Pedobiologia最新文献

Arbuscular mycorrhizal (AM) fungi contribute to soil structure, but little is known about the effect of individual fungal species on soil aggregation. In this study, the influence of 3 AM fungi species on soil aggregation in a Vitric Andosol was determined using physical, micromorphological, and imaging analyses. We used a pipe of polyvinyl chloride (PVC) with a six-way connector, which was filled with soil plus AM fungal inoculum (Funneliformis mosseae, Rhizophagus intraradices, Gigaspora gigantea or non-inoculated -control-). Then lateral pipe connectors (experimental units) were covered with mesh systems (0.5, 0.25, and 0.034 mm), and PVC tubes filled with sterile soil were connected laterally using a clamp. The greenhouse experiment consisted of four treatments each with 32 experimental units. Four experimental units of each treatment were separated and collected at different times during the year: three were used to determine water-stable aggregates (disturbed soils), and one was preserved (undisturbed soil) to elaborate soil thin sections. Thematic micro-maps were constructed with image mosaics from a whole soil thin section, and micromorphological analyses were conducted using spatial operators. Our results showed that AM fungi affect soil aggregation forming micro-aggregates and macro-aggregates of different sizes. The most significant effects were observed with F. mosseae > R. intraradices > Gi. gigantea > control. Aggregation hierarchy was observed in micromorphological analysis, where F. mosseae and R. intraradices start binding organo-mineral particles and microaggregates to form macroaggregates, modifying soil structure from intergrain (apedal= without peds) to crumb aggregates (pedal= with peds). Gigaspora gigantea only promoted macroaggregation, by associating with pumice particles. The two AM fungi from Glomeraceae possess similar morphology compared to that isolate belonging to Gigasporaceae, which explain in part, their differential contribution traits on soil aggregation, as highlighted by using together physical and micromorphological analyses of soil thin sections based on high-resolution image mosaics.

Microbial inoculants are recognized as environmentally friendly methods to promote plant growth and improve soil properties. However, the effects of inoculation on the rhizosphere and rhizoplane community structure of plants remain poorly documented and need further investigation. Rhodopseudomonas palustris (R. palustris) strain has nitrogen fixing ability and Bacillus subtilis (B. subtilis) strain is a plant growth-promoting rhizobacterium (PGPR). In this study, we investigated the effects of single and co-inoculation with R. palustris and B. subtilis on the increase of rice yield as well as on the microbial communities in the rhizosphere and rhizoplane of rice through potting experiments, respectively. The results showed that inoculation significantly increased rice yield and seed setting rate, with co-inoculation raising the yield by up to 13.7%. Inoculation influenced both rhizosphere and rhizoplane community structures and functions, amplifying the differences between them. The most significant changes were brought about by the combined inoculation treatment. Co-inoculation with R. palustris and B. subtilis had a synergistic effect. The profound alterations of rhizoplane bacterial community structures and functions were proved to be positively correlated with rice yield and seed setting rate (r = 0.59–0.76, p < 0.05). These results provide new ideas for the investigation of the potential microbiological mechanisms of microbial co-inoculation in practical agricultural applications.

The Atlantic Forest is the most threatened Brazilian biome, with less than 10% of its original surface cover remaining. Thus, several programs of payment for ecosystem services have been developed in this biome focusing on revegetation of degraded areas. Forest regeneration promotes the development of soil invertebrate communities that play an important role in soil processes, delivering a wide range of ecosystem services. We studied the changes in macrofauna communities in three forests under different regeneration stages and the relationship between these invertebrates and soil chemical and physical properties. Macrofauna and soil chemical and physical properties were sampled until 30 cm depth in three forest fragments of the Brazilian Atlantic Forest under different regeneration stages: young regenerating forest (∼8 years old), secondary forest in intermediate regeneration stage (∼20 years old) and native secondary forest fragment. No significant differences in saturated hydraulic conductivity (K_s) were observed among sites, however, the old native forest showed reduction in K_s in deeper layers compared to young regenerating forests. Several macrofauna taxa were positively correlated with K_s and soil carbon. The stage of regeneration modified the abundance and diversity of these invertebrates in general (except for earthworms), and the old native forest showed high abundance of most taxa. In conclusion, our study highlights the potential of macrofauna communities as robust indicators of soil functions re-establishment in regenerating forests within the Atlantic Forest biome. The observed positive correlations between macrofauna abundance and diversity with soil water infiltration and organic carbon content emphasize the key role of these invertebrates to essential ecosystem functions.

Scattered throughout the Namib Desert of Namibia are populations of Welwitschia mirabilis, a unique, low-lying, and slow-growing gymnosperm plant. We studied soils under Welwitschia plants and in adjacent interplant areas along a 400-km range to examine the potential of these plants as resource islands supporting nematode communities. We found significant differences in nematode density and community structure among the sites that were correlated to differences in climate, edaphic factors, and plant size and density. Soils from the Torra Conservancy site, which receives the most precipitation and had the highest density of Welwitschia plants, contained the highest organic matter and the most diverse nematode communities, with the broadest representation of nematode trophic groups. The largest and likely oldest Welwitschia plants occurred in the Messum Crater, the site with the least rainfall, which hosted the densest nematode communities (mean = 14,683 kg⁻¹ soil). These communities consisted almost entirely of the bacterial-feeding nematode Panagrolaimus sp. Two other sites, Welwitschia Plain, a well-known tourist destination, and Hope Mine, the southernmost known population, contained the fewest nematodes with moderate levels of diversity. Differences in nematode abundance between Welwitschia soils and interplant soils were not discernable at three of the four field sites, suggesting the resource island effect is not very strong. Interplant spaces also support diverse and abundant nematode communities, perhaps due to the growth of cryptobiotic crusts or ephemeral rainfall-induced vegetation.

Arbuscular mycorrhizal (AM) associations are multifunctional. Two important functions they perform are facilitating nutrient uptake in host plants and protecting plants from biotic stress, among other functions. AM fungal taxa vary in how capably they perform these functions and can also respond differently to environmental selection. Therefore, there is a need to better understand how particular environmental variables might alter the response of AM fungal communities. Here, we analysed data from a DNA-based survey of fungal communities in soils collected throughout Australia to observe relationships among soil nitrogen and phosphorus availability and the abundance of two AM fungal taxa that reportedly vary in function – the Gigasporaceae (putatively more important for nutrient uptake) and Glomeraceae (putatively more important for biotic stress). Relationships were assessed in three vegetation types – grasslands, forests and woodlands – to assess whether associations with soil nutrition varied depending on carbon availability for AM fungi. Fungi from the Gigasporaceae decreased in frequency as available phosphorus increased, while those from the Glomeraceae increased or were unresponsive as available phosphorus increased. Similar patterns were observed for nitrate availability, although only in woodlands. These patterns are consistent with expectations that AM fungi from the Gigasporaceae, in general, are better suited to alleviate nutrient limitation in hosts as soil chemical fertility decreases. This knowledge may aid in implementing optimal strategies involving AM fungal inoculum best suited to the local conditions of future land management and agricultural projects.

To date, a paucity of studies have examined bacterial communities in tuberospheres. However, the function of these bacterial communities in healthy potato plants is still largely unknown. Here, we aimed to describe the structure and composition of tuberosphere bacteriomes and its capability to make organosulfur plant available using the rhizosphere and bulk soil bacterial community characteristics as a reference. Rhizosphere, tuberosphere and bulk soil was collected from two field grown potato varieties. Bacterial communities were characterized by 16S rRNA gene amplicon sequencing. Bacterial organosulfur mobilization indicators were evaluated with cultivation dependent and independent methods and were correlated (Spearman) with the relative abundance of bacterial families. The structure of tuberosphere bacterial communities either overlapped with the bulk soil or had similarities with the rhizosphere. Relative abundance of specific bacterial families were distinct between bulk soil, tuberosphere and rhizosphere. Tuberospheres had a tendency for higher arylsulfonate utilization compared to bulk soil. The families Sphingomonadaceae, Sphingobacteriaceae and Rhizobiaceae which presented a decline in their relative abundances from the rhizosphere to tuberosphere and bulk soil had positive correlations with organosulfur mobilizing indicators. Potato variety and soil characteristics played a role in structuring the tuberosphere bacterial communities. Tuberospheres represent an environment in-between bulk soil and rhizosphere indicative from the intermediate relative abundances of specific bacterial families. A moderately higher bacterial organosulfur mobilization activity in tuberospheres suggests that this microbial function may serve specific biological roles for potato tubers.

The ratio of β-glucosidase (BG) to phosphomonoesterase (PME) activity (BG:PME) is often used to predict the intensity of microbial phosphorus (P) shortage, with lower BG:PME indicating stronger P shortage (enzymatic stoichiometry theory). Here, we demonstrated that 10-year continuous P fertilization as high as 150 kg P ha⁻¹ yr⁻¹ in the form of NaH₂PO₄ solution did not elevate the BG:PME up to the level of other terrestrial ecosystems. The BG:PME of primary, secondary, and planted forests were 0.094, 0.067, and 0.089, respectively in P-fertilized plots, which were much lower than global average (0.62 ± 0.04), despite the fact that Bray-extracted P contents were substantially elevated (more than 600 times). Thus, the findings of the current study suggest that BG:PME overestimates P shortage in our P-enriched forests, implying that the enzymatic stoichiometry theory may not be universally applicable.

Investment in non-native species management should be informed by knowledge of impact, including on native biodiversity and ecosystem function. Oribatid soil mites may be useful to evaluate the impacts of plant invasions since they are bioindicators of disturbance and soil ecosystem health. Still, more research is needed to characterize their responses to plant invasion, especially at the species level. Our objective was to determine the effect of invasion of urban forest understories by an allelopathic weed (garlic mustard, Alliaria petiolata (Brassicaceae)) on belowground oribatid mite species and communities. At two sites in central Alberta (Canada), over two years, we examined adult oribatid (≥ 300 µm) community assemblages, species richness, evenness, diversity, and abundance in plots invaded with garlic mustard and uninvaded plots with native vegetation. Environmental covariates known to be associated with soil invertebrate communities were also evaluated. Results suggest that the spatial extent of the garlic mustard invasion (patch area) mediates its impact on oribatid mite communities. However, there were no community-level impacts when considering invasion as binary (garlic mustard vs. native vegetation). Garlic mustard patch area influenced oribatid community composition and was positively related to species richness and several abundance metrics. The oribatid species we observed benefiting from garlic mustard invasion have been previously associated with disturbed soils. The mechanisms driving these patterns need more research, but we hypothesize they may relate to patch-specific resident times. Site was also a dominant factor influencing oribatid mite communities, and impacts of year, litter depth, and canopy cover were also detected at the species and/or community level. These findings contribute to our understanding of the impact of an invasive weed on bioindicating soil mite communities and species and highlight the importance of considering invasion context, including spatial extent when evaluating the impacts of invasive species on belowground invertebrate communities.

In addition to well-known effects on species ecophysiology, phenology, and distributions, climate change is widely predicted to impact essential ecosystem services such as decomposition and nutrient cycling. While temperature and soil moisture are thought to influence litter decomposition, elucidating consistent soil process responses to observed or predicted shifts in climate have proven difficult to evidence. Here we investigated how aspect (i.e., north-south orientation), a natural model for variation in soil temperature, influenced soil physico-chemical conditions and decomposition of two standardised litter types (Green tea and Rooibos teabags) in Pole-facing (PF) and Equator-facing (EF) roadside verges spanning a 3000 km and 27° latitudinal gradient across Europe. Despite average daily temperatures being 1.5 - 3.0 °C warmer on EF than PF slopes, there were only minor region-specific differences in initial soil physico-chemical conditions and short-term variation in litter decomposition (i.e., litter mass loss was higher in EF-verges for the first month of deployment only) associated with aspect. We conclude that previously observed differences in soil environments and the decomposition process associated with slope orientation, is largely litter or environment specific, although medium-term soil-decomposition in semi-natural grassland ecosystems may also be insensitive to the magnitude of temperature variation within the range predicted by the IPCC SSP1–2.6 emissions scenario. Nonetheless, consistent average and extreme temperature differences between adjacent PF- and EF-aspects along roadside verges provides a model system to explore exactly how resilient the soil environment and the micro-organisms responsible for decomposition, are to temperature variation.

Applications of mineral fertilizer to grasslands have become more frequent in recent decades to increase forage production. However, the impacts of mineral fertilizer on the soil microbiome is poorly understood in cold semiarid grassland ecosystems of Southern Patagonia, Argentina. Therefore, our objective was to analyze experimentally the influence of mineral nutrient fertilization (N, P, K, and NPK in combination) on soil microbial community attributes, such as microbial biomass carbon (MBC) and nitrogen (MBN), soil basal respiration (SBR), microbial metabolic coefficients, the colonization of endophytic fungi such as arbuscular mycorrhizal (AM) fungi, and dark septate endophytes (DSE), and aboveground plant productivity. Mineral fertilization with macronutrients (N, P, K, and NPK) decreased the SBR, qCO₂, AM fungi and DSE fungi, but did not generate changes in MBC and MBN. The magnitude of these responses depends on years after fertilization. We found that soil microbiome was strongly dependent on a range of biotic and abiotic factors, such as growing season precipitation, aboveground plant biomass the relationship between the microbial biomass and microbial respiration, and between endophytic fungi and plants. This work improved our understanding of the soil microorganisms’ response to mineral fertilizer application and provides new insights into soil nutrient dynamics and ecosystem functioning.