DOI: 10.5061/dryad.6t1g1jwvx
title: Data from: Carbon fixation by photosynthetic mats along a temperature gradient in a Tengchong hot spring

description: Geothermal hot springs, widely distributed on Earth, are important
 geological green-house 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 13C labeling approach along a
 gradient of temperature (~69 - ~75 oC) 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 (about 4,637 μg C/g TOC/h)
 was obtained in light at the lowest temperature (~69 oC) in the afternoon
 (1:00 to 6:00 pm), most of which (96.7%) was contributed by
 photosynthesis. The lowest carbon fixation rate (138 μg C/g TOC/h) was
 measured at the highest temperature (~75 oC), where chemosynthesis
 dominated over photosynthesis in carbon fixation. At these rates, the
 photosynthetic mats would fix 80% CO2 emission during the daytime. At the
 end of daytime, the photosynthetic mats respired 34% -70% newly fixed
 organic carbon in one hour. 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.
description: About 15 ml mat and surface sediment samples were collected for
 microbial community analysis. Samples were collected from sites DRCB-1,
 DRCB-2, DRCB-3, DRCB-4, DRCB-5 with sterilized spoons, and transferred
 into 50 ml polypropylene tubes. Genomic DNA was extracted from 0.5 wet
 sample using the FastDNA SPIN Kit (MP Biomedical, Solon, OH, USA)
 according to manufacturer’s protocol (Hou et al., 2013). PCR amplification
 was conducted with modified primers 515F (5’-GTG YCA GCM GCC GCG GTA A-3’)
 and 806R (5’-GGA CTA CHV GGG TWT CTA AT-3’) designed to be universal for
 bacteria and archaea (Caporaso et al., 2011; Caporaso et al., 2012). In
 order to identify individual samples from the reads, unique 8-bp barcodes
 were added at the 5′-end of both the forward and reverse primers. PCR
 products were purified following previously published literature (Hou et
 al., 2013). All PCR products were pooled together with equal molar
 amounts. Illumina MiSeq sequencing was performed with the MiSeq Reagent
 Kit v2 2× 250
 bp. Sequence demultiplexing and quality
 control were performed with Cutadapt 1.9.1 (Martin, 2011). The sequences
 that had an average quality score of lower than 27 were removed from
 subsequent analysis. Operational taxonomic unit (OTU) cluster at 97%
 sequence identity was determined by using UCLUST algorithm (Edgar, 2010).
 The first sequence from each OTU was picked as a representative, and
 taxonomy was assigned to each representative using the ribosome database
 project (RDP) classifier algorithm (Wang et al., 2007). Sequences that
 could not be classified with this algorithm were manually searched against
 the NCBI BLAST database using BlastN to find highly similar
 hits.
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