Thermal Acclimation of Foliar Carbon Metabolism in Pinus taiwanensis Along an Elevational Gradient

Climate change could negatively alter plant ecosystems if rising temperatures exceed optimal conditions for obtaining carbon. The acclimation of plants to higher temperatures could mitigate this effect, but the potential of subtropical forests to acclimate still requires elucidation. We used space-for-time substitution to determine the photosynthetic and respiratory-temperature response curves, optimal temperature of photosynthesis (Topt), photosynthetic rate at Topt, temperature sensitivity (Q10), and the rate of respiration at a standard temperature of 25°C (R25) for Pinus taiwanensis at five elevations (1200, 1400, 1600, 1800, and 2000 m) in two seasons (summer and winter) in the Wuyi Mountains in China. The response of photosynthesis in P. taiwanensis leaves to temperature at the five elevations followed parabolic curves, and the response of respiration to temperature increased with temperature. Topt was higher in summer than winter at each elevation and decreased significantly with increasing elevation. Q10 decreased significantly with increasing elevation in summer but not winter. These results showed a strong thermal acclimation of foliar photosynthesis and respiration to current temperatures across elevations and seasons, and that R25 increased significantly with elevation and were higher in winter than summer at each elevation indicating that the global warming can decrease R25. These results strongly suggest that this thermal acclimation will likely occur in the coming decades under climate change, so the increase in respiration rates of P. taiwanensis in response to climatic warming may be smaller than predicted and thus may not increase atmospheric CO2 concentrations.

Rapamycin induces autophagy and increases heat tolerance in Drosophila melanogaster

Autophagy is a physiological process that facilitates the recycling of intracellular cytosolic components as a response to diverse stressful conditions. By increasing the turnover of damaged structures and clearance of long-lived and larger protein aggregates, the induction of autophagy increases tolerance to abiotic stress in a range of organisms. However, the contribution of this process to heat-tolerance of insect models remains poorly studied to date. Here, we report that rapamycin exposure in Drosophila melanogaster induces autophagy in flies, which in turn correlates with an increase in heat tolerance and quicker recovery from heat-coma. This confirms the potentially important role of the autophagic process in heat tolerance mechanisms in this organism, opening the path to further characterization of its relationship to thermal acclimation and molecular level processes related to stress.

Nitrogen enrichment causes thermal acclimation of soil microbial respiration

The feedback between soil carbon (C) and climate has the potential to decrease in magnitude over time due to the thermal acclimation of microbial respiration, while, whose strength is highly uncertain, partly because the response of microbial respiration is regulated by multiple environmental factors simultaneously rather than by temperature alone. Using a 9-year two-way factorial experiment involving warming and multilevel nitrogen enrichment treatments from an alpine grassland, we show that microbial respiration acclimates to warming only under nitrogen enrichment and that the strength of thermal acclimation increases as nitrogen enrichment. We identified two contrasting pathways—via an enhancement of acclimation by soil acidification and a weakening of acclimation by the inhibition of soil C availability and stimulation of soil C-degrading enzymes—with a net positive effect of nitrogen enrichment on microbial thermal acclimation. Our findings emphasize the importance of considering multiple environmental factors in shaping the strength of thermal acclimation.

Compliance of the fish outflow tract is altered by thermal acclimation through connective tissue remodelling

To protect the gill capillaries from high systolic pulse pressure, the fish heart contains a compliant non-contractile chamber called the bulbus arteriosus which is part of the outflow tract (OFT) which extends from the ventricle to the ventral aorta. Thermal acclimation alters the form and function of the fish atria and ventricle to ensure appropriate cardiac output at different temperatures, but its impact on the OFT is unknown. Here we used ex vivo pressure–volume curves to demonstrate remodelling of passive stiffness in the rainbow trout ( Oncorhynchus mykiss ) bulbus arteriosus following more than eight weeks of thermal acclimation to 5, 10 and 18°C. We then combined novel, non-biased Fourier transform infrared spectroscopy with classic histological staining to show that changes in compliance were achieved by changes in tissue collagen-to-elastin ratio. In situ gelatin zymography and SDS-PAGE zymography revealed that collagen remodelling was underpinned, at least in part, by changes in activity and abundance of collagen degrading matrix metalloproteinases. Collectively, we provide the first indication of bulbus arteriosus thermal remodelling in a fish and suggest this remodelling ensures optimal blood flow and blood pressure in the OFT during temperature change.

Diet mediates thermal performance traits: implications for marine ectotherms

Thermal acclimation is a key process enabling ectotherms to cope with temperature change. To undergo a successful acclimation response, ectotherms require energy and nutritional building blocks obtained from their diet. However, diet is often overlooked as a factor that can alter acclimation responses. Using a temperate omnivorous fish, opaleye (Girella nigricans), as a model system, we tested the hypotheses that 1) diet can impact the magnitude of thermal acclimation responses and 2) traits vary in their sensitivity to both temperature acclimation and diet. We fed opaleye a simple omnivorous diet (ad libitum Artemia sp. and Ulva sp.) or a carnivorous diet (ad libitum Artemia sp.) at two ecologically relevant temperatures (12 and 20°C) and measured a suite of whole animal (growth, sprint speed, metabolism), organ (cardiac thermal tolerance), and cellular-level traits (oxidative stress, glycolytic capacity). When opaleye were offered two diet options compared to one, they had reduced cardiovascular thermal performance and higher standard metabolic rate under conditions representative of the maximal seasonal temperature the population experiences (20°C). Further, sprint speed and absolute aerobic scope were insensitive to diet and temperature, while growth was highly sensitive to temperature but not diet, and standard metabolic rate and maximum heart rate were sensitive to both diet and temperature. Our results reveal that diet influences thermal performance in trait-specific ways, which could create diet trade-offs for generalist ectotherms living in thermally variable environments. Ectotherms that alter their diet may be able to regulate their performance at different environmental temperatures.

Thermal Acclimation to the Highest Natural Ambient Temperature Compromises Physiological Performance in Tadpoles of a Stream-Breeding Savanna Tree Frog

Amphibians may be more vulnerable to climate-driven habitat modification because of their complex life cycle dependence on land and water. Considering the current rate of global warming, it is critical to identify the vulnerability of a species by assessing its potential to acclimate to warming temperatures. In many species, thermal acclimation provides a reversible physiological adjustment in response to temperature changes, conferring resilience in a changing climate. Here, we investigate the effects of temperature acclimation on the physiological performance of tadpoles of a stream-breeding savanna tree frog (Bokermannohyla ibitiguara) in relation to the thermal conditions naturally experienced in their microhabitat (range: 18.8–24.6°C). We quantified performance measures such as routine and maximum metabolic rate at different test (15, 20, 25, 30, and 34°C) and acclimation temperatures (18 and 25°C). We also measured heart rate before and after autonomic blockade with atropine and sotalol at the respective acclimation temperatures. Further, we determined the critical thermal maximum and warming tolerance (critical thermal maximum minus maximum microhabitat temperature), which were not affected by acclimation. Mass-specific routine and mass-specific maximum metabolic rate, as well as heart rate, increased with increasing test temperatures; however, acclimation elevated mass-specific routine metabolic rate while not affecting mass-specific maximum metabolic rate. Heart rate before and after the pharmacological blockade was also unaffected by acclimation. Aerobic scope in animals acclimated to 25°C was substantially reduced, suggesting that physiological performance at the highest temperatures experienced in their natural habitat is compromised. In conclusion, the data suggest that the tadpoles of B. ibitiguara, living in a thermally stable environment, have a limited capacity to physiologically adjust to the highest temperatures found in their micro-habitat, making the species more vulnerable to future climate change.