Termite guts harbor diverse yet-uncultured bacteria, including a non-photosynthetic cyanobacterial group, the class “Melainabacteria”. We herein reported the phylogenetic diversity of “Melainabacteria” in the guts of diverse termites and conducted a single-cell genome analysis of a melainabacterium obtained from the gut of the termite Termes propinquus. We performed amplicon sequencing of 16S rRNA genes from the guts of 60 termite and eight cockroach species, and detected melainabacterial sequences in 48 out of the 68 insect species, albeit with low abundances (0.02–1.90%). Most of the melainabacterial sequences obtained were assigned to the order “Gastranaerophilales” and appeared to form clusters unique to termites and cockroaches. A single-cell genome of a melainabacterium, designated phylotype Tpq-Mel-01, was obtained using a fluorescence-activated cell sorter and whole genome amplification. The genome shared basic features with other melainabacterial genomes previously reconstructed from the metagenomes of human and koala feces. The bacterium had a small genome (~1.6 Mb) and possessed fermentative pathways possibly using sugars and chitobiose as carbon and energy sources, while the pathways for photosynthesis and carbon fixation were not found. The genome contained genes for flagellar components and chemotaxis; therefore, the bacterium is likely motile. A fluorescence in situ hybridization analysis showed that the cells of Tpq-Mel-01 and/or its close relatives are short rods with the dimensions of 1.1±0.2 μm by 0.5±0.1 μm; for these bacteria, we propose the novel species, “Candidatus Gastranaerophilus termiticola”. Our results provide fundamental information on “Melainabacteria” in the termite gut and expand our knowledge on this underrepresented, non-photosynthetic cyanobacterial group.
Soil respiration in tropical forests is an important source of carbon dioxide in the atmosphere. Factors regulating spatial soil respiration are still unclear, and they may lead to an inaccurate estimation of soil respiration at the ecosystem level. The aim of this study was to investigate the seasonal changes in spatial variation of soil respiration in a dry evergreen forest of Sakaerat Biosphere Reserve, Nakhon Ratchasima Province, Thailand. Soil respiration, temperature, and moisture were measured in 100 subplots of five 1-ha main plots for four times from November 2014 to August 2016. The average rate ( ± SD) of annual aboveground soil respiration was 6.57 ± 4.29 µmol CO 2 m −2 s −1 . Soil respiration considerably varied with space and time. The mean ranges were from 2.66 to 11.72 µmol CO 2 m −2 s −1 with a maximum rate of 42.68 µmol CO 2 m −2 s −1 . The wet season soil respiration rate (8.81 µmol CO 2 m −2 s −1 ) was two times higher (p < 0.001) than in the dry season (4.33 µmol CO 2 m −2 s −1 ). The seasonal changes clearly affected the spatial variation of soil respiration. Wet season produced higher and more widespread soil respiration. Although soil respiration rates increase with increasing soil temperature and soil moisture content, the rate starts to drop at 27°C soil temperature (p < 0.001) and 21% soil moisture content (p < 0.05). This study suggests more investigation of soil features and animal influences on CO 2 emission hot spots in order to accurately estimate soil respiration in tropical forests.
Termites are one of the major contributors to high spatial variability in soil respiration. Although epigeal termite mounds are considered as a point of high CO2 effluxes, the patterns of mound CO2 effluxes are different, especially the mound of fungus-growing termites in a tropical forest. This study quantified the effects of a fungus-growing termite (Macrotermes carbonarius) associated with soil CO2 emission by considering their nesting pattern in dry evergreen forest, Thailand. A total of six mounds of M. carbonarius were measured for CO2 efflux rates on their mounds and surrounding soils in dry and wet seasons. Also, measurement points were investigated for the active underground passages at the top 10% of among efflux rates. The mean rate of CO2 emission from termitaria of M. carbonarius was 7.66 µmol CO2/m2/s, consisting of 2.94 and 9.11 µmol CO2/m2/s from their above mound and underground passages (the rate reached up to 50.00 µmol CO2/m2/s), respectively. While the CO2 emission rate from the surrounding soil alone was 6.86 µmol CO2/m2/s. The results showed that the termitaria of M. carbonarius contributed 8.4% to soil respiration at the termitaria scale. The study suggests that fungus-growing termites cause a local and strong variation in soil respiration through underground passages radiating out from the mounds in dry evergreen forest.
Restoration of watershed forest ecosystems can perform different disturbance regimes over remnant forests, which can ultimately affect plant diversity, soil formation, and carbon storage. To address an issue, this study assessed tree species diversity, aboveground biomass (AGB), and aboveground carbon (AGC) storage of the watershed forest in Phayao Province, Thailand. Data collection was conducted in 18 plots along nine watersheds along the topographic gradients. Tree height and diameter at breast height (DBH) were collected. AGB of vegetation was estimated by using the allometric equation. Likewise, AGC storage was evaluated from half of AGB. A total of 133 species belonging to 105 genera and 39 families were recorded from the watershed forests (1.8 ha). Mixed deciduous forest (MDF) and dry evergreen forest (DEF) exhibited high density and high diversity index, respectively. The highest value of total AGC storage was found in the MDF with 91.2 ton C/ha, following by DEF (78.3 ton C/ha) and dry dipterocarp forest (DDF) (60.5 ton C/ha). Detrended correspondence analysis (DCA) revealed that the occurrences of Albizia saman, Hopea odorata, Lagerstroemia calyculata, and Acrocarpus fraxinifolius related to AGB, AGC, slope, and tree canopy in the DEF. Intensity of slope influenced tree species occurrence in the watershed forest of Phayao.
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