Apparent thermal acclimation of soil heterotrophic respiration mainly mediated by substrate availability

Multiple lines of existing evidence suggest that increasing CO₂ emission from soils in response to rising temperature could accelerate global warming. However, in experimental studies, the initial positive response of soil heterotrophic respiration (R_H ) to warming often weakens over time (referred to apparent thermal acclimation). If the decreased R_H is driven by thermal adaptation of soil microbial community, the potential for soil carbon (C) losses would be reduced substantially. In the meanwhile, the response could equally be caused by substrate depletion, and would then reflect the gradual loss of soil C. To address uncertainties regarding the causes of apparent thermal acclimation, we carried out sterilization and inoculation experiments using the soil samples from an alpine meadow with 6 years of warming and nitrogen (N) addition. We demonstrate that substrate depletion, rather than microbial adaptation, determined the response of R_H to long-term warming. Furthermore, N addition appeared to alleviate the apparent acclimation of R_H to warming. Our study provides strong empirical support for substrate availability being the cause of the apparent acclimation of soil microbial respiration to temperature. Thus, these mechanistic insights could facilitate efforts of biogeochemical modeling to accurately project soil C stocks in the future climate.

Pathways regulating decreased soil respiration with warming in a biocrust-dominated dryland

A positive soil carbon (C)-climate feedback is embedded into the climatic models of the IPCC. However, recent global syntheses indicate that the temperature sensitivity of soil respiration (R_S ) in drylands, the largest biome on Earth, is actually lower in warmed than in control plots. Consequently, soil C losses with future warming are expected to be low compared with other biomes. Nevertheless, the empirical basis for these global extrapolations is still poor in drylands, due to the low number of field experiments testing the pathways behind the long-term responses of soil respiration (R_S ) to warming. Importantly, global drylands are covered with biocrusts (communities formed by bryophytes, lichens, cyanobacteria, fungi, and bacteria), and thus, R_S responses to warming may be driven by both autotrophic and heterotrophic pathways. Here, we evaluated the effects of 8-year experimental warming on R_S , and the different pathways involved, in a biocrust-dominated dryland in southern Spain. We also assessed the overall impacts on soil organic C (SOC) accumulation over time. Across the years and biocrust cover levels, warming reduced R_S by 0.30 μmol CO₂  m^-2  s^-1 (95% CI = -0.24 to 0.84), although the negative warming effects were only significant after 3 years of elevated temperatures in areas with low initial biocrust cover. We found support for different pathways regulating the warming-induced reduction in R_S at areas with low (microbial thermal acclimation via reduced soil mass-specific respiration and β-glucosidase enzymatic activity) vs. high (microbial thermal acclimation jointly with a reduction in autotrophic respiration from decreased lichen cover) initial biocrust cover. Our 8-year experimental study shows a reduction in soil respiration with warming and highlights that biocrusts should be explicitly included in modeling efforts aimed to quantify the soil C-climate feedback in drylands.

Pop-it beads to introduce catalysis of reaction rate and substrate depletion effects

A kinesthetic classroom activity was designed to help students understand enzyme activity and catalysis of reaction rate. Students served the role of enzymes by manipulating Pop-It Beads as the catalytic event. This activity illuminates the relationship between reaction rate and reaction progress by allowing students to experience first-hand the effect of substrate depletion on catalyzed reaction rate. Preliminary findings based on survey results and exam performance suggest the activity could prove beneficial to students in the targeted learning outcomes. Unique to previous kinesthetic approaches that model Michaelis-Menten kinetics, this activity models the effects of substrate depletion on catalyzed reaction rate. Therefore, it could prove beneficial for conveying the reasoning behind the initial rate simplification used in Michaelis-Menten kinetics. © 2016 by The International Union of Biochemistry and Molecular Biology, 45(2):179-183, 2017.

Introduction: Invited Speakers

The Alberta Prion Research Institute, part of Alberta Innovates Bio Solutions, is proud to host the world’s largest international prion research congress, PRION 2013: Conquering Frontiers, in Banff, Alberta, Canada from May 26–29, 2013. PRION 2013 will be only the second time this international meeting has been held outside of Europe since it began in 2004. The PRION 2013 International Scientific Advisory Committee includes leading international scholars and policy advisors in both human and animal protein misfolding research from 12 countries: Australia, Brazil, Canada, China, England, France, Germany, Japan, The Netherlands, Scotland, Spain and the United States. Prion and protein misfolding science can inform policy, risk management and mitigation, diagnoses and potential treatments in a range of areas from wildlife management to human dementias and neurodegenerative diseases. Compelling evidence is emerging that prion-like mechanisms may underlie a number of the human neurodegenerative diseases and dementias, providing the opportunity to seek out new treatments and for the cross-fertilization of ideas between the two related fields. This approach will be highlighted at PRION 2013. The theme of PRION 2013 is “Conquering Frontiers.” It will be a continuation of the science covered in previous meetings with an emphasis on looking toward investigations in the new frontiers created by the relationships between prion diseases and human neurodegenerative diseases and dementias. The four-day session features scientific talks, workshops and posters on the following themes: Prion and Prion-like Diseases in Humans; Prion Diseases in Animals; Protein Structure and Biology; and Socioeconomic Impacts. The knowledge exchange that will take place at PRION 2013 will help to shape the future of prion and protein misfolding research and its application around the world.