Microbial temperature sensitivity and biomass change explain soil carbon loss with warming

• Published in: Nature climate change Vol. 8; no. 10; pp. 885 - 889
• Main Authors: Walker, Tom W. N., Kaiser, Christina, Strasser, Florian, Herbold, Craig W., Leblans, Niki I. W., Woebken, Dagmar, Janssens, Ivan A., Sigurdsson, Bjarni D., Richter, Andreas
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.10.2018; Nature Publishing Group
• Subjects: 631/158/2165; 631/158/2445; 631/158/47; 631/158/855; 704/47; Acclimation; Acclimatization; Biogeochemistry; Biological activity; Biomass; Carbon; Carbon uptake; Climate; Climate Change; Climate Change/Climate Change Impacts; Climate system; Depletion; Earth; Earth and Environmental Science; Environment; Environmental Law/Policy/Ecojustice; Frameworks; Global warming; Letter; Microbial activity; Microorganisms; Sensitivity; Soil; Soil erosion; Soil microorganisms; Soil temperature; Soils; Substrates; Temperature effects; Temperature gradients; Uptake
• ISSN: 1758-678X; 1758-6798
• DOI: 10.1038/s41558-018-0259-x

Soil microorganisms control carbon losses from soils to the atmosphere 1 – 3 , yet their responses to climate warming are often short-lived and unpredictable 4 – 7 . Two mechanisms, microbial acclimation and substrate depletion, have been proposed to explain temporary warming effects on soil microbial activity 8 – 10 . However, empirical support for either mechanism is unconvincing. Here we used geothermal temperature gradients (>50 years of field warming) 11 and a short-term experiment to show that microbial activity (gross rates of growth, turnover, respiration and carbon uptake) is intrinsically temperature sensitive and does not acclimate to warming (+6 °C) over weeks or decades. Permanently accelerated microbial activity caused carbon loss from soil. However, soil carbon loss was temporary because substrate depletion reduced microbial biomass and constrained the influence of microbes over the ecosystem. A microbial biogeochemical model 12 – 14 showed that these observations are reproducible through a modest, but permanent, acceleration in microbial physiology. These findings reveal a mechanism by which intrinsic microbial temperature sensitivity and substrate depletion together dictate warming effects on soil carbon loss via their control over microbial biomass. We thus provide a framework for interpreting the links between temperature, microbial activity and soil carbon loss on timescales relevant to Earth’s climate system. Soil microbial activity is accelerated by warming and does not acclimate over periods of at least 50 years. Resulting soil carbon loss is nevertheless temporary because substrate depletion reduces microbial biomass and constrains the influence of microbes over the ecosystem.