Termite mound density and distribution patterns across three land-use types in the Vhembe District of the Limpopo Province,South Africa

This study investigated the effect of land-use on density and distribution patterns of termite mounds. A total area of 12 ha was investigated using four 1 ha plots from each of three land-use types (mango orchards, maize fields and communal rangelands). A total of 297 mounds from four termite species were recorded. Plotted GIS coordinates for each mound in ArcMap showed a random distribution pattern in all land-use types. The mean number of mounds per hectare was significantly higher (p < 0.001) in communal rangelands (52.5 ± 1.21), than in maize fields (14.75 ± 3.15) and mango orchards (7.5 ± 0.87), and dominated by small-sized mounds of Trinervitermes sp. Few mounds of Odontotermes sp. were found. Mounds of the edible termites, Macrotermes natalensis and M. falciger, were found in all land-use types, with the highest density for both species being in maize fields. Although the mound height for both species was similar, mound circumference for M. falciger was significantly larger (p < 0.001) which may limit land available for agricultural use. Density of mounds was influenced by land-use which may lead to changes in termite ecosystem functioning and availability of termites as a free source of protein.     

Influence of mound construction by red and hybrid imported fire ants on soil chemical properties and turfgrass in a sod production agroecosystem

Mound construction by imported fire ants (Solenopsis spp.) actively modify the biogeochemical and physical properties of soil; however, their influence on nutrient levels in surrounding vegetation is poorly understood. Aside from the reported persistence of elevated available P and K levels in clay-rich soils one year after mound abandonment, the relative stability of nutrient concentrations from one season to the next is largely unknown. Nutrient concentrations were concurrently analysed from ant mounds and undisturbed soils as well as plant samples collected from warm-season turfgrass in a commercial sod production agroecosystem. Initial collection of soil and turfgrass samples coincided with peak annual biomass (September 2006); the second soil sample collection occurred over twelve weeks later during turfgrass dormancy and ant brood minimum (December 2006). Total C, C/N ratios, organic matter (OM), and Zn²⁺ concentrations as well as pH of ant mound soils were significantly higher than control plot soils; these trends persisted across seasons. Turfgrass harvested from ant mound perimeters in September exhibited elevated N, P, Ca²⁺, S, Cu²⁺, Fe²⁺, and Na⁺ concentrations. Evaluation of the relative stability of soil parameters across seasons revealed a significant drop in ant nest pH from September to December 2006. Total N of mound soils was distinctively greater than control soil counterparts during September only. Soil P, K⁺, Ca²⁺, Mg²⁺ and S (all macronutrients), as well as Na⁺ concentrations from ant mound soils were substantially elevated during the late Autumn to Winter transition compared to control soil locations, whereas Fe²⁺ and Mn²⁺ levels (both micronutrients) were significantly lower in ant mound soils versus control soil environments. Continuous pedoturbation by imported fire ants as well as seasonal shifts in mound soil chemistry resulting from changes in assimilation/dissimilation among mound biota may influence the site-specific effectiveness of microfaunal pathogens (e.g., Thelohania solenopsae) or parasites (e.g., Orasema spp.) identified as classical biological control agents of non-native Solenopsis spp. Therefore, further study of the intrinsic complexities of soil ecosystem dynamics of imported fire ant mounds across several seasons is warranted. Received 10 September 2007; revised 23 April 2008; accepted 1 May 2008.     

Effects of the northern pocket gopher (Thomomys talpoides) on alpine soil characteristics, Niwot Ridge, CO

Effects of the northern pocket gopher (Thomomys talpoides) on surface soilcharacteristics were examined at the alpinesite of Niwot Ridge, CO. We measured erosionof soil from gopher mounds and compared thecharacteristics of gopher mound (disturbed) andundisturbed soils in two major plant communitytypes. Our measurements of erosion indicatelong-term susceptibility of gopher-disturbedsoils to redistribution by water and/or wind inthis ecosystem. Ecosystem heterogeneityintroduced by the gopher is reflected insignificantly lower SOM in gopher mounds thanin surrounding undisturbed soils, acharacteristic which appears to be causallyassociated with other effects of gopherdisturbance including changes in soil textureand significantly lower clays, total C, totalN, total P, and labile P. In contrast toplant-available P, NO₃ ^– was higherand steadily increased for the short term in both gopher mound soils and those beneath the mounds. These pools of NO₃ ^– thendecreased to pre-disturbance levels by thefollowing spring. Collectively our resultsindicate that, through the physicalmanipulation of soil and subsequent effects onsoil resources, the northern pocket gopherfunctions as an agent of increased ecosystemheterogeneity and soil mass and nutrientredistribution at Niwot Ridge.     

Effects of controlled livestock grazing and annual prescribed fire on epigeal termite mounds in a savannah woodland in Burkina Faso

The diversity and abundance of epigeal termite mounds were investigated in response to controlled livestock grazing and annual prescribed fire in a Sudanian savannah-woodland in Tiogo State Forest. Sampling of termite mounds was carried out in 4×4 subplots of 0.25 ha in a split-plot experimental design during the rainy season in 2002. There were two main plots of which one was fenced to exclude livestock grazing and the second exposed to grazing. Each of the main plots included 4 subplots with annual prescribed fire since 1992 and 4 subplots without fire. Data were collected on the number and characteristics of termite mounds. A mean density of 698 mounds ha⁻¹ was recorded. Mounds built by Trinervitermes spp. were the most abundant followed by Cubitermes spp., Macrotermes subhyalinus and M. bellicosus. The large mound-builders Macrotermes spp. dominated the community interms of basal area (96% of the total) and above-ground volume (99%). The diversity of mound types was notaffected by livestock grazing and annual early prescribed fire (P>0.05). There was no statistical effect of livestock grazing on mound density, whereas a strong depressive effect of annual fire was observed for Trinervitermes spp. mound density (P=0.012). In this ecosystem, annual prescribed fire appeared to be the major determinant for termite mound abundance. Received 2 February 2007; revised 23 October 2007 and 21 January 2008; accepted 22 Feburary 2008.     

Mulga log mounds: Fertile patches in the semi-arid woodlands of eastern Australia

In the semi-arid woodland of eastern Australia, soil mounds are often associated with fallen mulga (Acacia aneura) trees. Measurements of the physical and chemical properties of the soils in these mounds compared with surrounding soils, together with differences in herbage growth responses, indicate that these mounds are fertile patches, with possible importance as habitats for soil fauna and as refugia for a range of organisms during drought. The mound soil material may accumulate by fluvial, aeolian or rain-splash deposition about the fallen log, however, some of the mound material was derived from termite feeding gallery structures. The surface feeding gallery material may be comprised of soil particles from within the mound or from tunnels and storage galleries below the mound, and probably depends on the termite species.     

Termites (Isoptera) as secondary occupants in mounds of Macrotermes michaelseni (Sj?stedt) in Kenya

Termites were found as secondary occupants in mounds of Macrotermes michaelseni (Sj?stedt) in Kajiado District, in the Rift Valley Province of Kenya. Data are presented from 34 mounds that were completely demolished and extracted to analyse the population of the primary nest. Secondary occupants were found in 29 of the 34 mounds, averaging 2.4 species per occupied mound (or 2.1 species per mound overall). The termites belonged to nine species, three of which were not found anywhere else in the area of study. The frequency of occurrence of the different species and their degree of association with the host mounds are examined and discussed.     

Impact of Formica exsecta Nyl. on seed bank and vegetation patterns in a subalpine grassland ecosystem

The mound building ant Formica exsecta Nyl. is widely distributed in grassland ecosystems of the Central European Alps. We studied the impact of these ants on seed bank and vegetation patterns in a 11 ha subalpine grassland, where we counted over 700 active ant mounds. The mounds showed a distinct spatial distribution with most of them being located in tall‐grass, which was rarely visited by ungulates (red deer; Cervus elaphus L.). Heavily grazed short‐grass, in contrast, seemed to be completely avoided by ants as only few mounds were found in this vegetation type. The species composition of the ant mound and grassland seed banks was quite similar, i.e. from 15 common plant species 12 were found in both seed bank types. We found the same proportions of myrmecochorous seeds in ant mound and grassland soil samples. In contrast, the number of seeds was 15 times higher in mound compared with the grassland soil samples. Also, the vegetation growing on ant mounds significantly differed from the vegetation outside the mounds: graminoids dominated on ant mounds, herbaceous and myrmecochorous species in the grassland vegetation. We found significant continuous changes in vegetation composition on gradients from the ant mound centre to 1 m away from the mound edge. Overall, F. exsecta was found to have a considerable impact on seed bank and vegetation patterns in the grassland ecosystem studied. These insects not only altered grassland characteristics in the close surrounding of their mounds, but also seem to affect the entire ecosystem including, for example, the spatial use of the grassland by red deer.     

Role of termites in the restoration of soils and plant richness on bowé in West Africa

Bowé (hardened ferricrete soils formed by erosion, drought or deforestation) are often associated with termite mounds, but little is known about these mounds and their role in the restoration of soils and plant biodiversity on bowé. This study examined termite mounds on bowé and their effects on soil depth and plant richness. Sixty-four sampling plots were laid out randomly on bowé sites with mounds and on adjacent bowé sites without mounds. The height and circumference of each mound were measured. Species inventories were made and soil depth measured in each plot. Linear mixed effects and generalised mixed effects models with Poisson error distribution were used to assess the variation in soil depth and plant species richness in mound and nonmound microsites. Two types of mounds (small vs. large) associated with different termite species were observed on bowé, with the small mounds being most common. Plots with either large or small mounds had deeper soils and higher plant richness than the adjacent plots without mounds. Conservation of termite mounds is important for restoring soils and plant richness on bowé, and termite mounds should be taken into consideration in biodiversity and soil management strategies for bowé.     

Termite mounds as browsing hotspots: an exception to the rule

In African savannas, termite mounds usually serve as browsing hotspots for mammals because of their soil fertility. Van der Plas et al., in this issue, describe that browsers avoid the unpalatable, evergreen tree species on mounds of Macrotermes natalensis in a mesic savanna, preferring mainly leguminous species with high leaf N and P concentrations in the matrix. This exception is probably a consequence of the fertile soils of the study area, and highlights the importance of environmental context for assessing ecological interactions.     

Nest mounds of red wood ants (Formicaaquilonia): hot spots for litter-dwelling earthworms

A previously undocumented association between earthworms and red wood ants (Formicaaquilonia Yarr.) was found during an investigation of the influence of wood ants on the distribution and abundance of soil animals in boreal forest soil. Ant nest mounds and the surrounding soil of the ant territories were sampled. The ant nest mound surface (the uppermost 5-cm layer) harboured a much more abundant earthworm community than the surrounding soil; the biomass of the earthworms was about 7 times higher in the nests than in the soil. Dendrodrilusrubidus dominated the earthworm community in the nests, while in soils Dendrobaenaoctaedra was more abundant. Favorable temperature, moisture and pH (Ca content), together with abundant food supply (microbes and decomposing litter) are likely to make a nest mound a preferred habitat for earthworms, provided that they are not preyed upon by the ants. We also conducted laboratory experiments to study antipredation mechanisms of earthworms against ants. The experiments showed that earthworms do not escape predation by avoiding contact with ants in their nests. The earthworm mucus repelled the ants, suggesting a chemical defence against predation. Earthworms probably prevent the nest mounds from becoming overgrown by moulds and fungi, indicating possible mutualistic relationships between the earthworms and the ants. Received: 21 November 1996 / Accepted: 3 April 1997     

Short-Term Vegetation and Soil Responses to Mechanical Destruction of Rabbit (Oryctolagus cuniculus L.) Warrens in an Australian Box Woodland

We studied the impact of disturbance by rabbits on plants and soils along a gradient out from the center of ripped rabbit warrens in an Australian semiarid woodland. Five years after the warrens were ripped, the impact of rabbits was still apparent. The cover of bare soil declined, and the cryptogam cover increased with increasing distance from the warren mound. However, litter cover, plant cover, and plant diversity remained unchanged with increasing distance from the mounds. Differences in plant composition were apparent with increasing distance from the mounds, with three species, Schismus barbatus, Salsola kali var. kali, and Chenopodium melanocarpum dominating the mounds, whereas the perennial grass Austrostipa scabra dominated the nonwarren control surfaces. Two species, Crassula sieberana and S. barbatus, dominated the active soil seed bank on ripped warrens. The mounds had the lowest number of species in the soil seed bank, whereas the warren edge microsite had the greatest. Ripped and unripped warrens differed substantially in their complement of species, and ripped warrens contained an order of magnitude fewer active warren entrances compared with unripped warrens. Ripped warrens also had significantly more plant cover than unripped warrens. Taken together, our results reinforce the view that rabbits have a destructive effect on surface soils and vegetation in semiarid woodlands and suggest that restoration of the original woodland vegetation after warren ripping is likely to be a slow and ongoing process.     

Environmental Heterogeneity, Animal Disturbances, Microsite Characteristics, and Seedling Establishment in a Quercus havardii Community

In restoration experiments it is imperative to consider the study of mechanisms of how species are maintained and preserved in a system. This paper reports on the results of a field experiment examining the growth and survival of seedlings of Schizachyrium scoparium, a dominant perennial bunchgrass member of the Quercus havardii (sand shinnery oak) communities of semiarid western Texas, on mounds of displaced soil produced by Sylvilagus auduboni (rabbit). The central question posed is: does environmental heterogeneity created by small mammals influence seedling survival and growth? The specific questions addressed are: (1) Does seedling survival, growth, and nutrient uptake vary when grown on mounds, off-mound soils, and artificially created mounds?; (2) What is the influence of the microbial and litter components of mound soils on seedling survival?; and (3) In communities where animal disturbances create environmental heterogeneity and may impact seedling establishment, is it possible to artificially create mounds that could serve a similar function? Results show that characteristics of mound soils increase seedling survival, shoot and root biomass, root length, number of tillers, mycorrhizal infection, and nutrient uptake more in plants grown on mounds than off mounds. Both the microbial and litter components of mound soils are essential components of this effect. Artificial mounds generated from soils associated with the herbaceous community were more similar to intact rabbit mounds than artificial mounds generated from soils associated with the oaks. The results indicate that rabbits produce rich patches (both nutrient and microbial) favorable to the growth of seedlings of the dominant bunchgrass, and point to the potential importance of rabbit disturbances in shaping the dynamics of this plant community. Thus, rabbit-generated disturbances produce environmental heterogeneity in the sand shinnery oak community, similar to that produced by harvester ants in this community as shown by an earlier study. Small animal activity that results in soil displacement, and influences soil characteristics, may indirectly contribute to the persistence of certain plant species within a community. Thus, disturbances may well operate in semiarid communities to produce nutrient and microbe rich microsites which may function to maintain diversity.     

Effects of Erosion from Mounds of Different Termite Genera on Distinct Functional Grassland Types in an African Savannah

A key aspect of savannah vegetation heterogeneity is mosaics formed by two functional grassland types, bunch grasslands, and grazing lawns. We investigated the role of termites, important ecosystem engineers, in creating high-nutrient patches in the form of grazing lawns. Some of the ways termites can contribute to grazing lawn development is through erosion of soil from aboveground mounds to the surrounding soil surface. This may alter the nutrient status of the surrounding soils. We hypothesize that the importance of this erosion varies with termite genera, depending on feeding strategy and mound type. To test this, we simulated erosion by applying mound soil from three termite genera (Macrotermes, Odontotermes, and Trinervitermes) in both a field experiment and a greenhouse experiment. In the greenhouse experiment, we found soils with the highest macro nutrient levels (formed by Trinervitermes) promoted the quality and biomass of both a lawn (Digitaria longiflora) and a bunch (Sporobolus pyramidalis) grass species. In the field we found that soils with the highest micro nutrient levels (formed by Macrotermes) showed the largest increase in cover of grazing lawn species. By linking the different nutrient availability of the mounds to the development of different grassland states, we conclude that the presence of termite mounds influences grassland mosaics, but that the type of mound plays a crucial role in determining the nature of the effects.     

Soil type and microtopography influencing feeding above and below ground by the pine weevil Hylobius abietis

Abstract 1 The influence of soil type and microtopography on above and below ground feeding by adult pine weevils Hylobius abietis (L.) (Coleoptera: Curculionidae) was evaluated in a field experiment with enclosed weevil populations of known size. 2 Four soil treatments, each with a food source at the centre, were presented within each enclosure: (i) a flat surface with fine‐grained, cultivated humus; (ii) a flat surface with sand; (iii) a conical mound of sand; and (iv) a conical pit in sand. The food source consisted of a stem section of Scots pine Pinus sylvestris L. extending both above and below ground. 3 The majority of feeding on the half buried stem sections occurred below ground; only 2.7% of the total bark area consumed was situated above ground. The variation over time in bark area consumed was not significantly associated with any of the tested weather factors. 4 The amount of feeding was 10‐fold higher on food sources placed in fine‐grained humus than those in areas of flat sand. 5 Less pine bark was consumed on mounds of sand than flat sand surfaces, and there was more feeding in sandy pits than on flat sand. These effects on feeding are explained by the observation that the weevils had difficulties climbing the sandy slopes (27° gradient). 6 We conclude that pine weevil damage to conifer seedlings can be considerably reduced by planting on mounds of pure mineral soil and that planting deeply in the soil increases the risk of damage.     

Gopher mound soil reduces growth and affects ion uptake of two annual grassland species

Summary Portions of an annual serpentine grassland community in California are subject to frequent gopher mound formation. Consequently, studies were undertaken to characterize the effects of mound soils on plant growth and ion uptake. For two of the dominant annual species (Bromus mollis L. and Plantago erecta Morris), growth was reduced in gopher mound soil relative to that in inter-mound soil. A similar reduction in growth was found for plants grown in soils collected at a depth corresponding to the depth of gopher burrowing. This reduction in growth was associated with lower total P and N contents of the soil which were reflected in lower shoot contents of N and P. Additional experiments, however, showed that reduced N and P availabilities in mound soil were not entirely responsible for the growth reduction. Similarly, shoot Ca/Mg ratios were reduced in mound soil but additions of Ca improved the Ca/Mg ratio without improving growth. Growth reductions were associated with altered shoot concentrations of microelements, particularly elevated levels of Mn. A competition experiment between Plantago and Bromus showed that Bromus was more competitive than Plantago in mound and inter-mound soils and that soil type had only small affects on the nature of the interaction between the two species.     

不同形成时间高原鼢鼠鼠丘土壤养分分配规律

高原鼢鼠(Myospalax baileyi)作为青藏高原唯一营地下生活的鼠类,其造丘活动不仅能影响草地群落演替的方向和进程,而且对鼠丘土壤养分含量和分配造成空间异质性。关于不同形成时期的高原鼢鼠鼠丘养分含量及在垂直高度的分配规律研究报道尚少。基于此本研究以不同形成时期的鼢鼠鼠丘为研究对象,对鼠丘土壤养分含量及空间分配规律进行探讨。结果表明:随着鼠丘形成时间的推移,土壤养分总体表现为:1年鼠丘多年鼠丘对照区;与非鼠丘区相比,随着土壤土层增加,土壤养分未呈现规律性的变化。其中,土壤全氮和速效氮含量表现为1年鼠丘3年鼠丘5年鼠丘对照区;0—10cm土壤全磷和速效磷含量变化总体表现为多年鼠丘1年鼠丘对照区,10—30cm土层1年鼠丘土壤中全磷和速效磷含量最高。土壤速效钾和有机质含量随着鼠丘形成时间推移总体表现为:1年鼠丘5年鼠丘3年鼠丘;其中在10—30cm土层,1年鼠丘速效钾和有机质含量显著高于多年鼠丘和对照区。由此可见,高原鼢鼠造丘活动能显著改变土壤养分分配格局,短期内形成养分富集的肥力岛,为鼠丘土壤种子库中种子的萌发和植被生长提供必需的养分保证。     

Soil particle accumulation in termite (Macrotermes bellicosus) mounds and the implications for soil particle dynamics in a tropical savanna Ultisol

This study investigated the influence of mound-building termites on soil particle dynamics on the land surface and in soil-forming processes by examining the amount of soil particles in mound structures of Macrotermes bellicosus in a highly weathered Ultisol of tropical savanna. Soil particle turnover via the mounds was estimated using particle stock data and soil turnover data from previous studies. A 4-ha study plot with six mounds of relatively uniform shape and size was investigated. Soil mass constituting the mounds was 6,166 ± 1,581 kg mound⁻¹ within which the mound wall and nest body accounted for 5,002 ± 1,289 and 1,164 ± 293 kg, respectively. The mound wall contained a significantly larger amount of clay (252 ± 9.97 g kg⁻¹) balanced with a lower sand content (676 ± 26.5 g kg⁻¹) than in the adjacent surface (Ap1) horizon, (46.4 ± 12.8 g clay kg⁻¹; 866 ± 83.2 g sand kg⁻¹); the nest body had much higher clay content (559 ± 51.0 g kg⁻¹) but less sand (285 ± 79.2 g kg⁻¹) than the mound wall. As a result, the mounds of M. bellicosus accumulated clay of 2,874 ± 781 kg ha⁻¹ (corresponding to 2.52% of clay stock in the Ap1 horizon) along with an estimated clay turnover rate of 169 kg ha⁻¹ year⁻¹. These findings suggest a positive feedback effect from termite mound-building activity on soil particle dynamics in tropical savanna ecosystems: M. bellicosus preferentially use subsoil material for mound construction, resulting in relocation of illuvial clay in the subsoil to the land surface where clay eluviation from the surface soil and its illuviation in the subsoil are major soil-forming processes.     

Termite mound formation reduces the abundance and diversity of soil resistomes

Termites are pivotal ecosystem engineers in tropical and subtropical habitats, where they construct massive nests (‘mounds’) that substantially modify soil properties and promote nutrient cycling. Yet, little is known about the roles of termite nesting activity in regulating the spread of antimicrobial resistance (AMR), one of the major Global Health challenges. Here, we conducted a large-scale (> 1500 km) investigation in northern Australia and found distinct resistome profiles in termite mounds and bulk soils. By profiling a wide spectrum of ARGs, we found that the abundance and diversity of antibiotic resistance genes (ARGs) were significantly lower in termite mounds than in bulk soils (P < 0.001). The proportion of efflux pump ARGs was significantly lower in termite mound resistome than in bulk soil resistome (P < 0.001). The differences in resistome profiles between termite mounds and bulk soils may result from the changes in microbial interactions owing to the substantial increase in pH and nutrient availability induced by termite nesting activities. These findings advance our understanding of the profile of ARGs in termite mounds, which is a crucial step to evaluate the roles of soil faunal activity in regulating soil resistome under global environmental change.     

Facies of Liassic sponge mounds, central High Atlas, Morocco

Summary Liassic sponge mounds of the central High Atlas (Rich area, northern Morocco) have a stratigraphic range from the Lower/Upper Sinemurian boundary interval up to the lower parts of the Lower Pliensbachian (Carixian). The base of Liassic sponge mounds consists of a transgressive discontinuity, i.e., a condensed section of microbioclastic wackestones with firm- and hardgrounds, ferruginous stromatolites, sponge spicules and ammonites. The top of Liassic sponge mounds is an irregular palaeorelief covered by cherty marl-limestone rhythmites, namely hemipelagic spicular wackestones with radiolaria. In the Rich area, section Foum Tillicht, the sponge mound succession has a total thickness of about 250 meters. Within this succession we distinguished between three mound intervals. The lower mound interval shows only small, meter-scale sponge mounds consisting of boundstones with lyssakine sponges, commensalicTerebella and the problematicumRadiomura. This interval forms a shallowing-upward sequence culminating in a bedded facies withTubiphytes, calcareous algae (Palaeodasycladus), sponge lithoclasts, coated grains, and thin rims of marine cement. The middle mound interval is aggradational with decametric mounds and distinct thrombolitic textures and reefal cavities. The mound assemblage here consists of hexactinellid sponges, lithistid demosponges, non-rigid demosponges,Radiomura, Serpula (Dorsoserpula), Terebella, encrusting bryozoa, and minor contributions by calcareous sponges, and excavating sponges (typeAka). Thrombolites are dendrolitic and may reach sizes of several tens of centimeters, similar to the maximum size of siliceous sponges. The upper mound interval appears retrogradational and geometries change upsection from mound shapes to flat lenses and level-bottom, biostromal sponge banks. The biotic assemblage is similar to that of the middle mound interval and there is no difference between mound and bank communities. The demise of sponge mounds is successive from regional spread in the Sinemurian to more localised spots in the Lower Pliensbachian. This reduction correlates with an increasing influence of pelagic conditions. At Foum Tillicht, sponge mounds lack any photic contribution and there is virtually no differentiation into subcommunities between mound surface and cavity dwelling organisms. There is some evidence that the heterotrophic food web of mound communities was sourced by oxygen minimum zone edge effects, namely microbial recycling of essential elements such as N and P. Basin geometry suggests a waterdepth of several 100's of meters, well below the photic zone and possibly only controlled by the depth range of the oxygen minimum zone. Palaeoceanographic conditions of well-stratified deeper water masses diminished gradually during widespread transgression across the Sinemurian to Pliensbachian boundary culminating in the Lower Pliensbachianibex ammonite zone.     

Nutrient dynamics and plant assemblages of Macrotermes falciger mounds in a savanna ecosystem

Termites through mound construction and foraging activities contribute significantly to carbon and nutrient fluxes in nutrient-poor savannas. Despite this recognition, studies on the influence of termite mounds on carbon and nitrogen dynamics in sub-tropical savannas are limited. In this regard, we examined soil nutrient concentrations, organic carbon and nitrogen mineralization in incubation experiments in mounds of Macrotermes falciger and surrounding soils of sub-tropical savanna, northeast Zimbabwe. We also addressed whether termite mounds altered the plant community and if effects were similar across functional groups i.e. grasses, forbs or woody plants. Mound soils had significantly higher silt and clay content, pH and concentrations of calcium (Ca), magnesium (Mg), potassium (K), organic carbon (C), ammonium (NH₄⁺) and nitrate (NO₃⁻) than surrounding soils, with marginal differences in phosphorus (P) and sodium (Na) between mounds and matrix soils. Nutrient enrichment increased by a factor ranging from 1.5 for C, 4.9 for Mg up to 10.3 for Ca. Although C mineralization, nitrification and nitrification fraction were similar between mounds and matrix soils, nitrogen mineralization was elevated on mounds relative to surrounding matrix soils. As a result, termite mounds supported unique plant communities rich and abundant in woody species but less diverse in grasses and forbs than the surrounding savanna matrix in response to mound-induced shifts in soil parameters specifically increased clay content, drainage and water availability, nutrient status and base cation (mainly Ca, Mg and Na) concentration. In conclusion, by altering soil properties such as texture, moisture content and nutrient status, termite mounds can alter the structure and composition of sub-tropical savanna plant communities, and these results are consistent with findings in other savanna systems suggesting that increase in soil clay content, nutrient status and associated changes in the plant community assemblage may be a general property of mound building termites.