Amid accelerating global land degradation, establishing high-efficiency ecological restoration principles and frameworks is crucial. Here, we explore the application of threshold effects in the ecological restoration process based on field experiments and globally available experimental data from 173 sites. Combining data integration analysis and meta-analysis, we collectively verified the universality of threshold effects in grasslands. The global grasslands’ average nitrogen application threshold is 3.78 g·m−2·yr−1, while the threshold value of degraded grassland (3.65 g·m−2·yr−1) is lower than that of nondegraded grassland (5.90 g·m−2·yr−1). The low nitrogen-driven thresholds are affected by degradation status, climate (precipitation and temperature), and other site conditions, but not fertilization forms. Independent experiments further demonstrated that an increase in soil moisture content can lead to the disappearance of nitrogen threshold effects, revealing that ecological threshold effects are influenced by ecosystem stress factors. Following the significant increase in plant biomass triggered by the nitrogen threshold, the ecosystem undergoes systemic improvement. Soil organic carbon, urease activity, soil microbial diversity, and other soil properties are significantly enhanced. Soil nitrogen cycle-related microbial communities and soil physicochemical attributes are significantly activated. The results indicate that a threshold response pattern may develop before nitrogen saturation is reached, and low nitrogen input can boost productivity and improve the plant-soil-microbe system. Our findings reveal a nonprogressive path of restoration in degraded ecosystems, and thus, restoration based on threshold effects can offer an efficient and safe solution to combat ecological degradation.

Saline-alkali soils significantly hinder agricultural productivity in China's coastal areas. Although both plant growth-promoting rhizobacteria (PGPR) and biochar have individually demonstrated the capacity to boost crop yield and soil fertility, their synergistic effects on seawater rice and soil ecosystems remain uncertain. In this study, we examined the individual and interactive influences of lychee biochar (2.5% and 5% w/w) and PGPR inoculation on soil physicochemical properties and bacterial community assembly along a soil-root continuum, encompassing bulk soil, rhizosphere soil, rhizoplane, and root endosphere, in a controlled pot experiment with seawater rice. The application of biochar significantly altered soil pH, electrical conductivity, and nutrient availability in both bulk and rhizosphere soils, resulting in pronounced changes in bacterial community composition. The effects generated by biochar were partially mitigated when PGPR was co-applied. The relative abundances of Bacillota and Bacteroidota grew progressively from bulk soil to the root endosphere across all treatments, indicating a significant compartment-dependent selection. Co-occurrence network analysis and FAPROTAX-based functional predictions revealed several taxa and functions that were progressively enriched toward the root, including the halotolerant genera Exiguobacterium and Chryseobacterium, highlighting a significant host-mediated filtration process that functioned independently of the inoculated strains. Multivariate analyses further demonstrated that soil pH was the primary driver of bacterial community structure in bulk and rhizosphere soils, whereas plant-root selection dominated in the rhizoplane and endosphere. Overall, our results demonstrate that, within a seawater-rice and soil ecosystem, the selective influence of the host plant on root-associated microbiomes exceeds that of either biochar amendment or PGPR inoculation. This work improves our understanding of biochar-PGPR-plant interactions in saline-alkali soils and provides insight into sustainable strategies for enhancing rice production under salinity stress.

Selenium (Se) bioavailability often limits the production of Se-rich crops in naturally Se-enriched soils. While biochar and selenobacteria individually show promise in enhancing Se mobility, their synergistic effects and underlying mechanisms remain poorly understood. This work investigated the synergistic impact of rice straw-derived biochar and selenobacterium Bacillus megaterium on Se accumulation in rice and elucidated the associated shifts in root microbiome. The findings demonstrated a synergistic interaction between the treatments, inducing an increase in shoot Se content surpassing that observed with any single treatment. This effect was accompanied by an obvious decrease in total soil Se, particularly evident with co-application, highlighting their synergistic ability of mobilizing the native soil Se reservoir effectively. Biochar was the dominant driver of soil fertility improvement, causing increased availability of phosphorus, potassium and organic carbon. It also played key roles in reshaping root-associated bacterial communities, reducing rhizosphere bacterial diversity while simultaneously enriching specific beneficial taxa like Paenibacillaceae and Bdellovibrionaceae under co-application treatment. Co-occurrence network analysis further identified compartmentalized associations between specific microbial taxa and shoot Se content. Specifically, key taxa such as Planctomycetes and Mortierellaceae in the rhizosphere, Thermoleophilia, Solirubrobacterales, and Sordariomycetes in the rhizoplane, alongside Rubrivivax and Sphingomonadaceae in the endosphere, were revealed as being significantly correlated. Peroxidase activity showed strong correlative associations with Se accumulation across compartments. The combined use of biochar and Bacillus megaterium enhances Se bioavailability and translocation by beneficially restructuring the root microbiome, offering a sustainable strategy for the biofortification of rice in naturally Se-enriched soils.

Huge removal projects of Spartina alterniflora Loisel. have recently been carried out in China, which is of great significance for mitigating the biological invasion. However, these removal projects might lead to secondary soil and water loss, short-term biodiversity degradation, and ecosystem imbalance. Based on this perspective, this study synthesized the development timeline, invasion causes, advantages and disadvantages of removal projects, and remediation strategies. The results showed that the development timeline of S. alterniflora has gone through five stages: exploration and experimentation, coastal guardian, positive vs negative, ecological killer, biosecurity reclamation. Due to the high reproductive and favorable external environment of S. alterniflora, it has developed into an invasive species that threatens the coastal ecosystems. Moreover, after large-scale removal projects, it might threaten the ecosystem stability in the short term while promote biodiversity in the long term. During the removal projects, there should be developed in adopting a location-specific management approach, employing diverse approaches alongside ecological restoration, reducing costs by optimizing effectiveness, promoting technological innovation and resource reutilization. This study would provide new perspectives for managing S. alterniflora and the ecological restoration of ecosystems affected by similar invasive species.

Desert ephemerals complete rapid life cycles to survive aridity, yet the ontogenetic coordination of below-ground rhizosphere interactions with above-ground resource allocation remains unclear. This study examined six dominant ephemeral species (Eremurus inderiensis, Eremopyrum orientale, Erodium oxyrrhynchum, Allium mongolicum, Alyssum linifolium and Nepeta micrantha) in the Gurbant & uuml;ngg & uuml;t Desert across seedling and flowering stages, integrating plant biomass, rhizosphere metabolites and bacterial communities. This study detected consistent ontogenetic shifts at the overall level: a 44.4% decrease in root: shoot ratio shifting biomass from below-ground to above-ground with interspecific variations. Concurrently, rhizosphere metabolic space contracted by 86.4%, with species-specific metabolic plasticity strongly correlated with biomass reallocation magnitude. Bacterial communities exhibited reduced alpha-diversity, simplified co-occurrence networks and a predicted functional transition from carbon to nitrogen metabolism. Keystone microbe-metabolite associations shifted from carbon-based linkages at the seedling stage to nitrogen-centric correlations at flowering, accompanied by stage-specific turnover of keystone taxa and reconfiguration of microbe-metabolite networks. At the species level, however, the key taxa, metabolites and network dynamics underlying these shifts were highly specific, with divergent niche-width dynamics and stage-specific interactions corresponding to host metabolic plasticity. Path modelling revealed a universal, stage-dependent reversal in biomass drivers: below-ground biomass was initially supported by broad bacterial niche width, whereas flowering-stage above-ground biomass was directly driven by rhizosphere metabolites. These findings demonstrate that host developmental stage orchestrates a phased rhizosphere strategy in desert ephemerals. This strategy synchronizes keystone taxa succession and microbe-metabolite network reconfiguration with plant ontogenetic goals, enabling a conserved shift from microbial-assisted establishment to metabolite-driven reproduction despite species-specific pathways. This study provides novel insights for plant-microbe co-adaptation in resource-limited desert ecosystems.Read the free for this article on the Journal blog.

Many studies have reported that changes in nitrogen (N) deposition affect the structure and diversity of fungal communities in moss crust soils, but few studies have addressed the seasonal patterns of soil fungal community response to N inputs in desert habitats. Therefore, we conducted a one-time field N addition experiment in March 2017 in the Gurbantunggut Desert, northwestern China. Four N addition rates, 0 (CK), 1.8 (LN), 3.6 (MN), and 7.2 (HN) g N m(-2) yr(-1), were applied, and soil was sampled at different seasons. We found that the effects of N addition on soil fungal communities varied with season, with stronger effects in November and March compared to May. Seasonal variation strongly affected fungal community structure, composition, and function, with the highest diversity index in May. The impact of N addition on fungal communities is attributed to changes in soil pH, total phosphorus, and available phosphorus, while the effect of season on fungal communities is driven by changes in temperature, soil moisture and soil organic carbon. Additionally, season has a greater effect on fungal communities than N addition. Overall, the fungal communities in soils underlying moss crusts responded strongly to seasonal variation, but their response to N addition was seasonally dependent.

Red soils in China are essential for food security, ecological balance, and rural development. Red soil's varied microbial populations help maintain soil health, cycle nutrients, and sustain ecosystems. The variation in bacterial community assembly and distribution with soil depth in acidic dryland and paddy soils is unknown. We sampled dryland and paddy soil profiles from nearby farms in southern China's red soil region. Five soil layers (0-20 cm, 20-40 cm, 40-60 cm, 60-80 cm, 80-100 cm) were taken from a 1-meter soil profile at Yichun, Jiangxi, China. In paddy soils, ammonium nitrogen, available iron, and soil organic matter (SOM) were greater than in dryland soils. While both soil types showed considerable variation in diversity indices (Chao1, Sobs, PD) over the soil profile, paddy soils showed a more wave-like pattern in microbial diversity indicators. Dryland soils had higher relative abundances of Actinobacteriota (3.6-7.3 %) and GAL15 (1.3-8.6 %), while paddy soils had Bacteroidota (3.9-9.2 %), Desulfobacterota (4.2-7.7 %), and Nitrospirota (2.1-12.7 %). Acidobacteriota (29.5-59.1 %), Chloroflexi (6.3-30.9 %), and Proteobacteria (7.5-21.5 %) predominated at both soil types. Taxonomic alterations in Acidobacteriota, Chloroflexi, and Proteobacteria highlighted how microbial communities adapted to dryland vs paddy soils. The assembly of bacterial communities was mostly stochastic, with varied dispersion and assembly dynamics across soil types and depths. Network analysis showed that paddy soils had more complicated interspecies relationships than dryland soils, with a greater average clustering coefficient and lower modularity. Drylands had higher biosynthetic and metabolic activity, especially amino acid metabolism and secondary metabolite production, whereas paddy soils had higher energy metabolism. This research emphasizes how land use affects soil physicochemical properties and microbiological populations. Microbial profiles and functional adaptations of dryland and paddy soils provide soil management techniques to optimize soil health and production in diverse agricultural systems.

Humus (HS) reservoirs can embed microbial necromass (including cell wall components that are intact or with varying degrees of fragmentation) in small pores, raising widespread concerns about the potential for C/N interception and stability in composting systems. In this study, fresh cow manure and sawdust were used for microbial solid fermentation, and the significance of microbial residues in promoting humification was elucidated by measuring their physicochemical properties and analyzing their microbial informatics. These results showed that the stimulation of external carbon sources (NaHCO3) led to an increase in the accumulation of bacterial necromass C/N from 6.19 and 0.91 µg/mg to 21.57 and 3.20 µg/mg, respectively. Additionally, fungal necromass C/N values were about 3 times higher than the initial values. This contributed to the increase in HS content and the increased condensation of polysaccharides and nitrogen-containing compounds during maturation. The formation of cellular debris mainly depends on the enrichment of Actinobacteria, Proteobacteria, Ascomycota, and Chytridiomycota. Furthermore, Euryarchaeota was the core functional microorganism secreting cell wall lytic enzymes (including AA3, AA7, GH23, and GH15). In conclusion, this study comprehensively analyzed the transformation mechanisms of cellular residuals at different profile scales, providing new insights into C/N cycles and sequestration.

The invasion of Spartina alterniflora (S. alterniflora) significantly influences the stability and transformation of soil organic carbon in coastal ecosystems. However, the impact of this invasion on the assembly of soil bacterial communities along estuary coastlines and soil profiles remains unclear. This study involved collecting soil samples from different environments (areas covered with S. alterniflora vs. barren flats) along the coastline of an estuary. The samples were taken at different depths (0-20 cm, 20-40 cm, 40-60 cm, 60-80 cm, 80-100 cm) within a 1-meter soil profile in the intertidal area of Xiaoyangkou Estuary in Jiangsu, China. The invasion of S. alterniflora had a notable impact on soil SOM (soil organic matter), DOC (dissolved organic carbon), POC (particulate organic carbon), and MAOC (mineral-associated organic carbon). Concurrently, the soil layer primarily influenced the levels of soil DOC and MAOC. The dominant bacterial communities inside the soil consisted of Proteobacteria (27.4-50.2 %), Bacteroidota (5.2-23.3 %), and Desulfobacterota (9.5-19.8 %), which participates in several elemental cycles, such as the carbon, nitrogen, sulfur, and phosphorus cycles. The changes in the patterns and functions of bacterial communities related to carbon cycling were mostly associated with the estuary shoreline, rather than being influenced by the invasion of S. alterniflora or variations in soil depths. Soil total carbon (TC) and SOM displayed a greater influence than other soil organic fractions on the distribution of the bacterial community. Furthermore, elements such as As, Cr, and Zn also exerted a significant impact on the assembly of soil bacterial communities. Our research findings suggest that the influence of S. alterniflora invasion on the composition and functioning of soil bacterial communities is contingent upon the specific features of the area. These characteristics, in turn, control the stability of soil carbon and the transformation of various types of soil carbon.

Pinellia ternata (Thunb.) Breit is a traditional Chinese medicine with important pharmacological effects. However, its cultivation is challenged by soil degradation following excessive use of chemical fertilizer. We conducted an experiment exploring the effects of replacing chemical fertilizers with organic fertilizers (OF) on the growth and yield of P. ternata, as well as on the soil physicochemical properties and microbial community composition using containerized plants. Six fertilization treatments were evaluated, including control (CK), chemical fertilizer (CF), different proportions of replacing chemical fertilizer with organic fertilizer (OM1-4). Containerized P. ternata plants in each OF treatment had greater growth and yield than the CK and CF treatments while maintaining alkaloid content. The OM3 treatment had the greatest yield among all treatments, with an increase of 42.35% and 44.93% compared to the CK and CF treatments, respectively. OF treatments improved soil quality and fertility by enhancing the activities of soil urease (S-UE) and sucrase (S-SC) enzymes while increasing soil organic matter and trace mineral elements. OF treatments increased bacterial abundance and changed soil community structure. In comparison to the CK microbial groups enriched in OM3 were OLB13, Vicinamibacteraceae, and Blrii41. There were also changes in the abundance of gene transcripts among treatments. The abundance of genes involved in the nitrogen cycle in the OM3 has increased, specifically promoting the transformation of N-NO3- into N-NH4+, a type of nitrogen more easily absorbed by P. ternata. Also, genes involved in "starch and sucrose metabolism" and "plant hormone signal transduction" pathways were positively correlated to P. ternata yield and were upregulated in the OM3 treatment. Overall, OF in P. ternata cultivation is a feasible practice in advancing sustainable agriculture and is potentially profitable in commercial production.

To investigate the effects of growth-promoting bacteria and growth regulators on the salinity variations,rice yield and rice quality of the beach paddy,a rice planting experiment was conducted from June to November of 2020 in the coastal beach area of Nantong,Jiangsu Province.A two-factor split zone design was adopted,and the main zone was treated with seed immersion by growth-promoting bacteria,including clean water(CK),and growth-promoting bacteria of Rudong(RD)and Ningbo(NB).The second zone was treated by growth regulator spray,including clean water(W),"BiHu(0.136%Gibberellic Acid·indol-3-ylacetic Acid·brassinolide)"(T1)and"sodium nitrophenate"(T2).As the results,the salinity of irrigation water during rice cultivation ranged from 0.78 to 1.12 g·kg-1,and the soil salinity variations ranged from 1.11 to 1.87 g·kg-1 during the rice growth season in the CK,RD,and NB plots.Compared with CK,the rice yield increased by 4.65%and 1.83%in the RD and NB plots,respectively;and compared with W,the rice yield increased by 5.50%and 1.05%in the T1 and T2 plots,respectively.Compared with CK-W,the rice yield in RD-T1 increased the most by by 11.66%(P＜0.05),and the values of grain number per panicle and solid grain number were increased by 13.45%and 13.85%,respectively(P＜0.05).Compared with CK,the brown rice rate,amylose,and protein contents of rice in the RD plots were significantly reduced,but no significant effect was found on other quality indexes.According to the results of two-factor analysis,the growth regulator factor had a significant influence on panicle length,grains per panicle,filled grains per panicle and yield,while the growth-promoting bacteria factor had a significant influence on 1 000-grain weight.Moreover,a significant interaction was found between the growth regulators and growth-promoting bacteria specifically on 1 000-grain weight.In conclusion,growth-promoting bacteria combined with growth regulators had significant effect on the yield increase.Growth regulators mainly increased the number of grains per panicle and the number of solid grains,and growth-promoting bacteria mainly improved the 1 000-grain weight.This study provides a technical reference for exploring appropriate agronomic management measures to achieve the purpose of increasing rice yield in tidal flats areas.

Plant carbon (C) released into the rhizosphere will ultimately impact the bulk soil, varying with soil water status. However, the microbial communities involved, and how they vary between rhizosphere and bulk soil, and under varying water regimes, are little understood. Here, within a continuous 13CO2 labeling chamber, a rhizobox-like system was utilized to cultivate ryegrass (upland) and rice (paddy) to identify the root-derived C flow and associated active microbes. The 15N-labeled fertilizer was used to measure the N flow from the soils and plants. The 13C labeled soil organic C (13C-SOC) values of upland soil were greater than those of paddy soil. There was a reduction in 13C-SOC values from the rhizosphere to the bulk soils, but the total 15N labeled N (15N-TN) values exhibited an increase trend from this direction. The isotopic enrichment of PLFAs and DNA sequencing results indicated that the bacterial and fungal abundance and diversity exhibited augmentation in the rhizosphere soil under both cultures compared with the bulk soils. Bacteria played a much more important role than fungi in the C flow in the paddy soil. However, fungi dominantly contributed to this flow in the upland soils. Our findings revealed a vital role of Ascomycota fungi (especially Talaromyces) and Actinobacteria bacteria (Actinomycetales and Gaiellales) in contributing to the assimilation of root-derived C for the upland and paddy soils, respectively.

This study investigates the effect of biochar amendment on microbial community structure and soil nutrient status in paddy soil that has been fertilized for an extended period of time, shedding light on sustainable agricultural practices. A 90-day incubation period revealed that biochar amendment, as opposed to long-term fertilization, significantly influenced the physicochemical properties and microbial composition of the soil. The microcosm experiment conducted using six treatments analyzed soil samples from a long-term rice ecosystem. We employed microbial biomarkers (phospholipid fatty acids, PLFAs; isoprenoid and branched glycerol dialkyl glycerol tetraethers, iGDGTs and brGDGTs; DNA) to assess microbial biomass and community structure. Biochar addition led to a decrease in PLFA biomass (15–32

The sustainability of life on Earth is under increasing threat due to human-induced climate change. This perilous change in the Earth's climate is caused by increases in carbon dioxide and other greenhouse gases in the atmosphere, primarily due to emissions associated with burning fossil fuels. Over the next two to three decades, the effects of climate change, such as heatwaves, wildfires, droughts, storms, and floods, are expected to worsen, posing greater risks to human health and global stability. These trends call for the implementation of mitigation and adaptation strategies. Pollution and environmental degradation exacerbate existing problems and make people and nature more susceptible to the effects of climate change. In this review, we examine the current state of global climate change from different perspectives. We summarize evidence of climate change in Earth’s spheres, discuss emission pathways and drivers of climate change, and analyze the impact of climate change on environmental and human health. We also explore strategies for climate change mitigation and adaptation and highlight key challenges for reversing and adapting to global climate change.

Plant growth-promoting rhizobacteria(PGPR) have an important contribution to the plants nutrients uptake from soil, but less research has mentioned that how function of PGPR in farmland soil of tidal flat. In this study, 5PGPR strains were isolated from topsoil of paddy and maize-wheat rotation field in reclamation areas of Nantong and Ningbo, respectively. The strains were identified by 16S rRNA gene sequence as follows: Massilia varians(M.varians), Brevundimonas nasdae(Brv.nasdae), Microbacterium flavescens(Mib.flavescens), Pseudomonas chlororaphis(Ps.chlororaphis) and Pseudomonas jessenii(Ps.jessenii). Five factors including carbon source, nitrogen source, C/N,pH and temperature were used to test the phosphorus solubilizing ability of the isolated strains. Results show that compared with the control group, Mib.flavescens and Brv.nasdae show the best phosphorus-solubilizing activity under neutral conditions(80.27-85.51 mg/L), more phosphorus(13.59-81.94 mg/L) is released by Ps.jessenii at a wide range of temperature than other strains. These three strains have good potential application in microbial fertilizer, and provide a fundamental information for the development of microbial fertilizer in the future.

The effects of biochar additions on soil nutrients and biotic processes have been studied extensively. However, the impact of intact and acid washed biochar on the microbial community assembly process in a neutral-alkaline paddy soil remains unknown. A microcosm experiment with six treatments (CK: control; CB: CK-added intact biochar; CWB: CK-added acid washed biochar; NPK: N, P, and K fertilizer application; NPKB: NPK-added intact biochar; NPKWB: NPK-added acid washed biochar) was conducted using soil samples from a long-term rice–wheat rotation ecosystem. Soil microbial phospholipid fatty acids (PLFAs) and high-throughput sequencing were utilized to evaluate microbial biomass and community structure. Less than 24% of PLFA biomass dropped in CB and CWB treatments whereas 27% decreased in NPKB and NPKWB treatments. Archaeal diversity in NPK soils was lower than in CK soils but rose in NPKB and NPKWB soils. However, only intact biochar reduced bacterial diversity, whereas acid washed biochar reduced fungal diversity. Acidobacteria, Chloroflexi, Firmicutes, Nitrospirota, and Planctomycetota behaved differentially to both intact and acid washed biochar treatments. Biochar was more responsive to saprophytic than pathotrophic and symbiotrophic fungi. The soil pH and available P content influenced fungi community structure, whereas DOC, DON, NH4+-N, and NO3−-N influenced bacteria community structure. Archaeal taxa were dominated by ammonia oxidizing and methane cycling species, which were susceptible to biochar treatment. Our findings suggest that intact or acid washed biochar has a different effect on soil microbial sublineages (archaea, bacteria, and fungus) community, and then in turn modulated soil carbon and nitrogen cycling in the neutral-alkaline paddy soil.

Conversion of coastal mudflats to agricultural soil is one of the most important land use practices in Eastern China. However, effects of soil profile and reclamation time on soil microbial community, which play an important role in soil nutrient cycling, are still poorly documented. Soil profile (0–15 cm, 15–30 cm, 30–45 cm) samples were collected from four sites with different reclamation ages (R12: 12 years, R38: 38 years, R68: 68 years, R100: 100 years) in Rudong County, Nantong, Jiangsu, China. Soil bacterial communities were determined via Illumina 16S rRNA gene high-throughput sequencing. Soil electrical conductivity (EC) responded more rapidly to reclamation time than soil pH. Soil total carbon and nitrogen increased with increasing reclamation age. Soil available nutrients (ammonium, nitrate, dissolved organic carbon, and available phosphorus) were affected by the agricultural practice and did not show a unanimous tendency between different reclaimed sites. Proteobacteria, Acidobacteriota, and Bacteroidota dominated the bacterial community across different sites and soil profiles. However, Methylomirabilota- and Nitrospirota-associated species, which are involved in nitrogen cycling, increased with increasing soil depth. Canonical correspondence analysis (CCA) showed that bacterial community was grouped by soil depth and also significantly affected by soil pH, EC, and reclaimed time. Moreover, co-occurrence network analysis showed a potential role of low abundant phyla besides dominant phyla in stabilizing the bacterial community, and the connection between soil properties and bacterial amplicon sequence variant (ASV) numbers would shift along soil profiles. Reclamation time of the coastal mudflats is not the only reason for the shift of bacterial community. Here, we found soil profile had a strong influence on soil bacterial composition in the coastal reclaimed wheat-maize rotation soils.

Bacterial communities in soil serve an important role in controlling terrestrial biogeochemical cycles and ecosystem processes. Increased nitrogen (N) deposition in Northwest China is generating quantifiable changes in many elements of the desert environment, but the impacts of N deposition, as well as seasonal variations, on soil bacterial community composition and structure are poorly understood. We used high-throughput sequencing of bacterial 16S rRNA genes from Gurbantünggüt Desert moss crust soils to study the impacts of N addition on soil bacterial communities in March, May, and November. In November, we discovered that the OTU richness and diversity of soil bacterial community dropped linearly with increasing N input. In November and March, the diversity of the soil bacterial community decreased significantly in the medium-N and high-N treatments. In May, N addition caused a substantial change in the makeup of the soil bacterial composition, while the impacts were far less apparent in November and March. Furthermore, the relative abundance of major bacterial phyla reacted non-linearly to N addition, with high-N additions decreasing the relative richness of Proteobacteria, Bacteroidetes, and Acidobacteria while increasing the relative abundance of Actinobacteria and Chloroflexi. We also discovered that seasonality, as characterized by changes in soil moisture, pH, SOC, and AK content, had a significant impact on soil bacterial communities. Significant variations in the makeup of the community were discovered at the phylum and genus levels throughout the various months. In May, the variety of soil bacterial community was at its peak. Further investigation showed that the decrease in soil bacterial diversity was mostly attributed to a drop in soil pH. These results indicated that the impact of N deposition on the soil bacterial community was seasonally dependent, suggesting that future research should evaluate more than one sample season at the same time.

Soil salinity greatly influences soil organic carbon (SOC) stocks. However, how soil salinity affect SOC formation by changing microbial utilization of newly input organic C and subsequent microbial residues retention remains unclear. In this study, high salinity (HS, EC1:5 20.04 dS m-1) and low salinity (LS, EC1:5 0.90 dS m-1) soils were collected in a newly reclaimed coastal area in eastern China. Soil salt content decreased rapidly in the LS site due to irrigation and drainage management. The effect of soil salinity on microbial transformation of straw was investigated by adding 13C-labelled ryegrass straw into the HS and LS soils in a 180-day incubation experiment. Results showed that straw-derived dissolved organic C was higher in the HS soil. The higher availability of labile substrate in the HS soil offset the negative effect of high salinity on Gram-negative bacteria and fungi, but did not on Gram-positive bacteria. Microbial biomass C (MBC) and microbial C use efficiency (CUE) of straw were higher in the HS soil at 3 days due to the higher assimilation of straw C by Gram-negative bacteria and fungi. Strawderived MBC and microbial CUE decreased over time and were similar between both soils at 60 and 180 days. Thus, high salinity did not decreased quantity and efficiency of microbial utilization of straw C. However, newly formed amino sugars were lower in the HS soil at 60 and 180 days suggesting that high salinity was not beneficial to the retention of microbial residues after microbial cells died. In conclusion, high salinity reduced microbial-derived SOC formation primarily by affecting stabilization and recycling of microbial necromass rather than by decreasing microbial utilization of newly input organic carbon in the studied coastal soil.

Coastal mudflats reclamation activities show a strong influence on soil properties and microbial community activity, which drive soil carbon and nitrogen cycling. Studies have found there is a shift of bacterial community with reclamation time. However, effects of reclamation time on the soil archaeal community are still largely unknown. Here, we determined soil properties and archaeal community in the soil profiles (0-15, 15-30, 30-45 cm) of different reclaimed sites with different reclamation ages (R12: 12-year; R38: 38-year; R68: 68-year; R100: 100-year) in Rudong County, Jiangsu, China. Soil archaeal communities were identified via Illumina high-throughput sequencing. Soil archaeal communities were dominated by two phyla, the Crenarchaeota (82.1-93.3%) and Thermoplasmatota (4.2-17.9%), which are associated with nitrogen cycle (Nitrosopumilaceae, Nitrososphaeraceae, and Nitrosotaleaceae) and organic carbon metabolism (Marine_Group_II), respectively. Ammonia oxidizing archaea showed a divergent response to the reclamation, i.e. Nitrosotaleaceae increased with reclamation time whereas Nitrosopumilaceae showed a decreasing trend. Soil total carbon, total nitrogen, pH, EC, C:N ratio, NO3--N content, soil moisture, depth, and reclamation age determined archaeal community distribution in our reclaimed sites. Our findings suggest that both reclamation time and soil depth significantly shaped the archaeal community composition, and then in turn modulated soil carbon and nitrogen cycling in the reclaimed mudflats.