Shifts In Community Structure Research Articles

Mechanisms of cadmium release from manganese-rich sediments driven by exogenous DOM and the role of microorganisms

Dissolved organic matter (DOM) is a crucial component of natural sediments that alters Cd sequestration. Nevertheless, how different types of DOM fuel Cd mobilization in Mn-rich sediments has not been elucidated. In the present study, four typical DOM, fluvic acid (FA), bovine serum albumin (BSA), sodium alginate (SA), and sodium dodecyl benzene sulfonate (SDBS), were used to amend Cd-contaminated sediment to study their effects on Cd/Mn biotransformation and microbial community response. The results demonstrated that different DOM drive microbial community shifts and enhance microbially mediated Mn oxide (MnO) reduction and Cd release. The amendment of terrestrial- and anthropogenic-derived DOM (FA and SDBS) mainly contributed to enriching Mn-reducing bacteria phylum Proteobacteria, and its abundance increased by 38.16–74.47 % and 56.41–73.98 %, respectively. Meanwhile, microbial-derived DOM (BSA and SA) mainly stimulated the abundances of metal(loid)-resistant bacteria phylum Firmicutes. Accompanied by microbial community structure, diversity, and co-occurrence network shifts, the DOM concentration and oxidation-reduction potential changed, resulting in enhanced Cd mobilization. Importantly, FA stimulated Cd release most remarkably, probably because of the decreased cooperative interactions between bacterial populations, stronger reduction of MnOs, and higher aromaticity and hydrophobicity of the sediment DOM after amendment. This study linked DOM types to functional microbial communities, and explored the potential roles of different DOM types in Cd biotransformation in lake sediments.

Body size modulates demographic patterns of top predators and their native and invasive prey: A biomathematical approach

The arrival of invasive species in native communities impacts the structure and functioning of ecosystems, and is considered a critical indicator of loss of biodiversity. Exploring the effects of new species in communities presents challenges addressable through theoretical ecology. Species body size not only shapes trophic relationships, but may also impact predator success and facilitate species coexistence. However, little attention has been paid to the effects of differences in species body size on interactions between native and invasive primary consumers, which could be relevant to their coexistence with higher-level predators. Our aim is to investigate demographic patterns using a dynamic, mechanistic model of two age-structured primary consumers (one invasive and one native) sharing a plant resource and preyed upon by a common predator. In our model, we highlight three crucial phenomena: the structuring of primary consumers into adults and juveniles, reproduction occurring in discrete pulses, and the seasonal addition of new individuals to the population. Hence, the success of one species over the other relies on its reproductive capacity to incorporate individuals in each reproductive cycle. Our simulations reveal that abundance patterns are influenced by body size, suggesting that changes in predator body size could serve as key indicators of shifts in community structure.

Elevation-driven modifications in tissue architecture and physiobiochemical traits of Panicum antidotale Retz. in the Pothohar Plateau, Pakistan

Mountainous ecosystems are experiencing rapid shifts in distribution patterns and community structure due to the impacts of climate change and vegetation dynamics. This study offers a comprehensive insight into the adaptive mechanisms of Panicum antidotale to varying elevations within the Pothohar Plateau, shedding light on its survival strategies in climate-affected regions. The findings reveal that populations at lower elevations exhibit maximum height, leaf area, shoot length, and fresh weight, whereas those at higher elevations display significant decrease in these parameters. Moreover, a significant decline in species density, frequency and cover is evident at high elevation. High-elevation populations demonstrate decreased photosynthetic traits, including chlorophyll, carotenoid, and Na and Ca content. Furthermore, there are notable variations in the antioxidant enzyme activity across elevation gradients. Populations at lower elevations exhibit higher activities of superoxide dismutase and peroxidase. Across the gradient, there were significant reductions in root and stem radius, sclerenchyma thickness, bulliform cell size, metaxylem vessels, and phloem area. Populations at moderate elevations displayed thicker lamina and epidermis, larger cortical cells, wider xylem vessels, and increased phloem area; however, these traits declined at higher elevations. High-elevation populations showed thicker lamina and epidermis, extensive sclerenchyma, greater cortical cell area, and higher stomatal density. Photosynthetic traits and enzymatic activity were major contributors at moderate elevations while stem and leaf traits were significantly changed at high elevations. Overall, this research contributes significantly to the broader knowledge of plant adaptation in mountainous ecosystems and stresses the importance of considering elevation as a critical factor in ecological studies.

Afforestation-Induced Shifts in Soil Bacterial Diversity and Community Structure in the Saihanba Region.

Afforestation plays a pivotal role in ecosystem restoration, exemplified by the Saihanba Mechanized Forest Farm, the world's largest planted forest; however, the assembly mechanisms and interactions of soil microbial communities in such forests remain inadequately understood. This study aimed to elucidate the impact of different afforestation tree species, namely Larix gmelinii var. principis-rupprechtii, Picea asperata, and Pinus sylvestris var. mongolica, on soil bacterial diversity and community structure in comparison to grassland. Sixty soil samples were collected at a 20 cm depth, and high-throughput sequencing was employed to identify bacterial communities and assess their interactions with environmental factors. A total of 6528 operational taxonomic units (OTUs) were identified, with Solirubrobacter, Conexibacter, Bacillus, Massilia, Gaiella, Acidibacter, and Vicinamibacter being the dominant genera. Afforestation significantly impacted soil bacterial alpha diversity, with notable influence from key soil chemical properties, including available phosphorus (AP), cation exchange capacity (CEC), and the carbon-to-nitrogen ratio of soil organic matter (SOM-C/N). The Mantel test highlighted pH, the Normalized Difference Vegetation Index (NDVI), and spatial variable (dbMEM) as primary environmental factors influencing dominant bacterial genera. The bacterial community structure demonstrated deterministic homogeneous selection, wherein SOM-C/N emerged as a significant factor influencing the dissimilarity of soil bacterial communities. Furthermore, plantation soils exhibited a more complex network structure than grassland soil, highlighting the crucial role of bacterial communities in vegetation changes and providing valuable insights into their response to environmental factors during the reforestation process.

Consequences of kelp forest ecosystem shifts and predictors of persistence through multiple stressors.

Ecological communities can be stable over multiple generations, or rapidly shift into structurally and functionally different configurations. In kelp forest ecosystems, overgrazing by sea urchins can abruptly shift forests into alternative states that are void of macroalgae and primarily dominated by actively grazing sea urchins. Beginning in 2014, a sea urchin outbreak along the central coast of California resulted in a patchy mosaic of remnant forests interspersed with sea urchin barrens. In this study, we used a 14-year subtidal monitoring dataset of invertebrates, algae, and fishes to explore changes in community structure associated with the loss of forests. We found that the spatial mosaic of barrens and forests resulted in a region-wide shift in community structure. However, the magnitude of kelp forest loss and taxonomic-level consequences were spatially heterogeneous. Taxonomic diversity declined across the region, but there were no declines in richness for any group, suggesting compositional redistribution. Baseline ecological and environmental conditions, and sea urchin behaviour, explained the persistence of forests through multiple stressors. These results indicate that spatial heterogeneity in preexisting ecological and environmental conditions can explain patterns of community change.

The Effects of Vermicompost and Steel Slag Amendments on the Physicochemical Properties and Bacterial Community Structure of Acidic Soil Containing Copper Sulfide Mines

Acidification and heavy metal stress pose challenging threats to the terrestrial environment. This investigation endeavors to scrutinize the combined effects of vermicompost and steel slag, either singularly or in concert with Ryegrass (Lolium perenne L.), on the remediation of acidic soil resulting from sulfide copper mining. The findings illuminate substantial ameliorations in soil attributes. The application of these amendments precipitates an elevation in soil pH of 1.39–3.08, an augmentation in organic matter of 4.05–8.65, a concomitant reduction in total Cu content of 43.2–44.7%, and a marked mitigation in Cu bioavailability of 64.2–80.3%. The pronounced reduction in soil Cu bioavailability within the steel slag treatment group (L2) is noteworthy. Characterization analyses of vermicompost and steel slag further elucidate their propensity for sequestering Cu2+ ions in the soil matrix. Concerning botanical analysis, the vermicompost treatment group (L1) significantly enhances soil fertility, culminating in the accumulation of 208.35 mg kg−1 of Cu in L. perenne stems and 1412.05 mg kg−1 in the roots. Additionally, the introduction of vermicompost and steel slag enriches soil OTU (Operational Taxonomic Units) quantity, thereby augmenting soil bacterial community diversity. Particularly noteworthy is the substantial augmentation observed in OTU quantities for the vermicompost treatment group (L1) and the combined vermicompost with steel slag treatment group (L3), exhibiting increments of 126.04% and 119.53% in comparison to the control (CK). In summation, the application of vermicompost and steel slag efficaciously diminishes the bioavailability of Cu in the soil, augments Cu accumulation in L. perenne, induces shifts in the soil microbial community structure, and amplifies soil bacterial diversity. Crucially, the concomitant application of vermicompost and steel slag emerges as a holistic and promising strategy for the remediation of sulfide copper mining acidic soil.

Demographic recovery of corals at a wave-exposed reef following catastrophic disturbance

Rapid recovery of coral cover following acute disturbance has been documented on many reefs. Yet measuring coverage alone can mask shifts in community and demographic structure. Here, we quantify long-term changes in population size structure for three common genera (Acropora, Pocillopora, and Stylophora) at an eastern outer reef in Palau, Micronesia, following catastrophic loss of corals due to typhoon Bopha in 2012, based on size measurements from 3648 coral colonies. Mean colony size returned to pre-disturbance levels within 4 and 6 years for Stylophora and Pocillopora, respectively. By 2020, Pocillopora colony density far exceeded pre-disturbance levels, with rapid successful recruitment following typhoon Bopha. Despite recovery of Acropora colony density by 2020, populations remained dominated by smaller colonies. We demonstrate that full demographic recovery can occur more rapidly for pocilloporids (within 6 years) compared to Acropora which had not fully recovered by 8 years post-disturbance, possibly due to fewer annual recruitment events and larger maximum colony sizes. Our results highlight the value of demographic metrics as early indicators of recovery.

Drying as an effective method to store soil samples for DNA-based microbial community analyses: a comparative study

Soil sampling for environmental DNA in remote and semi-remote locations is often limited due to logistical constraints surrounding sample preservation, including no or limited access to a freezer. Freezing at − 20 °C is a common DNA preservation strategy, however, other methods such as desiccation, ethanol or commercial preservatives are available as potential alternative DNA preservation methods for room temperature storage. In this study, we assessed five preservation methods (CD1 solution, 95% Ethanol, Dry & Dry silica gel packs, RNAlater, LifeGuard) along with freezing at − 20 °C, against immediate extraction on organic and mineral soils for up to three weeks of preservation. We assessed direct effects on DNA concentration and quality, and used DNA metabarcoding to assess effects on bacterial and fungal communities. Drying with Dry & Dry led to no significant differences from immediate extraction. RNAlater led to lower DNA concentrations, but effects on community structures were comparable to freezing. CD1, LifeGuard and Ethanol either caused immediate significant shifts in community structure, degradation of DNA quality or changes in diversity metrics. Overall, our study supports the use of drying with silica gel packs as a cost-effective, and easily applied method for the short-term storage at room temperature for DNA-based microbial community analyses.

Benthic cyanobacterial metabolites interact to reduce coral larval survival and settlement

Benthic cyanobacterial mats (BCMs) are becoming increasingly abundant on coral reefs worldwide. High growth rates and prolific toxin production give them the potential to cause widespread coral recruitment failure through allelopathic effects, but few studies have made the link between their toxicity for coral larvae and in situ toxin concentrations. Here we investigated the allelopathic effects of the benthic cyanobacterium Anabaena sp.1 on larvae of the coral Pocillopora acuta. This cyanobacterium produces several non-ribosomal cyclic lipopeptides of the laxaphycin family with cytotoxic properties. Therefore, we measured the concentration of laxaphycins A and B in Anabaena mats and in the water column and tested their effects on coral larvae. We found that Anabaena crude extract reduces both larval survivorship and settlement and that laxaphycin B reduces settlement. When larvae were exposed to both laxaphycins, there was a reduction in both larval survival and settlement. In the natural reef environment, laxaphycin A and B concentrations increased with increasing proximity to Anabaena mats, with concentrations being consistently above LC50 and EC50 thresholds within a 1 cm distance of the mats. This study demonstrates that laxaphycins reduce the survival and inhibit the settlement of coral larvae at concentrations found near Anabaena mats in situ. It further shows a combined effect between two cyanobacterial metabolites. As BCMs become more common, more of their secondary metabolites might be released in the water column. Their occurrence will lead to a reduction in coral recruitment rates, contributing to the continuing decline of coral reefs and shift in community structure.

Pioneering gut health improvements in piglets with phytogenic feed additives

This research investigates the effects of phytogenic feed additives (PFAs) on the growth performance, gut microbial community, and microbial metabolic functions in weaned piglets via a combined 16S rRNA gene amplicon and shotgun metagenomics approach. A controlled trial was conducted using 200 pigs to highlight the significant influence of PFAs on gut microbiota dynamics. Notably, the treatment group revealed an increased gut microbiota diversity, as measured with the Shannon and Simpson indices. The increase in diversity is accompanied by an increase in beneficial bacterial taxa, such as Roseburia, Faecalibacterium, and Prevotella, and a decline in potential pathogens like Clostridium sensu stricto 1 and Campylobacter. Shotgun sequencing at the species level confirmed these findings. This modification in microbial profile was coupled with an altered profile of microbial metabolic pathways, suggesting a reconfiguration of microbial function under PFA influence. Significant shifts in overall microbial community structure by week 8 demonstrate PFA treatment’s temporal impact. Histomorphological examination unveiled improved gut structure in PFA-treated piglets. The results of this study indicate that the use of PFAs as dietary supplements can be an effective strategy, augmenting gut microbiota diversity, reshaping microbial function, enhancing gut structure, and optimising intestinal health of weaned piglets providing valuable implications for swine production.Key points• PFAs significantly diversify the gut microbiota in weaned piglets, aiding balance.• Changes in gut structure due to PFAs indicate improved resistance to weaning stress.• PFAs show potential to ease weaning stress, offering a substitute for antibiotics in piglet diets.

Wetland soil organic carbon balance is reversed by old carbon and iron oxide additions.

Iron (Fe) oxides can stabilize organic carbon (OC) through adsorption and co-precipitation, while microbial Fe reduction can disrupt Fe-bound OC (Fe-OC) and further increase OC mineralization. The net effects of OC preservation and mineralization mediated by Fe oxides are still unclear, especially for old carbon (formed from plant litters over millions of years) and crystalline Fe oxides. Accelerating the recovery of wetland carbon sinks is critical for mitigating climate change and achieving carbon neutrality. Quantifying the net effect of Fe-mediated OC mineralization and preservation is vital for understanding the role of crystalline Fe oxides in carbon cycling and promoting the recovery of soil carbon sinks. Here, we explored the OC balances mediated by hematite (Hem) and lignite addition (Lig) to freshwater wetland (FW, rich in C and Fe) and saline-alkaline wetland (SW, poor in C and Fe) soil slurries, incubated under anaerobic conditions. Results showed that Lig caused net OC accumulation (FW: 5.9 ± 3.6 mg g-1; SW: 8.3 ± 3.2 mg g-1), while Hem caused dramatic OC loss, particularly in the FW soils. Hem inhibited microbial Fe(III) reduction by decreasing the relative abundance of Fe respiration reducers, while substantially enhancing OC mineralization through the shift in the microbial community structure of FW soils. Lig resulted in carbon emission, but its contribution to preservation by the formation of Fe-OC was far higher than that which caused OC loss. We concluded that crystalline Fe oxide addition solely favored the increase of OC mineralization by adjusting the microbial community structure, while old carbon enriched with an aromatic and alkyl promoted Fe-OC formation and further increased OC persistence. Our findings could be employed for wetland restoration, particularly for the recovery of soil carbon sinks.

Dietary β-hydroxybutyric acid improves the growth performance of young ruminants based on rumen microbiota and volatile fatty acid biosynthesis.

The ketone body β-hydroxybutyric acid (BHB) plays critical roles in cellular proliferation and metabolic fuel utilization; however, its effects on the rumen microbiota remain unknown. Here, three doses of BHB (low, medium, and high) were supplemented to early-weaned goat kids. Compared with controls, the beneficial effects of BHB on growth and rumen development were observed in goats at 90 days of age (d). The low dose of dietary BHB increased the concentration of rumen acetate, propionate, and butyrate on d90. The sequencing results of the rumen microbiota revealed marked shifts in rumen microbial community structure after early-weaned goat kids consumed BHB for 2 months. The signature bacterial ASVs for each treatment were identified and were the main drivers contributing to microbial interactions in the rumen. The bacteria associated with rumen weight were also correlated with body weight. Some classified bacterial signatures, including Prevotella, Olsenella umbonate, and Roseburia faecis, were related to rumen volatile fatty acids and host development. Overall, dietary BHB altered rumen microbiota and environments in young goats, which contributed to rumen development and growth.

Impact of salinity and time on structure and functional potential of wastewater treatment biofilms in intermittent sand bioreactors.

High salt wastewater is produced in industries, including seafood and pickling processing. The salinity in such wastewaters has been shown to negatively impact biological treatment efficacy. Little is known about the changes in the microbial community structure in the mature biological 2 treatment systems, the impacts of salinity on community composition, and the shifts over time during operation. This study aimed to identify the changes in the microbial community due to both salt and days of operation through 16s rRNA sequencing and KEGG functional predictions. Intermittent sand bioreactors (ISBs) with a focus on ammonia treatment were utilized. Results showed that the overall community structure and diversity were distinct as wastewater salinity varied from 0%-1.3%. At 1.3% salinity Zoogloea, a common genus in wastewater treatment plants, was not present and Aequorovita, Thauera and Dokdonella became the dominant genera. Nitrosomonas, an important ammonia oxidizing bacteria, increased in abundance with days of operation but was not significantly impacted by an increase in salinity. This finding was further supported by an increase in predicted nitrification potential with time of operation within all intermittent sand bioreactors tested. These results provide a deeper understanding of the impacts of salinity on microbial community development in biological treatment systems and elucidate the shifts in community structure occurring during early operations and into system maturity.

Functional changes across marine habitats due to ocean acidification.

Global environmental change drives diversity loss and shifts in community structure. A key challenge is to better understand the impacts on ecosystem function and to connect species and trait diversity of assemblages with ecosystem properties that are in turn linked to ecosystem functioning. Here we quantify shifts in species composition and trait diversity associated with ocean acidification (OA) by using field measurements at marine CO2 vent systems spanning four reef habitats across different depths in a temperate coastal ecosystem. We find that both species and trait diversity decreased, and that ecosystem properties (understood as the interplay between species, traits, and ecosystem function) shifted with acidification. Furthermore, shifts in trait categories such as autotrophs, filter feeders, herbivores, and habitat-forming species were habitat-specific, indicating that OA may produce divergent responses across habitats and depths. Combined, these findings reveal the importance of connecting species and trait diversity of marine benthic habitats with key ecosystem properties to anticipate the impacts of global environmental change. Our results also generate new insights on the predicted general and habitat-specific ecological consequences of OA.

Potential influence of bacterial community structure on the distribution of brGDGTs in surface sediments from Yangtze River Estuary to East China Sea

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are special components of bacterial membrane lipids and are ubiquitously found in diverse terrestrial and marine environments. Acidobacteria have been recently evidenced as one of their source microorganisms in terrigenous environments, such as acidic soils and peats. However, the biological sources of brGDGTs, their distributions and ecophysiological responses, and these biotic impacts on the relationships between brGDGT-based proxies and environmental variables (e.g., ambient temperature, pH, and dissolved oxygen content) in the marine realm are poorly understood. In this study, we analyzed C5- and C6-methylated brGDGTs as well as bacterial communities in the surface sediment samples from the Yangtze River Estuary (YRE) to the East China Sea (ECS), aiming to explore the relationship between brGDGT distribution and bacterial composition and to examine how benthic conditions and bacterial communities jointly influence the spatial patterns of brGDGTs from marine sediments. Substantial differences in the spatial distribution of brGDGTs from coast to shelf were observed. The increase in the proportion of brGDGTs with cyclopentyl and C6-methyl moieties (e.g., Ic and IIc’) and #ringstetra values of >0.7 indicate the occurrence of marine-sourced brGDGTs in the shelf. Statistical analyses suggest that the bacterial community structure and the geochemical and environmental variables may contribute 43.56% and 29.97% to the brGDGT distribution, respectively. Multiple significant correlations between bacterial groups at the order level and brGDGT compounds suggest that bacteria such as Gemmatimonadetes, Planctomycetes and Proteobacteria may potentially contribute to the brGDGT production in marine environments. With the consideration of benthic environmental changes, the shift in bacterial community structure could further result in the variations of brGDGT-based proxies incorporating cyclopentyl and C6-methyl moieties that are likely to be produced by benthic marine bacteria. Overall, in addition to environmental conditions of the ocean bottom, the potential influence of bacterial community structure on the distribution of brGDGTs highlights the caution of using brGDGT-based proxies as terrestrial indicators in coastal oceans.

A lag bloom pattern of phytoplankton after freshwater input events revealed by daily samples during summer in Qinhuangdao coastal water, China.

Phytoplankton blooms have become a global concern due to their negative impacts on public health, aquaculture, tourism, and the economic stability of coastal regions. Therefore, elucidating the shifts in phytoplankton community structure and abundance, as well as their environmental drivers, is crucial. However, existing studies often fail to capture the detailed dynamics of phytoplankton blooms and their environmental triggers due to low temporal observation resolution. In this study, high temporal resolution (daily) samples were collected over 43 days to investigate the influence of environmental factors on phytoplankton in Qinhuangdao in the summer. During the observation period, a total of 45 phytoplankton species were identified, comprising 26 Bacillariophyta species, 16 Dinophyta species, 2 Euglenophyta species, and 1 Chromophyta species. Interestingly, a lag bloom pattern of phytoplankton behind freshwater input was observed across day-to-day samples. Phytoplankton blooms typically lagged 1-3 days behind periods of decreased salinity and nutrient input, suggesting that freshwater influx provides the foundational materials and benefits for these blooms. Moreover, the phytoplankton blooms were triggered by six dominant species, i.e., Chaetoceros spp., Pseudo-nitzschia delicatissima, Skeletonema costatum, Protoperdinium spp., Leptocylindrus minimus, Pseudo-nitzschia pungens, and Thalassiosira spp. Consequently, the succession of phytoplankton showed a predominant genera shift in the following sequence: Nitzschia, Protoperdinium, and Prorocentrum - Skeletonema - Pseudo-nitzschia - Gymnodinium - Leptocylindrus. Besides that, a deterministic process dominated phytoplankton community assembly across time series, and DIP is a key factor in shifting the phytoplankton community structures in this area. In summary, our study offers high-resolution observations on the succession of phytoplankton communities and sheds light on the complex and differentiated responses of phytoplankton to environmental factors. These findings enhance our understanding of the dynamics of phytoplankton blooms and their environmental drivers, which is essential for the effective management and mitigation of their adverse impacts.

Enhancing anaerobic digestion performance of oxytetracycline-laden wastewater through micro-nano bubble ozonation pretreatment

This study investigated the potential of micro-nano bubble (MNB) ozonation pretreatment to eliminate oxytetracycline (OTC) from wastewater and improve subsequent anaerobic digestion (AD) performance. The findings revealed that MNB ozonation achieved efficient OTC oxidation (>99 % in 60 min), and significantly enhanced methane production by 51 % compared to conventional ozonation (under 30 min of pretreatment). Additionally, MNB ozonation resulted in a decrease in the soluble chemical oxygen demand and reduced volatile fatty acid accumulation compared to conventional ozonation. Furthermore, the study sheds light on the profound impact of OTC and its oxidation by-products on the sludge microbiome. Exposure to OTC and its oxidation by-products resulted in alterations in extracellular polymeric substances composition and led to significant shifts in microbial community structure. This study highlights the promise of MNB ozonation as an effective approach for pharmaceutical pollutant removal and the optimization of AD performance in wastewater treatment, with implications for improved environmental sustainability.

Grazing-driven shifts in soil bacterial community structure and function in a typical steppe are mediated by additional N inputs

Herbivore grazing and nitrogen (N) fertilization affect soil microbial diversity and community composition both in direct and indirect pathways (e.g., via alterations in soil microenvironment and plant communities); however, their combination effects are still largely unexplored. We carried out a field study to investigate how soil abiotic properties, plant community composition and functional traits altered soil bacterial community structure and function in response to a long-term herbivore grazing (17-year sheep grazing with four stocking rates) and anthropogenic N inputs (6-year N addition with four levels) experiment. We show that a high stocking rate of 8.7 sheep ha−1 (SR8.7) decreased soil bacterial α- and β-diversity, while α- and β-diversity showed hump-shaped and saddle-shaped responses, respectively, with increasing N addition rate, reaching tipping points at the N application rate of 10 g N m−2 year−1 (N10). The synergistic effects of grazing and N addition induced the highest soil bacterial α-diversity at SR2.7 with N10. The contrasting effects of grazing and N addition induced higher soil bacterial β-diversity at SR8.7 with N20. Plant factors (e.g., aboveground biomass of Stipa bungeana and community-weighted mean carbon [CWM_C]), edaphic factors (e.g., soil moisture, pH, NO3−-N, and C:nutrients ratios) and their interactions were the most significant factors affecting the diversity and community composition of bacteria. Our structure equation model (SEM) shows that grazing-induced negative effects on soil pH and plant community composition indirectly increased the β-diversity of soil bacteria, while grazing-induced decreased CWM_C had positive effects on bacterial α-diversity and community structure. However, N addition indirectly increased β-diversity of soil bacteria via changes in soil NO3−-N and plant community composition, while N addition had negative impacts on bacterial α-diversity and community structure via variations in CWM_C. The interaction of grazing and N addition increased the complexity and stability of the bacterial network. Based on the KEGG database, grazing and N addition could accelerate the soil functional potential of C and N cycling. Our findings suggest that N application at a rate of <10 g N m−2 year−1 with a stocking rate of <5.3 sheep ha−1 could maintain the development of soil bacteria in supporting the most important ecosystem functions and services. Complex responses of soil microbes to grazing and N addition indicate the need for deeper investigations of the impacts of global change on microbial involvement in biogeochemical cycles.

Reconnoitre on ichthyofauna of Mahanadi River of India: shifting diversity down the river continuum and linking ecological traits with patterns in biodiversity.

Anthropogenic alterations have paramount impacts on the alpha and beta diversity of aquatic resources, and fishes are predominantly susceptible to such impacts. Mahanadi River, one of the major peninsular rivers of India, has abundant fish resources, which play a significant role in supporting the fishers' livelihoods. The exploratory study in the river conducted for three consecutive years recorded 148 species under 53 families. Cyprinids dominated the fish diversity with 41 species, followed by Bagrids (9) and Sciaenids (7). One hundred-one species under 29 families were reported from the freshwater stretch. With a total of 111 species reported under 48 families, the estuarine and tidal freshwater stretch was more speciose, due to marine migrant species which advent the estuarine and tidal freshwaters stretch for breeding and feeding purposes. Tikarpara, a conserved site within a sanctuary, was the most species-diverse as well as a species-even site. The study also recorded the extension of the distributional range of 3 fish species and also 4 exotic species from the river. The seasonal variations in diversity indicated that the deviations were not prominent in freshwater sites, whereas in tidal brackish water sites, species richness was relatively higher in post-monsoon, and species evenness was higher during monsoon. Taxonomic distinctness test showed that the average taxonomic distinctness was high for tidal estuarine locations as they harbour taxonomically distant fishes. The hierarchical clustering of sites showed the inordinate effect of river gradient and fragmentation on the fish community structure. Analyzing the key drivers of the assemblage structure of the entire river, salinity was the major deterministic factor, and within the freshwater stretch, the major influences were depth, transparency, and specific conductivity. The study concluded that, despite all of its ecological stresses, Mahanadi still supports rich fish diversity, yet there is a notable shift in the fish community structure. There is a need for integrating molecular and morphological tools for the taxonomic revision of many genera and species for proper in situ and ex situ conservation measures and to formulate future biodiversity management plans addressing to reduce the impacts of the ecological threats.

Fungal community structure shifts in litter degradation along forest succession induced by pine wilt disease

Fungi play a crucial role in decomposing litter and facilitating the energy flow between aboveground plants and underground soil in forest ecosystems. However, our understanding how the fungal community involved in litter decomposition responds during forest succession, particularly in disease-driven succession, is still limited. This study investigated the activity of degrading enzyme, fungal community, and predicted function in litter after one year of decomposition in different types of forests during a forest succession gradient from coniferous to deciduous forest, induced by pine wilt disease. The results showed that the weight loss of needles/leaves and twigs did not change along the succession process, but twigs degraded faster than needles/leaves in both pure pine forest and mixed forest. In pure pine forest, peak activities of enzymes involved in carbon degradation (β-cellobiosidase, β-glucosidase, β-D-glucuronidase, β-xylosidase), nitrogen degradation (N-acetyl-glucosamidase), and organic phosphorus degradation (phosphatase) were observed in needles, which subsequently declined. The fungal diversity and evenness (Shannon’s diversity and Shannon's evenness) dropped in twig from coniferous forest to mixed forest during the succession. The dominant phyla in needle/leaf and twig litters were Ascomycota (46.9%) and Basidiomycota (38.9%), with Lambertella pruni and Chalara hughesii identified as the most abundant indicator species. Gymnopus and Desmazierella showed positively correlations with most measured enzyme activities. Functionally, saprotrophs constituted the main trophic mode (47.65%), followed by Pathotroph-Saprotroph-Symbiotroph (30.95%) and Saprotroph-Symbiotroph (10.57%). The fungal community and predicted functional structures in both litter types shifted among different forest types along the succession. These findings indicate that the fungal community in litter decomposition responds differently to disease-induced succession, leading to significant shifts in both the fungal community structure and function.