Pedobiologia最新文献

Invasive plant species pose serious threats to biodiversity and stability of native ecosystems. Kudzu (Pueraria montana var. lobata) is an abundant and highly aggressive invasive plant in the Southeast United States. Herbicides, bioherbicides, and cultural practices are integral parts of integrated management of kudzu, yet few studies have evaluated the impact of kudzu management strategies on soils and their biological and chemical properties. To examine whether kudzu management options impact edaphic chemistry and/or soil microbial communities, we implemented a randomized complete block design (RCBD) with kudzu control treatments, which included synthetic, biological, and combined herbicide applications as well as mowing. Changes in edaphic chemistry, soil activity, and in bacterial and fungal communities were then measured across a single growing season. Treatments included the herbicides glyphosate and aminopyralid, the fungal bioherbicide Albifimbria verrucaria, mowing, as well as the combined treatments of aminopyralid and A. verrucaria, glyphosate and mowing, and two controls (untreated control and the surfactant used as a carrier for aminopyralid and A. verrucaria spores). Soils were collected at multiple points across the growing season between May and September. Soil enzymatic activity and edaphic chemistry were generally stable across treatments and time. Further, our community analyses indicates that the interaction between treatments and time structures fungal and bacterial soil communities, but only weakly. This study suggests that soil microbial communities are generally stable in response to different management strategies and had no discernable adverse non-target effects. We conclude that land managers likely can use any control strategies that are best suited for their circumstances without undue concern about how kudzu control strategies might impact soils.

Soil mesofauna, such as Collembola and mites, are important decomposers in many ecosystems. In lawns, soil mesofauna have been implicated in the decomposition of thatch, an unsightly and problematic by-product of management found in many urban grasslands. In this study, we utilized a model lawn mesocosm experiment and ubiquitous soil mesofauna (Collembola: Isotomidae) to understand their role in thatch decomposition under a variety of simulated lawn management conditions. Our results showed that Collembola enhanced thatch decomposition by 6–8% over Collembola-absent treatments, with clipping additions moderating, and in some cases diminishing the role of Collembola in thatch decomposition. This finding was likely caused by substrate switching in the presence of clippings, and Collembola and clipping additions favoring unique aspects of microbial decomposition: Collembola enhanced oxidative enzymes, enhanced microbial biomass carbon, and marginally reduced microbial respiration, which are associated with oligotrophic microbes. Clipping additions generally increased hydrolytic enzymes, had little effect on microbial biomass, and enhanced respiration, which are associated with copiotrophic microbes. These contrasting results highlight the nuanced effects of soil mesofauna in enhancing thatch decomposition and suggest that management decisions related to lawn mowing may be equally important in mitigating thatch in lawns.

In 2015, the Fundão Dam collapse released over 40 million m³ of iron mine tailings, causing several environmental damages. Certain affected areas were revegetated with a mix of fast-growing species that can allowed the return of some organisms of soil fauna. Nematodes are the most abundant multicellular organisms in soil and are commonly used as bioindicators. Therefore, this study aimed to use the nematode community as bioindicators of the restoration process of an area affected by iron tailings at the margins of the Gualaxo do Norte River. Soil samples were collected from affected and native forest areas to perform physical, chemical, biochemical, and biological analyses. Nematodes were identified and classified according to feeding habits and on a colonizer-persisters (cp) scale. A non-metrical multidimensional scaling and PERMANOVA were conducted to assess differences between communities. Shannon’s diversity index and the maturity index were significantly higher in the restoration area. There was a difference in the composition and the structure of nematode communities of the restoration and reference area, nematode genus occurrence and abundance were different between the areas resulting in differences in feeding habits and life strategies according to the cp scale. The cp-5 nematodes are more abundant in the restoration area and cp-1 in the forest reference area. Bacterivore nematodes were more abundant in the reference forest area. In addition, the soil attributes in the restoration area were altered following the tailings deposition. Such alterations include high pH, low organic matter content, and low microbial biomass, which consequently influenced the structure and the composition of the nematode community. This is likely the first report of soil nematode community diversity in the areas of the Rio Doce Basin impacted by the Fundão tailings, and nematodes proved to be good bioindicators to show the differences between the restoration and forest reference area.

The predicted increases in drought in many forest ecosystems may alter soil microbial community diversity and activity, which may further depend on tree species richness. Shifts in microbial community composition and activity could engender changes in ecosystem function, notably, in soil greenhouse gas emissions and C storage. Using soils from mono-specific and mixed three-species forest stands from across Europe, we performed a microcosm experiment to test how soil microbial taxonomic and catabolic diversity are affected by repeated drying-rewetting (DRW) cycles and tree species mixing. We used Illumina sequencing and MicroResp™ analyses to explore community-level changes between microbial functional groups. DRW decreased bacterial richness and carbon substrate use diversity and increased fungal Shannon diversity. Additionally, microbial communities exposed to DRW changed their consumption of 11 out of 15 substrates significantly, suggesting microbial functional shifts. The legacy effect of tree species mixing influenced the structure of the microbial communities (i.e. taxonomic differential abundance) although, community weighted mean (CWM) values of absorptive root traits appeared to affect more strongly microbial richness, relative abundance, and Shannon diversity. No significant tree species mixing:DRW interaction was found for most microbial variables, except for the use of certain substrates and potentially differential abundance. Our data from a laboratory experiment with soils from different forest ecosystems underline that drought may cause shifts in microbial taxonomic and catabolic diversity, while tree species influences primarily taxonomic diversity through root traits.

In heathlands, high mineral N input causes replacement of Calluna vulgaris, the dominant plant, by fast-growing grasses such as Molinia caerulea. The vegetation shift signifies altered litter quality from low- to high-quality litter due to differences in lignin content. Litter quality usually affects decomposition processes, which can, in turn, alter nutrient cycling. Therefore, the change in plant dominance in this ecosystem possibly alters soil carbon and nutrient cycles, and consequently, ecosystem services (e.g. biodiversity conservation, groundwater recharge, …). We hypothesise that, because of its higher litter quality, nutrient turnover becomes faster with grass encroachment. We tested this hypothesis in a field set-up consisting of 14 plots presenting a gradient of increasing grass dominance (from 0% to 100%). We measured nine soil parameters and assessed possible associations between grass dominance and the soil parameters using multivariate analysis and linear mixed models. We found that grass dominance significantly impacted net N mineralisation and the root biomass. Our results showed very low net N mineralisation rates (0.09 ± 0.04 mg N (kg soil)⁻¹ day⁻¹) and relative nitrification rates (1.99 ± 0.62%). At high grass levels, acid phosphatase activity was significantly lower than at lower grass percentages. These results show that grass encroachment has a minimal impact on heathland soil biochemistry at this point. Still, we consider that it may take many years to translate a change in litter quality and dynamics into a change in soil functioning.

Global climate models predict that precipitation regimes will change, generating great impacts on various ecosystem processes and functions. Therefore, it is important to know how drought and precipitation increases would affect the soil microorganims and plants. We established a precipitation manipulation experiment, with treatments ranging from 54% reduction (drought) to 54% increases (irrigation) in a semiarid ecosystem, and measured microbial carbon (MBC) and nitrogen (MBN), soil basal respiration (SBR), microbial metabolic coefficients (qCO₂), and estimated the sequestration and fluxes of CO₂ by soil microorganisms. While simulated drought did not modify the microbial community attributes, the microbial biomass increased with greater precipitation, which in the long term could lead to greater carbon (C) sequestration by the microbial pathway and a decline in potential CO₂ emissions into the atmosphere. This study shows that microorganisms of the semiarid soil are able to withstand drought and are possibly able to adopt resistance mechanisms under dry conditions. However, drought or increased precipitation did not affect SBR. The results showed that plants’ and soil microorganisms’ responses to precipitation change were asymmetric and different. The study quantifies the contributions of microorganisms to sequestered C by soil microbial biomass (≈35 g MBC m⁻²) and CO₂ fluxes to the atmosphere (removed in MBC ≈127 g CO₂ m⁻² and emission by SBR ≈876 g CO₂ m⁻² yr⁻¹) in semiarid ecosystems. This study not only increases our understanding of the adaptation of soil microorganisms to precipitation changes but also provides new insight into the contributions of the microorganisms when modeling and projecting implications for C cycling.

The influence of non-stressing temperatures on life-history traits of enchytraeids (e.g. growth and reproduction) is well described in the literature, but less is known about the influence of stressful temperatures, especially at the high end of the scale. In light of predicted climate changes, where the frequency and intensity of extreme weather events are increasing, it is important to provide detailed knowledge of the thermal limits of species. Experiments leading to a comprehensive understanding of species´ Thermal Death Time (TDT) landscape are particularly valuable because this allows modelling and predicting mortality under dynamic thermal scenarios. In static assays, we determined TDT₅₀ of adult worms at a range of temperatures showing that 50% mortality (TDT₅₀) was reached by exposure to 35.5 °C for only 6 min, whereas TDT₅₀ at 31 °C was 257 min. By fitting the TDT curve to the measurements, we described the influence of temperature on the rate of injury accumulation leading to 50% mortality. Based on injury accumulation rates derived from static assays, we predicted the TDT₅₀ in dynamic assays of various temperature ramping rates with high precision. Additional experiments showed that eggs and juveniles had the same sensitivity to high temperature as adult worms. Combined with previous research, our results show that E. albidus has a wide thermal niche in which survival is possible, from ca. − 25 to + 35 °C. However, exposure time is of the essence for surviving stressful temperatures in the high and low temperature ranges. We discuss that the wide thermal niche of E. albidus may partly explain how this species has become so widely distributed, from the temperate coastal climate in northern Spain to the high Arctic in Svalbard.

Land management for conservation alters the abiotic and biotic components that underly belowground ecosystem health and function. We know that prescribed burning and grazing influence soil characteristics, nutrients, and biota individually, but rarely have these management effects been explored holistically, affecting an interacting belowground system. Since most belowground functions (e.g., nutrient cycling) arise from feedbacks among many soil factors, a better understanding of system-level responses to distinct management practices, rather than individual component responses, can help us better predict these ecosystem functions. In a late successional tallgrass prairie ecosystem, we contrasted how prescribed fire and mowing altered nutrient cycles through changes to the abiotic soil environment, microbial community structure, and microbial enzyme functions. Individual soil factors responded rapidly to both fire and mowing, and remained different from pre-treatment values. However, as a system, many relationships among soil factors that were present before management and lost directly after management, returned 1 month after management. This shows the system-level resilience to management supported by the long evolutionary history between grasslands, fire, and grazing, and illustrates the importance of understanding management effects from a holistic perspective. Since global disturbance regimes and anthropological influence are predicted to change in the future, understanding how belowground components respond to change as a system can help land managers and ecologists alike conserve endangered ecosystems.

The invasion of exotic grasses in the neotropical savannas is closely linked to the conversion of the native landscape into agriculture and cultivated pastures. Molasses grass (Melinis minutiflora P.Beauv.) is one of the main invasive species in abandoned fields and native vegetation areas with the potential to alter both the structure and functioning of these ecosystems. We used the dual-isotope approach to evaluate the impact of molasses grass invasion on nitrogen dynamics in the soil of a savanna formation located in the Cerrado region of Central Brazil. We divided three plots (70×80 m) in 300 sampling units (7×8 m each) classified by predominant vegetation type: native grasses (NG), native cerrado sensu stricto (CSS), or molasses grass (MG). We interpolated the soil δ¹⁵N and δ¹³C (0–10 cm depth) in the three plots to continuous surfaces using semivariogram fit and ordinary kriging models. We also compared the aboveground biomass, litter decomposition rates, and soil N pools among vegetation types. MG and NG had higher litter decomposition rates than CSS. Soil pH was higher under MG compared to CSS and NG. The local soil δ¹⁵N isoscapes show the presence of MG in areas with higher soil δ¹⁵N. Soil δ¹³C under all vegetation types indicates a mixture between the C₃ and C₄ sources present in the soil organic matter, with the highest soil δ¹³C under MG. The dual-isotope approach showed the altered processes in the invaded areas with an intensification of the soil N dynamics in the long term compared to the areas dominated by the wood strata and by native grasses. The C and N isoscapes indicated that plant-soil interactions yielded different patterns and showedthe effect of the molasses grass invasion. Therefore, the spatial distribution must be accounted for when assessing the effects and outcome of species interactions and invasion pressure.

Forest fires can greatly affect soil properties and processes. In the study of the fire effects on soil, the soil thickness affected by heat depends on the characteristics of the fire and soil itself, but also on the attribute to be measured. The objective of this work is to know to what thickness (up to 1, 2 or 3 cm) various sensitive soil properties are immediately affected by a controlled burning. To achieve this aim, unaltered fresh topsoil (mollic horizon) of a fire-prone Aleppo pine forest in the semiarid Ebro Valley (NE-Spain) were sampled and, without destroying their original structure, burned from the surface in an outdoor combustion tunnel in triplicate. Biological properties are measured, including basal and normalized soil respiration (bSR and nSR), β-D-glucosidase (GLUase) and phosphomonoestarase (PHOase) activities, and related parameters, such as total organic matter (TOM), oxidizable organic C (OxC), nonhydrolyzable carbon (NHC), P-Olsen, pH, soil moisture and soil water repellency (WR). In the unburned soil, most of these properties showed a decreasing gradient with depth which is modified after burning, in some cases inverted (as enzymatic activities and WR), in others intensified (P-Olsen) and in most, truncated, with a maximum value in the second cm. The depth of the soil in which changes were recorded varied according to the attibute considered; thus, burning significantly decreased only up to the first cm: bSR (73 %) and TOM (81 %), up to 2 cm: PHOase (89 %), OxC (17 %) and WR (96 %) and up to 3 cm depth GLUase (58 %), NHC (24 %) and moisture (73 %). However, P-Olsen and pH both increased after burning up to 1 and 3 cm soil depths, with increases of up to 240 % and 11 %, respectively. In conclusion, fire effects on soil are depth dependent, and this dependency is not uniform across soil properties.