The ant Lasius flavus alters the viable seed bank in pastures

The creation of small-scale vegetation mosaics by mound building is an important aspect of ant activity in grasslands. The consequences of this process for the composition of the viable soil seed bank are poorly understood. In this study we quantified the impact of the yellow ant Lasius flavus on both aboveground vegetation and seed bank of a low-intensity pasture located in the Vogelsberg area (Hesse, Germany). A few species of the mound vegetation (mainly therophytes) were restricted to the mounds, but most species also occurred in the surrounding area. The seed bank of ant mounds differed from that of the pasture soil between the mounds, with the abundance of germinating seeds being twice as high in the mounds. This was mainly due to the very large number of seeds originating from winter annuals and Thymus pulegioides. Seed abundance of most other species was lower in the mounds. Our results showed that this is partly due to dispersule weight limiting dispersal of seeds from the surrounding vegetation onto the mounds.     

Contributions of ant mounds to soil carbon and nitrogen pools in a marsh wetland of Northeastern China

Ant mounds often occur at high densities in marsh wetlands. However, little information is available regarding their impacts on soil nutrient pools in these ecosystems. We studied C_org, dissolved organic carbon (DOC), total nitrogen (TN), NO₃⁻ and NH₄⁺ concentrations in above-ground ant mounds and in soils under mounds for three ant species (Lasius flavus, Lasius niger and Formica candida), and estimated their contribution to the total soil nutrient pools in a marsh wetland. Ant impacts were greatest in above-ground soils. All measured nutrient concentrations in above-ground mounds were significantly higher than the average values in reference soils (upper 25 cm). However, except for DOC, no significant differences for nutrient concentrations existed between soils under mounds and reference soils. The impacts of ant mounds on soil C and nutrient concentrations varied by ant species. L. niger above-ground mounds stored less C_org, TN and NO₃⁻ than F. candida and L. flavus mounds, or reference soils. At the ecosystem scale, soils in above-ground mounds and under ant mounds all contained less C_org per hectare than the reference soils. Total amounts in nutrient pools from mounds of the three ant species comprised from 5.3% to 7.6% of the total in natural marsh soils. More importantly, ant mounds increased the spatial heterogeneity of nutrient pools. Thus, ant mounds can be important to a fully integrated understanding of the structure and function of wetland nutrient cycles and balances.     

The influence of different vegetation patches on the spatial distribution of nests and the epigeic activity of ants (Lasius niger) on a spoil dump after brown coal mining (Czech Republic)

A study was carried out during 2001 on mine tailings in NW Bohemia aimed at describing the spatial patterns of nests distribution and epigeic activity of ants in relation to the vegetation mosaic. Lasius niger was the most abundant species of ant and its nest mounds were significantly more numerous in patches with sparse vegetation than inside dense Calamagrostis epigejos vegetation; this was particularly true for small and medium-sized nests. Small and medium nests also occurred more frequently near the edges of a given patch than in the center. Large and medium nests were randomly distributed in the area, whereas small nests had an aggregated distribution. Pitfall trapping reveal significantly higher activity of L. niger workers in tall and dense vegetation stands in comparison with low and sparse vegetation. This pattern was particularly pronounced during the peak of foraging activity in summer and was not so significant in spring or autumn. We expect that ant preferentially forage in shaded habitats during the summer months when bare soil may be too hot. The results indicated that nesting and foraging may differ in their microclimatic requirements and the formation of vegetation mosaics may be important to changes in the ant population during succession.     

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.     

Biogenic structures of two ant species Formica sanguinea and Lasius flavus altered soil C,N and P distribution in a meadow wetland of the Sanjiang Plain,China

Biogenic structures produced by soil ecosystem engineers influence the soil architecture and mediate soil functions and ecosystem services. Ant mounds in meadow wetlands are important biogenic structures with the potential of altering carbon storage and nutrient cycling in these ecosystems. In this study, we examined the soil nutrient concentrations of ant mounds and their effects on the wetland nutrient storage functions in meadow wetlands of the Sanjiang Plain, in northeastern China. The aims of this study were to investigate C, N and P variation in active ant mounds produced by Formica sanguinea Latreille and Lasius flavus Fabricius to estimate the C, N and P pools of ant mounds in comparison with control soil. The average total N (TN), total P (TP) and available P (AP) concentrations in the ant mounds of both species were higher than in the control soil. Organic carbon (C_org), DOC, NH₄⁺ and NO₃⁻ in F. sanguinea mounds were higher than in the control soil, but not for L. flavus mounds. Average concentrations of all the five types of nutrient were higher in F. sanguinea mounds than in L. flavus mounds. The variations in C_org, DOC, TN and TP concentrations in ant mounds were not significant at depths from 0 to 25 cm. NH₄⁺ and NO₃⁻ concentrations differed by soil layers for F. sanguinea mounds but not for L. flavus mounds. The C/N ratios were generally lower in the mounds than in the control soil (at 5–25 cm), but no significant differences were found for C/P ratios (except at 10–15 cm). Carbon and DOC pools were smaller, TN and AP pools were larger in ant mounds compared with the control soil, but there was no significant difference for TP pools. NH₄⁺and NO₃⁻ pools were substantially larger in F. sanguinea mounds, but smaller in L. flavus mounds, than those in the control soil. All of the five types of nutrient pools were larger in F. sanguinea than in L. flavus mounds. Ant mounds increased the spatial variability of soil nutrient pools in the wetland.     

Ant-induced soil modification and its effect on plant below-ground biomass

Lasius flavus is a dominant mound-building ant species of temperate grasslands that significantly modifies soil parameters. These modifications are usually the result of workers’ activities such as food accumulation and nest construction. An alternative hypothesis that could explain changes in soil is colony founding in areas of higher soil fertility.In our study we investigated several soil parameters sampled in 10 ant nests and adjacent (control) plots in mountain grassland in Slovakia. The alternative hypothesis was tested by comparing occupied and abandoned mounds. While we found increased concentrations of available P and K in the nests, concentrations of total C, total N, Ca²⁺ and Mg²⁺ were lower there. We propose that differences found between the soil of nests and control plots are entirely a product of ant activity during mound occupancy and not due to initial soil differences during nest establishment. This was confirmed by the comparison of occupied and abandoned nests in which the soil fertility of abandoned nests was similar to conditions in the surrounding soil.Along with the modification of soil chemistry, we recorded changes in soil physical properties and the vertical distribution of nutrients. Ant nests were characterized by the dominance of 0.02–0.1 mm particles and lower bulk density. In the same habitat, nutrient concentrations did not change along the vertical gradient in contrast to control plots where soil nutrients decreased and bulk density increased with depth. Root biomass followed the vertical pattern observed with nutrients: in control plots, most roots were concentrated in the uppermost layer (0–3 cm), whereas they were evenly distributed along the vertical gradient in the nests. We also found that rhizome internodes of Agrostis capillaris were thinner and longer in plants from the mounds. Changes in soil physical properties, vertical distribution of nutrients and root biomass in the nests are most probably a consequence of mounding and soil mixing (bioturbation), which has been less reported on in ant-soil studies.     

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.     

Unique soil microbial assemblages associated with grassland ant species with different nesting and foraging strategies

Ants are important ecosystem engineers and can be abundant in extensively managed grassland ecosystems. Different ant species create nests varying in structure and size, and tend to have a variety of feeding strategies. Differences in food imported to the nest and contrasting nesting behaviour may control soil microbial community structure in nest soil, with cascading effects on nutrient cycling, but this has not been tested in grassland ants. Soil and ants were sampled from nests of three ant species: two formicines; Lasius flavus (aphid farmer/scavenger, mound builder) and Formica lemani (scavenger/hunter, non-mound builder), and a myrmicine; Myrmica sabuleti (hunter/scavenger, non-mound builder), in an extensively grazed temperate grassland and compared to similar soils without ants. Microbial assemblages were determined using molecular approaches (terminal restriction length polymorphism and automated ribosomal intergenic spacer analysis). Both aboveground (vegetation diversity) and belowground (soil physico-chemical properties) components were measured to assess the potential of the different ant species to modify the environment. Stable isotope ratios (δ¹³C and δ¹⁵N) of ant tissues and nest soil organic matter confirmed differences in trophic distances. Significant changes in soil pH, moisture content, total C and total N, and in vegetation composition, demonstrated ant ecosystem engineering effects. In turn, nests of L. flavus, M. sabuleti and F. lemani had different microbial activities and harboured significantly different microbial assemblages (total bacteria, total fungi, ammonia-oxidising bacteria and nitrogen-fixing bacteria), but the diversity was similar. These findings suggest that grassland ants can control microbial assemblages via changes in physical and biological soil characteristics in their nests, and as such, different ant species harbour unique microbial assemblages in nests.     

Nest-mounds of the yellow meadow ant (Lasius flavus) at the “Alter Gleisberg”, Central Germany: Hot or cold spots in nutrient cycling?

Nests of the yellow meadow ant (Lasius flavus) occur at high densities in grasslands worldwide. Although many studies have shown that L. flavus nests influence soil nutrient contents, little is known about their effect on soil nutrient cycling rates. The aim of this study was to examine the role of nest-mounds inhabited by L. flavus as potential ‘hot spots’ for soil nutrient cycling. Six pairs of nest-mounds and control soils were selected at a grassland site at the plateau of the Alter Gleisberg (Thuringia, Central Germany). L. flavus significantly modified the soil environment within the nest. In comparison to the control soils, nest-mounds were characterized by slightly higher soil temperatures during the summer months. In addition, we found that nests were related to decreased potential C mineralization rates and increased potential net N mineralization rates. Nest-mound soil exhibited lower amounts of SOC, hot-water extractable DOC and DN, and higher concentrations of leachable DOC and DN. Moreover, ants promoted the enrichment of base cations in the nest. Differences in the soil environment between nests and control soils were possibly a result of the burrowing activity of ants, soil mixing, accumulation of aphid honeydew, and decreased plant-derived nutrient inputs into the nest-mound soil. In conclusion, L. flavus nest-mounds had a significant but element dependent effect on the soil nutrient cycling and may represent cold spots for C cycling and hot spots for N cycling. Thus, L. flavus nests increase the spatial heterogeneity of soil properties and create unique micro-sites within grassland ecosystems.     

The impact of harvester ants on decomposition, N mineralization, litter quality, and the availability of N to plants in the Mojave Desert

In arid areas of North America, nests of the seed-harvesting ant Pogonomyrmex rugosus tend to be elevated in mineral nitrogen and other soil nutrients relative to other microhabitats. We investigated the roles of decomposition, N mineralization, and plant nutrient uptake in maintaining high standing stocks of nutrients in P. rugosus ant nests. Decomposition rates of standard cellulose substrates placed on the surface of ant nests and other desert microhabitats suggest that conditions found in ant nests and bare areas are conducive to higher rates of decomposition than conditions under shrubs. In laboratory incubations of moist soil, net N mineralization rates were significantly higher in soil from ant nests than from bare areas and under two of three plant species. Net N mineralization rates measured in situ were much lower than those measured in laboratory incubations, but ant nest soil still exhibited higher rates at one of two sites. Litter collected from ant mounds, composed chiefly of seed chaff, was similar in N content to litter collected from underneath the dominant plant species, but had a significantly higher mean δ¹⁵N. Using this distinctive isotope signature as a tracer, we found no evidence that large perennial shrubs tap ant nests as a source of N. An invasive, annual grass species was significantly enriched in ¹⁵N, had higher leaf %N, and produced more seeds when growing on the mound than when growing several meters away; however P. rugosus nest surfaces are typically free of such annuals. We conclude that both high rates of nutrient cycling relative to other Mojave Desert microhabitats and low N utilization by the surrounding vegetation contribute to high standing stocks of mineral N in P. rugosus nests.     

Carbon,nitrogen and phosphorus dynamics of ant mounds (Formica rufa group) in managed boreal forests of different successional stages

Wood ants (Formica rufa group) are ubiquitous in European boreal forests and their large long-lived mound nests, which mainly consist of forest litter and resin, accumulate carbon (C) and nutrients. The C and nutrient dynamics of wood ant mounds in response to forest succession have received minor attention in boreal forests. We aimed to study whether the C, nitrogen (N) and phosphorus (P) concentrations and the bulk density of ant mounds differ from those of the surrounding forest soil, to estimate the C, N and P pools in ant mounds, and to test whether the concentrations and pools change with forest age. Norway spruce (Picea abies (L.) Karst.) stands on medium-fertile sites in 5-, 30-, 60- and 100-year stand age classes were studied in eastern Finland. Carbon and P concentrations in the above-ground mound material were higher than those in the surrounding organic layer. The C, N and extractable P concentrations were higher in the soil under the ant mounds than in the surrounding mineral soil (0–21 cm). The low bulk densities in the ant mounds and the soil below them could be a result of the porous structure of ant mounds and the soil-mixing activities of the ants. The C/N ratios were higher in the mounds than in the organic layer. Carbon concentrations in the ant mounds increased slightly with stand age. Carbon, N and P pools in the ant mounds increased considerably with stand age. Carbon, N and P pools in ant mounds were <1% of those in the surrounding forest soil. Nevertheless, the above- and belowground parts of the ant mounds contained more C, N and P per sampled area than the surrounding forest soil. Wood ants therefore increase the spatial heterogeneity in C and nutrient distribution at the ecosystem level.     

Occurrence of Platyarthrus schoblii (Isopoda, Oniscidea) and its ant hosts in Hungary

The myrmecophilous Platyarthrus schoblii Budde-Lund, 1885 is widely distributed and native in the Mediterranean region. In Hungary it was first found at Budapest, in 2001, in a colony of Lasius neglectus van Loon, Boomsma and Andrásfalvy, 1990 (Hymenoptera: Formicidae). This invasive and polygynous ant species is dispersing in an antropochorous way throughout Europe. There are 16 known colonies of L. neglectus in Hungary. Fourteen of them have been surveyed for the isopod, which was detected in eight cases (57%). In addition to L. neglectus, the isopod has been recently found with other native ant species [Lasius niger (Linnaeus, 1758), Lasius emarginatus (Olivier, 1791) and Tetramorium caespitum (Linnaeus, 1758)] in the country. We have also found the joint occurrence of P. hoffmannseggii Brandt, 1833 and P. schoblii. The co-occurrence and joint expansion of the ranges of L. neglectus and P. schoblii indicates their co-habitation and antropochorous dispersal while the appearance with L. emarginatus, L. niger and T. caespitum supports our hypothesis about possible adoption by different ant species.     

Soil engineering ants increase grass root arbuscular mycorrhizal colonization

The role of edaphic factors in driving the relationship between plant community structure and ecosystem processes is a key issue of the current debate on functional implications of biodiversity. In this study, we draw a direct link between aboveground/belowground relationships, vegetation structure, and aboveground management. We used ground nesting ants and arbuscular mycorrhizal fungi (AMF) as an example for quantifying the role of biotic interactions in soil. Although both groups are known to have a major impact on grasslands, the interactive effect of these taxa on vegetation structure and its sensitivity to grassland management is poorly understood. We show that the ant Lasius flavus increases the root arbuscular mycorrhizal colonization (AMC) of grasses by modifying biotic and abiotic soil properties. As a possible consequence, the shoot length of grass growing on ant mounds was shorter and shoot N and P concentrations were higher than in grass growing off of the mounds. In addition, management affected ant nest architecture and soil and, in turn, AMC. These results emphasize the need to consider the interactions between plants, soil microorganisms, soil fauna, and aboveground management to increase the understanding of the drivers of biodiversity and ecosystem functioning in grasslands both aboveground and belowground.     

Decomposition of organic matter and nutrient mineralisation in wood ant (<Emphasis Type="Italic">Formica rufa</Emphasis> group) mounds in boreal coniferous forests of different age

Wood ants (Formica rufa group) are dominating ecosystem elements of the boreal region due to their wide and abundant occurrence. They collect and concentrate organic material from the surrounding forest floor by building large above-ground mounds. These mounds have higher temperature and lower water content than the surrounding forest floor. We studied how these peculiar environmental conditions affected mass loss and carbon (C), nitrogen (N), phosphorus (P) and potassium (K) mineralisation of organic matter in boreal Norway spruce (Picea abies L. Karst.)-dominated mixed forest stands of four different age classes (5-, 30-, 60-, and 100-year-old) situated in eastern Finland using the litter bag technique. Norway spruce needle litter was incubated in inhabited and abandoned wood ant mounds as well as on the surrounding forest floor. We expected decomposition to be extremely slow due to the dryness of the mounds. Mass losses inside inhabited mounds were lower compared to the surrounding forest floor (on average 30 vs 50% after 2 years) but not as low as we expected, which might be a result of ant and microbial activity in the mounds. Decomposition in the abandoned mounds proceeded similarly as on the forest floor. Nutrient mineralisation proceeded more slowly in the ant mounds than on the surrounding forest floor. Mineralisation occurred for all studied nutrients in the ant mounds, except for N, which net amount remained stable during the years of the experiment. When wood ant mounds are abandoned and their porous and dry structure is no longer maintained by the ants, their decomposition is accelerated, and nutrients may be available for uptake by plants, although the nutrient mineralisation seems still to remain lower compared to the surrounding forest floor. However, eventually the mound material will be decomposed and nutrients mineralised, thus providing a nutrient hot spot increasing the heterogeneity of forest floor nutrient availability.     

Wood ant nests as potential hot spots for carbon and nitrogen mineralisation

Red wood ants (the Formica rufa group) build large nests which can last for many years. The ants often bring large quantities of conifer litter to their mounds. In this study we compared chemical properties of the forest floor and ant-nest materials of red wood ants at two different sites in Sweden. We also did an incubation study in the laboratory to determine C and N mineralisation rates of soil and nest materials at two moisture levels. Some chemical properties, e.g. pH and C/N ratio, differed between sites. Nests were always drier, had a higher C/N ratio and often had higher NH₄⁺ concentrations than the surrounding forest floor. This indicates that the nests increase spatial heterogeneity of the forest floor not only because they contain large amounts of organic matter but also because of qualitative differences in nest composition. In the incubation study, experimentally increased moisture levels in the nest material resulted in net N immobilisation, while surrounding litter and humus materials showed net N mineralisation. The CO₂ evolution was clearly increased by increased moisture. Dry conditions in the nest material prevented it from being decomposed and, since there were no plants to take up N, inorganic N accumulated. However, based on our results we hypothesise that ant nests do not produce large amounts of inorganic N as long as the ants bring fresh litter with high C/N ratio to the nests and keep the nests dry. However, the nests can be considered as potential "compost heaps" which probably decompose faster and will be a source of N leaching when the ants no longer maintain the specific dry conditions.     

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.     

Nutrient storage in soils and nests of mound-building <Emphasis Type="Italic">Trinervitermes</Emphasis> termites in Central Burkina Faso: consequences for soil fertility

Nest structures of two termite species (Trinervitermes spp.) with epigeal (above-ground) mounds were analyzed to compare their nutrient status with that of adjacent soils. To take into account soil variability, the observations and samplings were made in three toposequences of different and representative West African savanna soils. The data showed the high degree of adaptation of these termite species to a large range of soil types and environments. Mounds of Trinervitermes geminatus and Trinervitermes trinervius, both grass-feeders, contained more clay, organic matter (OM), and exchangeable cations than the surrounding surface layer soil. The storage of OM and exchangeable cations was determined for T. geminatus nests and compared to the surrounding soil. Despite substantial nutrient storage in mounds, its total weight appeared low when compared to the nutrient storage in the surrounding 0–15 cm of soil surface layer. This illustrates how contradictory points of view on the use of termite mounds in agriculture need to be clarified using a classical approach that takes into account data by species; and this also evaluates the contribution of different termite mounds to nutrient fluxes and storage and the exact stocking rate of living mounds.     

Scots pine (Pinus sylvestris L.) roots and soil moisture did not affect soil thermal sensitivity

Through their effects on microbial metabolism, temperature and moisture affect the rate of decomposition of soil organic matter. Plant roots play an important role in SOM mineralization and nutrient cycling. There are reports that rhizosphere soil exhibits higher sensitivity to temperature than root-free soil, and this can have implications for how soil CO₂ efflux may be affected in a warmer world. We tested the effects of 1-week incubation under different combinations of temperature (5, 15, 30 ^°C) and moisture (15, 50, 100% WHC) on the respiration rate of soil planted with Scots pine and of unplanted soil. Soil respiration in both soils was the highest at moderate moisture (p < 0.0001) and, increased with temperature (p < 0.0001). There was also marginally significant effect of soil kind on respiration rate (p < 0.055), but the significant interaction of temperature effect with soil kind effect, indicated, that soil respiration of planted soil was higher than unplanted soil only at 5 ^°C (p < 0.05). The soil kind effect was compared also as Q₁₀ coefficients for respiration rate, showing the relative change in microbial activity with increased temperature. However, there was no difference in the thermal sensitivity of soil respiration between planted and unplanted soils (p = 0.99), irrespective of the level of soil moisture. These findings were similar to the latest studies and confirmed, that in various models, being useful tools in studying of soil carbon cycling, there is no need to distinguish between planted and unplanted soil as different soil carbon pools.     

The effect of stand age on CO2 efflux from wood ant (Formica rufa group) mounds in boreal forests

Recent studies suggest that wood ants (Formica rufa group) mounds are point sources of carbon dioxide (CO₂), which increase the heterogeneity of soil carbon (C) emissions in forest ecosystems. However, little is known about the impact of anthropogenic activities, such as logging and subsequent forest succession, on these fluxes. In this study, we measured the CO₂ efflux and temperature of wood ant mounds and the surrounding forest floor in managed Finnish boreal forests of different ages (5, 30, 60, and 100 years old) to assess how the effluxes vary with stand age. We conducted efflux measurements from the mounds and the surrounding forest floor throughout the ants' active season (May–September) and during the onset of hibernation (October). The annual CO₂ efflux was then estimated using mound or forest floor temperatures, which were measured for one year. The average annual CO₂ efflux from the ant mounds was 10.2 (±5.8 SD) kg m⁻² year⁻¹, increasing from 3.9 (±0.3 SD) kg m⁻² year⁻¹ in the 5 year-old stands to 14.3 (±3.0 SD) kg m⁻² year⁻¹ in the 100 year-old stands. Temperatures was significantly higher in the ant mounds than in the forest floor, and the average temperature difference between mounds and forest floor increased with stand age, being the lowest in the 5 year-old (4.1 (±3.1 SD) °C) and highest in the 100 year-old stands (10.3 (±5.2 SD) °C). There were no statistical differences in the mound CO₂ efflux per volume among forest age classes, suggesting higher ant CO₂ efflux in the older stands likely come from larger ant populations in the bigger mounts. The different mound temperature regimes among stand age classes indicates that the activity of wood ants changes with forest succession, particularly after clear-cutting, which alters CO₂ efflux from the mounds. The impact of ant mounds on total CO₂ efflux from the soil, estimated from mound area and volume, respectively, increased with forest age, from 0.05 (±0.05 SD) % to 0.31 (±0.18 SD) % and from 0.05 (±0.06 SD) % to 0.90% (±1.11 SD).     

Respiratory substrate availability plays a crucial role in the response of soil respiration to environmental factors

We examined the response of the temperature coefficient (Q₁₀) for soil respiration to changes in soil temperature and soil moisture through a laboratory incubation experiment. Two types of soils differing in vegetation and moisture status were collected and incubated under two temperatures (10 and 30 °C) and two soil moisture regimes (35 and 75% of water holding capacity, WHC) for 5 weeks. Before and after the incubation experiment, the temperature coefficient of soil respiration was measured using soda-lime method by changing temperature in a water bath. For both soils, the mean Q₁₀ values of the respiration rate were 2.0 in the 30 °C and 2.3 in the 10 °C soil treatments. Higher temperature with lower soil moisture treatment significantly decreased the Q₁₀ value, whereas lower temperature with higher soil moisture treatment significantly enhanced the Q₁₀ value (ANOVA, p < 0.05). These results indicate that soils became less sensitive to temperature when incubated under higher temperature with higher moisture conditions, and more sensitive in lower temperature with higher moisture conditions.There was a significant correlation (r² = 0.67, p < 0.05) between water-soluble carbon (WSC) and soil respiration rate. However, the correlation between soil respiration rate and microbial biomass carbon (MBC) was weak (r² = 0.27, p > 0.05). Although incubation temperature and moisture accounted for 40 and 29% (as r² × 100%), respectively, of variations in Q₁₀, soil water-soluble carbon content alone could have explained 79% of the variation, indicating that the availability of respiratory substrate, rather than the pool of soil microorganisms, played a crucial role in the response of the temperature coefficient to environmental factors. These results suggest that biotic factors should also be taken into consideration when using the Q₁₀ function to predict the response of soil respiration to global warming.