Organic Soil Horizons Research Articles

Ectomycorrhizal community composition of organic and mineral soil horizons in silver fir (Abies alba Mill.) stands.

Vertical ectomycorrhizal (ECM) community composition was assessed on silver fir (Abies alba Mill.) in beech-silver fir forests in Bosnia and Herzegovina. Organic and upper mineral horizons were described by pedological analyses. Silver fir root tips were divided into vital ECM, old and non-mycorrhizal for each horizon separately. Morpho-anatomical classification of vital ECM root tips with an assessment of abundance was followed by ITS-based molecular characterization and classification into exploration types. The percentage of vital ECM root tips was not affected by the soil horizon. Altogether, 40 ECM taxa were recorded. Several taxa have not previously been reported for silver fir: Hebeloma laterinum, Inocybe fuscidula, I. glabripes, Lactarius acris, L. albocarneus, L. blennius, L. fluens, Ramaria bataillei, Russula badia, R. lutea, R. mairei, Sistotrema sp., Tarzetta catinus, Tomentella atroarenicolor, T. badia, T. cinerascens, T. bryophylla, and T. ramosissima, indicating high potential for diversity of ECM fungi in silver fir stands. No significant differences in community composition and species richness and diversity were detected between mineral and organic horizons. Community composition was affected by CaCO3, organic carbon concentration, organic carbon stock, total nitrogen stock, C/N ratio and soil bulk density. No significant effects of soil parameters were detected for exploration types. The contact exploration type was dominant in both soil horizons. Significantly different relative abundances of dominant taxa Tomentella stuposa, Cenococcum geophilum and Piloderma sp. 1 were detected in the two horizons. Twelve taxa were limited to the organic horizon and eight to the mineral horizon.

Convergence, divergence or chaos? Consequences of tree trunk decay for pedogenesis and the soil microbiome in a temperate natural forest

The biochemical effects of trees may significantly influence local pedogenesis as well as pedocomplexity, biodiversity and forest dynamics on both stand and landscape scales. One such effect is the decay of tree trunks, which is driven by organisms, and especially by the microbiome. Decomposition modifies soil formation, which due to the existence of many feedbacks affects the composition of the decomposer community. We aimed to uncover general trends in the evolution of Entic Podzols as well as individual trajectories of soil properties below decaying beech trunks in an old-growth mountain forest. In particular, we used mathematical models to distinguish soil convergence, divergence and chaotic behaviour to enhance a general theory of pedogenesis. We further aimed to calculate the depth and time of convergence if this scenario is prevailing in the study plot. Pedogenetic pathways were assessed regarding the changing composition of fungal and bacterial communities in soils to obtain a complex picture of the decaying trunk-soil microbiome system.We sampled the decaying wood layer under 24 lying beech trunks and corresponding organic horizons on adjacent control microsites occupied by decaying beech leaves. At the same time we sampled underlying mineral soil horizons at both microsites (wood vs. leaves), all on Entic Podzols and granite (in total 192 soil samples). Individual trunk fall events were dated using precise dendrochronology, with the resulting chronosequence covering trunks lying for 8–52 years. We analysed decomposition processes (with a wide spectra of organic acids and ions analysed), soil chemistry (28 additional soil properties assessed), and the microbiome composition in both decaying organic matter and soils (relative abundances of the 200 most common bacterial and fungal OTUs analysed).During the first stage of trunk decay, underlying Entic Podzols responded with a significant increase of nutrients, pH, and CEC, and the maximal divergence compared to control sites was reached between 12 and 60 years after the trunk fall. Subsequently, a majority of soil properties slowly converged over a few decades to match the soil properties of control sites. The modelled convergence point occurred at ages between 39 (SO42−) and 229 (Alw) years, with a median convergence time of 53 years. The majority of soil properties converged within 20 cm below the trunk, but mathematical models predicted footprints of some soil properties down to depths of ca 60 cm. In addition, 11 soil properties did not converge at any depth, and for some properties the models even diverged. Differences in bacterial and fungal communities between below-trunk and control positions were relatively minor. Pedochemical drivers of fungal and bacterial communities (nutrients content, Ntot, Cox, Al, Fe, Mn forms) changed significantly in the mineral soil below trunks, and the microbiome partly reflected these depth-related changes. However, we propose that there is a threshold between organic and mineral soil horizons limiting the impacts of trunk decay and pedogenesis in changes to the microbiome.

Tree planting in organic soils does not result in net carbon sequestration on decadal timescales.

Tree planting is increasingly being proposed as a strategy to combat climate change through carbon (C) sequestration in tree biomass. However, total ecosystem C storage that includes soil organic C (SOC) must be considered to determine whether planting trees for climate change mitigation results in increased C storage. We show that planting two native tree species (Betula pubescens and Pinus sylvestris), of widespread Eurasian distribution, onto heather (Calluna vulgaris) moorland with podzolic and peaty podzolic soils in Scotland, did not lead to an increase in net ecosystem C stock 12 or 39years after planting. Plots with trees had greater soil respiration and lower SOC in organic soil horizons than heather control plots. The decline in SOC cancelled out the increment in C stocks in tree biomass on decadal timescales. At all four experimental sites sampled, there was no net gain in ecosystem C stocks 12-39years after afforestation-indeed we found a net ecosystem C loss in one of four sites with deciduous B. pubescens stands; no net gain in ecosystem C at three sites planted with B. pubescens; and no net gain at additional stands of P. sylvestris. We hypothesize that altered mycorrhizal communities and autotrophic C inputs have led to positive 'priming' of soil organic matter, resulting in SOC loss, constraining the benefits of tree planting for ecosystem C sequestration. The results are of direct relevance to current policies, which promote tree planting on the assumption that this will increase net ecosystem C storage and contribute to climate change mitigation. Ecosystem-level biogeochemistry and C fluxes must be better quantified and understood before we can be assured that large-scale tree planting in regions with considerable pre-existing SOC stocks will have the intended policy and climate change mitigation outcomes.

Stable Carbon Isotopes δ13C as a Proxy for Characterizing Carbon Sources and Processes in a Small Tropical Headwater Catchment: Nsimi, Cameroon

Stream carbon fluxes are one of the major components in the global C cycle, yet the discrimination of the various sources of stream carbon remains to a large extent unclear and less is known about the biogeochemical transformations that accompany the transfer of C from soils to streams. Here, we used patterns in stream water and groundwater δ13C values in a small forested tropical headwater catchment to investigate the source and contribution from the soil carbon pools to stream organic and inorganic carbon behavior over seasonal scales. Stream organic carbon (DOC and POC) comes mainly from the upper rich soil organic carbon horizons and derived from total organic carbon (TOC) of biogenic source. The isotopic compositions δ13CTOC, δ13CDOC and δ13CPOC of these carbon species were very close (− 30‰ to − 26‰) and typical of the forested C3 vegetation. The relationship observed between DOC and log pCO2 and δ13CDIC indicated that besides the considerable CO2 evasion that occurs as DIC is transported from soils to streams, there were also other processes affecting the stream DIC pool. In-stream mineralization of DOC and mixing of atmospheric carbon had a significant influence on the δ13CDIC values. These processes which varied seasonally with hydrological changes represent the main control on DOC and DIC cycling in the wet tropical milieu. The rapid turnover of carbon on hillside soils, the transformation of TOC to DOC in wetland soils and further mineralization of stream DOC to DIC favor the evasion of C, making the zone a source of carbon to the atmosphere.

Temperate Forests Dominated by Arbuscular or Ectomycorrhizal Fungi Are Characterized by Strong Shifts from Saprotrophic to Mycorrhizal Fungi with Increasing Soil Depth.

In temperate and boreal forests, competition for soil resources between free-living saprotrophs and ectomycorrhizal (EcM) fungi has been suggested to restrict saprotrophic fungal dominance to the most superficial organic soil horizons in forests dominated by EcM trees. By contrast, lower niche overlap with arbuscular mycorrhizal (AM) fungi could allow fungal saprotrophs to maintain this dominance into deeper soil horizons in AM-dominated forests. Here we used a natural gradient of adjacent forest patches that were dominated by either AM or EcM trees, or a mixture of both to determine how fungal communities characterized with high-throughput amplicon sequencing change across organic and mineral soil horizons. We found a general shift from saprotrophic to mycorrhizal fungal dominance with increasing soil depth in all forest mycorrhizal types, especially in organic horizons. Vertical changes in soil chemistry, including pH, organic matter, exchangeable cations, and extractable phosphorus, coincided with shifts in fungal community composition. Although fungal communities and soil chemistry differed among adjacent forest mycorrhizal types, variations were stronger within a given soil profile, pointing to the importance of considering horizons when characterizing soil fungal communities. Our results also suggest that in temperate forests, vertical shifts from saprotrophic to mycorrhizal fungi within organic and mineral horizons occur similarly in both ectomycorrhizal and arbuscular mycorrhizal forests.

Dissolved and colloidal phosphorus affect P cycling in calcareous forest soils

Dissolved and colloidal phosphorus (P) represent the mobile P fractions in soils, but their role in P cycling in forests is still largely unclear. In this study of four calcareous forest soil profiles, the elemental compositions of different size fractions of water dispersible colloids (WDC) were investigated by asymmetric field flow fractionation. Nuclear magnetic resonance spectroscopy (NMR) was applied to identify the organic P compounds in soils, WDC, and soil solutions. Carbon was the dominant element in WDC of all soil horizons, including mineral soils that were rich in Ca or Si. Although chemical composition of P varied dramatically with increasing depth, the colloidal P composition remained unchanged. This contrasting difference between mineral soil and its WDC fraction indicated that the colloids were not locally generated but originated from the overlying organic soil horizons. Carbonate minerals were unlikely involved in colloid formation under acidic condition. Instead, Ca2+ probably drove colloid formation by bridging organic matter, including P-containing compounds released from litter degradation. Colloid formation was influenced by climate, vegetation, and soil characteristics. No dissolved P was detected in deeper mineral soil horizons due to efficient retention by Ca minerals. Colloidal P was still present in deeper soil layers and thus of significance for potential P vertical transfer.

Invasive red oak (Quercus rubra L.) modifies soil physicochemical properties and forest understory vegetation

This study assessed the effects of invasive Quercus rubra on soil physicochemical properties and understory vegetation in native plant communities. Chemical properties of senesced tree leaves were also analysed. The study was performed at paired invaded-native plots in managed forests in southern Poland. Freshly fallen senesced leaves were characterized in terms of C, Ca, K, Mg, N, P, total phenolics and condensed tannins concentrations. Soil physicochemical parameters, namely bulk soil density, moisture, water holding capacity (WHC), pH, organic C, total Ca, K, Mg, N, P, exchangeable Ca, K, Mg, N-NH4, N-NO3, P-PO4, and total phenolics were analysed in organic and mineral soil horizons, and condensed tannins were analysed in organic soil horizon. The diversity, cover and composition of understory vegetation were assessed. Although, senesced leaves of Q. rubra and native trees, Quercus robur, Fagus sylvatica, Carpinus betulus and Acer pseudoplatanus among others, differed only in total K, N and C/N ratio, we observed considerable differences in soil physicochemical parameters between the plot types. Soil beneath Q. rubra was characterised by significantly lower WHC, organic C, total Mg, N, P, exchangeable Ca, Mg, N-NH4, N-NO3, total phenolics and higher moisture in organic and mineral soil horizons as well as lower content of P-PO4 and condensed tannins in organic soil horizon relative to native plant communities. Q. rubra negatively influenced species richness and cover of understory vegetation. The changes in soil physicochemical parameters and understory vegetation under Q. rubra may be associated with low quality (low N, high C/N) litter that decomposes slowly and generates a physical barrier, limiting seed germination and seedling growth. The changes in soil properties and vegetation under invasive Q. rubra indicate that this species may alter the structure and function of forest ecosystems and should be avoided in forest management practices.

Prescribed burn frequency, vegetation cover, and management legacies influence soil fertility: Implications for restoration of imperiled pine barrens habitat

In fire-dependent ecosystems, the absence of fire can contribute to a positive feedback in which increased vegetation cover leads to increased accumulation of soil organic matter and nutrient stocks. These changes in turn can influence competitive shifts among plant communities, resulting in increased woody plant establishment, canopy closure, and ultimately leading toward mesophication. Poor soil conditions may be especially important for maintaining the open structure characteristic of pine barrens ecosystems, which are imperiled due to loss of key ecosystem processes such as fire and land conversion to cropland or pine plantations. Our objectives were to determine how soil characteristics are related to recent prescribed fire management, and how soils vary along gradients of current and historic vegetation cover in a barrens-forest mosaic in northern Wisconsin, USA. We sought to understand whether management with prescribed fire shifts soils toward barrens-type soil conditions, and whether soil conditions typify barrens habitat relative to shrub and forest habitat We analyzed organic (i.e. forest floor) and mineral soil horizons collected along gradients of recent prescribed burn history and current (barrens, pine woodlands, brush, and closed-canopy forest) and historic vegetation cover types (barrens, pine plantations, deciduous forests) to investigate the influence of each on specific components of soil fertility. Using a model selection approach, we found forest floor soil properties were most frequently associated with differences in current vegetation cover; for instance, pine woodland sites had greater organic matter stocks than barrens sites, and cation stocks were generally greater at brush sites than barrens and pine woodland sites. Some soil properties, including pH, however, appeared to be driven by prescribed burn frequency. Using ordination techniques to characterize multidimensional characterizations of soils, we identified a soil legacy effect related to historic vegetation cover and land management; native barrens sites had soil characteristics intermediate to restored barrens of pine woodland and deciduous forest origin. Our findings suggest restoration of pine plantations to barrens could benefit from fire activities that enhance consumption of the forest floor, while restoration of deciduous forest and brush habitats will likely be more related to the effective control of hardwood regeneration, after which soil conditions may return to a more archetypical barrens state.

Rooting depth and below ground biomass in a freshwater coastal marsh invaded by European Reed (<i>Phragmites australis</i>) compared with remnant uninvaded sites at Long Point, Ontario

Invasive European Reed (Phragmites australis subsp. australis) outcompetes native vegetation, reducing floristic diversity and habitat value for wildlife. Research in coastal salt marshes has indicated that P. australis invasion may be facilitated by its relatively deep rooting depth, but in freshwater marshes the growth pattern of below ground tissues in relation to water depth is uncertain. To determine if P. australis is rooting more deeply than resident wetland plant species in a freshwater coastal marsh on Lake Erie, Ontario, we measured the vertical distribution of below ground biomass in P. australis invaded marsh sites and compared it to the below ground biomass distribution in nearby sites not yet invaded by P. australis. These invaded and uninvaded sites were paired by water depth, which is known to influence resource allocation and rooting depth. Below ground biomass in invaded sites was greater than in uninvaded sites (t28 = 3.528, P = 0.001), but rooting depth (i.e., the depth at which 90% of total below ground biomass is accounted for) was comparable (t28 = 0.992, P = 0.330). Using water depth and site type, general linear models could predict below ground biomass (F2,55 = 9.115, P < 0.001) but not rooting depth (F2,55 = 1.175, P = 0.316). Rooting depth is likely affected by other factors such as substrate type and the depth of the organic soil horizon.

Heavy metals in the organic soil horizon of the Northern taiga forests resulting from industrial air pollution

This study focuses on heavy metals contained in organic soil horizons resulting from the industrial air pollution caused by local enterprises. Polymetallic dust containing heavy metals is one of the main by-products in the smelting of non-ferrous metals. We evaluated the contents of Ni, Cu, and Co in the upper soil horizons containing the maximum amount of these pollutants (due to the formation of stable compounds with organic components of these horizons). Sampling was carried out at various distances from the source of pollution at previously established test sites. The study found acid-soluble heavy metals at various distances from the source of pollution and revealed the regularity of their content, both qualitative and quantitative.

C:N stoichiometry of stable and labile organic compounds determine priming patterns

Priming effects (PE) can greatly influence global carbon (C) storage in soil and lead to climate feedbacks by accelerating the decomposition of organic matter (OM). Although nitrogen (N) availability can alter the magnitude and direction of priming (stoichiometric constrains), it remains unclear whether additions of NO3− (nitrate) and NH4+ (ammonium) have distinct effects on the decomposition of various OM. Thus, the aims of this study were to investigate the responses of OM decomposition along a decay continuum (i.e. decreasing decomposition degree) to labile C and N inputs and determine the PE induced by the two N forms. Four OM forms, namely leaf litter, wood litter, organic soil horizon, and mineral soil, with a broad range of C:N ratios were collected along a decay continuum in a typical subtropical forest and incubated for 38 days with labile C (13C labeled glucose) and N (NO3−) additions. Based on the very broad range of C:N ratios in OM in soil and inputs of labile C and N, we demonstrated the OM decomposition within a decay continuum as well as PE intensities and the thresholds for the switch of PE directions. In contrast to NH4+ additions, NO3− generally accelerated the decomposition of all OM. Priming of plant litter was dependent on the C:N ratios of the labile inputs. However, leaf litter decomposition was more controlled by N addition than wood litter. Glucose addition greatly increased the priming of OM decomposition in soils, demonstrating energy limitation for microorganisms. Distinct priming patterns were observed between NO3− and NH4+ additions, both for the individual OM types and for all four types of OM. On a basis of C balance between primed C and the remaining added C, PE induced by labile C and N inputs can increase or reduce C sequestration depending on C:N stoichiometric ratios of labile inputs. Our findings provide important insights into the specific role of NO3− or NH4+ together with labile C inputs (e.g. from root exudation), and thus changes in the composition of deposited N (atmospheric deposition and fertilization) may induce distinct climate feedbacks.

The distribution distance of polycyclic aromatic hydrocarbons in the tundra zone under the impact of thermal power plant

Being widely distributed in the tundra zone and highly sensible to temporal or spatial changes in composition of polycyclic aromatic hydrocarbons (PAHs) in ecosystems, Pleurozium schreberi Brid. can serve a pollution indicator of tundra biocenoses with polyarenes. The purpose of the present study is estimating the PAH distribution distance in the tundra zone under the impact of thermal power plant (TPP). The study was conducted in the Bolshezemelskaya tundra area of the Vorkuta region (Komi Republic, Russia). The surface accumulation and total content of PAHs in Pleurozium schreberi and organic horizon of tundra surfacegley soils (Stagnic Cambisols) at the background site and sites removed from the TPP at 0.5; 1; 1.5; 3; 5 and 12 km were studied. The PAH content in Pleurozium schreberi under the impact of TPP changes with distance not linearly. The maximum accumulation was noted at 3 km distance, then the content of PAHs decreased and reached a background level of 12 km from the source. The high molecular weight structures seemed to be transported at distance of no more than 3 km and fell down to the moss surface. The light structures could fly further. This fact responded for concentration of heavy and light structures on particles with different diameter. The moss surface at the background and polluted sites did not contain naphthalene. The total polyarene capacity on the moss surface is relatively the same for the background and polluted sites. At 3 km site, there was a sharp increase in the mass fraction of surface PAH by a factor of 3 due to an increase in the mass fraction of 4-5 - nuclear polyarenes. Being contaminated, the moss activates the bioaccumulation processes of PAHs and so transports polyarenes from its surface to inner organs. The exclusion is a site at a distance of 3 km where the proportion of surface accumulation increased with maximum pollution, i.e., PAH ingress into moss decreased. Determined that the dead part of Pleurozium schreberi or the whole plant is to be used for true identification of polyarenes. The changes in polyarene content in organic soil horizons are the same as in Pleurozium schreberi . By the obtained data, PAHs in tundra can move at large distances. The background-like PAH values are estimated for the site as 12 km from the pollution source for Pleurozium schreberi . The background-like PAH values for organic soil horizons are not estimated. The obtained results agree with the cluster analysis data.

Soil and Tree Nutrient Status of High Elevation Mixed Red Spruce (Picea rubens Sarg.) and Broadleaf Deciduous Forests

Anthropogenic and industrial emissions have resulted in historically high levels of acidic deposition into central Appalachian forests. Despite the reduction in acidic inputs due to legislation curbing industrial emissions in the United States, continued N deposition may impact forest ecosystems. Soil and foliar samples were collected from four high elevation red spruce sites along a modeled gradient of historic N deposition. The three most abundant tree species at all sites, Acer rubrum L., Betula alleghaniensis Britt., and Picea rubens Sarg., were sampled. Bulk soil beneath the canopies of individual trees were collected from the top 15-cm and separated into organic and mineral fractions for analysis. Mehlich-III soil extracts of soil fractions and foliar digests from these trees were subjected to elemental analysis. Soil N concentrations supported the presence of a N deposition gradient: in organic horizon soil fractions, N concentrations were driven by precipitation volume and elevation; whereas in mineral soil fractions, N concentration was explained by modeled N deposition rate and elevation. In organic fractions, significant reductions in Ca, K, and P were evident as N deposition increased, whereas the Ca:Sr ratio increased. Foliar Ca, K, and Sr declined in foliage with increasing N deposition, with concomitant increases in foliar Ca:Sr ratios. Although the three species were sympatric in mixed stands at all four sites, the foliar–soil nutrient associations differed among them across the gradient, indicating differential uptake and cycling of nutrients/metals by these forest tree species.

Effect of natural and anthropogenic acidification on aluminium distribution in forest soils of two regions in the Czech Republic

To elucidate the dynamics of aluminium (Al), an element potentially toxic and strongly affected by acidification processes, in soils, we selected two regions that were similar in relief, soil types, and vegetation cover but differed markedly in their history of acid precipitation: the Jizerské Mountains (anthropogenically acidified) and the Novohradské Mountains (naturally acidified) in the Czech Republic. The levels of Al forms (exchangeable and organically bound) associated with different environmental impacts were measured and univalent, divalent and trivalent Al species were quantified using HPLC/IC. Exchangeable and organically bound Al concentrations were higher in the anthropogenically acidified area. Only the concentrations of the least-dangerous species, the univalent, in organic soil horizons were similar for both mountains. The concentrations of exchangeable Al forms were correlated with Ca concentrations and with pH in the organic horizon. The known relationship of Al with soil pH was stronger in the mineral horizons. Relationships of exchangeable Al forms concentrations with sulphur concentrations or even more with the sulphur calcium molar ratio were found only in the Jizerské Mountains, not in the Novohradské. Generally, the obtained results support the hypothesis that mechanisms differed between natural and anthropogenic acidification.

Carbon Pools in Old-Growth Scots Pine Stands in Hemiboreal Latvia

Old-growth forests are widely recognised for the benefits they provide for biodiversity; however, a more comprehensive understanding of their role in climate change mitigation must still be established to find the optimal balance between different forest ecosystem services at a national or regional scale. Very few studies have assessed carbon pools in old-growth Scots pine (Pinus sylvestris L.)-dominated boreal forests, and none have been conducted in hemiboreal forests. Therefore, we assessed the carbon storage of the living tree biomass, deadwood, forest floor (soil organic horizon, including all litter and decomposed wood), and mineral soil in 25 hemiboreal old-growth (163–218 years) unmanaged Scots pine stands in Latvia. The studied stands were without known records of any major natural or human-made disturbance in the visible past. Our results show, that the total ecosystem carbon pool (excluding ground vegetation) was 291.2 ± 54.2 Mg C ha−1, which was primarily composed of living tree biomass (59%), followed by mineral soil (31%), deadwood (5%), and the forest floor (5%). Within the studied stand age group, the total carbon pool remained stable; however, interchanges among the carbon pools, i.e., living biomass and laying deadwood, did occur.

New insights on lake sediment DNA from the catchment: importance of taphonomic and analytical issues on the record quality

Over the last decade, an increasing number of studies have used lake sediment DNA to trace past landscape changes, agricultural activities or human presence. However, the processes responsible for lake sediment formation and sediment properties might affect DNA records via taphonomic and analytical processes. It is crucial to understand these processes to ensure reliable interpretations for “palaeo” studies. Here, we combined plant and mammal DNA metabarcoding analyses with sedimentological and geochemical analyses from three lake-catchment systems that are characterised by different erosion dynamics. The new insights derived from this approach elucidate and assess issues relating to DNA sources and transfer processes. The sources of eroded materials strongly affect the “catchment-DNA” concentration in the sediments. For instance, erosion of upper organic and organo-mineral soil horizons provides a higher amount of plant DNA in lake sediments than deep horizons, bare soils or glacial flours. Moreover, high erosion rates, along with a well-developed hydrographic network, are proposed as factors positively affecting the representation of the catchment flora. The development of open and agricultural landscapes, which favour the erosion, could thus bias the reconstructed landscape trajectory but help the record of these human activities. Regarding domestic animals, pastoral practices and animal behaviour might affect their DNA record because they control the type of source of DNA (“point” vs. “diffuse”).

Comparing Negative Impacts of Prunus serotina, Quercus rubra and Robinia pseudoacacia on Native Forest Ecosystems

The introduction of invasive alien plant species (IAPS) can modify plant-soil feedback, resulting in an alteration of the abiotic and biotic characteristics of ecosystems. Prunus serotina, Quercus rubra and Robinia pseudoacacia are IAPS of European temperate forests, where they can become dominant and suppress the native biodiversity. Assuming that the establishment of these invasive species may alter native forest ecosystems, this study comparatively assessed their impact on ecosystems. This study further investigated plant communities in 12 forest stands, dominated by the three IAPS and native trees, Quercus robur and Carpinus betulus (three plots per forest type), in Northern Italy, and collected soil samples. The relationships between the invasion of the three IAPS and modifications of humus forms, soil chemical properties, soil biological quality, bacterial activity and plant community structure and diversity (α-, β-, and γ-diversity) were assessed using one-way ANOVA and redundancy analyses (RDA). Our comparative study demonstrated that invaded forests often had unique plant and/or soil properties, relative to native forests, and the degree of dissimilarity depended on the invasive species. Particularly, Q. rubra is related to major negative impacts on soil organic horizons and low/modified levels of microarthropod and plant biodiversity. R. pseudoacacia is associated with an altered base content of soil and, in turn, with positive feedback to the soil biological quality (QBS-ar) and plant diversity, but with a high cover compared with other alien plant species. P. serotina is associated with intermediate impacts and exhibits a plant species assemblage that is more similar to those of native forest stands. Our work suggests impact-based management decisions for the three investigated IAPS, since their effects on the diversity and composition of resident ecosystems are very different.

Loss of a Foundation Species, Eastern Hemlock (Tsuga canadensis), May Lead to Biotic Homogenization of Fungal Communities and Altered Bacterial Abundance in the Forest Floor

Tsuga canadensis (Eastern Hemlock) is a key forest foundation species that is currently declining across the eastern US due to attack by exotic insect species, primarily Adelges tsugae (Hemlock Woolly Adelgid). In the northeastern US, declining Eastern Hemlock stands are typically replaced by fast-growing deciduous Betula lenta (Black Birch) trees, altering ecosystem processes and ecological communities. In this study, we used an approach that substituted space for time to explore how the forest floor's soil organic horizon, macrofungal communities, and bacterial abundance might be altered following Eastern Hemlock replacement by Black Birch. We compared intact, mature Eastern Hemlock forest plots at 2 sites in western Massachusetts to adjacent areas of vigorous regeneration of young Black Birch triggered by logging activity at the sites ∼25–30 years ago. Forest-floor soil organic horizons were significantly thicker under Eastern Hemlock forests and exhibited a higher carbon:nitrogen (C:N) ratio, suggesting slower decomposition and greater accumulation of organic material under Eastern Hemlock compared to deciduous Black Birch canopies. Macrofungal communities emerging from the forest floor did not differ strongly in morphospecies richness between Eastern Hemlock and Black Birch plots. However, a greater number of rare fungi taxa, defined in this study as those represented by a single observation, were detected in Eastern Hemlock plots, and the composition of Black Birch plots was more homogenized and less variable. The abundance of bacterial colony forming units (CFUs) in the soil organic horizon appeared to follow a seasonal pattern of variation between mature Eastern Hemlock versus young Black Birch plots; CFUs were most abundant in Black Birch soils in the fall, potentially tracking input of new deciduous leaf litter, whereas Eastern Hemlock plots had higher CFU counts in the summer. The results of this study suggest that forest-floor characteristics will be substantially altered by the impending loss of Eastern Hemlock, associated macrofungal communities may become simplified and homogenized, and the timing of peak bacterial abundance in the forest floor might be shifted to the fall.

Pollen Preservation in Alluvial Soils: Implications for Paleoecology and Land Use Studies

Core Ideas Floodplain soils preserve pollen that can reconstruct past climate and land uses. Pre‐evaluation of soil properties will save future researchers time and money. Alluvial pollen preservation data expand where paleoecology studies can be done. Floodplain landscapes with fluctuating water tables are nontraditional sites for palynology studies, and therefore intrinsic alluvial soil properties and their relationship to pollen preservation are poorly understood. The primary objective of this study was to identify soil properties that are most related to pollen preservation in floodplains to aid in predicting soil pollen presence and abundance. Our results indicate that all organic soil horizons had preserved pollen, whereas mineral horizons had variable pollen concentrations (range, 0–59,000 grains g−1 soil). Mineral samples with preserved pollen (>0 grains g−1 soil) had significantly greater (p < 0.001) soil organic matter (SOM) and silt + clay, and were located closer to the modern soil surface. Regression analyses indicated that only SOM and C/N ratios were significant predictors of pollen abundance. The guidelines developed in this study can be used to identify samples that likely contain enough pollen for palynological analysis and save future researchers considerable laboratory time, effort, and cost.

Invasive Quercus rubra negatively affected soil microbial communities relative to native Quercus robur in a semi-natural forest

Invasive tree species can exert a profound effect on soil properties and ecosystem processes. Quercus rubra is a Northern American species that has an invader status in many European countries. However, the direction and magnitude of its effect on soil physicochemical and microbial properties relative to native tree species in forests are largely unknown. The aim of this study was to investigate the influence of invasive Q. rubra on physicochemical and microbial properties of soil organic and mineral horizons in comparison to native Quercus robur in a semi-natural forest. The study was performed on 23 Q. rubra and 10 Q. robur stands in the Niepołomice Forest (southern Poland). A number of soil parameters were assessed, namely moisture, water holding capacity, electrical conductivity, pH, organic C, total N, respiration, bacterial and fungal biomass and community structure (phospholipid fatty acid and ergosterol analyses). As soil properties are influenced by the quality of leaf litter deposited by trees, senesced Q. rubra and Q. robur leaves were characterized in terms of C, Ca, Mg, K, N, P, total phenolics and condensed tannins concentrations. It was found that total microbial and bacterial biomass was significantly lower under Q. rubra than Q. robur in both soil horizons. Microbial community structure of organic horizon also differed between the two Quercus species. In contrast, no differences were found in fungal biomass and soil physicochemical variables. The reduction in microbial and bacterial biomass beneath Q. rubra may be associated with the quantity and quality of its litter. Senesced Q. rubra leaves were characterized by significantly higher C/N and C/P ratios relative to those of Q. robur. Preliminary data indicate that although they had lower concentrations of phenolics and condensed tannins, the pools of these compounds supplied to the soil were higher due to higher litter production by Q. rubra.