Altered Community Composition Research Articles

Soil bacterial community diversity and life strategy during slope restoration on an uninhabited island: changes under the aggregate spray-seeding technique.

We investigated the effects of the aggregate spray-seeding (ASS) technique on soil bacterial community diversity, life strategies, and seasonal change. Soil from six plots with original vegetation (CK, n=6) was compared to soil from 15 plots with spray-seeding restoration (SR, n=15) using environmental DNA sequencing. The bacterial Shannon and Chao1 indices of SR soils were significantly greater (P<0.05) than those of CK soils. The Chao1 index for the SR soil bacterial community was significantly greater in summer (P<0.05) than in winter. The ratio of the relative abundance of bacterial K-strategists to r-strategists (K/r) and the DNA guanine-cytosine (GC) content in the SR soil were significantly lower (P<0.05) than those in the CK soil. Principal coordinate analysis revealed significant differences between the SR and CK bacterial communities. The GC content was positively correlated with the K/r ratio. Soil conductivity was negatively associated with the K/r ratio and GC content, indicating that ionic nutrients were closely related to bacterial life strategies. The ASS technique improved soil bacterial diversity, altered community composition, and favored bacterial r-strategists.

The effects of straw return on soil bacterial diversity and functional profiles: A meta-analysis

Returning straw directly to agricultural fields increases soil carbon sequestration and influences soil microbial activities. However, the precise impacts of straw return on soil bacterial diversity, composition, and function profiles remain unclear, necessitating a comprehensive synthesis and standardized analysis. In this study, we conducted a meta-analysis of 729 original bacterial sequencing samples from fields with and without straw return to elucidate how soil bacteria respond to different experimental conditions after straw return (e.g., straw and fertilizer management practices and return duration). Our analysis revealed that overall straw return slightly increased the Chao 1 index while the Shannon index remained unaffected. However, we found strong responses depending on the experimental conditions of straw return. Particularly, bacterial community diversity increased significantly, particularly under high nitrogen, low straw addition, or continuous straw return. Furthermore, straw return altered bacterial community composition, elvating the abundance of Proteobacteria and Bacteroidetes, while decreasing Chloroflexi, Firmicutes, and Nitrospirae. Straw return also increased modularity in bacterial co-occurrence networks. Functional annotation analysis highlighted that straw return substantially enriched microbes involved in chemoheterotrophy, nitrogen fixation, and functional groups related to straw decomposition (chitinolysis, cellulolysis, xylanolysis), while inhibiting microbes associated with nitrification and nitrate reduction. Surprisingly, straw return did not impact the relative abundance of plant pathogens. Overall, our findings offer an in-depth understanding the effects of straw return on soil bacterial communities, including increased diversity, modified structure, and enhanced functional profiles related to straw decomposition.

Non-selective microbiota reduction after the elicitation of a seaweed's immune response.

Pattern-triggered immunity (PTI) is an integral part of the innate immune system of many eukaryotic hosts, assisting in the defence against pathogen invasions. In plants and animals, PTI exerts a selective pressure on the microbiota that can alter community composition. However, the effect of PTI on the microbiota for non-model hosts, including seaweeds, remains unknown. Using quantitative polymerase chain reaction complemented with 16S rRNA gene and transcript amplicon sequencing, this study profiled the impact that PTI of the red seaweed Gracilaria gracilis has on its microbiota. PTI elicitation with agar oligosaccharides resulted in a significant reduction in the number of bacteria (by >75% within 72 h after treatment). However, the PTI elicitation did not cause any significant difference in the community diversity or structure. These findings demonstrated that PTI can be non-selective, and this might help to maintain a stable microbiota by uniformly reducing bacterial loads.

Impact of a Whole-Food, High-Soluble Fiber Diet on the Gut-Muscle Axis in Aged Mice.

Previous studies have identified a role for the gut microbiome and its metabolic products, short-chain fatty acids (SCFAs), in the maintenance of muscle mass and physical function (i.e., the gut-muscle axis), but interventions aimed at positively impacting the gut-muscle axis during aging are sparse. Gut bacteria ferment soluble fiber into SCFAs, and accordingly, to evaluate the impact of a high-soluble-fiber diet (HSFD) on the gut-muscle axis, we fed a whole-food, 3×-higher-soluble fiber-containing diet (relative to standard chow) to aged (98 weeks) C57BL/6J mice for 10 weeks. The HSFD significantly altered gut bacterial community structure and composition, but plasma SCFAs were not different, and a positive impact on muscle-related measures (when normalized to body weight) was not identified. However, when evaluating sex differences between dietary groups, female (but not male) HSFD-fed mice had significant increases for SCFAs, the quadriceps/body weight (BW) ratio, and treadmill work performance (distance run × BW), which suggests that an HSFD can positively impact the gut-muscle axis. In contrast, consistent effects in both male and female HSFD-fed mice included weight and fat loss, which suggests a positive role for an HSFD on the gut-adipose axis in aged mice.

Microplastics change soil properties, plant performance, and bacterial communities in salt-affected soils

Microplastics (MPs) are emerging contaminants found globally. However, their effects on soil-plant systems in salt-affected habitats remain unknown. Here, we examined the effects of polyethylene (PE) and polylactic acid (PLA) on soil properties, maize performance, and bacterial communities in soils with different salinity levels. Overall, MPs decreased soil electrical conductivity and increased NH4+-N and NO3−-N contents. Adding NaCl alone had promoting and inhibitive effects on plant growth in a concentration-dependent manner. Overall, the addition of 0.2% PLA increased shoot biomass, while 2% PLA decreased it. Salinity increased Na content and decreased K/Na ratio in plant tissues (particularly roots), which were further modified by MPs. NaCl and MPs singly and jointly regulated the expression of functional genes related to salt tolerance in leaves, including ZMSOS1, ZMHKT1, and ZMHAK1. Exposure to NaCl alone had a slight effect on soil bacterial α-diversity, but in most cases, MPs increased ACE, Chao1, and Shannon indexes. Both MPs and NaCl altered bacterial community composition, although the specific effects varied depending on the type and concentration of MPs and the salinity level. Overall, PLA had more pronounced effects on soil-plant systems compared to PE. These findings bridge knowledge gaps in the risks of MPs in salt-affected habitats.

Interactions between Epichloë endophyte and the plant microbiome impact nitrogen responses in host Achnatherum inebrians plants.

The clavicipitaceous fungus Epichloë gansuensis forms symbiotic associations with drunken horse grass (Achnatherum inebrians), providing biotic and abiotic stress protection to its host. However, it is unclear how E. gansuensis affects the assembly of host plant-associated bacterial communities after ammonium nitrogen (NH4+-N) treatment. We examined the shoot- and root-associated bacterial microbiota and root metabolites of A. inebrians when infected (I) or uninfected (F) with E. gansuensis endophyte. The results showed more pronounced NH4+-N-induced microbial and metabolic changes in the endophyte-infected plants compared to the endophyte-free plants. E. gansuensis significantly altered bacterial community composition and β-diversity in shoots and roots and increased bacterial α-diversity under NH4+-N treatment. The relative abundance of 117 and 157 root metabolites significantly changed with E. gansuensis infection under water and NH4+-N treatment compared to endophyte-free plants. Root bacterial community composition was significantly related to the abundance of the top 30 metabolites [variable importance in the projection (VIP) > 2 and VIP > 3] contributing to differences between I and F plants, especially alkaloids. The correlation network between root microbiome and metabolites was complex. Microorganisms in the Proteobacteria and Firmicutes phyla were significantly associated with the R00693 metabolic reaction of cysteine and methionine metabolism. Co-metabolism network analysis revealed common metabolites between host plants and microorganisms.IMPORTANCEOur results suggest that the effect of endophyte infection is sensitive to nitrogen availability. Endophyte symbiosis altered the composition of shoot and root bacterial communities, increasing bacterial diversity. There was also a change in the class and relative abundance of metabolites. We found a complex co-occurrence network between root microorganisms and metabolites, with some metabolites shared between the host plant and its microbiome. The precise ecological function of the metabolites produced in response to endophyte infection remains unknown. However, some of these compounds may facilitate plant-microbe symbiosis by increasing the uptake of beneficial soil bacteria into plant tissues. Overall, these findings advance our understanding of the interactions between the microbiome, metabolome, and endophyte symbiosis in grasses. The results provide critical insight into the mechanisms by which the plant microbiome responds to nutrient stress in the presence of fungal endophytes.

An investigation into the potential for upward range expansion in high-montane species on the roof of the world.

Climate warming is occurring in high-mountain areas at a faster rate than the global average. To escape the increasing temperatures, alpine species may shift in distribution upwards, threatening cold-adapted nival plant specialists. However, little is known about the success of seedling emergence and establishment at high altitudes outside the current range, particularly in the highest mountain areas of the Himalayas. We selected four native alpine species occurring around 4000 m a.s.l. and sowed seeds at the natural growing site (GS), at a high elevation site (HS; 5000 m a.s.l.) and at high elevation with soil from the growing site (HS-S) in the Khumbu Valley, north-eastern Nepal. We monitored seedling emergence and establishment for two consecutive years. Seedling emergence and establishment varied between species. Emergence was similar between GS and HS and improved at HS-S. Establishment was low at high elevations with all but one species having high mortality after winter. Seedling emergence of low elevation plants is possible at high elevations in the Everest region, indicating species may be able to shift their distribution range upwards. However, successful establishment may be limited by the soil and high winter mortality at high elevations, although not in all species. Climate warming will potentially lead to upward migration of some Himalayan plant species, leading to altered community composition in high-mountain areas.

Drought shifts soil nematode trophic groups and mediates the heterotrophic respiration

Abstract As the most diverse metazoan taxa, soil nematodes serve a diversity of functions in soil food webs and thus can regulate microbial community composition and affect organic matter decomposition and nutrient turnover rates. Because nematodes depend on water films to access food resources, drought can negatively affect nematode–microbial food webs, yet the impacts of drought on nematode diversity and abundance and how these changes may influence food web members and their functions are hardly explored. Here, we coupled research along a drought gradient in arid and semiarid grasslands with a detailed intact plant–soil microcosm experiment to explore the patterns and mechanisms of how drought impacts nematode abundance and carbon footprint, microbial phospholipid fatty acid (PLFA) and heterotrophic soil respiration. Overall, in the field and the microcosm experiments, we found that nematode abundance, carbon footprint and diversity, microbial PLFA and heterotrophic respiration were reduced under drier conditions. In addition, drought altered nematode and microbial community composition, through reducing the nematode channel ratio and increasing the relative fungivorous nematode abundance and the fungal to bacterial ratio. The soil decomposition channel shifted from a bacterial to a fungal pathway in response to drought, indicating decelerated heterotrophic respiration under drought. These results highlight the important contribution of soil nematodes and their associated microbial food web to soil carbon cycling. Our findings underscore the need to incorporate key soil fauna into terrestrial ecosystem model evaluation.

Rewilding soil and litter invertebrates and fungi increases decomposition rates and alters detritivore communities.

Habitat degradation and associated reductions in ecosystem functions can be reversed by reintroducing or 'rewilding' keystone species. Rewilding projects have historically targeted restoration of processes such as grazing regimes or top-down predation effects. Few projects focus on restoring decomposition efficiency, despite the pivotal role decomposition plays in global carbon sequestration and nutrient cycling. Here, we tested whether rewilding entire communities of detritivorous invertebrates and fungi can improve litter decomposition efficiency and restore detritivore communities during ecological restoration. Rewilding was conducted by transplanting leaf litter and soil, including associated invertebrate and fungal communities from species-rich remnant sites into species-poor, and geographically isolated, revegetated farmland sites in a temperate woodland region of southeastern Australia. We compared communities in sites under the following treatments: remnant (conservation area and source of litter transplant), rewilded revegetation (revegetated farmland site with litter transplant) and control revegetation (revegetated site, no transplant). In one 'before' and three 'after' sampling periods, we measured litter decomposition and the abundance and diversity of detritivorous invertebrates and fungi. We quantified the effect of detritivores on the rate of litter decomposition using piecewise Structural Equation Modelling. Decomposition was significantly faster in rewilding sites than in both control and remnant areas and was largely driven by a greater abundance of invertebrate detritivores. Similarly, the abundance of invertebrate detritivores in rewilding revegetation sites exceeded the level of remnant communities, whereas there was little difference between control and remnant sites. In contrast, rewilding did not increase saprotrophic fungi relative abundance/diversity and there was no strong relationship between decomposition and fungal diversity. Our findings suggest the relatively simple act of transplanting leaf litter and soil can increase functional efficiency during restoration and alter community composition. Our methods may prove important across a range of contexts where other restoration methods have failed to restore ecosystem processes to pre-degradation levels.

Something in the water: aquatic microbial communities influence the larval amphibian gut microbiota, neurodevelopment and behaviour.

Microorganisms colonize the gastrointestinal tract of animals and establish symbiotic host-associated microbial communities that influence vertebrate physiology. More specifically, these gut microbial communities influence neurodevelopment through the microbiota-gut-brain (MGB) axis. We tested the hypothesis that larval amphibian neurodevelopment is affected by the aquatic microbial community present in their housing water. Newly hatched Northern Leopard Frog (Lithobates pipiens) tadpoles were raised in pond water that was unmanipulated (natural) or autoclaved. Tadpoles raised in autoclaved pond water had a gut microbiota with reduced bacterial diversity and altered community composition, had decreased behavioural responses to sensory stimuli, were larger in overall body mass, had relatively heavier brains and had altered brain shape when compared with tadpoles raised in natural pond water. Further, the diversity and composition of the gut microbiota were associated with tadpole behavioural responses and brain measurements. Our results suggest that aquatic microbial communities shape tadpole behaviour and brain development, providing strong support for the occurrence of the MGB axis in amphibians. Lastly, the dramatic role played by aquatic microbial communities on vertebrate neurodevelopment and behaviour should be considered in future wildlife conservation efforts.

Vegetation responses to large dam removal on the Elwha River, Washington, USA

Large dam removal can trigger changes to physical and biological processes that influence vegetation dynamics in former reservoirs, along river corridors downstream of former dams, and at a river’s terminus in deltas and estuaries. We present the first comprehensive review of vegetation response to major fluvial disturbance caused by the world’s largest dam removal. After being in place for nearly a century, two large dams were removed along the Elwha River, Washington, USA, between 2011 and 2014. The exposure, erosion, transport, and deposition of large volumes of sediment and large wood that were impounded behind the dams created new fluvial surfaces where plant colonization and growth have occurred. In the former reservoirs, dam removal exposed ~290 ha of unvegetated sediment distributed on three main landforms: valley walls, high terraces, and dynamic floodplains. In addition to natural revegetation in the former reservoirs, weed control and seeding and planting of desirable plants influenced vegetation trajectories. In early years following dam removal, ~20.5 Mt of trapped sediment were eroded from the former reservoirs and transported downstream. This sediment pulse, in combination with transport of large wood, led to channel widening, an increase in gravel bars, and floodplain deposition. The primary vegetation responses along the river corridor were a reduction in vegetated area associated with channel widening, plant establishment on new gravel bars, increased hydrochory, and altered plant community composition on gravel bars and floodplains. Plant species diversity increased in some river segments. In the delta, sediment deposition led to the creation of ~26.8 ha of new land surfaces and altered the distribution and dynamics of intertidal water bodies. Vegetation colonized ~16.4 ha of new surfaces: mixed pioneer vegetation colonized supratidal beach, river bars, and river mouth bars, and emergent marsh vegetation colonized intertidal aquatic habitats. In addition to the sediment-dominated processes that have created opportunities for plant colonization and growth, biological processes such as restored hydrochory and anadromous fish passage with associated delivery of marine-derived nutrients may influence vegetation dynamics over time. Rapid changes to landforms and vegetation growth were related to the large sediment pulse in the early years following dam removal, and the rate of change is expected to attenuate as the system adjusts to natural flow and sediment regimes.

Effects of reductive soil disinfestation on potential pathogens and antibiotic resistance genes in soil

Reductive soil disinfestation (RSD) is commonly employed for soil remediation in greenhouse cultivation. However, its influence on antibiotic resistance genes (ARGs) in soil remains uncertain. This study investigated the dynamic changes in soil communities, potential bacterial pathogens, and ARG profiles under various organic material treatments during RSD, including distillers’ grains, potato peel, peanut vine, and peanut vine combined with charcoal. Results revealed that applying diverse organic materials in RSD significantly altered bacterial community composition and diminished the relative abundance of potential bacterial pathogens (P < 0.05). The relative abundance of high-risk ARGs decreased by 10.7%-30.6% after RSD treatments, the main decreased ARG subtypes were AAC(3)_Via, dfrA1, ErmB, lnuB, aadA. Actinobacteria was the primary host of ARGs and was suppressed by RSD. Soil physicochemical properties, such as total nitrogen, soil pH, total carbon, were crucial factors affecting ARG profiles. Our findings demonstrated that RSD treatment inhibited pathogenic bacteria and could be an option for reducing high-risk ARG proliferation in soil.

Environmental change legacies attenuate disturbance response of desert soil microbiome and multifunctionality

Abstract Deserts are predicted to be one of the ecosystems most vulnerable to global climate change, with dramatic fluctuations of temperature and water, even over the span of a single day. These previous disturbances could influence the response of the soil microbiome and its functions to subsequent disturbances, which is known as legacy effect. However, how legacy effects shape the response of soil microbiome and its functions to environmental fluctuations (e.g. temperature and water availability) in desert ecosystems remains to be investigated. Here, we firstly exposed desert soils to drought, freezing or their combination, and then followed by a second disturbance, resulting in a temporally full factorial treatment. We found that environmental change legacies affected the response of soil multifunctionality, microbial abundance and richness to second drought and freezing, except for eukaryotic richness. Initial disturbances caused legacy effects on microbial composition and weakened their responses to later disturbances, and these effects were stronger for prokaryotes than eukaryotes. The attenuated response to later disturbances is largely due to that almost half of the taxa affected by the earlier disturbances were also affected by the second disturbances. The phylogenetic depth of these responses varied minimally among the types of disturbances but were more conserved for negative responses, indicating a result of historical adaptation. Moreover, the altered community composition was associated with functional changes in the disturbed soils. These findings will improve our understanding of the mechanisms underlying the legacy impacts of multiple environmental disturbances on desert microbial communities and strengthen our ability to develop management strategies for protection prior to disturbance events. Read the free Plain Language Summary for this article on the Journal blog.

Global change progressively increases foliar nitrogen-phosphorus ratios in China's subtropical forests.

Globally increased nitrogen (N) to phosphorus (P) ratios (N/P) affect the structure and functioning of terrestrial ecosystems, but few studies have addressed the variation of foliar N/P over time in subtropical forests. Foliar N/P indicates N versus P limitation in terrestrial ecosystems. Quantifying long-term dynamics of foliar N/P and their potential drivers is crucial for predicting nutrient status and functioning in forest ecosystems under global change. We detected temporal trends of foliar N/P, quantitatively estimated their potential drivers and their interaction between plant types (evergreen vs. deciduous and trees vs. shrubs), using 1811 herbarium specimens of 12 widely distributed species collected during 1920-2010 across China's subtropical forests. We found significant decreases in foliar P concentrations (23.1%) and increases in foliar N/P (21.2%). Foliar N/P increased more in evergreen species (22.9%) than in deciduous species (16.9%). Changes in atmospheric CO2 concentrations ( ), atmospheric N deposition and mean annual temperature (MAT) dominantly contributed to the increased foliar N/P of evergreen species, while , MAT, and vapor pressure deficit, to that of deciduous species. Under future Shared Socioeconomic Pathway (SSP) scenarios, increasing MAT and would continuously increase more foliar N/P in deciduous species than in evergreen species, with more 12.9%, 17.7%, and 19.4% versus 6.1%, 7.9%, and 8.9% of magnitudes under the scenarios of SSP1-2.6, SSP3-7.0, and SSP5-8.5, respectively. The results suggest that global change has intensified and will progressively aggravate N-P imbalance, further altering community composition and ecosystem functioning of subtropical forests.

Occupancy trends of overwintering coastal waterbird communities reveal guild-specific patterns of redistribution and shifting reliance on existing protected areas.

Climate change and anthropogenic stressors are redistributing species and altering community composition globally. Protected areas (PAs) may not sufficiently protect populations of species undergoing distributional shifts, necessitating that we evaluate existing PAs and identify areas for future protection to conserve biodiversity across regional and temporal scales. Coastal waterbirds are important indicators of marine ecosystem health, representing mobile, long-lived, higher trophic-level consumers. Using a 20-year citizen science dataset (1999-2019) with a before-after control-intervention sampling framework for habitat protection, we applied dynamic occupancy models to assess winter occupancy trends along the Pacific coast of Canada. Specifically, we sought to understand potential drivers of regional declines, spatial commonalities among guilds, and changes in habitat use before and after PA designation, as well as between PAs and non-PAs. Occupancy trends varied regionally, with greater declines in the south compared to the north. Regional differences underlined potential range shifts, particularly for species with traits linked to temperature tolerance, movement, and high productivity foraging, as cold-tolerant, migratory benthivores and piscivores wintered farther north relative to 20 years ago or retreated to cold-water fjords. While 21 of 57 (36.8%) species responded positively to PA designation (before-after), greater occupancy declines tended to occur in PAs established pre-1999 relative to non-PAs (control-intervention). Since PAs are currently concentrated in the south, negative associations were most apparent for species retreating northward, but existing PAs may have a stabilizing or transitory effect on southern wintering species shifting into the region from farther south. We emphasize that conservation strategies must balance persistence of current communities with preserving the climate-adapted biodiversity of tomorrow by accounting for community-level effects of species moving into and out of existing PAs. Incorporating range shifts into PA planning by predicting distributional changes will allow conservation practitioners to identify priority habitats, such as cold-water refugia, for persistent wildlife communities.

Functional Attributes of Seeds as Indicators of Germination Sensitivity to Global Warming

Climate change has profound impacts on ecosystems, and one critical aspect is its effect on seed germination, a crucial stage in plant life cycles. Various studies have explored the responses of plant species to rising temperatures, and there is now a pressing need to integrate this wealth of information into a coherent framework. The aim of this study was to survey literature about seed traits and thence to evaluate germination responses to climate change and to propose functional groups for germination. Increased temperature affects seed traits, particularly germinability. Many species show increased germination percentages in warmer temperatures, although the extent varies among species and temperature ranges. Some maintain a consistent percentage, whereas others reduce it to retain seeds in the seed bank. Temperature changes also affect the timing and season of germination, with some species accelerating germination, others delaying it, thereby influencing competition and exposure to adverse conditions. Shifts in temperature can alter seed requirements, affecting responses to temperature, humidity, light, chemical stimuli, and dormancy. Modifications in germination have profound effects on seed bank and seedling bank dynamics, affecting plant populations and ecological community resilience. Changes in germination can disrupt competitive dynamics, favoring some over others, altering community composition and potentially impairing ecosystem functionality. Germination Niche, Germination Potential, and Germination Phenology are fundamental concepts in the evaluation of climate change's implications for germination.

Declines in ice cover are accompanied by light limitation responses and community change in freshwater diatoms.

The rediscovery of diatom blooms embedded within and beneath the Lake Erie ice cover (2007-2012) ignited interest in psychrophilic adaptations and winter limnology. Subsequent studies determined the vital role ice plays in winter diatom ecophysiology as diatoms partition to the underside of ice, thereby fixing their location within the photic zone. Yet, climate change has led to widespread ice decline across the Great Lakes, with Lake Erie presenting a nearly "ice-free" state in several recent winters. It has been hypothesized that the resultant turbid, isothermal water column induces light limitation amongst winter diatoms and thus serves as a competitive disadvantage. To investigate this hypothesis, we conducted a physiochemical and metatranscriptomic survey that spanned spatial, temporal, and climatic gradients of the winter Lake Erie water column (2019-2020). Our results suggest that ice-free conditions decreased planktonic diatom bloom magnitude and altered diatom community composition. Diatoms increased their expression of various photosynthetic genes and iron transporters, which suggests that the diatoms are attempting to increase their quantity of photosystems and light-harvesting components (a well-defined indicator of light limitation). We identified two gene families which serve to increase diatom fitness in the turbid ice-free water column: proton-pumping rhodopsins (a potential second means of light-driven energy acquisition) and fasciclins (a means to "raft" together to increase buoyancy and co-locate to the surface to optimize light acquisition). With large-scale climatic changes already underway, our observations provide insight into how diatoms respond to the dynamic ice conditions of today and shed light on how they will fare in a climatically altered tomorrow.

Mechanistic insights into mitigating N2O emissions by the nitrification inhibitor dicyandiamide (DCD) in a tropical sandy soil after six years of manure amendment

Organic amendments (OM) can profoundly affect soil nitrous oxide (N2O) emissions via changing nitrogen (N) cycles. However, mechanistic insights into how nitrification inhibitors modulate the responses of soil N2O emissions to successive application of OM are currently lacking. In this study, we performed a laboratory-scale experiment to examine N2O emissions from tropical vegetable soils subjected to six years of chemical fertilization (CF) or chemical fertilization combined with manure application (CFM), and further evaluated the mitigation effectiveness of the nitrification inhibitor dicyandiamide (DCD) under each management regime. Isotopocule mapping (δ15NSPN2O and δ18ON2O/H2O map) showed bacterial nitrification/fungal denitrification contributed 77.4%–88.5% of total N2O production among treatments during the emission peak. The cumulative N2O emissions from the CFM-treated soils were nearly 8-fold of those from the CF-treated soils. CFM stimulated N2O production from bacterial nitrification and denitrification by increasing the abundance of genes linked to nitrifers (AOB and comammox) and denitrifiers (nirK/S and qnorB), respectively. Moreover, DCD decreased cumulative N2O emissions by averagely 73.3%, with better mitigation performance observed in the CFM treatment due to stronger inhibited nitrification and increased abundance of nosZ, and altered bacterial community composition. The 16S sequencing further revealed that adding DCD to CFM-treated soils resulted in declines in abundance of bacterial phylum Actinobacteria and Chloroflexi that positively affected N2O emissions; while the opposite pattern prevailed for Gemmatimonadetes that negatively affected N2O emissions. This study highlights manure application coupled with nitrification inhibitors can achieve the dual goals of enhancing soil fertility while reducing environment risk in tropical agricultural soils.

Ofloxacin weakened treatment performance of rural domestic sewage in an aerobic biofilm system by affecting biofilm resistance, bacterial community, and functional genes

Ofloxacin (OFL) is a typical fluoroquinolone antibiotic widely detected in rural domestic sewage, however, its effects on the performance of aerobic biofilm systems during sewage treatment process remain poorly understood. We carried out an aerobic biofilm experiment to explore how the OFL with different concentrations affects the pollutant removal efficiency of rural domestic sewage. Results demonstrated that the OFL negatively affected pollutant removal in aerobic biofilm systems. High OFL levels resulted in a decrease in removal efficiency: 9.33% for chemical oxygen demand (COD), 18.57% for ammonium (NH4+-N), and 8.49% for total phosphorus (TP) after 35 days. The findings related to the chemical and biological properties of the biofilm revealed that the OFL exposure triggered oxidative stress and SOS responses, decreased the live cell number and extracellular polymeric substance content of biofilm, and altered bacterial community composition. More specifically, the relative abundance of key genera linked to COD (e.g., Rhodobacter), NH4+-N (e.g., Nitrosomonas), and TP (e.g., Dechlorimonas) removal was decreased. Such the OFL-induced decrease of these genera might result in the down-regulation of carbon degradation (amyA), ammonia oxidation (hao), and phosphorus adsorption (ppx) functional genes. The conventional pollutants (COD, NH4+-N, and TP) removal was directly affected by biofilm resistance, functional genes, and bacterial community under OFL exposure, and the bacterial community played a more dominant role based on partial least-squares path model analysis. These findings will provide valuable insights into understanding how antibiotics impact the performance of aerobic biofilm systems during rural domestic sewage treatment.

Trophic niches of macrobenthos: Latitudinal variation indicates climate change impact on ecosystem functioning.

Benthic food-web structure and organic matter (OM) utilization are important for marine ecosystem functioning. In response to environmental changes related to the ongoing climate change, however, many benthic species are shifting their ranges to colder regions, which may lead to altered community composition, but it remains largely unknown how it will affect ecosystem functioning. Here, stable isotope analysis was used to study benthic OM utilization and food-web structure and to assess whether their spatial patterns reflect today's community differentiation among biogeographic regions and depth zones. Benthic fauna and OM mixtures were collected from two depth zones (100-150 m vs. 200-250 m) within a temperate, two sub-Arctic, and an Arctic fjord along a latitudinal gradient (59-78° N) that was used as a space-for-time substitution to assess the impact of climate change. Our results showed that Arctic and temperate communities are functionally different. Arctic communities were characterized by a strong resource partitioning among different feeding types, irrespective of depth zone. In contrast, all feeding types in temperate communities seemed to rely on sedimentary OM. The sub-Arctic presented a transition zone. In the sub-Arctic, shallower communities resembled Arctic communities, suggesting a functional transition between temperate and sub-Arctic regions. Deeper sub-Arctic communities resembled temperate communities, suggesting a functional transition between the sub-Arctic and Arctic regions. This implies that the regions north of the current transitions (deep Arctic and shallow sub-Arctic) are most likely to experience functional changes related to an altered OM utilization in benthic food webs in response to climate change.