Mineral Soil Horizons Research Articles

How ambient temperature rise affects mercury dynamics and its pools in secondary forests

The forest ecosystem is a significant pool for capturing atmospheric mercury (Hg) deposition, with most Hg accumulating in forest soils. As secondary forests now dominate global forest cover, they are particularly sensitive to changes in ambient temperature. However, the impact of these changes on Hg dynamics in secondary forests remains poorly understood. Here, we quantified Hg inputs, outputs, and mass balances in two secondary forests in China, each with different ambient temperatures. We found that elevated ambient temperature (~1.0℃) advanced the germination of leaves by 2-3 days and extended the growing season by approximately one week, resulting in increased litterfall biomass by 1.18 Mg hm-2 yr-1 and a thicker litterfall layer by 0.22cm over 34 years. This temperature rise also facilitated Hg methylation within forest and enhanced methylmercury (MeHg) export, heightening the potential risk of MeHg exposure to surrounding ecosystems. Additionally, higher ambient temperature not only increased soil Hg emissions (2.75µgm-2 yr-1) but also led to significant Hg deposition via litterfall (9.26µgm-2 yr-1), resulting in a net annual Hg deposition of 6.88µgm-2 yr-1. This net Hg deposition accumulated in the topsoil, increasing the Hg pool by 0.51mgm-2 in organic and 0-10cm mineral soil horizons. Our findings suggest that even a ~1.0℃ temperature rise could enhance the role of secondary forests as atmospheric Hg sink by 45.10%. Therefore, the impact of ongoing climate warming on Hg cycling and pools in forests should receive increased attention and warrants further research.

Resource availability enhances positive tree functional diversity effects on carbon and nitrogen accrual in natural forests

Forests harbor extensive biodiversity and act as a strong global carbon and nitrogen sink. Although enhancing tree diversity has been shown to mitigate climate change by sequestering more carbon and nitrogen in biomass and soils in manipulative experiments, it is still unknown how varying environmental gradients, such as gradients in resource availability, mediate the effects of tree diversity on carbon and nitrogen accrual in natural forests. Here, we use Canada’s National Forest Inventory data to explore how the relationships between tree diversity and the accumulation of carbon and nitrogen in tree biomass and soils vary with resource availability and environmental stressors in natural forests. We find that the positive relationship between tree functional diversity (rather than species richness) and the accumulation of carbon in tree biomass strengthens with increasing light and soil nutrient availability. Moreover, the positive relationship between tree functional diversity and the accumulation of carbon and nitrogen in both organic and mineral soil horizons is more pronounced at sites with greater water and nutrient availabilities. Our results highlight that conserving and promoting functionally diverse forests in resource-rich environments could play a greater role than in resource-poor environments in enhancing carbon and nitrogen sequestration in Canada’s forests.

Molecular Composition of Humic Acids and Soil Organic Matter Stabilization Rate of the First Arctic Carbon Measurement Supersite “Seven Larches”

In the framework of the implementation of the all-Russian climatic project “Carbon measurement test sites”, reference soils of “Seven Larches” carbon supersite, which is a benchmark and the only monitoring site in the Artistic latitudes, were investigated. The morphological structure of representative soils was specified, and it was found that soils are classified as Cryosols of different types (Histic, Stagnic or Gleyic). The basic physico-chemical characteristics of the soils were studied. By means of elemental analysis and 13C NMR spectroscopy, the composition and molecular structure of humic acids from organic and mineral soil horizons were studied. The surface (organic) soil horizons are characterized by high values of H:C molar ratios (1.2–1.3), which indicates a lower degree of the molecular structure aromaticity of humic acids from organic soil horizons. Analysis of the molecular structure of humic acids by 13C NMR spectroscopy showed that humic acids of the studied soils are characterized by the predominance of non-substituted aliphatic (0–47 ppm) and aromatic (108–164 ppm) fragments. Mineral soil horizons are characterized by higher stabilization of organic matter (with lower SOC content—0.5–0.9%) and higher hydrophobicity of humic acid molecules. Comparison of the obtained results with previously published data on the structural and elemental composition of humic acids isolated from soils of similar genesis and geographical location did not reveal any significant differences between the data obtained by us and previously published data. Thus, for “Seven Larches” carbon supersite “reference” parameters of elemental composition of humic acids, their molecular composition and degree of stabilization of soil organic matter were identified.

Effects of large-scale restoration on understory plant communities in an industrial landscape

Starting in the mid 1970’s, researchers, industry leaders, and residents collaborated on one of the world’s largest regreening programs in the industrial region of Sudbury, Canada. The Sudbury Regreening Recipe included the application of crushed dolomitic limestone, nitrogen–phosphorus–potassium fertilizers, grass–legume seed mixtures across 8200 ha, and subsequent tree planting across 25 000 ha of acidic metal-contaminated land. The current study evaluated shifts in understory vegetation diversity and soil geochemistry on a chronosequence of sites treated the same way between 1982 and 2012. Fifty-six plant species were identified across the 24 sites, only four of which were planted in the initial remediation effort. Key factors influencing plant community composition and diversity were related to shifts in soil properties over time: bulk density, LFH layer depth, and mineral soil horizon pH. Plant communities differed with stand age and rocky sites had significantly different plant communities and lower canopy cover than less rocky sites. Mineral soil horizon pH increased with age, reflecting the movement of applied dolomite in soil. Despite high concentrations of total copper and nickel in soil, plant succession patterns were generally similar to those in naturally recovering forests demonstrating the overall success of the restoration program.

Tracing sources of dissolved organic matter along the terrestrial-aquatic continuum in the Ore Mountains, Germany

There is growing concern about the rising levels of dissolved organic matter (DOM) in surface waters across the Northern hemisphere. However, only limited research has been conducted to unveil its precise origin. Compositional changes along terrestrial-aquatic pathways can help determine the terrestrial sources of DOM in streams. Stream water, soil water and soil horizons were sampled at four sites representing typical settings within a forested catchment in the Ore Mountains (Erzgebirge, Germany) from winter 2020 to spring 2022. The samples were analyzed using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The resulting data were successfully subjected to semi-automatic processing of the molecular composition of DOM, reaching a percentage of identified peaks up to 98 %. Principal component analysis (PCA) and cluster analyses were carried out to identify distinct differences between DOM from the potential sources and in the streams. According to the PCA, organic soil horizons, soil water, and stream water samples could be clearly distinguished. Cluster analysis revealed that soil water DOM at all depths of Peats and deeper horizons of the Peaty Gleysols contributed the most to DOM in the stream section dominated by organic soils. In areas dominated by mineral soils, stream DOM resembled the DOM from the deeper mineral horizons of Cambisols and Podzols. Overall, our results suggested that most of the DOM exported from the catchment was derived from deeper mineral soil horizons, with little contribution of DOM derived from organic soils. Therefore, DOM fingerprint analysis of in-situ soil water proved to be a promising approach for tracing back the main sources of stream water DOM.

Physical Properties of Upper Mineral Soil Horizons in a Cutover Area of the Middle Boreal Forest in the Komi Republic

Physical Properties of Upper Mineral Soil Horizons in a Cutover Area of the Middle Boreal Forest in the Komi Republic

PHYSICAL PROPERTIES OF UPPER MINERAL HORIZONS OF CUTTING AREA (MIDDLE TAIGA, KOMI REPUBLIC)

Changes in the physical properties of podzolic soils were analysed three years after a cutting of coniferous-deciduous plantings in the territory of the middle taiga of the Komi Republic with three- and ten-fold forwarder passes, as well as after leveling deep ruts formed after ten passes. The influence of different number of passes on soil density, filtration coefficient, penetration resistance is shown. An assumption about various mechanisms of soil change has been made: three forwarder passes lead to compression, ten - to compression and turbation, which was confirmed by indications of soil density and hardness. It was revealed that compression leads to an increase in density by 0.15 g·cm-3 and penetration resistance by 25%. Meanwhile, filtration rate did not change. Ten passes lead to turbation, which levels the possible compaction due to an introduction of forest litter into the upper mineral soil horizons. Moreover, hardness values decreased by 2-3 times and water permeability decreased from 70 to 1 cm·day-1. It was revealed that leveling deep ruts causes a noticeable decrease in soil density after three years, including in comparison with the undisturbed soil. Furthermore, filtration rate increases several times. Penetration resistance is also increased. An estimation of the water retention curve approximation parameters by the van Genuchten equation made it possible to identify changes in soil of ruts compared to the a mechanically undisturbed site. A decrease in the range of mobile moisture was noted as a result of compaction after heavy equipment usage, leading to moisture stagnation in ruts.

Differential structure and function of phosphorus-mineralizing microbial communities in organic and upper mineral soil horizons across a temperate rainforest chronosequence.

Microbial community structure and function were assessed in the organic and upper mineral soil across a ~4000-year dune-based chronosequence at Big Bay, New Zealand, where total P declined and the proportional contribution of organic soil in the profile increased with time. We hypothesized that the organic and mineral soils would show divergent community evolution over time with a greater dependency on the functionality of phosphatase genes in the organic soil layer as it developed. The structure of bacterial, fungal, and phosphatase-harbouring communities was examined in both horizons across 3 dunes using amplicon sequencing, network analysis, and qPCR. The soils showed a decline in pH and total phosphorus (P) over time with an increase in phosphatase activity. The organic horizon had a wider diversity of Class A (phoN/phoC) and phoD-harbouring communities and a more complex microbiome, with hub taxa that correlated with P. Bacterial diversity declined in both horizons over time, with enrichment of Planctomycetes and Acidobacteria. More complex fungal communities were evident in the youngest dune, transitioning to a dominance of Ascomycota in both soil horizons. Higher phosphatase activity in older dunes was driven by less diverse P-mineralizing communities, especially in the organic horizon.

Estimation of Carbon Stocks in Soils of Forest Ecosystems as a Basis for Monitoring Climatically Active Substances

The eluvozems and soddy eluvozems on two-layer deposits dominating in the soil cover of the Zvenigorod biostation of Moscow State University contain, on average, 65–83 t/ha of organic carbon in the litter and a meter-deep layer of mineral strata. Carbon stocks are minimal in the soddy eluvozem of the complex spruce forest (59–68 t/ha), which is characterized by a lighter granulometric composition, and reach 76–92 t/ha in the soils of the birch–spruce and complex pine–spruce forests. At the same time, 3.3–5.8 t C/ha or 4–9% of the total organic carbon reserves are concentrated in the litter, and 64–69% in the upper mineral layer (0–20 cm). Different levels and profile distribution of organic carbon reserves in soils are determined by lithological and granulometric features and the nature of vegetation. The contribution of water-extractable organic carbon compounds to their total content in the upper mineral horizons of soils does not exceed 1.3–1.8%, microbial carbon, 1.7–2.4%. In acidic light loamy soils, the enrichment in calcium and potassium, the cation exchange capacity, the content of exchangeable bases, and the degree of saturation can serve as indicators of the content and reserves of organic carbon at the ecosystem level. The relationship with the content of finely dispersed fractions and oxalate-extractable Al and Fe is manifested to a lesser extent due to the similar origin and properties of soils. The variability of organic carbon stocks in soils is determined to the greatest extent by its content, the influence of which decreases with depth. Accounting for spatial heterogeneity, field measurements of the density and proportion of fine earth, and correct analytical determinations are essential components of the assessment of carbon stocks in soils of forest ecosystems as part of a national monitoring system for carbon pools and greenhouse gas fluxes under development.

Assessing soil carbon dynamics following mechanical site preparation in boreal lichen woodlands of Québec, Canada

Soil scarification is a common soil mechanical preparation (MSP) method in forestry aimed to enhance the success of reforestation. However, by turning over and displacing the humus (forming a mound; M), and producing furrows of bare mineral soil (F), it is believed that this method has a substantial effect on soil C stocks. Here, we assessed the influence of this MSP on soil C stocks in two boreal lichen woodlands (LWs) in Québec, Canada, scarified ten and two years before sampling (2012 and 2020 sites, respectively).Carbon stocks averaged 11.8–15.4 kg C m−2 in the undisturbed section of the LWs (IF) with 9–15 % located in the vegetation, 36–42 % in the humus and 42–55 % in the mineral soil (0–30 cm). MSP caused a C concentration decline of ∼105 g C kg−1 in the displaced humus. Unexpectedly, this decrease was similar at both sites, suggesting that most C losses from this horizon occurred within two years. Higher C stock in the mineral horizons of the M than of the IF compartment at the 2012 site, suggests that a fraction of the C lost from the displaced humus may not have been released to the atmosphere but rather translocated to the underlying mineral soil. However, no such phenomenon was detected at the 2020 site, where a net C loss from the mineral soil was observed. Overall, the use of mass balance equations did not show evidence of net C losses at the scale of the whole profile in the disturbed sections of both LWs following MSP. This was partly due to site heterogeneity and a sampling bias, but also to mechanisms such as C translocation from the organic to the mineral soil horizons, and the replenishment of the soil C pool owing to natural regeneration occurring at the surface of the furrows. Overall, this study suggests that MSP may not have as strong an impact on soil C stocks as previously believed. Additionally, it highlights the challenges associated with estimating C changes in the soil following MSP and discusses ways to improve the assessment of C dynamics in such heterogeneous habitats.

Increasing plant species diversity suppresses free‐living N2 fixation in litter and soil of a subtropical karst forest

Abstract Free‐living N2 fixation (FNF) is an important source of bioavailable nitrogen for forests. Though increasing plant species diversity (PSD) benefits soil nitrogen accumulation, how it impacts FNF rate has not been explored. Forty‐five plots covering a PSD gradient were selected in a subtropical karst forest, southwest China. FNF rates in leaf litter and soil were measured using acetylene reduction assay calibrated with a 15N2 fixation method. Diazotrophic community, litter and soil properties were determined as well. The nifH gene abundance was not significantly altered in litter but was significantly decreased in soil by higher PSD. Diazotrophic community's Shannon diversity was significantly increased by higher PSD in both litter and soil. Increasing PSD inhibited litter FNF rate via aggravating phosphorus limitation and decreasing the relative abundance of Betaproteobacteria and Deltaproteobacteria. For the mineral soil horizon, increasing PSD suppressed FNF rate via decreasing nifH gene abundance caused by elevated N availability and lowered phosphorus and iron availability or through decreasing the relative abundance of Deltaproteobacteria but increasing that of Betaproteobacteria. Our findings, for the first time, reveal the microbial and abiotic controls on FNF in litter and soil in response to PSD, and hence benefit the prediction of nitrogen input via biological N2 fixation under changes in PSD. Read the free Plain Language Summary for this article on the Journal blog.

Fire-excluded and frequently burned longleaf pine forests have contrasting soil microbial communities

Prescribed fires are common in forest management, yet we lack a clear picture of how different fire frequencies impact soil systems. Here, we present evidence of microbial community and soil chemistry shifts following sixty years of continuous prescribed fire interval manipulation at the Olustee Experimental Forest in Northeastern Florida. We investigated three fire interval treatments (1 year, 2 years, and 4 years) in addition to an unburned control treatment. We sampled three mineral soil horizons (A, E, and Bh) to elucidate prescribed fire impacts across the soil profile. Our results indicate that only the A horizon was affected by the fire interval manipulations, whereas the deeper E and Bh horizons were minimally impacted. Richness of both bacterial and fungal communities in recurring fire treatments was higher than, and their community composition different from, those in the unburned control in A horizon soils. Similar to the biotic soil attributes, fire interval treatments altered soil chemistry only in the top-most A horizon: the burned treatments had higher total nitrogen, total carbon, phosphorus, and NH4+ than the fire exclusion treatment; the soil chemistry of the deeper E and Bh horizons did not differ among the treatments. All soil chemistry properties correlated with bacterial community composition of the A horizon and nearly all properties correlated with fungal community composition of the A horizon as well, especially when comparing the more frequent burns to the fire exclusion treatment. Indicator taxon analyses identified fire-responsive bacteria and fungi, such as Ktedonobacteria sp. and an unclassified ascomycete that were abundant in the fire exclusion treatment and the ectomycorrhizal Russula spp. that were most abundant in the annual burn treatment. The different fire intervals also impacted fungal guilds, suggesting shifts in community function. The fire exclusion treatment was enriched with ectomycorrhizal, lichenized, and wood saprotrophic fungi, whereas the annual burn treatment was enriched with arbuscular mycorrhizal fungi compared to the other treatments. Our results indicate that long-term changes in the type and amount of detrital inputs and changes in the plant community associated with differing fire frequencies can induce shifts in the soil microbial community.

Indicators of the biological cycle of 90Sr in birch forests of the Bryansk region 30 years aft er the Chernobyl fallout

In the paper, the features of the biological cycle of 90Sr in the birch forests of the Bryansk region in the remote period aft er the Chernobyl fallout are discussed. Specific activity and inventories of 90Sr in soil, diff erent structures and types of tree and herbaceous-shrubby stories, higher fungi, and litter are given. It is shown that at present the major part of 90Sr in the contaminated birch forests of the Bryansk Polesie is accumulated in the soil (82,3%), of which about 71% is in the mineral soil horizons. The biota contains only 17,7% of the total radionuclide inventory with maximum values in the tree story. Th e contribution of herbaceous-shrubby vegetation and higher fungi is small, <0,5%. In birch forests 3,07 kBq·m-2 90Sr is involved in the biological cycle, which is about 3% of its total stock in the ecosystem and approximately corresponds to the radioactive decay of this radionuclide. The main part of the 90Sr goes for formation of annual growth of the stand, while the contribution of higher fungi to the cycle exceeds the contribution of the herbaceous-shrubby layer. Th e 90Sr return to soil is lower (48,2%) than its fi xation in annual biomass growth (51,8%).

Earthworm-invaded boreal forest soils harbour distinct microbial communities

Abstract. Earthworm invasion in North American forests has the potential to greatly impact soil microbial communities by altering soil physicochemical properties, including structure, pH, nutrient availability, and soil organic matter (SOM) dynamics. While most research on the topic has been carried out in northern temperate forests, little is known about the impact of invasive earthworms on soil microbial communities in hemiboreal and boreal forests, characterized by a slower decay of organic matter (OM). Earthworm activities can increase OM mineralization, altering nutrient cycling and biological activity in a biome where low carbon (C) and nitrogen (N) availability typically limits microbial and plant growth. Here, we characterized and compared microbial communities of earthworm-invaded and non-invaded soils in previously described sites across three major soil types found in the Canadian (hemi)boreal forest using a space-for-time approach. Microbial communities of forest floors and surface mineral soils were characterized using phospholipid fatty acid (PLFA) analysis and metabarcoding of the 16S rRNA gene for bacteria and archaea and of the internal-transcriber-spacer-2 (ITS2) region for fungi. In forest floors, the effects of earthworm invasion were minor. In mineral soil horizons, earthworm invasion was associated with higher fungal biomass and greater relative abundance of ectomycorrhizal fungi. Oligotrophic bacteria (Acidobacteriota and Chloroflexi) were less abundant in invaded mineral soils, where Gram(+) : Gram(−) ratios were also lower, while the opposite was observed for the copiotrophic Bacteroidota. Additionally, earthworm-invaded mineral soils harboured higher fungal and bacterial species diversity and richness. Considering the important role of soil microbial communities for ecosystem functioning, such earthworm-induced shifts in their community composition are likely to impact nutrient cycling, as well as vegetation development and forest productivity at a large scale, as the invasion progresses in these (hemi)boreal systems.

Strong above-ground impacts of a non-native ungulate do not cascade to impact below-ground functioning in a boreal ecosystem.

1. Experimental studies across biomes demonstrate that herbivores can have significant effects on ecosystem functioning. Herbivore effects, however, can be highly variable with studies demonstrating positive, neutral or negative relationships between herbivore presence and different components of ecosystems. Mixed effects are especially likely in the soil, where herbivore effects are largely indirect mediated through effects on plants. 2. We conducted a long-term experiment to disentangle the effects of non-native moose in boreal forests on plant communities, nutrient cycling, soil composition and soil organism communities. 3. To explore the effect of moose on soils, we conduct separate analyses on the soil organic and mineral horizons. Our data come from 11 paired exclosure-control plots in eastern and central Newfoundland, Canada that provide insight into 22-25 years of moose herbivory. We fit piecewise structural equations models (SEM) to data for the organic and mineral soil horizons to test different pathways linking moose to above-ground and below-ground functioning. 4. The SEMs revealed that moose exclusion had direct positive impacts on adult tree count and an indirect negative impact on shrub percent cover mediated by adult tree count. We detected no significant impact of moose on soil microbial C:N ratio or net nitrogen mineralization in the organic or mineral soil horizon. Soil temperature and moisture, however, was more than twice as variable in the presence (i.e. control) than absence (i.e. exclosure) of moose. Overall, we observed clear impacts of moose on above-ground forest components with limited indirect effects below-ground. Even after 22-25 years of exclusion, we did not find any evidence of moose impacts on soil microbial C:N ratio and net nitrogen mineralization. 5. Our long-term study and mechanistic path analysis demonstrates that soils can be resilient to ungulate herbivore effects despite evidence of strong effects above-ground. Long-term studies and analyses such as this one are relatively rare yet critical for reconciling some of the context-dependency observed across studies of ungulates effects on ecosystem functions. Such studies may be particularly valuable in ecosystems with short growing seasons such as the boreal forest.

Macrofauna and Organic Matter in Postagrogenic Sandy Soils at the NW Smolensk Region (Russia)

Natural reforestation on the abandoned arable lands is one of the characteristic processes that triggers the transformation of soils, accompanied by the change in the abundance, biomass, and taxonomic structure of the soil macrofauna. The assessment of the restoration potential of the soil properties and soil macrofauna to the natural state, the duration of this period, the dynamics of soil organic carbon stocks, and the role of macrofauna in this process at different stages of post-agrogenic successions is relevant for prediction of changes in ecosystem components and their role in the storage of organic carbon under various land use scenarios. The work is based on the data on organic carbon reserves, morphological properties of soils, abundance, biomass and taxonomic structure of the soil macrofauna of arable lands, primary forests and 5 stages of pine forest restoration (fallow meadows and pine forests of different ages) at the Smolenskoye Poozerye National Park (Smolensk region). It was revealed that in the soils of the 85–100-year-old pine forests, signs of plowing are preserved in the form of the smooth lower boundary of the humus horizon. At the same time, signs of soil regradation appear already at the meadow stage and are expressed in the formation of a thin humus horizon penetrated by roots, which transforms further at the next stages. In the litter and mineral part of the soil, the carbon stocks change non-monotonically with a maximum at the meadow stage and a minimum in 70–80-year-old forests. By the age of 80, the stock of organic carbon in the mineral part of soils is almost restored to the background values. The composition of soil macrofauna changes drastically during the transition from meadow to forest communities. At the initial stages (in agrocenoses and fallow meadows), the fauna of mineral soil horizons predominates: endogeic earthworms and larvae of lamellar beetles. Further, the fauna of organic horizons is restored, among which there is a high proportion of saprophages – epigeic and epi-endogeic earthworms, which contribute to the differentiation of litter. The biomass of saprophages has a negative correlation with the carbon reserves in the mineral part of forest soils, the thickness and reserves of organic carbon in the litter, and a positive correlation with the share of the easily decomposable litter fraction.

The features of Cs sorption onto peaty-podzolic-gleyic soil

This article studies sorption regularities and estimates the strength of 137Cs fixation by various soil horizons in peaty-podzolic-gleyic soils under a model experiment. The interaction time varied from 1 week to 3 months while Cs concentration varied from trace to micromolar concentrations. To understand the interaction mechanisms of cesium with individual soil components, we used the method of sequential removal of organic matter and non-silicate iron compounds from the soil before the sorption experiment.Illite and vermiculite were found to be the main soil components for radiocesium sorption in the mineral soil horizons. The highly selective positions (FES – frayed edge sites) of the abovementioned minerals fixed radiocesium so strongly that even strong acid solutions could not extract it from soil. Organic matter significantly contributed to the fixation of radiocesium in the soil only in the ELih horizon which contained 4.71% Corg. In the ELg horizon, a small amount of organic matter was able to inhibit sorption by blocking highly selective to radiocesium FES. The Tessier sequential extraction method of radiocesium revealed that all the studied soil samples could strongly fix the radionuclide. Increasing the interaction period up to three months under periodic wetting and drying contributed to the increased proportion of strongly bound 137Cs. The results of sorption experiments carried out before and after the removal of non-silicate iron compounds from the soil indicate that 137Cs has little or no sorption on the surface of iron hydroxides.

The Role of Greenery in Adaptation of Urban Ecosystems to Climate Change

In order to develop proposals for managing the functioning of the city’s green frame, a study has been carried out, regarding tree plantations and their litter layers, as well as some aspects of the urban ecosystems’ biological cycle of as part of the optimisation of the carbon footprint. The topic’s relevance is due to the global warming and the need to identify sources of direct and indirect anthropogenic impact on the carbon balance, as well as the need to assess the contribution of carbon emissions to the atmosphere of urban areas. The litter, despite its small contribution to the total carbon stock of the ecosystem, is the most mobile horizon, connecting vegetation and mineral soil horizons, thus its typology and properties are the most important characteristics that can be used to monitor urban ecosystems. It has been established that in urban ecosystems, compared to the natural analogues, there is an increase in the biological cycle intensity, which is associated with the following factors: a shift in the ratio of tree species in the city’s green frame towards a significant increase in the proportion of deciduous trees, the use of a greenery maintenance system and the destructive impact of recreation on litter layers. The percentage decrease in the amount of carbon in the litter of coniferous plantations as a result of recreational impact is 20–57%, in the case of the leaf litter collection – up to 90%, while in absolute terms the loss of carbon reserves is comparable and equal to 20–23 kg/100 m2 (we note that that the litter variant of larch plantations shows the absolute values of carbon losses 3 times higher). All studied variants of urban greenery subject to pronounced anthropogenic impact, demonstrate a decrease in the biological cycle isolation compared to undisturbed ones. A change in the organic matter circulation direction in urban ecosystems towards its depositing as a part of terrestrial detritus can be implemented both by regulating the intensity of the greenery maintenance, and by reducing its loss during recreation – design solutions for the organisation of landscape objects with the diversion of visitors’ transit flows from the locations of conifers ecosystems.

Variations in litter-soil properties between planted and naturally restored forests drive microbial community structure and function

How forest restoration can affect soil microbial composition and functionality remains unclear, limiting our ability to evaluate restoration approaches. Here, we used metagenomes, 16S rRNA, and ITS gene sequencing to distinguish the composition and functional attributes of soil microbial communities between plantation forest of Pinus massoniana (PF) and naturally restored secondary forest (SF) in their organic horizon and mineral soil from a typical karst region in Southwest China. Our results showed that fungal communities differed more than bacterial communities between PF and SF, while the differences in archaeal communities were not significant. The most abundant fungal phylum in both mineral soil and organic horizon was Ascomycota at SF and Basidiomycota at PF, respectively. The PF soil had lower nitrogen (N) cycling gene abundance and lower inorganic N availability compared to SF soil probably because of the poor soil and lower litter quality. The SF soil had higher abundances of genes associated with labile carbon (C) (i.e., starch, hemicellulose, cellulose, pectin, and chitin) degradation compared with PF soil, but lower abundances of genes responsible for recalcitrant C (i.e., lignin and aromatics) degradation, which was strongly correlated with the litter properties. Simultaneous effects of soil and litter variables explained >50 % of the variation in microbial community structure and functional gene composition; soil nitrate-N had the strongest effect on the soil bacterial and fungal community structure. Our results highlight the superiority of naturally restored secondary forests for improving both soil fertility and soil microbial-mediated C and N cycling functions, which can support forest managers in selecting forest restoration approaches that optimize C and N storage in forest stands.

Water-soluble organic carbon release from mineral soils and sediments in an irrigated agricultural system

Water interactions with soil and vegetation are greatly altered in agricultural watersheds compared to natural landscapes, which impacts sources and fates of organic carbon (OC). While mineral soil horizons in natural ecosystems primarily act as filters for dissolved organic carbon (DOC) leached from organic surface horizons, tilled soils largely lack an organic horizon and their mineral horizons therefore act as a source for both DOC and sediment to surface waters. Irrigated watersheds highlight this difference, as DOC and total suspended sediment (TSS) concentrations simultaneously increase during the low-discharge irrigation season, suggesting that sediment-associated OC may constitute a significant source of DOC. While water-soluble OC (WSOC) from sediments and soils has been found to be compositionally similar to stream DOC, these contributions remain poorly quantified in agricultural streams. To address this, we conducted abiotic solubilization experiments using sediments (suspended and bed) and soils from an irrigated agricultural watershed in northern California, USA. Sediments (R2 > 0.99) and soils (0.74 < R2 < 0.89) displayed linear solubilization behaviors over the range of concentrations tested. Suspended sediment from the irrigation season exhibited the largest solubilization efficiency (10.9 ± 1.6% TOCsediment solubilized) and potential (1.79 ± 0.26 mg WSOC g−1 dry sediment), followed by suspended sediment from a winter storm, then bed sediment and soils. Successive solubilization experiments increased the total release of WSOC by ∼50%, but most (88–97%) of the solid-phase OC remained insoluble in water. Using these solubilization potential estimates and measured TSS concentrations, we estimated that WSOC from suspended sediment in streams represented 4–7% of the annual DOC export from the watershed. However, field sediment export is much higher than what is represented by suspended sediment in the water column, therefore field-scale contributions from sediments could be much higher than estimated.