Carbon Fixation by Photosynthetic Mats Along a Temperature Gradient in a Tengchong Hot Spring. Issue 9 (9th September 2020)

• Record Type: Journal Article
• Authors: Zhang, Yidi; Qi, Xiao; Wang, Shang; Wu, Geng; Briggs, Brandon R.; Jiang, Hongcheng; Dong, Hailiang; Hou, Weiguo
• Is Part Of: Journal of geophysical research. Volume 125:Issue 9(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-09-09
• Subjects: carbon fixation -- hot spring -- photosynthesis -- chemosynthesis -- photosynthetic mats -- 13C isotope labeling; Geobiology -- Periodicals; Biogeochemistry -- Periodicals; Biotic communities -- Periodicals; Geophysics -- Periodicals; 577.14
• DOI: 10.1029/2020JG005719
• Languages: English
• ISSNs: 2169-8953

Abstract

Abstract: Geothermal hot springs, widely distributed on Earth, are important geological greenhouse gas sources which contribute large amounts of CO2 emission to the atmosphere. Exploring microbial carbon fixation in these springs is vital to fully understand the carbon budget in these terrestrial aquatic systems. In this study, carbon fixation rate by photosynthetic mats was determined with a 13 C‐labeling approach along a gradient of temperature (~69– ~75 °C) in a geothermal pool at Rehai Park in Tengchong, Yunnan Province, China. Light experiments were performed to determine carbon fixation rate by both photosynthesis and chemosynthesis, while dark experiments were performed by chemosynthesis. The results showed that the highest carbon fixation rate (4, 637 μg C/g TOC/hr) was obtained in light at the lowest temperature (~69 °C) in the afternoon (1:00 to 6:00 p.m.), most of which (96.7%) was contributed by photosynthesis. The lowest carbon fixation rate (138 μg C/g TOC/hr) was measured at the highest temperature (~75 °C), where chemosynthesis dominated over photosynthesis in carbon fixation. At these rates, the photosynthetic mats would fix 80% of CO2 emission during the daytime. At the end of daytime, the photosynthetic mats respired 34–70% of newly fixed organic carbon in 1 hr. Interestingly, both the carbon fixation rate and respiration rate decreased exponentially with increasing temperature, which may be ascribed to a temperature dependence of both microbial community composition and enzymatic activity. In summary, our study revealed that biological carbon fixation by photosynthetic mats is highly temperature dependent and significantly affects carbon cycling in hot springs. Plain Language Summary: Volcanoes and hot springs vigorously emit greenhouse gases from magma sources, while microbes dwelling in hot springs can reduce greenhouse gas emission by fixing CO2 to organic carbon. However, little is known about these processes despite their importance for understanding the role of hot springs in modulating CO2 fluxes. We conducted experiments to measure carbon fixation rate in a phototrophic mat along a temperature gradient of 69–75 °C. The results showed that carbon fixation rate by phototrophic mats decreased exponentially with temperature. A large fraction of CO2 emission can be microbially fixed during daytime if spring temperature is lower than 70 °C. However, at the end of day, much newly synthesized organic carbon is respired to CO2 . Briefly, microorganisms play a key role in carbon cycling in terrestrial hot springs. Key Points: Rates of microbial carbon fixation by photosynthetic mats is negatively and exponentially related with high temperature (69–75 °C) Rapid organic carbon transformation to CO2 occurred at the end of daytime Photosynthetic mats in the study site fixed about 80% CO2 emission from the hot spring in the daytime