Introduction
Tropical forests significantly impact global climate by regulating
greenhouse gas and storing 45-50% of global terrestrial carbon stocks
(IPCC, 2007). Soil CO2 emission (soil respiration) plays
an important role in global carbon cycling with contributing more than
50% of the total ecosystem respiration (Janssens et al., 2001; Xu et
al., 2001; Chambers et al., 2004). Soil CO2 emission
from tropical forests could strongly influence future concentrations of
atmospheric carbon dioxide. However, soil respiration considerably
varied with space and time (Boonriam et al., 2021a). Spatial variability
in soil respiration from tropical forests remains difficult to assess
and it may lead to inaccurate soil respiration estimates at ecosystem
level. Consequently, understanding of above and belowground soil
activities on carbon cycle in tropical forest is necessary.
Soil respiration comes from CO2 production of all living
organisms in the soil, including plant roots, soil microbes, and animals
(Lavelle et al., 2001; Luo and Zhou, 2006. Soil microorganisms and roots
are thought to dominate most soil respiration. However, soil respiration
rate has been shown to fluctuate unexpectedly (10-90%) at large scales
(Hanson et al., 2000). The known environmental factors: soil, water
content, and temperature are unable to completely explain this
variation. According to Ohashi et al. (2007; 2017), certain areas
displayed extremely higher rates of soil respiration (hot spots) and
soil macrofauna were focused as a predominant driver in tropical
forests. Events were attributed to the undisclosed activities of soil
animals, particularly social insects such as termites. Because it is
widely known that termites are superabundant soil insects in seasonal
tropical forests (Yamada et al., 2003, 2005; Inoue et al., 2006).
Termites are major structural components of soil partition up to 95% of
the total soil insect biomass (Jones and Eggleton 2000) and population
density in the tropics could reaches up to 1000 termites per
m2 (Eggleton et al., 1996). Termites are widely
distributed along an altitudinal gradient from lowland to mountain
(Kayani et al., 1979; Akhtar et al. 1992). Termites are significantly
important to drive carbon cycle by litter decomposition as much as half
of the primary litter production (e.g. Matsumoto and Abe, 1979; Bignell
and Eggleton, 2000; Coleman et al., 2004). Termites can be divided into
two major feeding groups, wood/litter feeders (fungus and non-fungus
growers) and soil feeders (non-fungus growers) (Wood, 1976; Collins,
1989; Bignell et al., 1997; Bignell and Eggleton, 2000). Fungus growing
termites cultivate symbiotic fungi on fungus gardens (fungus combs)
consisting of plant litter materials built with partially digested
termite faeces (Korb, 2003). Termite CO2 emissions were
estimated to contribute up to 2% of global terrestrial emissions
(Sugimoto et al., 2000). Several studies considered epigeal termite
mounds as high CO2 emission point sources. As the
epigeal termite mounds in tropical savanna emitted higher
CO2 than surrounding soils with emphasis on fungus
growing termite (Macrotermitinae) (Konate et al., 2003; Brümmer et al.,
2009; Risch et al., 2012), except in seasonal tropical forest (Boonriam
et al., 2021b). Besides, De Gerenyu et al. (2015) reported that termite
mounds contributed up to 10% of the total soil respiration in a
tropical monsoon forest in Vietnam. Thai-tropical forests also contain
various epigeal termite mounds, especially non-fungus growing termites
(Termitidae) due to the number of species and nests were higher than
fungus growing termites (Yamada et al., 2003). According to Korb (2003),
epigeal termite mounds have a different complex architecture to maintain
a constant temperature and humidity. While the seasonal tropical forests
have sometimes a fluctuation of the climate. Consequently, determining
epigeal mound CO2 emission in terms of non-fungus
growing termites is one of the best approaches for evaluating soil
biological activities in relation to carbon and energy flow in
terrestrial ecosystems.
This study aimed to 1) compare CO2 emission from epigeal
mounds of different non-fungus growing termites in a seasonal tropical
forest, 2) compare CO2 emission from the mounds and
their surrounding soils, and 3) determine the relationship between the
surrounding soil CO2 emissions and soil environmental
factors in the dry and wet seasons.