Physicochemical and morphological properties of termite (Macrotermes bellicosus) mounds and surrounding pedons on a toposequence of an inland valley in the southern Guinea savanna zone of Nigeria

Termites play a significant role in soil-forming processes of the tropics. The influence of termites on pedogenesis as affected by the toposequence, however, has rarely been explored. We investigated the soil physicochemical and morphological characteristics of epigeal mounds constructed by Macrotermes bellicosus (Smethman) compared with those of surrounding pedons along a toposequence (bottom, fringe and upland sites) of an inland valley in central Nigeria. The physicochemical and morphological properties of the mound soils varied according to structural units but were generally different from those of the adjacent pedons. The differences included finer texture, higher electrical conductivity, total N, exchangeable bases (Ca, Mg and K) and effective cation exchange capacity and lower C/N ratio and exchange acidity in the mound than the pedon at each toposequence position. This tendency to modify the soil properties was more prominent in the nest body where the termites actually live, that is, in the hives, royal cell and base-plate, than in the soils below the nest and the other mound parts, that is, the external wall, internal wall and pillars. We found this trend to a greater or lesser degree at all toposequence positions. Our findings suggest that: (1) M. bellicosus can manipulate the mound soils according to functional applications of structure units or environmental requirements for its livelihood, regardless of local soils; (2) M. bellicosus makes ecological patches (hot spots) at all toposequence positions in the same measure; (3) the influence of M. bellicosus on the pedogenesis is reduced in the lowlands compared with the uplands because the number and volume of the mounds were substantially lower in the bottom and fringe sites compared with the upland site.     

Possible influence of termites (Macrotermes bellicosus) on forms and composition of free sesquioxides in tropical soils

There has been less concern about soil mineralogical alteration than about soil physical, chemical and biological changes induced by termite nest-building activity. Furthermore, much less attention has been paid to free sesquioxides than to phyllosilicate minerals. In the present study, we conducted field morphological observations and selective dissolution analysis to characterize free sesquioxides in termite (Macrotermes bellicosus) mounds as compared with surrounding pedons in different toposequence positions, i.e., seasonally flooded valley bottom, hydromorphic fringe and well-drained upland sites. Distinctive redoximorphic features, such as surface yellowish layers on mound structures from the fringe site, indicate possible alteration of iron sesquioxide forms in the mounds due to the transportation of soil from reductive (aquic subsoil) to oxidative (epigeal mound) environments by the nest-building activity of M. bellicosus. On the other hand, the iron-soluble content in the dithionite-citrate-bicarbonate (DCB) system (Fe_d) was generally higher in the mound structures than at the adjacent sub-surface (Ap2) horizon at each toposequence position, while there was less difference in the content of acid ammonium oxalate (AAO) extractable iron (Fe_o) as compared to Fe_d. As a consequence, the iron activity index (Fe_d/Fe_o ratio) was found for the most part to be lower in the mound structures than in the neighboring Ap2 horizon. In addition, the content of Fe_d, AAO-soluble Al (Al_o) and DCB-extractable Al (Al_d) was significantly correlated with clay content in these soils. These findings suggest that M. bellicosus preferentially collects clay particles, probably from the clay-rich subsoils, such as the argillic horizon, which has been formed by the co-migration of phyllosilicate minerals and relatively crystalline sesquioxides. The species then likely incorporates them into the mounds, which induces an increase in the Fe_d content relative to that of Fe_o, resulting in a decreased iron activity index in the mound structures.     

Accumulation of free oxyhydroxides in termite (Macrotermes bellicosus (Smeathman)) mounds and the implications for their dynamics in an African savannah Ultisol

The present study aimed to assess the dynamics of oxyhydroxides via termite mounds in a tropical savannah of Central Nigeria, where the soils often contain oxyhydroxides as a major component of soil minerals. To this end, the quantities of oxyhydroxides stored in mounds built by Macrotermes bellicosus (Smeathman) were compared to those stored in surface (Ap1) soils, and their turnover rates were estimated. Both the mound wall and nest of M. bellicosus were enriched two- to 10-fold with acidified ammonium oxalate soluble iron (Fe_o) and aluminum (Al_o) and dithionite-citrate-bicarbonate (DCB) soluble iron (Fe_d) and aluminum (Al_d) relative to the adjacent surface soil horizon. These oxyhydroxide contents were positively correlated with the clay content (P < 0.05), suggesting that M. bellicosus preferentially used silicate clay-associated oxyhydroxides for mound construction. The Fe_d, Al_d and DCB-soluble manganese (Mn_d) preserved in the M. bellicosus mounds ran up to 112 ± 25.6, 5.72 ± 1.41 and 2.17 ± 0.68 kg ha^?1, accounting for 1.91 ± 0.23%, 1.00 ± 0.60% and 0.35 ± 0.09% of the total amount stored in the surface soil horizon, respectively. Furthermore, the estimated turnover rates of Fe_d, Al_d and Mn_d were 6.6, 0.33 and 0.14 kg ha^?1 year^?1, respectively. These findings suggest that the mound-building termites significantly impacted the dynamics of free oxyhydroxides in an African savannah soil.     

Effect of different termite feeding groups on P sorption and P availability in African and South American savannas

Nest structures of six termite species, four with epigeous (above-ground) and two with subterranean nests were analysed to find out how their building and feeding habits could be related to their nests phosphorus status compared with control soils. Termite nest structure was found to affect significantly the P status in savanna soils: mounds of the African Trinervitermes geminatus and the South American Nasutitermes ephratae (both grass-feeders) displayed a greater amount of available P, especially in the inner part of the nest, than the surrounding soil. The abundant quantities of dead grass material stored in the mound can explain the available soil P increase. A similar increase in P availability was also found for the soil-feeder Cubitermes severus. In mounds of Macrotermes bellicosus, on the other hand, there was a drastic increase in P sorption (and a corresponding decrease in available P) compared to adjacent soils, which was attributed to the building strategy of this species. M. bellicosus selected clay from subsoil to build its nest structure. The data obtained for the subterranean species Ancistrotermes cavithorax and Microtermes toumodiensis indicated also that there is an increase in P sorption in mounds when compared with associated topsoils. Consequently, the nest structures of only certain termite species should be considered, and utilised, as a soil amendment in place of fertilisers. This impact on the P cycle in savannas seems to be related to the termite feeding status and to the type of material utilised in nest building. This should be taken into account before using termite nest material in soil fertility status improvement.     

Nutrient storage in termite (Macrotermes bellicosus) mounds and the implications for nutrient dynamics in a tropical savanna Ultisol

The role of mounds of the fungus-growing termite Macrotermes bellicosus (Smeathman) in nutrient recycling in a highly weathered and nutrient-depleted tropical red earth (Ultisol) of the Nigerian savanna was examined by measuring stored amounts of selected nutrients and estimating their rates of turnover via the mounds. A study plot (4?ha) with a representative termite population density (1.5?mounds?ha^?1) and size (3.7?±?0.4?m in height, 2.4?±?0.2?m in basal diameter) of M. bellicosus mounds was selected. The mounds were found to contain soil mass of 9249?±?2371?kg?ha^?1, composed of 7502?±?1934?kg?ha^?1 of mound wall and 1747?±?440?kg?ha^?1 of nest body. Significant nutrient enrichment, compared to the neighboring topmost soil (Ap1 horizon: 0–16?cm), was observed in the nest body for total nitrogen (N) and exchangeable calcium (Ca), magnesium (Mg) and potassium (K), and in the mound wall for exchangeable K only. In contrast, available (Bray-1) phosphorus (P) content was found to be lower in both the mound wall and the nest body than in the adjacent topmost soil horizon. Consequently, the mounds formed by M. bellicosus contained 1.71?±?0.62?kg?ha^?1 of total N, 0.004?±?0.003?kg?ha^?1 of available P, 3.23?±?0.81?kg?ha^?1 of exchangeable Ca, 1.11?±?0.22?kg?ha^?1 of exchangeable Mg and 0.79?±?0.21?kg?ha^?1 of exchangeable K. However, with the exception of exchangeable K (1.2%), these nutrients amounted to less than 0.5% of those found in the topmost soil horizon. The soil nutrient turnover rate via M. bellicosus mounds was indeed limited, being estimated at 1.72?kg?ha^?1 for organic carbon (C), 0.15?kg?ha^?1 for total N, 0.0004?kg?ha^?1 for available P, 0.15?kg?ha^?1 for exchangeable Ca, 0.05?kg?ha^?1 for exchangeable Mg, and 0.06?kg?ha^?1 for exchangeable K per annum. These findings suggest that the mounds of M. bellicosus, while being enriched with some nutrients to create hot spots of soil nutrients in the vicinity of the mounds, are not a significant reservoir of soil nutrients and are therefore of minor importance for nutrient cycling at the ecosystem scale in the tropical savanna.     

Chemical,physical and micromorphological properties of termite mounds and adjacent soils along a toposequence in Zona da Mata,Minas Gerais State,Brazil

Little is known about the effects of neotropical mound-building termites in soil chemical and physical properties. The influence of soil termite activity on soil characteristics was studied by assessing chemical, physical and micromorphological properties of a toposequence of Latosols (Oxisols). Soil samples were collected from the walls and inner parts of termite mounds and also from adjacent soil. A high diversity of termite genera was found in the mounds along the toposequence, together with the inquiline termites and other soil-dwelling arthropods. Chemical analyses showed that pH and the contents of organic C and N, P, Ca and Mg were significantly higher in termite mounds compared with adjacent areas, with an inverse trend for Al content. Significant differences in pH and exchangeable Al were observed between soil and mound across the slopes. The mound density across the landscape was higher at the upper slope segment, followed by the hill top, middle slope and lower slope segments. Considering a lifespan of 30 years and dimensions of termite mounds found in the toposequence we conclude that the textural and chemical uniformity of Latosols may be increased, following the pedobiological turnover during mound building, with local rates varying from 2.1 to 7.5 m³ ha^− 1.     

THE MORPHOLOGICAL, PHYSICAL AND CHEMICAL PROPERTIES OF TWO MOUNDS OF MACROTERMES BELLICOSUS (SMEATHMAN) COMPARED WITH SURROUNDING SOILS IN SIERRA LEONE

The mounds are situated in the Makeni Area, Northern Province, Sierra Leone. Seventy five percent of this area consists of clayey upland soils that belong to the Makeni series (Typic Paleudult), which contain about 80 per cent of gravel-sized hardened plinthite glaebules. The upland is dissected by numerous streams along which gravel-free fine-loamy terrace soils occur that belong to the Masuba series (‘Plin thic’Udoxic Dystropept) occupying about 15 per cent of the area. Mound 1 is a young inhabited mound on a Masuba soil, whilst mound II is an old abandoned mound on a Makeni soil. A trench was dug from the centre of the mounds into the surrounding soils. Profiles were described and samples were analyzed for organic carbon, CEC, exchangeable Ca, Mg, K, Na, and pH, and for particle size analysis with 5 sand fractions. The material used to build the mounds is derived from the subsoil (between 30 and 100 cm depth). Termite channels extended laterally for at least 10 m for mound I, but could not be traced so clearly for mound II. Mound I and the nest of mound II contain a higher percentage of particles less than 250 μm than the surrounding subsoil. Material over 2 mm is not carried by termites. Both mounds show a higher base saturation and higher values of exchangeable Ca, Mg and K, compared to the surrounding subsoil. Increased CEC and pH are noted in mound I and the nest part of mound II, the latter also showing increased values of exchangeable Na. Organic carbon values are equal to those of the surrounding subsoil. Accumulation of mineral elements from organic matter collected as food, including small contributions from the fungus combs and termite bodies, is primarily responsible for the observed differences. In view of the water analyses no contribution is expected from the fluctuating groundwater table.     

SOME EFFECTS OF MOUND-BUILDING TERMITES ON SOILS IN UGANDA

Most large mounds in Uganda are built by termites of the genus Macrotermes. Except for those in valley bottoms they are composed of subsoil which is thought to be collected mainly from depths of 0.5 to 1.0 m, although the evidence is inconclusive. Mounds of both M. bellicosus and M. subhyalinus contain less sand than the subsoil when this is sandy, but only M. subhyalinus mounds contain less clay when the subsoil has a high clay content. In general both species tend to produce a stone-free topsoil whose physical properties are closer to a loam than the average subsoil. Mounds of both species in valley bottoms appear to be built from topsoil. The amounts of organic matter, nitrogen, calcium, phosphorus, and potassium in mounds were estimated together with their rates of turnover. In terms of the demands of two typical crop plants the quantities held in mounds and their rate of release to the surrounding topsoil were small. Only calcium was likely to be cycled in significant amounts. It seems that termites only slightly affect the physical and chemical properties of Ugandan soils, even where mounds are comparatively abundant.     

Effects of termites on the physical and chemical properties of the acid sandy soils of southern Nigeria

Abstract

This study was aimed at characterizing the effects of the activity of termites of the genus Nasutitermes on the physico‐chemical properties of the acid sandy soils of southern Nigeria. Selected morphological properties of the termite mounds were measured in the field. Outside portions of the termite mound and surface (0–15 cm) soil were collected and analyzed for some physical and chemical properties. Results obtained showed a density of 112 mounds ha^‐1 with average height of 0.85 m. There were significantly higher proportions of clay, silt, and organic carbon, and higher pH, exchangeable potassium (K), calcium (Ca), magnesium (Mg), available phosphorus (P), effective cation exchange capacity and base saturation in the mounds of the Nasutitermes than in the surrounding topsoil. Mounds of Nasutitermes termites, if returned to the soil, could improve the properties of the soil in areas where termites occur in large numbers.     

Species specific effects of ants on microbial activity and N-availability in the soil of an old-field

Microbial biomass and activity as well as N-availability were measured in the mounds of three ant species strongly differing in foraging strategy and mound architecture: Myrmica scabrinodis, Lasius niger and L. flavus. Soil microbial biomass (C_mic) was significantly increased in the mounds of all three ant species. This positive effect was due to the accumulation of organic matter (C_org) within the mounds. Microbial activity was increased in M. scabrinodis mounds only. Available N_min was accumulated in all mound types, independent of the feeding mode of the ants, with Lasius mounds having significantly higher N_min content than M. scabrinodis mounds. It is hypothesised that the differences between the mound types are due to differences in nest architecture, especially the integration of grassy vegetation. Higher microbial activity in M. scabrinodis mounds may be a consequence of supplementary energy provided by root exudates. The amount of N_min in M. scabrinodis mounds may be reduced by increased plant uptake and by immobilisation within the microbial biomass.     

Some effects of mound-building termites on the soils of a semi-arid area of Kenya

The nutrient status of soils from Macrotermes termite mounds, in and around Kajiado District, reflects that of the subsoils more closely than in some other studies, notably Watson (1977). Consequently the growth of vegetation on and around mounds was not noticeably enhanced, except in grasslands and in higher rainfall areas. There was no evidence that mounds acted as wicks. Mound soils contained greater concentrations of calcium, magnesium and potassium than subsoils in almost all cases where subsoil values were low, suggesting that the termites’ activities enhanced the nutrient status of mound soils. The nutrients were probably derived from their food, and the effects increased in some cases by their selection of clay on clay-poor soils. Nevertheless, the overall effects of Macrotermes on rangeland soils are probably small. The distribution of Macrotermes is remarkably unaffected by soil types; they construct mounds on almost all soils except those consisting largely of montmorillonite.     

埃塞俄比亚罗毕高原含铬雏形土地区凋落物饲喂的白蚁(Macrotermes spp)的化学性质及其生化活动的研究

Termite(Macrotermes spp.) mounds are complex biological habitats originated by the termite activity and possessing peculiar physical, chemical and biochemical properties. In this study we examined the concentration of nutrients and the biochemical activity of abandoned soil and mounds colonized by termites of the genera Macrotermes located in the Borana District, Ethiopia. To elucidate the magnitude and persistence of the termite-induced effects, we also studied an abandoned mound, previously colonized by termites of the same genera formed on the same soil. Results confirmed that termite-colonized mounds are ‘hot spots' of nutrient concentration and microbial activity in tropical soils. This is due to the termite driven litter input and decomposition. The abandoned mounds showed higher microbial biomass and activity and displayed a nutrient redistribution and a greater microbial activity than the adjacent soils. These findings allowed us to hypothesize a model of nutrient cycling in colonized soils and a partition of the relative roles of termites and soil microorganisms in nutrient location and turnover in tropical soils. These results may be also useful for the optimal management of termite-colonized soils.     

Effects of Ant Mounds on the Plant and Soil Microbial Community in an Alpine Meadow of Qinghai–Tibet Plateau

Ants are important soil engineers, affecting the structure and function of ecosystems. To address the impacts of ants (Camponotus herculeanus ) on the properties of an alpine meadow ecosystem of Qinghai–Tibet Plateau, we investigated the effects of ant mounds on plant biomass, soil physicochemical properties, microbial diversity, and functions. We found that the total biomass of plant community was significantly greater in ant mound periphery. Plant species richness in ant mounds was reduced compared with that of control plots without ant mounds. Significant changes in physicochemical properties of soil were also observed. Soil organic matter, total nitrogen, available phosphorous, total potassium, and available potassium increased in ant mound soil due to the excavation activities by ants as well as the accumulation of organic matter and other nutrients during mound construction. For example, roots/soil contents (g/g) and soil moisture in ant mound soils were lower than those in controls. Microbial community composition and microbial biomass were clearly changed in ant mound soils. BIOLOG analysis further indicated that the functional diversity of the microbial community of ant mound soil increased and differed from that of controls. This study indicates that ant‐induced modification of soil properties indirectly influences plant biomass and species composition, and ant mounds have different microbial communities from those of control soil. Copyright © 2016 John Wiley & Sons, Ltd.     

Soil mixing and genesis as affected by tree uprooting in three temperate forests

The purpose of this study was to identify general patterns of pedoturbation by tree uprooting in three different, forested landscapes and to quantify post‐disturbance pedogenesis. Specifically, our study illustrates how the effects of ‘tree‐throw’ on soils gradually become diminished over time by post‐uprooting pedogenesis. We studied soil development within 46 pit‐mounds in two regions of the Czech Republic, one on Haplic Cambisols and one on Entic Podzols. A third study site was in Michigan, USA, on Albic Podzols. Uprooting events were dated by using tree censuses, dendrochronology and radiometry. These dates provided information on several chronosequences of pedogenesis in the post‐uprooting pits and mounds, dating back to 1816 AD (dendrochronological dating, Haplic Cambisols), 322 AD (median of calibration age, ¹⁴C age = 1720 ± 35 BP, Entic Podzols) and 4077 BC (¹⁴C age = 5260 ± 30 BP, Albic Podzols). Post‐uprooting pedogenesis was most rapid in pits and slowest on mounds. Linear chronofunction models were the most applicable for pedogenesis, regardless of whether the soils were in pit or mound microsites. These models allowed us to estimate the time required for horizons in such disturbed sites to obtain the equivalent thicknesses of those in undisturbed sites. These ranged from 5 (O horizon in pits on the Haplic Cambisols) to > 16 000 years (E horizon on mounds on the Albic Podzols). On the Albic Podzols, development of eluvial and spodic horizon thicknesses suggested that pathways involving divergent pedogenesis may occur at these small and localized spatial scales.     

Incidence of fungus-growing termites (Isoptera, Macrotermitinae) on the structure of soil microbial communities

The aim of this study was to investigate the impact of subterranean fungus-growing termites on the structure of soil microorganism communities. We tested whether termites significantly modify the abundance and structure of microbial communities within their below-ground nests (fungus-comb chambers) and whether these effects are species-specific.The investigations were carried out in a humid savanna reserve with material collected from the fungus-comb chamber walls of two widespread species differing in the mode of nest construction. Ancistrotermes builds diffuse and ephemeral nests while chambers of Odontotermes are mostly concentrated and occupy the same area for a comparatively much longer period of time then creating lenticular mounds. The soil properties (pH, texture and C, N content) and the microbial biomass were analysed and automated rRNA intergenic spacer analysis (ARISA) was used to characterise bacterial (B-ARISA) and fungal (F-ARISA) communities. Our results illustrate that the nest structures created by termites offer a diverse range of physical and chemical environments that differ strongly from those present in the general soil mass. Odontotermes had strong effects on microbial properties at the scale of the fungus-comb chamber and at the scale of the lenticular mound. In the fungus-comb chambers, the microbial biomass is not affected by termites but the structure of microbial community is different from that in the control open savanna soil. In the lenticular mound, the microbial biomass is higher and the structure of bacterial community is distinct than that in the fungus-comb chambers. Ancistrotermes also strongly influenced the structure of soil bacterial and fungal communities in the open savanna. However, we did not find any significant modification of bacterial and fungal community structures in the lenticular mound. The impact of fungus-growing termites is, therefore, species-specific and varies depending on the study site (open savanna vs. lenticular mound).     

Phosphatase activity in Nasutitermes ephratae termite nests

Summary The relationship between phosphatase activity and soil was studied in 14 mounds and adjacent control soils of plant debris-feeding termites from a Venezuelan savanna. The soils were assayed for acid phosphatase activity with p-nitrophenyl phosphate as substrate and for the effect of inorganic P (300 g P g^–1). The proportion of organic matter in the mounds was four times that found in topsoils, indicating strong selection by the termites for organic-rich soil fractions. A comparison of phosphatase activities found no difference between mounds and adjacent soils. It seems possible that the expected increase of enzyme activity in mounds, due to a higher C content, was counteracted by enzyme inhibition due to higher levels of available inorganic P in the mounds. Addition of inorganic P to soil and mound material reduced enzyme activities by 10%–45%, but after a 2-day incubation period differences between the treated soil and the control tended to disappear.     

High performance liquid chromatography studies on the polysaccharides in the walls of the mounds of two species of termite in Senegal,Cubitermes oculatus and Macrotermes subhyalinus: their origin and contribution to structural stability

 The origin, nature and quantity of polysaccharides in the walls of the epigeal mounds of a species of soil-feeding termite, Cubitermes oculatus, and a fungus-growing termite, Macrotermes subhyalinus, found in Senegal, and of soil not considered to be under the influence of termites, were studied to obtain a clearer picture of the structural stability of these materials. The compounds were extractedand analysed by high performance liquid chromatography. We found that the walls of mounds made by soil-feeding species were very rich in sugars soluble in aqueous acid or hot water. Most of the sugars originated from cellulose and hemicellulose, and only a small proportion from microorganisms. There were also significant amounts of stachyose in the mound walls and in the reference soil. This sugar was probably formed by the surrounding vegetation, which was mainly leguminous crops. Comparison of the mineral and organic-mineral particle sizes of samples confirmed that the walls of soil-feeding termite mounds where there is the greatest redistribution of clay have the best aggregating capacity. The results therefore show that the polysaccharides in mound walls of soil-feeding termites are mostly of plant origin. Their influence on the stability of these structure is discussed. The walls of fungus-growing termite mounds contain little organic matter and hence low levels of polysaccharides, which are mainly of plant origin. Received: 19 July 1999     

Soil genesis and heterogeneity of phosphorus forms and carbon below mounds inhabited by primary and secondary termites

Termite activities are known to significantly influence small-scale soil properties in tropical savannas. The lateral and vertical extent of the alterations to the nest's surrounding, and particularly resulting impacts on diagnostic soil horizons remain largely unresolved until today. We examined the effects of mound-building termites on soil genesis and constitutive chemical soil properties in and below their nests. Two transects to a soil depth of 100 cm were dug below three younger mounds of Cornitermes silvestrii (the primary nest builder), three older mounds in which C. silvestrii had died out and which were secondarily colonized mainly by Nasutitermes kemneri, and three reference sites in the Brazilian Cerrado. The samples were characterized by standard procedures for soil classification; in addition, phosphorus extractions were conducted on selected samples using NaHCO₃ for labile P forms, and concentrated HCl for stable P forms. This data set was then used to build calibration models for the prediction of labile and stable inorganic (P_i) and organic (P_o) P forms, as well as for contents of organic carbon (OC), for the remaining samples applying mid-infrared spectroscopy in combination with partial least squares regression (MIRS-PLSR). We can show that the termite influence on the soil was sufficiently large to change diagnostic characteristics of the soils under termite mounds. The MIRS-PLSR predictions were suitable for quantifying organic carbon and most of the labile and stable phosphorus fractions. They showed an enrichment of OC, NaHCO₃-P_o and NaHCO₃-P_i contents in nests inhabited by primary and secondary termites by factors of 1.6–2.0 and 1.4–1.5, respectively. The soils surrounding the nests had higher contents of OC and NaHCO₃-P under both nest types vertically down to 30 cm below the lower nest border, and OC and NaHCO₃-P_i contents were elevated at minimum to a lateral distance of 60 cm away from the nest border. As the pattern of HCl_conc-P_i, which comprised 95% of total P, showed no variations, we conclude that the higher NaHCO₃-P_i amount was formed in termite nests by changing the availability of the more stable HCl_conc-P_i. In contrast to the contents, the OC and NaHCO₃-P stocks below the mounds inhabited by primary termites were comparable to those inhabited by secondary ones, because the bulk density of the secondarily inhabited nests was elevated. This was due to a transport of clay-rich material from the subsurface argic horizons into the nests. Here, the secondary termites even reverted the lessivation observed in the reference soils and under mounds inhabited by primary termites, thus causing the soil types to change from Alisols and Acrisols to the properties of Umbrisols.     

Geomorphological and paleoclimatic implications of soil development from siliceous materials on the coral-reef terraces of Liuchiu Island in southern Taiwan

Liuchiu Island is an uplifted coral-reef island located off southwestern Taiwan. A total of four soil pedons, labeled as LC-1 and LC-2 from the Holocene terraces and LC-3 and LC-4 from the Pleistocene terraces, were sampled on the island for this work. These soils were siliceous, and were characterized by enrichment of clay and free iron (Fe_d). According to Soil Taxonomy, pedons LC-3 and LC-4 were classified as Paleudults and pedons LC-1 and LC-2 were Dystrudepts. The soil properties showed progressive changes from pedon LC-1 to pedon LC-4 in morphology, physical and chemical properties, and clay mineralogy. The contents of total Fe and dithionite-citrate-bicarbonate extractable Fe were significantly higher in pedons LC-3 and LC-4 with high weathering degree than in pedons of LC-1 and LC-2 with less weathering degree. Enrichment of kaolinite and gibbsite in pedons LC-3 and LC-4 also suggested high chemical weathering degree of the soils. The estimated soil ages for all studied pedons were consistent with their degrees in pedogenesis, where pedons LC-3 and LC-4 were located at older terraces and pedons LC-1 and LC-2 were located at younger terraces. Namely, it complied with the geologic interpretation of the continuous and simultaneous uplift and tilt of the island over time. Instead of the in situ weathering from the underlying coral reef limestone, all soils developed from siliceous parent materials deposited onto the surfaces. The SiO₂/Al₂O₃ ratios of soils indicated a component of loess may have been incorporated from continental China as part of the parent material, which confirmed a climate change of strong monsoons or severe dust storms occurred before the Holocene. However, soil development increased by the subsequent warm and humid climates of the interglacial stage over time.     

Soil engineering ants increase CO2 and N2O emissions by affecting mound soil physicochemical characteristics from a marsh soil: A laboratory study

As ecosystem engineers, ants can mediate soil processes and functions by producing biogenic structures. In their mounds, ants not only directly produce CO₂ by respiration, but may also indirectly impact soil greenhouse gas emissions by affecting substrate availability and soil physicochemical characteristics. Recent studies focused on overall gas production from ant mounds. However, little is known about mound material respiration and N₂O emissions in ant mounds in wetlands. We measured CO₂ and N₂O emissions from mound soils of three different ant species (Lasius niger Linnaeus, Lasius flavus Fabricius, and Formica candida Smith) and natural marsh soils in a laboratory incubation experiment. On the whole, average soil CO₂ and N₂O emission rates from ant mounds were significantly higher than from the natural marsh soils. Over the 64 days incubation, the cumulative soil CO₂ and N₂O production from ant mounds was, respectively, 1.5–3.0 and 1.9–50.2 times higher than from the natural soils. Soil gas emissions from ant mounds were significantly influenced by the specific ant species, with soil CO₂ and N₂O emissions from L. niger mounds being higher than those from F. candida or L. flavus mound soils. Cumulative CO₂ and N₂O emissions from ant mound soils were positively correlated with soil clay, total carbon, dissolved organic carbon, total nitrogen and NH₄⁺ content. Our laboratory results indicated that mound soil is an important source of CO₂ and N₂O emission from ant mounds in marshes, making mounds potential “hot spots” for CO₂ and N₂O emissions. Ants may increase the spatial heterogeneity of soil gas emissions by changing mound soil physicochemical properties, especially carbon and nutrition content, and soil texture. Contributions from ant mound materials should be considered when describing soil C and N cycles and their driving factors in wetland ecosystems.