced synthesis of ROS causes lipid peroxidation of biological membranes, denaturation of proteins and damage to the nucleic acid eventually disturbing homeostasis (Mittler, 2002).…”