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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.

Nanoparticles (NP), Nanoaerosols (NA), ultrafine particles (UFP), and PM0.1 (particles with a diameter ≤ 0.1 µm or 100 nm) are interchangeably used in the field of atmospheric studies. PM0.1 are emitted from both natural and anthropogenic sources. The main emission sources of PM0.1 are combustion processes, including biomass and fossil fuel. Moreover, secondary formation via atmospheric photochemical reactions can also occur depending on meteorological conditions and the suspended pollutant species. Identifying the physical and chemical characteristics and spatial and temporal variations is vital in terms of understanding the effect of NPs on the environment, the global climate, and human health risks. This review article summarizes recent research on PM0.1 in Thailand. The review involves peer-reviewed papers from Scopus and the Web of Science databases, and includes the most recently published articles in the past ten years (2013-2022). UFPs mainly come from the combustion processes such as motor vehicles. The high mass concentration of PM0.1 that occurs during the dry season in which open fires depend on the specific region of Thailand. Particulate pollution from local and cross-border countries also needs to be considered in terms of the concentrations of ambient nanoparticles. The overall conclusions reached will likely have a beneficial long-term impact on achieving a blue sky over Thailand through the development of coherent policies and managing new air pollution challenges and sharing knowledge with a broader audience.