Biotic Mechanisms Research Articles

How restoration engineering measures can enhance the ecological value of intertidal flats

Restoration engineering measures, such as managed realignments or building groins, modify the environmental characteristics of coastal intertidal ecosystems. Creating physical modifications that are beneficial to an intertidal system's ecology necessitates an in‐depth understanding of the relationships between the abiotic and biotic components of a given intertidal habitat. In this study, we evaluate how hydrodynamics and sediment characteristics drive the development of the benthic macrofauna community during the first 5 years following engineering measures to enhance benthic macrofauna diversity at three locations. The creation of low‐energy habitats through groins (Knuitershoek and Baalhoek) and a managed realignment dike breach (Perkpolder) led to the accumulation of fine sediments in all three impact sites. Biomass of benthic macrofauna quickly increased between 2016 and 2020, with successional processes being more important in Perkpolder, where the habitat was started completely from scratch due to a managed realignment, than at Knuitershoek or Baalhoek, where habitat conditions were improved by adding groins. In addition, the density of benthos‐eating birds, especially oystercatchers, increased at some of the modified sites. While a low‐energy habitat may harbor more diverse assemblages of benthic macrofauna than a highly dynamic one, the extremely high silt content, which is typical for low‐energy habitats, may slow benthic community development. The observed increase of biomass at our impact sites highlights the value of the interventions, while the delays in the response of the benthic macrofauna community emphasizes the need for extensive monitoring both in time and space and the identification of underlying abiotic–biotic mechanisms.

Biotic/abiotic transformation mechanisms of phenanthrene in iron-rich constructed wetland under redox fluctuation

Iron-rich constructed wetlands (CWs) could promote phenanthrene bioremediation efficiently through biotic and abiotic pathways, which have gained increasing attention. However, the biotic/abiotic transformation mechanisms of trace organic contaminants in iron-rich CW are still ambiguous. Herein, three CWs (i.e., CW-A: Control; CW-B: Iron-rich CW, CW-C: Iron-rich CW + tidal flow) were constructed to investigate the transformation mechanisms of phenanthrene through Mössbauer spectroscopy and metagenomics. Results demonstrated CW-C achieved the highest phenanthrene removal (94.0 %) and bacterial toxicity reduction (92.1 %) due to the optimized degradation pathway, and subsequently achieved the safe transformation of phenanthrene. Surface-bound/low-crystalline iron regulated hydroxyl radical (·OH) production predominantly, and its utilization was promoted in CW-C, which also improved electron transfer capacity. The enhanced electron transfer capacity led to the enrichment of PAH-degrading microorganisms (e.g., Thauera) and keystone species (Sphingobacteriales bacterium 46–32) in CW-C. Additionally, the abundances of phenanthrene transformation (e.g., EC:1.14.12.-) and tricarboxylic-acid-cycle (e.g., EC:2.3.3.1) enzyme were up-regulated in CW-C. Further analysis indicated that the safe transformation of phenanthrene was mainly attributed to the combined effect of abiotic (·OH and surface-bound/low-crystalline iron) and biotic (microbial community and diversity) mechanisms in CW-C, which contributed similarly. Our study revealed the essential role of active iron in the safe transformation of phenanthrene, and was beneficial for enhanced performance of iron-rich CW.

Thermal tolerance as a driver of reef fish community structure at the isolated tropical Mid-Atlantic Ridge Islands

Reef fish communities are shaped by historical and ecological factors, including abiotic and biotic mechanisms at different spatial scales, determining species composition, abundance and biomass. The oceanic islands in the Mid-Atlantic Ridge (St. Peter and St. Paul's Archipelago - SPSPA, Ascension, and St. Helena), exhibiting differences in community structure along a 14-degree latitudinal and a 10 °C thermal gradient. We investigate the influence of sea surface temperature, area, age, isolation and phosphate on reef fish community structures. Reef fish trophic structure varies significantly across the islands, with planktivores and herbivore-detritivores showing the highest abundances in SPSPA and Ascension, while less abundant in St. Helena, aligning with the thermal gradient. Variations in reef fish community structures were predominantly influenced by thermal regimes, corroborating the expansion of species' thermal niche breadth at higher latitudes and lower temperatures. This study highlights that in addition to biogeographic factors, temperature is pivotal on shaping oceanic island reef fish community structure.

Climate mismatches with ectomycorrhizal fungi contribute to migration lag in North American tree range shifts

Climate change will likely shift plant and microbial distributions, creating geographic mismatches between plant hosts and essential microbial symbionts (e.g., ectomycorrhizal fungi, EMF). The loss of historical interactions, or the gain of novel associations, can have important consequences for biodiversity, ecosystem processes, and plant migration potential, yet few analyses exist that measure where mycorrhizal symbioses could be lost or gained across landscapes. Here, we examine climate change impacts on tree-EMF codistributions at the continent scale. We built species distribution models for 400 EMF species and 50 tree species, integrating fungal sequencing data from North American forest ecosystems with tree species occurrence records and long-term forest inventory data. Our results show the following: 1) tree and EMF climate suitability to shift toward higher latitudes; 2) climate shifts increase the size of shared tree-EMF habitat overall, but 35% of tree-EMF pairs are at risk of declining habitat overlap; 3) climate mismatches between trees and EMF are projected to be greater at northern vs. southern boundaries; and 4) tree migration lag is correlated with lower richness of climatically suitable EMF partners. This work represents a concentrated effort to quantify the spatial extent and location of tree-EMF climate envelope mismatches. Our findings also support a biotic mechanism partially explaining the failure of northward tree species migrations with climate change: reduced diversity of co-occurring and climate-compatible EMF symbionts at higher latitudes. We highlight the conservation implications for identifying areas where tree and EMF responses to climate change may be highly divergent.

Litter accumulation suppresses grass production but facilitates shrub expansion in a long‐term fenced grassland

AbstractShrub expansion is increasing in grasslands worldwide and has profound effects on biodiversity and ecosystem functions. Shrub expansion has primarily been explained by extrinsic factors such as climate change and human activities, yet the roles of intrinsic shrub demographic population dynamic and shrub–grass interaction remain poorly understood. With a paired mown and exclosure comparison experiment and baseline levels of shrub abundance in a semiarid grassland, we confirmed that long‐term livestock exclusion promotes expansion of two native shrubs, Artemisia sacrorum and Caragana brachypoda. Shrub abundance increased during the livestock exclusion period. Shrub biomass in fenced plots was about 5‐ to 10‐fold greater than in mown plots. Both increase in population density and individual size (especially height) contributed to shrub increase. The mechanism behind this was the divergent effects of litter accumulation on shrubs and grasses. Litter accumulation suppressed grass production, while facilitating shrub recruitment and growth. Our findings highlight the potential role of litter accumulation‐mediated shifts in shrub–grass interactions, which should be incorporated into grazing top‐down control to better predict the restoration outcomes of grassland management changes. The identified internal biotic mechanism raises the possibility that removal of accumulated litter by grazing or mowing may be an alternative way to maintain or restore a grass‐dominated state in shrub expansion areas.

Increased density of conspecifics caused niche contraction in a multispecific passerine assemblage.

Competition is a prominent mechanism driving population dynamics and structuring community assemblage, which can be investigated by linking shifts in species' ecological niche and the densities of sympatric species because the ecological release from competitive constraints is a density-dependent process. In this work we determine how a steppe passerine community segregates their ecological niches and evaluate the role of competition in inducing changes in the ecological niche of species. We built multidimensional ecological niches (with Gaussian kernel density estimators) using data on the habitat features used by 10 bird species collected from seven sites in the natural steppes of Central Spain over 2 consecutive years. We computed distance and niche similarity metrics to explore the ecological niche partitioning of the bird community. Next, we ran multivariate linear regression models to evaluate the effects of conspecific and heterospecific density (as proxies of intraspecific and interspecific competition, respectively) on niche breadth and/or position of the three most abundant species. We found low niche overlap in the community assemblage but varying levels of niche similarity among pairs of species, which could increase the likelihood of current competition operating in the community. However, we found no effect of heterospecific density on niche breadth or position, although conspecific density was negatively related to niche breadth. Contrary to predictions of competition theory, increased density of conspecifics caused niche contraction. Our results from a multispecies system contribute to advanced knowledge of the biotic mechanisms structuring wildlife communities within the framework of ecological niche theory.

Dependence of Biotic and Abiotic H2O2 and •OH Production on the Redox Conditions and Compositions of Sediment during Oxygenation.

Reactive oxygen species (ROS) production in O2-perturbed subsurface environments has been increasingly documented in recent years. However, the constraining conditions under which abiotic and/or biotic mechanisms predominate for ROS production remain ambiguous. Here, we demonstrate that the ROS production mechanism, biotic and abiotic, is determined by sediment redox properties and sediment compositions. Upon the oxygenation of 10 field sediments, the cumulative H2O2 concentrations reached up to 554 μmol/kg within 2 h. The autoclaving sterilization experiments showed that H2O2 could be produced by both biotic and abiotic processes depending on the redox conditions. However, only the abiotic process could produce significant levels of •OH, and the production yield was closely related to the sediment components, particularly sediment Fe(II) and organic matter. Fe(II) bound with organic matter led to high yields of H2O2 and •OH production. Sediment oxygenation contributed to the appearance of H2O2 in groundwater, with the abiotic mechanism producing higher instantaneous H2O2 concentrations than the biotic mechanism. These findings reveal that the redox conditions, compositions, and texture of sediments collectively control abiotic and biotic mechanisms for ROS production, which assists the identification of ROS production hotspots and the understanding of ROS distribution and utilization in the subsurface.

Both the selection and complementarity effects underpin the effect of structural diversity on aboveground biomass in tropical forests

AbstractAimDespite mounting empirical evidence regarding the positive effects of forest structural diversity (STRDIV) on forest functioning, the underlying biotic mechanisms and controlling abiotic factors remain poorly understood. This study provides the first assessment of the interactive effects of STRDIV and diversity in species and functional traits on aboveground biomass (AGB) in natural forests in West and East Africa.LocationWest and East Africa.Time period2014–2020.Major taxa studiedWoody plants.MethodsUsing data from 276 plots and 7993 trees of 207 species distributed across various types of natural forests and major climatic zones of Africa, linear mixed‐effects and structural equation models, we have evaluated how alternative causal relationships between STRDIV and taxonomic and functional diversity attributes influence AGB, while accounting for the effects of environmental covariates. We also assessed the consistency of these relationships across floristically and environmentally homogenous forest types.ResultsWe found that the positive effects of STRDIV on AGB were underpinned by both the community‐weighted mean (CWM) of trait values (selection effects) and species richness (niche complementarity), but the relative importance of these effects varied depending on forest types. Across the forest types, STRDIV primarily mediated the effects of CWM of traits and species richness on AGB. We also found that STRDIV–AGB relationships were constrained by resource (water and nutrient) availability.Main conclusionsOur findings provide novel insights into the role of functional traits as key determinants of the effects of STRDIV on AGB in tropical forests. We suggest that forest management and climate change mitigation strategies aimed at conserving biodiversity, and fostering biomass storage through increased STRDIV should focus on maintaining high levels of functionally dominant species while also increasing tree species diversity.

Changes in Biotic Mechanisms of Phytoplankton Biomass Stability Along a Eutrophic Gradient

Changes in Biotic Mechanisms of Phytoplankton Biomass Stability Along a Eutrophic Gradient

Effects of increasing complexity in biogeochemistry and hydrology on variability of total phosphorus concentration in models of a low flow subtropical wetland

In south Florida, treatment wetlands known as stormwater treatment areas (STAs) are used to reduce total phosphorus (P) concentrations of agricultural and urban stormwater runoff before discharging into the Everglades Protection Area. The remobilization of P from immobile forms stored in soils and litter has the potential to negatively affect STA treatment efficiency. Phosphorus biogeochemical dynamics in one of the best performing Everglades STA flow-ways, STA-2 FW1, were modeled mechanistically and empirically using diverse streams of data (flow, total P in water, soil, floc, vegetation). We evaluated the effect of P wetland uptake and hydrologic transport on STA-2 FW1's simulated outflow P concentrations by juxtaposing varying complexities of biogeochemistry (1–2 vs 13 wetland P pools) and hydrology (uniform vs. nonuniform flow) models. The uniform flow model considers a constant velocity with each time step while velocity in the nonuniform flow model is a stochastic ensemble mimicking spatial flow variability. When coupled with uniform or nonuniform flow, the variability of water column P concentration in the most complex model was significantly different from the two simple biogeochemistry models, although it was lower compared to data in all models. Regardless of the biogeochemistry model, uniform versus nonuniform transport did not affect simulated outflow P concentration. Significant interaction effects between the choices of biogeochemistry and hydrology models were observed. The most complex model included specific compartments for vegetation, floc and soil and reproduced data trends of more P accumulated in upstream areas that decreases with increasing distance away from inflow. Modeling biotic mechanisms and tracking P in vegetation and sediments, confirms the importance of including biogeochemistry in understanding and predicting outflow P concentrations in STA-2 FW1. This modeling tool could be used to guide future STA data collection needs and inform Everglades STA performance optimization efforts.

Effects of nitrogen deposition on N2O emission in a wet meadow on the Qinghai-Tibet Plateau

Northwest China wet meadows with large organic carbon storage have the potential to be N2O hot spots under elevated nitrogen (N) deposition due to climate change. However, the main controlling factors of N2O fluxes in wet meadows at different N deposition levels are not well-known. Here, we conducted a wet meadow experiment simulating different amounts of N deposition to study N inputs induced changes in N2O flux and the underlying abiotic and biotic mechanisms. We found that the amount of N deposition significantly affected the N2O flux. The N2O flux increased first and then decreased with the increase of N deposition, and the high concentration of N addition (15 g·m−2·a−1) limited the N2O emission, mainly because the high nitrogen content changes the nutrient limiting (nitrogen confinement is transformed into phosphorus confinement) factors in Qinghai-Tibet Plateau area, resulting in the lack of substrate (soil available phosphorus) for N2O production. The N deposition effect on N2O emissions was related to the amount of N input and date of measurement, which was mainly attributed to changes in soil properties (soil available nutrients, non-capillary porosity and aeration) after nitrogen input. Furthermore, vegetation biomass was found to be a key controlling factor for N2O fluxes under N addition conditions. Our results emphasize that the interaction of abiotic (soil nutrients, water content and temperature) and biotic factors (microbial community structure changes) on N2O fluxes should be taken into account in order to accurately project N2O fluxes in wetland ecosystems.

White-rot fungi scavenge reactive oxygen species, which drives pH-dependent exo-enzymatic mechanisms and promotes CO2 efflux.

Soil organic matter (SOM) decomposition mechanisms in rainforest ecosystems are governed by biotic and abiotic procedures which depend on available oxygen in the soil. White-rot fungi (WRF) play an important role in the primary decomposition of SOM via enzymatic mechanisms (biotic mechanism), which are linked to abiotic oxidative reactions (e.g., Fenton reaction), where both processes are dependent on reactive oxygen species (ROS) and soil pH variation, which has yet been studied. In humid temperate forest soils, we hypothesize that soil pH is a determining factor that regulates the production and consumption of ROS during biotic and abiotic SOM decomposition. Three soils from different parent materials and WRF inoculum were considered for this study: granitic (Nahuelbuta, Schizophyllum commune), metamorphic (Alerce Costero, Stereum hirsutum), and volcanic-allophanic (Puyehue, Galerina patagonica). CO2 fluxes, lignin peroxidase, manganese peroxidase, and dye-decolorizing peroxidase levels were all determined. Likewise, the production of superoxide anion (O2•-), hydrogen peroxide (H2O2), and hydroxyl radicals (•OH) were assessed in soils microcosms after 36 days of anaerobic incubation with WRF inoculum and induced Fenton reaction under pH variations ranging from 2.5 to 5.1. ROS significantly increased biotic and abiotic CO2 emissions in all tested soils, according to the findings. The highest values (217.45 mg C kg-1) were found during the anaerobic incubation of sterilized and inoculated soils with WRF at a natural pH of 4.5. At pH 4.0, the lowest levels of C mineralization (82 mg C kg-1) were found in Nahuelbuta soil. Enzyme activities showed different trends as pH changed. The Fenton reaction consumed more H2O2 between pH 3 and 4, but less between pH 4.5 and 2.5. The mechanisms that oxidized SOM are extremely sensitive to variations in soil pH and the stability of oxidant radical and non-radical compounds, according to our findings.

Modeling biological denitrification in the presence of metal ions and elevated chloride content: Insights into abiotic and biotic mechanisms regulating metal bioprecipitation

Biological denitrification is a critical process in which microorganisms convert nitrate to nitrogen gas. Metal ions, such as those found in industrial wastewater, can be toxic to microorganisms and impede denitrification. It is critical to identify the mechanisms that allow microorganisms to tolerate metal ions and understand how these mechanisms can be utilized to improve denitrification efficiency by modeling the process. This study presents a mathematical model of biological denitrification in the presence of metal ions. The model includes key biotic and abiotic mechanisms and is based on pilot scale results. The model predicts the bioprecipitation of metal ions due to pH shift and alkalinity production during the metabolic activity of microorganisms. The model parameters are estimated to fit the experimental results and the mechanisms regulating metal detoxification via biological metal precipitation are presented. The model provides a valuable tool for understanding the behavior of denitrification systems in the presence of metal ions and can be used to optimize these systems for more efficient and effective treatment of industrial wastewater.

Coupling geochemical and microbial molecular techniques to reveal catchment-scale nitrate yield and fluvial export dynamics

The disturbance of reactive nitrogen (N) on ecosystems and biogeochemical cycles is now one of the most severe environmental problems worldwide. Nitrate (NO3−) is usually a dominant reactive N species in river ecosystems. Excessive NO3− concentrations in rivers have led to eutrophication and consequent ecological and environmental damages. Quantifying catchment-scale NO3− yield and export dynamics is crucial for effective remediation of river NO3− pollution. Frequently, natural abundance isotopes of NO3− in a river (δ15N/δ18O-NO3−) are applied to identify sources and potential transformations of NO3− at a catchment scale, while microbial molecular techniques and 15N pairing experiments are employed to reveal the NO3− production and removal processes and their underlying mechanisms in microenvironments (e.g., sediments and soils). In this study, we developed a novel protocol that couples these complementary geochemical and molecular techniques to quantify catchment-scale NO3− yield and fluvial export dynamics. The protocol links microscopic processes with catchment-scale geochemical characteristics to explicitly describe the NO3− cycling processes and their underlying abiotic and biotic mechanisms within a catchment. We applied the protocol to the Dadu and Jiazela catchments on the Qinghai-Tibet Plateau, and demonstrated the effectiveness of the protocol in determining NO3− yield and export dynamics in the catchments.

Wetland Removal Mechanisms for Emerging Contaminants

In recent decades, previously unobserved trace compounds have become more widely detected in wastewater treatment effluents and freshwater ecosystems. Emanating from various sources and presenting potential human health and ecological risks at much lesser concentrations than traditional contaminants, detection of “emerging contaminants” has increased with improvements in analytical techniques. The behavior of emerging contaminants in wetlands is a topic of increasing interest, as natural wetlands are known to transform and sequester pollutants and constructed or treatment wetlands are widely utilized to address elevated concentrations of constituents of concern. Both natural and constructed wetlands are complex biogeochemical systems with interrelated abiotic and biotic mechanisms leading to the removal of emerging contaminants. A literature review was performed to assess the current state of knowledge of various wetland mechanisms involved in removing these contaminants from surface waters and effluents. The primary mechanisms discussed in the literature are sorption, photodegradation, microbial biodegradation and phytoremediation. The most influential mechanisms are dependent on the properties of the contaminants and wetland systems studied. Common trends exist for different constructed wetland designs to leverage various mechanisms based on hydrology, substrate and vegetation plantings. Much remains to be understood about the various processes occurring in wetlands as they relate to emerging contaminant removal. Improving the understanding of the potential role of wetland mechanisms can help manage this environmental challenge more effectively.

Aridity determines the effects of warming on community stability in Inner Mongolian grassland

Ongoing climate warming affects biodiversity and ecosystem functions and services. However, the mechanisms underlying the effects of climate warming on biodiversity-stability relationships are unclear. Whether these effects depend on environmental factors such as aridity remains an open question. Here, we conducted a factorial field experiment to investigate the effects of warming on nine grasslands in a transect spanning ∼1500 km with increasing aridity in Inner Mongolia, China. Our results showed that warming-induced decrease in species richness did not alter community variability across nine grasslands. However, species richness was negatively related to community variability under warming conditions, but not under control conditions. This indicated that warming regulated the species diversity-stability relationship. Warming increased species synchrony, species variability, and dominant species variability. These outcomes lead to increases in temporal variability of community productivity. Climate fluctuation increased species variability and species synchrony within communities, thereby reducing community stability. Importantly, the size of warming effects on community variability via biotic mechanisms grew with increasing aridity. Our results indicate that species diversity plays a crucial role in regulating community stability under climate warming. Our findings reveal the generality of biotic mechanisms responsible for grassland stability under future climate warming, and highlight that the geographic variation in aridity determines the effect sizes of warming on grassland stability. We suggest that ongoing and future climate warming might disrupt grasslands stability with high aridity, thereby reducing ecosystem functions and services.

Water‐level drawdowns can improve surface water quality and alleviate bottom hypoxia in shallow, eutrophic water bodies

Abstract Water‐level drawdowns are a management option for improving water quality in shallow, eutrophic lakes, but how much water levels should be reduced and what abiotic and biotic mechanisms can be expected to reduce the adverse effects of eutrophication are unclear. We conducted a study with two experimental pools (10 m wide, 30 m long, and approx. 2.5 m water depth) in a before‐after‐control‐impact design to examine whether water‐level drawdowns could influence surface water quality and bottom‐water conditions, as well as how physicochemical and biological variables contributed to improvements. In the experiment, we fertilised the pools to increase productivity and induce hypoxia, and then reduced water levels four times in increments of 0.5 m. Our experiment using high‐frequency sensors showed that water‐level drawdowns could decrease cyanobacterial blooms and alleviate hypoxia relatively quickly by changing physicochemical conditions. Water‐level reductions quickly increased bottom light illuminance, increased bottom‐water temperatures, and weakened stratification. The result was a dramatic increase in bottom‐water dissolved oxygen concentrations. Water‐level drawdowns also decreased the relative fluorescence of chlorophyll and phycocyanin, probably because of a decrease of internal nutrient loadings from sediment. Total nitrogen and NH4‐N concentrations in the water column decreased after water‐level reductions, and NH4‐N and PO4‐P concentrations in sediment pore waters were reduced in the water‐level treatment. Periphyton biomass did not change after the water‐level drawdowns. Water‐level manipulations increased the abundance of cyclopoids and calanoids but not large cladocerans. These biological processes responded slowly to water‐level drawdowns and are unlikely to have contributed to water quality improvement. Overall, the size of the water‐level reduction required to start changing water quality was 0.5–1.0 m. Our results suggested that a temporary reduction in water‐level of 20%–40% of the depth might help to suppress cyanobacterial blooms and hypoxia in shallow lakes, reservoirs, and agricultural ponds. Such water‐level management may help resolve conflicting demands for water and may be incorporated into management plans for flood control.

Calcite Dissolution and Bioneutralization of Acidic Wastewater in Biosand Reactors

Acidic wastewaters such as winery wastewater require treatment to increase the pH before discharge into the environment. Biosand filters have been shown to reduce the organic load while simultaneously providing a buffering function. Previous research has shown increases in pH which was assumed to mainly take place via dissolution of calcite from the sand particles. This study investigated the possible role of biotic mechanisms for pH adjustment in sand column experiments by comparing results obtained from irradiated (biotic) and non-irradiated (biotic and abiotic) sand columns extracted from biosand filters used to treat winery wastewater. The columns were fed with either synthetic winery wastewater or filtered water (control). It was shown that the specific hydroxide concentrations in the eluant from the non-irradiated columns was significantly (p < 0.05) higher than in the eluant from the irradiated columns (1.1 × 10−5 vs. 4.0 × 10−6 M/kgsand−1), indicating the presence of both biotic (average 4.5 ± 0.13%) and abiotic (average 95.5 ± 0.16%) pH increases. Using multivariate statistical tools to analyze a combination of parameters linked with biotic and abiotic pH adjustment, significant differences (ANOVA, p < 0.05) were found between the four treatment groups (irradiated/non-irradiated SWW and control) and the groups showed good clustering in cluster plots (group average) linkages, and principal component analysis plots.

Emission mitigation of CH4 and N2O during semi-permeable membrane covered hyperthermophilic aerobic composting of livestock manure

Membrane-covered composting and hyperthermophilic composting technologies have been proven to be effective and have been widely applied as organic waste recycling strategies. However, attempts to combine the two technologies have not been reported. Thus, this study constructed a novel semi-permeable membrane covered hyperthermophilic composting (smHTC) and investigated its potential in CH4 and N2O mitigation. Results showed that smHTC reduced the average emission flux of CH4 and N2O in the thermophilic phase of composting by 79% and 45%, compared to conventional thermophilic composting (cTC). The abiotic mechanism of CH4 and N2O emission mitigation could be attributed to the double barrier of semi-permeable membrane and sub-membrane water layer, which made it difficult for CH4 and N2O to escape, resulting in less CH4 and N2O being released into environment. As for the biotic mechanism, smHTC could suppress the abundance of mcrA gene and methanogens participated in methanogenic process through the high-temperature, which also contribute to the reduction of CH4 emissions. smHTC also could reduce the abundance of denitrification-related functional genes and related microbial taxa, this also facilitated the N2O mitigation. Overall, this work demonstrated the advantages of smHTC in greenhouse gas mitigation and could be a promising recycling strategy for organic waste.

Soil microbial community structure dynamics shape the rhizosphere priming effect patterns in the paddy soil

Microbial community structure plays a crucial part in soil organic carbon (SOC) decomposition and variation of rhizosphere priming effects (RPEs) during plant growth. However, it is still uncertain how bacterial community structure regulates RPEs in soil and how RPE patterns respond to plant growth. Therefore, we conducted an experiment to examine the RPE response to plant growth and nitrogen (N) addition (0 (N0), 150 (N150), and 300 (N300) kg N ha−1) using the 13C natural abundance method in a C3 soil (paddy soil) - C4 plant (maize, Zea mays L.) system; we then explored the underlying biotic mechanisms using 16S rRNA sequencing techniques. Networks were constructed to identify keystone taxa and to analyze the correlations between network functional modules of bacterial community and C decomposition. The results indicated that negative and positive RPEs occurred on Day 30 and Day 75 after maize planting, respectively. Bacterial community structure significantly changed and tended to shift from r-strategists toward K-strategists with changing labile C: N stoichiometry and soil pH during plant growth stages. The different network modules of bacterial community were aggregated in response to RPE pattern variation. Caulobacteraceae, Bacillus, and Chitinophagaceae were keystone taxa on Day 30, while Gemmatimonas, Candidatus Koribacter, and Xanthobacteraceae were keystone taxa on Day 75. Moreover, keystone taxa with different C utilization strategies were significantly different between the two growth stages and related closely to different RPE patterns. This study provides deeper insights into the network structure of bacterial communities corresponding to RPE patterns and emphasizes the significance of keystone taxa in RPE variation.