This study aimed to understand the relationship between termite foraging activity and the ecological benefits derived from their activity in soil dynamics and water infiltration. A field study was ...carried out for six months, between pre-wet and wet seasons, with different food baits (elephant dung, Acacia auriculiformis leaves, twigs and leaves of Lantana camara as well as Ficus religiosa, Pterocarpus marsupium, Prosopis juliflora, Michelia champaca, Azadirachta indica and Hevea brasiliensis wood stakes) installed on the soil surface in a semi-deciduous forest in southern India. At the end of the experiment we determined bait consumption, water infiltration rate in soil, and the amount of soil sheetings covering the different baits. The initial infiltration rates under the baits were compared to those at the end of the experiment. Three termite species, Odontotermes obesus, O. feae and Microtermes obesi, were found associated with some of the baits in the study area. Among the different baits, elephant dung and Acacia leaves were the most preferred and a positive relationship was observed between the quantity of soil sheetings and the bait consumption rate. Termite preference for elephant dung and Acacia leaves was also associated with higher water infiltration rates. However, this difference was only significant at the beginning of the experiment and no significant difference was measured once the steady state was reached. In conclusion, we showed that resource quality was of primary importance for soil sheeting production but that the influence of termites on water infiltration remained limited, most likely because of the low stability of their tunnels in the soil.
Understanding how soil fauna impact soil aggregate dynamics remains a critical issue in soil science, especially because of the influence on soil aggregate stability on key ecological and ...environmental processes. This question is even more crucial in tropical countries, where soils are particularly vulnerable to erosion. In many tropical environments, soil bioturbation is mostly carried out by termites. Based on their different building strategies, termites are usually differentiated into two functional groups: the fungus growing (FG) and non-fungus growing termites (non-FG). In this study, we focused on the properties of soil sheeting, i.e., small sized soil aggregates that are built on the ground or on plant materials by termites. Using partial least squares structural equation modeling (PLS-SEM), we showed that the stability of non-FG sheeting was associated with the properties of the surrounding soil, thus suggesting (i) a low ability or need of termites to adapt the stability of their sheeting to their biotic and abiotic environments, (ii) a rapid turnover of the organic matter incorporated by non-FG, which is only superficially incorporated into soil aggregates. The sheeting of FG termites was generally enriched in clay and impoverished in carbon. However, despite changes in soil properties, PLS-SEM did not satisfactorily account for sheeting stability (i.e., no direct or indirect path correlations between the stability of soil sheeting and the other measured variables). Therefore, this study suggested a reorganization of soil aggregates and an adaptation of sheeting properties to the environment with a positive impact of termites on soil sheeting stability restricted to semi-arid to arid environments (mean annual precipitation <500 mm year−1), in agro-ecological biotopes, and when sheeting covered leaves in comparison to wood. Hence building strategies between FG and non-FG termites can have functional consequences in terms of soil aggregate stability in tropical soils.
•Fungus and non-fungus growing termites have different building strategies.•Sheeting stability of non-fungus growing termites is explained by the properties of the reference soil.•Sheeting stability of fungus-growing termites could not be explained by the properties of the reference soil nor by those of sheeting.•Positive impact of fungus-growing termites on sheeting stability is restricted to dryland and agro-pastoral biotopes.
Progressive fragmentation of larger plastic debris due to the mechanical action of wind/waves, prolonged exposure to ultraviolet radiation, or biological degradation has led to the formation of ...microplastics or MPs (<5 mm). MPs are pervasive in nature and hence, ubiquitous in distribution across the global marine systems. The Arctic Ocean, despite its remoteness, has been reported to contain a high concentration of MPs. However, studies on the presence of MPs in the sediment compartments of the Arctic Ocean are relatively lesser than that of the water column, surface water and Arctic fauna. Similarly, MP pollution of the Arctic fjords remains understudied. Here, we present the occurrence of MPs in the sediments of Kongsfjorden, an Arctic fjord in the Svalbard archipelago. Sediment samples from eight locations in Kongsfjorden, when analyzed, reveal the presence of MPs in three sites, with values ranging from 4 to 24 MPs/kg (dry weight) sediment. The highest number of MPs was observed at site K5 (24 particles/kg). On an average, 2.87 MPs/kg were recorded and their size ranged from 55 μm to 381 μm. Stereomicroscopic observation of MPs indicated fragment and fibers as the morphotypes of MPs. Polymer profile analysis with micro-Raman spectroscope confirmed high-density polyethylene (HDPE), low-density polyethylene (LDPE) and polyamide (PA) as the polymer components of the MPs found in the sediment samples. Of these, HDPE was the predominant polymer. Further detailed studies are needed to understand the source and the mechanisms involved in transporting MPs to the sediment and their impact on Arctic fjords.
•Microplastics (MPs) have been observed in the sediment samples of Kongsfjorden.•MPs have been found in fragments and fibers in the size range of 55–381 μm.•Raman spectroscopy has identified HDPE, LDPE, and PA as the polymers of MPs.•HDPE and LDPE in sediments have indicated vertical flux of MPs in the water column.
In the tropics, termites and beetles are considered key soil bioturbators regarding their impacts on many ecosystem services. The aim of this study was to compare the functional impacts of these two ...soil engineers in a seasonally dry tropical forest in southern India. The soil excavated by dung beetles and termite sheeting found at the soil surface were sampled and compared to the surrounding topsoil environment. We showed that soil sheeting had very similar soil particle sizes and C content as the surrounding topsoil while the soil excavated by beetles was enriched in C and gravels in comparison with the topsoil. Bioturbation by dung beetles was also associated with the production of vertical tunnels that significantly decreased soil bulk density and constituted a preferential flow path for water to infiltrate (37-fold increase in comparison with the surrounding topsoil). Termite activity was also associated with the production of macropores. However, termite galleries were narrower and less vertical than dung beetle macropores, consequently leading to a positive but rather limited impact on the water hydraulic conductivity (Ksat) in comparison with that of dung beetles (i.e. from 2 to 8-fold increase). In conclusion, this study showed that soil engineers have different bioturbation impacts, dung beetles having locally a larger impact on soil dynamics and properties than termites. More research is now needed to understand the consequences of these bioturbations on the fate of C in soil and on water dynamics at larger scales.
•We compare the functional impact of termites and beetles on soil and water dynamics.•Termite sheetings have similar properties than the topsoil.•Soil excavated by beetles was enriched in gravels and C.•Soil macroporosity made by beetles and termites were studied using X-ray CT.•Beetles and termites’ burrows impact differently soil macroporosity.•Results suggest different impact of termites and beetles on soil and water dynamics.
Termites are considered soil engineers and key bioturbators in tropical and subtropical soils. A large number of studies have described the specific properties of the aboveground mounds that termites ...construct to protect their colonies from environmental hazards. However, there is a paucity of information on properties of soil sheetings; more temporary but often extensive structures are covering over or inserted within substrates on the ground such as leaves and woody materials or components of arboreal runways. Such sheetings are conspicuously produced not only by the Macrotermitinae but also by many other unrelated taxa. Here, we review the available literature and discuss (i) the relationship between rainfall and soil sheeting production and (ii) how termites affect the clay and C contents in soil sheetings. This reveals that sheeting production is highly variable and site specific. We also found that soil sheetings are always enriched in clay, but their impacts on soil C content are variable and related to the C content of the parent soil and to the quality of the substrates consumed by termites.
•Termites produce subterranean galleries for collecting litter and dung in vertisols.•Termite activity increases Ksat in comparison with the surrounding soil.•Galleries were found beyond 3 cm of ...depth.•C content in soil sheetings was reduced in comparison with the surrounding topsoil.•Termite produce unstable galleries.
In the tropics, termites are key litter decomposers and soil bioturbators. Termite foraging activity involves the production of sheetings and galleries that influence the physical, chemical and hydraulic properties of soils. The functional impacts of these biogenic structures and biopores have been acknowledged for a long time in soils dominated by 1:1 minerals. Less is known, however, on their functional impacts in soils dominated by 2:1 minerals, such as vertisol which represent 22% of the land surface in India. Therefore, an experiment was carried out in a vertisol in southern India where elephant (Elephas maximus) dung pats (ED) and Lantana camara twigs (LT) were applied on the ground and protected (+) or not (−) from termite activity. Termite activity was only measured below ED−, showing a clear preference for organic matter derived from elephant dung. Soil sheetings had similar properties to the surrounding topsoil, with the exception of their C content that was reduced. This result raised the question of the origin of the soil used by termites for covering ED. ED− was also associated with the presence of effective macropores up to 5 cm depth and a significant increase in water hydraulic conductivity (12-fold). However, the utilization of the coefficient of linear extensibility showed that these galleries were unstable and most likely short-lived. In conclusion, this study confirmed that the structure of soils dominated by 2:1 minerals is mainly controlled by physical processes (i.e., the shrinking and swelling of soils). This study also stresses the need to better understand the dynamic of termite galleries in soil and to quantify the origin and fate of organic matter in soil sheetings.
Despite the acknowledged roles of termites in tropical ecosystems, the majority of published studies of epigeal mounds still address the African fauna and are principally concerned with spatial ...patterns and putative inter-colony competition, rather than the links between parent soil properties and mound establishment. Further, information about the effects of habitat disturbance, and especially fragmentation, is lacking. This study assessed the abundance and distribution of the cathedral- and lenticular-type aboveground mounds of fungus-growing termites (Macrotermitinae), which are a common feature of South Indian woodlands, in relation to soil properties (vertisol vs. ferralsol) and habitat fragmentation (forest vs. highway margins). Mound abundance averaged 3.5 (standard error, SE 0.8) ha⁻¹ (cathedral) and 12.9 (SE 2.1) ha⁻¹ (lenticular), but was not influenced either by soil properties or disturbance. However, the volume of soil stored in the mounds varied between 27 (SE 8) m³ ha⁻¹ (ferralsol) and 47 (SE 6) m³ ha⁻¹ (vertisol). At the watershed scale, such volumes are equivalent to a 3.1-mm layer of soil if spread evenly across the landscape, roughly the same as the estimated erosion over the life of a typical mound. Significantly more nutrients were stored in lenticular mounds, especially on the vertisol, but the significance of these at the ecosystem level was considered small. In conclusion, this study suggests that termite mounds, and especially lenticular mounds, have a significant impact on soil dynamics at the watershed scale but a limited impact on the distribution of C and nutrients.
This communication assesses advances in our knowledge of the beneficial influences of termites on ecosystem functioning and services. Termites are amongst the main macroinvertebrate decomposers in ...arid and semi-arid environments and exert additional impacts through the creation of biostructures (mounds, galleries, sheetings, etc.) with different soil physical and chemical properties. Unfortunately, the positive ‘or bright’ role of termites is often overshadowed by their dark side, i.e. their status as pests threatening agriculture in the tropics (635 vs. 164 articles referenced in WoS with termites and either pest or ecosystem engineer as keywords. Source: WoS, April 2019).
Termite impacts on soil properties and water dynamics can be differentiated at four different scales: (i) at the landscape scale, where termites act as heterogeneity drivers; (ii) at the soil profile scale, where termites act as soil bioturbators; (iii) at the aggregate scale, where they act as aggregate reorganizers; (iv) and last, at the clay mineral scale, where they can act as weathering agents 1.
In this communication, two examples of ecosystem services provided by termites are given.
The first describes the positive impact of termites on water infiltration and nutrient guidance at small scale through the production of foraging galleries in soil 2 and how this activity can be used to improve agro-ecosystem functioning in arid and semi-arid environments 3.
The second example deals with the construction of mounds and sheeting by termites in “natural” environments 4 and how these “patches of biodiversity and fertility” can be used in the lower Mekong Basin to reduce food insecurity and to provide a better access to health 5 (Fig. 1).
Finally, the perception of termite mounds in Southern Indian rural environments (Fig. 2) is discussed and used as example of the cultural services that can be provided by termites in some circumstances. The story of Valmiki, the author of the Ramayana, is explained and used as a parable for highlighting the interconnection between the “bright” and “dark” sides of termites, and more generally that to get the bright we also need the dark.
•Soil hydrostructural properties of termite mounds were compared.•Soils from termite mounds were more compact than their surrounding control soils.•Cathedral mounds had lower macroporosity than the ...control soil.•Soils from lenticular mounds had a higher microporosity than the control soil.•Soils from lenticular mounds had a higher water holding capacity than the control soil.
Mounds built by fungus-growing termites are often considered to be patches or fertile areas in tropical ecosystems because they contain more nutrients than the surrounding soil environments. However, the mechanism of how these habitats influence soil physical properties remains unknown. Therefore, this study aimed at comparing the soil hydrostructural properties of two common termite mounds in southern India, namely, cathedral and lenticular mounds. The shrinkage curves of the soil eroded from three cathedral mounds and of the soil sampled in the center or in the periphery of three lenticular mounds were measured and compared to those of their surrounding soil environment. This study revealed that the soil in the periphery of cathedral mounds was compact with a lower soil specific volume and macroporosity than the control soil. On the other hand, the accumulation of clay in lenticular mounds was associated with a lower soil specific volume at the end of the shrinkage period, higher microporosity, increased swelling capacity and higher water holding capacity than the control soil. These parameters reached intermediate values in the periphery of the lenticular mounds between those of the lenticular mound soil and the surrounding control soil. In conclusion, this study showed that cathedral and lenticular mounds impacted soil hydrostructural properties in two opposing directions. It also highlighted the link between the impact of termites on the clay and carbon contents of soil and their influence on soil porosity and water dynamics, and then the need for a better understanding of the influence of termites on the dynamic of carbon and clay in ecosystems.
•Termites have harmful (their dark side) and beneficial (their bright side) impacts on SGDs.•Negative impacts are mainly linked with their status as pests (SDGs 1–3).•Positive impacts concern SDGs ...1–3, 9, 13 and 15.•The dilemma between harmful and beneficial impacts are intertwined and both are needed for the sustainable management of ecosystems.
Termites are amongst the main macroinvertebrate decomposers in tropical ecosystems and they exert additional impacts through the creation of biostructures (mounds, galleries, sheetings, etc.) with different soil physical and chemical properties, thereby impacting positively on numerous ecosystem services for humankind. Unfortunately, this positive or ‘bright’ role of termites is often overshadowed by their ‘dark’ side, that is, their status as pests threatening agriculture and constructions. This article assesses advances in our knowledge of the impact of termites on several sustainable development goals (SDGs 1 ‘no poverty’, 2 ‘zero hunger’, 3 ‘good health’, 9 ‘innovation’, 11 ‘sustainable cities’, 13 ‘climate action’ and 15 ‘life on land’). Finally, using the Indian myth of Valmiki as a parable, we illustrate that a reconciliation between the termite's dark and bright sides is needed if we want to reduce our dramatic impact on biodiversity and more generally achieve SDGs.
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