Soil Carbon, Nitrogen, and Phosphorus Cycling Microbial Populations and Their Resistance to Global Change Depend on Soil C:N:P Stoichiometry

The urgent need to reduce phosphorus discharges for sustainable mangrove wetland management

Phosphorus affects microbial metabolic activity, nitrogen and carbon cycling in mangrove sediment, but its influence on carbon stability and greenhouse gases emission remains unclear. This study compared greenhouse gases (CO2, N2O, and CH4) emissions from mangrove sediment receiving wastewater containing various phosphorus concentrations, and evaluated its long term effect on sediment carbon flux when phosphorus pollution is eliminated. Significant increases in greenhouse gases flux and decrease of total organic carbon and readily oxidizable organic carbon in the sediment were observed after phosphorus discharge. Specifically, the N2O flux was reduced significantly at high phosphorus levels while the CO2 flux and the microbial biomass organic carbon was increased. The copy numbers of ammonia oxidation (AOA-amoA, AOB-amoA) gene, denitrification (narG, nirK) gene and methanogenesis (mcrA) gene increased with the increasing phosphorus concentration. During the wastewater discharge period for 70 days, the global warming potential of sediment flux at high phosphorus discharge condition was more than 4 times that of the control group, and the loss of total organic carbon and readily oxidizable organic carbon was 4.66 % and 7.1 %, respectively. During the remediation period (71-101 days), the greenhouse gases flux decreased rapidly, ends up with a similar level of the control group. Our results indicate that using mangrove wetland for pollution minimization in the coastal aquaculture industry could increase greenhouse gases emisison significantly, it is therefore essential to reduce phosphorus discharges from various anthropogenic activities, and local authorities must set up more stringent discharge standards in the future.

The impact of microbial community structure changes on the migration and release of typical heavy metal (loid)s during the revegetation process of mercury-thallium mining waste slag

The effect of changes in microbial community structure on the migration and release of toxic heavy metal (loid)s is often ignored in ecological restoration. Here, we investigated a multi-metal (mercury and thallium, Tl) mine waste slag. With particular focus on its strong acidity, poor nutrition, and high toxicity pollution characteristics, we added fish manure and carbonate to the slag as environmental-friendly amendments. On this basis, ryegrass, which is suitable for the remediation of metal waste dumps, was then planted for ecological restoration. We finally explored the influence of changes in microbial community structure on the release of Tl and As in the waste slag during vegetation reconstruction. The results show that the combination of fish manure and carbonate temporarily halted the release of Tl, but subsequently promoted the release of Tl and arsenic (As), which was closely related to changes in the microbial community structure in the waste slag after fish manure and carbonate addition. The main reason for these patterns was that in the early stage of the experiment, Bacillaceae inhibited the release of Tl by secreting extracellular polymeric substances; with increasing time, Actinobacteriota became the dominant bacterium, which promoted the migration and release of Tl by mycelial disintegration of minerals. In addition, the exogenously added organic matter acted as an electron transport medium for reducing microorganisms and thus helped to reduce nitrate or As (Ⅴ) in the substrate, which reduced the redox potential of the waste slag and promoted As release. At the same time, the phylum Firmicutes, including specific dissimilatory As-reducing bacteria that are capable of converting As into a more soluble form, further promoted the release of As. Our findings provide a theoretical basis for guiding the ecological restoration of relevant heavy-metal (loid) mine waste dumps.

Effects of crayfish shell powder and bamboo-derived biochar on nitrogen conversion, bacterial community and nitrogen functional genes during pig manure composting

This study investigated the effects of crayfish shell powder (CSP) and bamboo-derived biochar (BDB) on nitrogen metabolism, bacterial community and nitrogen functional genes during pig manure composting. Four treatments were established: CP (with no additives), TP1 (5 % BDB), TP2 (5 % CSP) and TP3 (2.5 % BDB + 2.5 % CSP). Compared to CP, the germination index (GI) of TP reached > 85 % 10 days earlier. Meanwhile, TP3 reduced NH3 and N2O emissions by 42.90 % and 65.9 %, respectively, while increased TN (total nitrogen) concentration by 5.43 g/kg. Furthermore, additives changed the bacterial structure and formed a beneficial symbiotic relationship with essential N-preserving bacteria, thereby enhancing nitrogen retention throughout the composting process. Metagenomic analysis revealed that additives upregulated nitrification genes and downregulated denitrification and nitrate reduction genes, ultimately improving nitrogen cycling and mitigating NH3 and N2O emissions. In conclusion, the results confirmed that TP3 was the most effective treatment in reducing nitrogen loss.

Intercropping improves maize yield and nitrogen uptake by regulating nitrogen transformation and functional microbial abundance in rhizosphere soil

Intercropping-driven changes in nitrogen (N)-acquiring microbial genomes and functional expression regulate soil N availability and plant N uptake. However, present data seem to be limited to a specific community, obscuring the viewpoint of entire N-acquiring microbiomes and functions. Taking maize intercropped with legumes (peanut and soybean) and non-legumes (gingelly and sweet potato) as models, we studied the effects of intercropping on N transformations and N-acquiring microbiomes in rhizosphere soil across four maize growth stages. Meanwhile, we compiled promising strategies such as random forest analysis and structural equation model for the exploitation of the associations between microbe-driven N dynamics and soil-plant N trade-offs and maize productivity. Compared with monoculture, maize intercropping significantly increased the denitrification rate of rhizosphere soils across four maize growth stages, net N mineralization in the elongation and flowering stages, and the nitrification rate in the seedling and mature stages. The abundance of most N-acquiring microbial populations was influenced significantly by intercropping patterns and maize growth stages. Soil available N components (NH4+-N, NO3--N, and dissolved organic N content) showed a highly direct effect on plant N uptake, which mainly mediated by N transformations (denitrification rate) and N-acquiring populations (amoB, nirK3, and hzsB genes). Overall, the adaptation of N-acquiring microbiomes to changing rhizosphere micro-environments caused by intercropping patterns and maize development could promote soil N transformations and dynamics to meet demand of maize for N nutrient. This would offer another unique perspective to manage the benefits of the highly N-effective and production-effective intercropping ecosystems.

Improvement and the relationship between chemical properties and microbial communities in secondary salinization of soils induced by rotating vegetables

Choosing a good crop rotation plan helps maintain soil fertility and creates a healthy soil ecosystem. However, excessive fertilization and continuous cultivation of vegetables in a greenhouse results in secondary salinization of the soil. It remains unclear how crop rotation affects Yunnan's main place for vegetable growing in the greenhouse. Six plant cultivation patterns were chosen to determine how different rotation patterns affect the chemical properties and the soil microbial communities with secondary salinization, including lettuce monoculture, lettuce-large leaf mustard, lettuce-red leaf beet, lettuce-cabbage, lettuce-romaine lettuce, and lettuce-cilantro (DZ, A1, A2, A3, A4, and A5). The results showed that all treatments increased the proportion of nutrients available in the soil, and the effect of the A1 treatment was the most significant compared to the monoculture mode. The high-throughput sequencing findings revealed that distinct crop rotation patterns exerted varying effects on the microbial communities. Microbial community diversity was significantly lower in the monoculture than in the other treatments. The number of microbial operational taxonomic units OTUs was significantly higher in the crop rotation modes (P < 0.05), and the A1 treatment had larger numbers and diversity of bacterial and fungal OTUs (Shannon's and Simpson's) than other treatments (P < 0.05). Prominent bacterial and fungal communities were readily observable in the soils planted with rotational crops. Proteobacteria had the highest relative abundance of bacteria, whereas Ascomycota was the most abundant fungus. The principal coordinate analysis at the OTU level separated soil bacterial and fungal growth communities under the different treatments. Among the six treatments, The first two axes (PC1 and PC2) described 46.44 % and 42.42 % of the bacterial and fungal communities, respectively. Network-based analysis showed that Bacteroidota and Gemmatimonadota members of the genus Bacteroidota were positively correlated with Proteobacteria. Members of Ascomycota and Chytridiomycota exhibited positive relationships. These results extend the theoretical understanding of how various crop rotation patterns affect soil chemical properties, microbial community diversity, and metabolic functions. They reveal the beneficial effects of crop rotation patterns on enhanced soil quality. This study provides theoretical guidance for the future enhancement of sustainable agriculture and soil management planning.

Regulation of wheat growth by soil multifunctionality and metagenomic-based microbial functional profiles under mulching treatments

Soil microbial functional genes play key roles in biogeochemical processes that are closely related to crop development. However, the regulation of crop growth by the composition and potential interactions of metagenomic-based functional genes is poorly understood. Therefore, in a long-term mulching experiment, the regulation of wheat growth by soil multifunctionality, microbial functional profiles driven by soil properties and microbial activity was studied. Soil properties and microbial activity were significantly separated into distinct mulching treatments, and were significantly declined by plastic film mulching treatment, similar to soil multifunctionality. Only carbon (C) and phosphorus (P) cycling gene compositions were divided significantly into distinct mulching treatments to varying degrees. Similarly, intra- and inter-connected sub-networks associated with C and P cycling genes were more complex and stable than the sub-networks containing nitrogen cycling genes. Despite core functional genes being located in the middle of each network, they were rarely observed in the metagenomic assembly genomes. Subsequently, the dominant soil properties and microbial activity had greater effects on C cycling gene composition and network, which played essential roles in wheat growth regulation. Overall, wheat yield and biomass were affected differently by straw and plastic film mulching treatments, and were mainly regulated by C cycling gene network and soil multifunctionality, respectively. The results of the present study provide novel insights into wheat growth regulation by soil microbial functional profiles, with potential implications for sustainable crop production in mulching conservation agroecosystems.

Mycorrhizal mediation of soil carbon in permafrost regions depends on soil nutrient stoichiometry and physical protection

Mycorrhizal associations are considered as one of the key drivers for soil carbon (C) accumulation and stability. However, how mycorrhizal associations influence soil organic C (SOC) and its fractions (i.e., particulate organic C [POC] and mineral-associated organic C [MAOC]) remain unclear. In this study, we examined effects of plant mycorrhizal associations with arbuscular mycorrhiza (AM), ectomycorrhiza (ECM), and their mixture (Mixed) on SOC and its fractions as well as soil stoichiometric ratios across 800-km transect in permafrost regions. Our results showed that soil with only ECM-associated trees had significantly higher SOC and POC compared to only AM-associated tree species, while soil in Mixed plots with both AM- and ECM- associated trees tend to be somewhat in the middle. Using structural equation models, we found that mycorrhizal association significantly influenced SOC and its fraction (i.e., POC, MAOC) indirectly through soil stoichiometric ratios (C:N, C:P, and N:P). These results suggest that selecting ECM tree species, characterized by a "slow cycling" nutrient uptake strategy, can effectively enhance accumulation of SOC and its fractions in permafrost forest ecosystems. Our findings provide novel insights for quantitatively assessing the influence of mycorrhiza-associated tree species on the management of soil C pool and biogeochemical cycling.

Microbial resistance and resilience to drought and rewetting modulate soil N2O emissions with different fertilizers

Future climate models indicate an enhanced severity of regional drought and frequent rewetting events, which may cause cascading impacts on soil nitrogen cycle and nitrous oxide (N2O) emissions, but the underlying microbial mechanism remains largely unknown. Here we report an incubation study that examined the impacts of soil moisture status and nitrification inhibitor (DCD) on the N2O-producers and N2O-reducers following the application of urea and composted swine manure in an acid soil. The soil moisture treatments included 100 % water-holding capacity (WHC) (wetting, 35.3 % gravimetric soil water content), 40 % WHC (drought, 7 % gravimetric soil water content), and 40 % to 100 % WHC (rewetting). The results showed that N2O emissions were significantly decreased under drought conditions and were significantly increased after rewetting. The resistance of ammonia-oxidizing bacteria and nosZII, which was inhibited by urea or manure application, modulated N2O emissions under drought conditions. The resilience of the functional guilds modulated their dominant role in N2O emissions with rewetting. Ammonia-oxidizing bacteria, nirS-type denitrifying bacteria and nosZI showed significant resilience in response to rewetting. Significant negative relationships were observed between N2O emissions and nosZII clade under wetting condition and between N2O emissions and nosZI clade after rewetting. Our results highlighted the importance of microbial resistance and resilience in modulating N2O emissions, which help to better understand the dominant way of N2O emissions, and consequently make efficient mitigation strategies under the global climate change.

Green manuring relocates microbiomes in driving the soil functionality of nitrogen cycling to obtain preferable grain yields in thirty years

Fertilizers are widely used to produce more food, inevitably altering the diversity and composition of soil organisms. The role of soil biodiversity in controlling multiple ecosystem services remains unclear, especially after decades of fertilization. Here, we assess the contribution of the soil functionalities of carbon (C), nitrogen (N), and phosphorus (P) cycling to crop production and explore how soil organisms control these functionalities in a 33-year field fertilization experiment. The long-term application of green manure or cow manure produced wheat yields equivalent to those obtained with chemical N, with the former providing higher soil functions and allowing the functionality of N cycling (especially soil N mineralization and biological N fixation) to control wheat production. The keystone phylotypes within the global network rather than the overall microbial community dominated the soil multifunctionality and functionality of C, N, and P cycling across the soil profile (0-100 cm). We further confirmed that these keystone phylotypes consisted of many metabolic pathways of nutrient cycling and essential microbes involved in organic C mineralization, N2O release, and biological N fixation. The chemical N, green manure, and cow manure resulted in the highest abundances of amoB, nifH, and GH48 genes and Nitrosomonadaceae, Azospirillaceae, and Sphingomonadaceae within the keystone phylotypes, and these microbes were significantly and positively correlated with N2O release, N fixation, and organic C mineralization, respectively. Moreover, our results demonstrated that organic fertilization increased the effects of the network size and keystone phylotypes on the subsoil functions by facilitating the migration of soil microorganisms across the soil profiles and green manure with the highest migration rates. This study highlights the importance of the functionality of N cycling in controlling crop production and keystone phylotypes in regulating soil functions, and provides selectable fertilization strategies for maintaining crop production and soil functions across soil profiles in agricultural ecosystems.

Nitrogen starvation modulates the sensitivity of rhizobacterial community to drought stress in Stevia rebaudiana

Alterations in water regimes or nitrogen (N) availability lead to shifts in the assemblage of rhizosphere microbial community; however, how the rhizosphere microbiome response to concurrent changes in water and N availability remains largely unclear. Herein, we investigated the taxonomic and functional characteristics of rhizobacteria associated with stevia (Stevia rebaudiana Bertoni) under varying combinations of water and N levels. Community diversity and predicted functions of rhizobacteria were predominantly altered by drought stress, with N-starvation modulating these effects. Moreover, N fertilization simplified the ecological interactions within rhizobacterial communities and heightened the relative role of stochastic processes on community assembly. In terms of rhizobacterial composition, we observed both common and distinctive changes in drought-responsive bacterial taxa under different N conditions. Generally, the relative abundance of Proteobacteria and Bacteroidetes phyla were depleted by drought stress but the Actinobacteria phylum showed increases. The rhizobacterial responses to drought stress were influenced by N availability, where the positive response of δ-proteobacteria and the negative response of α- and γ-proteobacteria, along with Bacteroidetes, were further heightened under N starvation. By contrast, under N fertilization conditions, an amplified negative or positive response to drought were demonstrated in Firmicutes and Actinobacteria phyla, respectively. Further, the drought-responsive rhizobacteria were mostly phylogenetically similar, but this pattern was modulated under N-rich conditions. Overall, our findings indicate an N-dependent specific restructuring of rhizosphere bacteria under drought stress. These changes in the rhizosphere microbiome could contribute to enhancing plant stress tolerance.

Green manure incorporation enhanced soil labile phosphorus and fruit tree growth

Introduction

The incorporation of green manures substantially enhances the conversion of external phosphorus (P) fertilizers and soil-reserved P into forms readily available to plants. The study aims to evaluate the influence of green manure additions on soil phosphorus dynamics and citrus growth, considering different green manure species and initial soil phosphorus levels. Additionally, the research seeks to elucidate the microbiological mechanisms underlying the observed effects.

Methods

A citrus pot experiment was conducted under both P-surplus (1.50 g·P·kg-1) and P-deficient (0.17 g·P·kg-1) soils with incorporating legume (Leg), non-legume (Non-Leg) or no green manure residues (CK), and 18O-P labeled KH2PO4 (0.5 g, containing 80‰ δ18Op) was additionally introduced to trace the turnover characteristics of chemical P fertilizer mediated by soil microorganisms.

Results and discussion

In P-surplus soil, compared with the CK treatment, the Leg treatment significantly increased soil H2O-Pi (13.6%), NaHCO3-Po (8.9%), NaOH-Pi (9.5%) and NaOH-Po (30.0%) content. It also promoted rapid turnover of P sources into H2O-Pi and NaHCO3-Pi pools by enhancing the phoC (576.6%) gene abundance. In contrast, the Non-Leg treatment significantly augmented soil H2O-Pi (9.2%) and NaHCO3-Po (8.5%) content, facilitating the turnover of P sources into NaHCO3-Pi pools. Under P-deficient soil conditions, compared with the CK treatment, the Leg treatment notably raised soil H2O-Pi (150.0%), NaHCO3-Pi (66.3%), NaHCO3-Po (34.8%) and NaOH-Pi (59.0%) content, contributing to the transfer of P sources into NaHCO3-Pi and NaOH-Pi pools. This effect was achieved through elevated ALP (33.8%) and ACP (12.9%) activities and increased pqqC (48.1%), phoC (42.9%), phoD (21.7%), and bpp (27.4%) gene abundances. The Non-Leg treatment, on the other hand, led to significant increases in soil NaHCO3-Pi (299.0%) and NaHCO3-Po (132.6%) content, thereby facilitating the turnover of P sources into NaHCO3-Pi and NaOH-Pi pools, except for the phoC gene abundance. Both Leg and Non-Leg treatments significantly improved citrus growth (7.3-20.0%) and P uptake (15.4-42.1%) in P-deficient soil but yielded no substantial effects in P-surplus soil. In summary, introducing green manure crops, particularly legume green manure, emerges as a valuable approach to enhance soil P availability and foster fruit tree growth in orchard production.

Responses of C:N:P stoichiometric correlations among plants, soils and microorganisms to warming: A meta-analysis

Plants, soils and microorganisms play important roles in maintaining stable terrestrial stoichiometry. Studying how nutrient balances of these biotic and abiotic players vary across temperature gradients is important when predicting ecosystem changes on a warming planet. The respective responses of plant, soil and microbial stoichiometric ratios to warming have been observed, however, whether and how the stoichiometric correlations among the three components shift under warming has not been clearly understood and identified. In the present study, we have performed a meta-analysis based on 600 case studies from 74 sites or locations to clarify whether and how warming affects plant, soil and microbial stoichiometry, respectively, and their correlations. Our results indicated that: (1) globally, plants had higher C:N and C:P values compared to soil and microbial pools, but their N:P distributions were similar; (2) warming did not significantly alter plant, soil and microbial C:N and C:P values, but had a noticeable effect on plant N:P ratios. When ecosystem types, duration and magnitude of warming were taken into account, there was an inconsistent and even inverse warming response in terms of the direction and magnitude of changes in the C:N:P ratios occurring among plants, soils and microorganisms; (3) despite various warming responses of the stoichiometric ratios detected separately for plants, soils and microorganisms, the stoichiometric correlations among all three parts remained constant even under different warming scenarios. Our study highlighted the complexity of the effect of warming on the C:N:P stoichiometry, as well as the absence and importance of simultaneous measurements of stoichiometric ratios across different components of terrestrial ecosystems, which should be urgently strengthened in future studies.

Effectiveness of a 10-year continuous reduction of controlled-release nitrogen fertilizer on production, nitrogen loss and utilization of double-cropping rice

Considerable literature has demonstrated the advantage of controlled-release nitrogen (CRN) fertilizer in improving crop productivity. However, few researches have explored the long-term impacts of using CRN fertilizers as alternative to common urea on production and N utilization in double-cropping paddy. To address this gap, our study utilized a database derived from a 10-year field experiment from 2013 to 2022. During early and late rice seasons, compared to common urea (early rice, 150 kg hm-2; late rice, 180 kg hm-2), CRN fertilizer (150 kg hm-2; 180 kg hm-2) input significantly increased yield by 7.4 %, and 11.7 %, as well as N use efficiency (NUE) from 23.0 % and 24.6 % to 33.0 % and 37.5 %, respectively. CRN application significantly reduced N losses, evidenced by decrease in runoff (23.1 % and 19.4 %), leaching (12.7 % and 12.1 %), ammonia volatilization (28.9 % and 30.2 %), and N2O emissions (10.4 % and 16.1 %). A reduction of 10 % in CRN fertilizer input maintained yield. Compared with normal amount, reducing 10, 20, and 30 % CRN input increased NUE by 7.0-7.6 %, 7.3-7.4 %, and 11.6-12.6 %; reduced runoff loss by 16.1-17.9 %, 27.9-30.7 %, and 35.0-37.2 %; decreased leaching loss by 7.6-12.8 %, 18.1-22.6 %, and 26.5-31.4 %; decreased ammonia volatilization by 9.9-12.3 %, 16.3-22.7 %, and 23.2-29.3 %, and decreased N2O loss by 7.8-13.3 %, 12.8-32.8 %, and 20.3-36.9 %, respectively. Soils with CRN input showed higher total and inorganic N contents than the soils with common urea, and the content increased in parallel with CRN fertilizer input. Soil N content and N runoff loss were significantly related to yield and N uptake, and N runoff and leaching losses were significantly related to NUE. These results support the sustainable use of CRN fertilizers as a viable alternative to common urea, indicating that application rate of 135 and 162 kg N hm-2 of early and late rice, respectively, maintain yield and enhance N utilization in double-season paddy of southern China.

Biogeography and assembly processes of abundant and rare soil microbial taxa in the southern part of the Qilian Mountain National Park, China

Soil microorganisms play vital roles in regulating multiple ecosystem functions. Recent studies have revealed that the rare microbial taxa (with extremely low relative abundances, which are still largely ignored) are also crucial in maintaining the health and biodiversity of the soil and may respond differently to environmental pressure. However, little is known about the soil community structures of abundant and rare taxa and their assembly processes in different soil layers on the Qinghai-Tibet Plateau (QTP). The present study investigated the community structure and assembly processes of soil abundant and rare microbial taxa on the northeastern edge of the QTP. Soil microbial abundance was defined by abundant taxa, whereas rare taxa contributed to soil microbial diversity. The results of null model show that the stochastic process ruled the assembly processes of all sub-communities. Dispersal limitation contributed more to the assembly of abundant microbial taxa in the different soil layers. In contrast, drift played a more critical role in the assembly processes of the rare microbial taxa. In addition, in contrast to previous studies, the abundant taxa played more important roles in co-occurrence networks, most likely because of the heterogeneity of the soil, the sparsity of amplicon sequencing, the sampling strategy, and the limited samples in the present study. The results of this study improve our understanding of soil microbiome assemblies on the QTP and highlight the role of abundant taxa in sustaining the stability of microbial co-occurrence networks in different soil layers.

Ecological strategies of bacterial communities in prehistoric stone wall paintings across weathering gradients: A case study from the Borana zone in southern Ethiopia

Rock art paintings represent fragile ecosystems supporting complex microbial communities tuned to the lithic substrate and climatic conditions. The composition and activity of these microbial communities associated with different weathering patterns affecting rock art sites remain unexplored. This study aimed to explore how bacterial communities adapt their ecological strategies based on substrate weathering, while also examining the role of their metabolic pathways in either biodeterioration or bioprotection of the underlying stone. SEM-EDS investigations coupled with 16S rRNA gene sequencing and PICRUSt2 analysis were applied on different weathered surfaces that affect southern Ethiopian rock paintings to investigate the relationships between the current stone microbiome and weathering patterns. The findings revealed that samples experiencing low and high weathering reached a climax stage characterized by stable microenvironments and limited resources. This condition favored K-strategist microorganisms, leading to reduced α-biodiversity and a community with a positive or neutral impact on the substrate. In contrast, moderately-weathered samples displayed diverse microhabitats, resulting in the prevalence of r-strategist bacteria, increased α-biodiversity, and the presence of specialist microorganisms. Moreover, the bacterial communities in moderately-weathered samples demonstrated the highest potential for carbon fixation, stress responses, and complete nitrogen and sulfur cycles. This bacterial community also showed the potential to negatively impact the underlying substrate. This research provided valuable insights into the little-understood ecology of bacterial communities inhabiting deteriorated surfaces, shedding light on the potential role of these microorganisms in the sustainable conservation of rock art.

Community structure and niche differentiation of endosphere bacterial microbiome in Camellia oleifera

IMPORTANCE

Microorganisms inhabited various tissues of plants and play a key role in promoting plant growth, nutritional absorption, and resistance. Our research indicates that the diversity of Camellia oleifera endophytic bacterial communities is highly dependent on the plant compartment. Proteobacteria, Acidobacteria, Actinobacteria, Bacteroidetes, Firmicutes, Chloroflexi, and Verrucomicrobia are dominant bacteria phyla. The tissues of Camellia oleifera contain various bacteria with nitrogen fixation potential, host life promotion, and plant defense. This study provides a scientific theoretical basis for an in-depth discussion of plant-endosphere microbial interaction and better exploration of benign interaction of beneficial microorganisms and plants.

Stimulation of primed carbon under climate change corresponds with phosphorus mineralization in the rhizosphere of soybean

Elevated CO2 and temperature likely alter photosynthetic carbon inputs to soils, which may stimulate soil microbial activity to accelerate the decomposition of soil organic carbon (SOC), liberating more phosphorus (P) into the soil solution. However, this hypothesis on the association of SOC decomposition and P transformation in the plant rhizosphere requires robust soil biochemical evidence, which is critical to nutrient management for the mitigation of soil quality against climate change. This study investigated the microbial functional genes relevant to P mineralization together with priming processes of SOC in the rhizosphere of soybean grown under climate change. Soybean plants were grown under elevated CO2 (eCO2, 700 ppm) combined with warming (+ 2 °C above ambient temperature) in open-top chambers. Photosynthetic carbon flow in the plant-soil continuum was traced with 13CO2 labeling. The eCO2 plus warming treatment increased the primed carbon (C) by 43 % but decreased the NaHCO3-extratable organic P by 33 %. Furthermore, NaHCO3-Po was negatively correlated with phosphatase activity and microbial biomass C. Elevated CO2 increased the abundances of C degradation genes, such as abfA and ManB, and P mineralization genes, such as gcd, phoC and phnK. The results suggested that increased photosynthetic carbon inputs to the rhizosphere of plants under eCO2 plus warming stimulated the microbial population and metabolic functions of both SOC and organic P mineralization. There is a positive relationship between the rhizosphere priming effect and P mineralization. The response of microorganisms to plant-C flow is decisive for coupled C and P cycles, which are likely accelerated under climate change.

Microbial fertilizer regulates C:N:P stoichiometry and alleviates phosphorus limitation in flue-cured tobacco planting soil

Fertilization can be optimized and managed during the flue-cured tobacco growing period by studying the response of soil and microbial biomass stoichiometric characteristics to fertilization. In this study, we investigated the effect of compound fertilizers combined with microbial fertilizer treatments on the stoichiometric characteristics of the rhizosphere soil and the limitations of microbial resources during the flue-cured tobacco growing period. The results indicated that soil and microbial C:N:P varied greatly with the growing period. The effect of sampling time was usually greater than that of fertilization treatment, and microbial C:N:P did not vary with the soil resource stoichiometric ratio. The microbial metabolism of the tobacco-growing soil was limited by phosphorus after extending the growing period, and phosphorus limitation gradually increased from the root extension to the maturation periods but decreased at harvest. The rhizosphere soil microbial nitrogen and phosphorus limitations were mainly affected by soil water content, soil pH, microbial biomass carbon, and the ratio of microbial biomass carbon to microbial biomass phosphorus. Applying microbial fertilizer reduced phosphorus limitation. Therefore, applying microbial fertilizer regulated the limitation of microbial resources by affecting the soil and microbial biomass C:N:P in flue-cured tobacco rhizosphere soils.

Biochar amendments combined with organic fertilizer improve maize productivity and mitigate nutrient loss by regulating the C-N-P stoichiometry of soil, microbiome, and enzymes

Coupled amendments of biochar and organic fertilizers may be one of the effective practice to ensure high cropland productivity and resource use efficiency, but there is little field-based evidence for this. Herein, we employed a eight-years (2014-2021) field experiment to explore the effectiveness of biochar and organic fertilizer amendments on crop productivity and nutrient runoff losses, as well as to further explored their relationships with the carbon:nitrogen:phosphorus (C:N:P) stoichiometry of soil, microbiome, and enzymes. Experiment treatments include No fertilizer (CK), chemical-only fertilizer (CF), CF + biochar (CF + B), 20% chemical N was replaced by organic fertilizer (OF), and OF + biochar (OF + B). Compared with the CF, the CF + B, OF, and OF + B treatments increased average yield by 11.5%, 13.2%, and 32%, average N use efficiency by 37.2%, 58.6%, and 81.4%, average P use efficiency by 44.8%, 55.1%, and 118.6%, average plant N uptake by 19.7%, 35.6%, and 44.3%, as well as average plant P uptake by 18.4%, 23.1%, and 44.3%, respectively (p ≤ 0.05). Compared with the CF, the CF + B, OF, and OF + B decreased average average total N losses by 65.2%, 97.4%, and 241.2%, and average total P losses by 52.9%, 77.1%, and 119.7%, respectively (p ≤ 0.05). Organic-amended treatments (CF + B, OF, and OF + B) significantly changed soil total and available C, N, and P content, soil microbial C, N, and P content, as well as the potential activities of soil C-, N-, and P-acquiring enzymes. Plant P uptake and P-acquiring enzyme activity were the main drivers of maize yield, which was influenced by the contents and stoichiometric ratios of soil available C, N, and P. These findings suggest that organic fertilizer applications combined with biochar have the potential to maintain high crop yields while reducing nutrient losses by regulating the stoichiometric balance of soil available C and nutrients.

Functional Potential of Soil Microbial Communities and Their Subcommunities Varies with Tree Mycorrhizal Type and Tree Diversity

Soil microbial communities play crucial roles in the earth's biogeochemical cycles. Yet, their genomic potential for nutrient cycling in association with tree mycorrhizal type and tree-tree interactions remained unclear, especially in diverse tree communities. Here, we studied the genomic potential of soil fungi and bacteria with arbuscular (AM) and ectomycorrhizal (EcM) conspecific tree species pairs (TSPs) at three tree diversity levels in a subtropical tree diversity experiment (BEF-China). The soil fungi and bacteria of the TSPs' interaction zone were characterized by amplicon sequencing, and their subcommunities were determined using a microbial interkingdom co-occurrence network approach. Their potential genomic functions were predicted with regard to the three major nutrients carbon (C), nitrogen (N), and phosphorus (P) and their combinations. We found the microbial subcommunities that were significantly responding to different soil characteristics. The tree mycorrhizal type significantly influenced the functional composition of these co-occurring subcommunities in monospecific stands and two-tree-species mixtures but not in mixtures with more than three tree species (here multi-tree-species mixtures). Differentiation of subcommunities was driven by differentially abundant taxa producing different sets of nutrient cycling enzymes across the tree diversity levels, predominantly enzymes of the P (n = 11 and 16) cycles, followed by the N (n = 9) and C (n = 9) cycles, in monospecific stands and two-tree-species mixtures, respectively. Fungi of the Agaricomycetes, Sordariomycetes, Eurotiomycetes, and Leotiomycetes and bacteria of the Verrucomicrobia, Acidobacteria, Alphaproteobacteria, and Actinobacteria were the major differential contributors (48% to 62%) to the nutrient cycling functional abundances of soil microbial communities across tree diversity levels. Our study demonstrated the versatility and significance of microbial subcommunities in different soil nutrient cycling processes of forest ecosystems. IMPORTANCE Loss of multifunctional microbial communities can negatively affect ecosystem services, especially forest soil nutrient cycling. Therefore, exploration of the genomic potential of soil microbial communities, particularly their constituting subcommunities and taxa for nutrient cycling, is vital to get an in-depth mechanistic understanding for better management of forest soil ecosystems. This study revealed soil microbes with rich nutrient cycling potential, organized in subcommunities that are functionally resilient and abundant. Such microbial communities mainly found in multi-tree-species mixtures associated with different mycorrhizal partners can foster soil microbiome stability. A stable and functionally rich soil microbiome is involved in the cycling of nutrients, such as carbon, nitrogen, and phosphorus, and their combinations could have positive effects on ecosystem functioning, including increased forest productivity. The new findings could be highly relevant for afforestation and reforestation regimes, notably in the face of growing deforestation and global warming scenarios.

The effectiveness of eight-years phosphorus reducing inputs on double cropping paddy: Insights into productivity and soil-plant phosphorus trade-off

Abundant evidence has demonstrated the feasibility of reducing phosphorus (P) input to face diminishing phosphate rock resources and deteriorating environmental quality in double-cropping paddy. However, the sustainability of reduced P input in the context of maintaining productivity and P efficient utilization is not yet clear. Herein, an 8-year (2013-2021) field-based database was built to explore the effects of reduced P input on rice productivity and the soil-plant P trade-off in double-cropping paddy. In the early and late rice seasons, compared with conventional P fertilization (early rice, 90 kg hm^-2; late rice, 60 kg hm^-2), the average yield of reduced 10 % P treatment increased by 4.3 % and 2.1 %, respectively; reduced 10-30 % P treatments increased average P use efficiency by 17.1-18.4 % and 14.0-17.2 %, decreased average total P runoff loss by 14.9-33.2 % and 20.8-36.4 %, and decreased average total P leaching loss by 18.5-49.0 % and 24.0-46.1 %, respectively. Compared with conventional fertilization, reduced P fertilizer input by 10 % significantly increased the content of the soil labile-P fraction while reducing that of the soil stable-P fraction. Soil ligand-P and exchangeable-P content decreased with the gradient reduction of P fertilizer input (10-30 %). The main predictors of the change in rice yield and plant P uptake were soil ligand-P and exchangeable-P content, respectively. The dominant predictor of both the P runoff loss and the P activation coefficient was the inorganic P content extracted by NaHCO₃. These findings suggest that reduced P input by 10 % could maintain rice productivity and P use efficiency in the double-cropping paddy, and the transformations between soil P components and increases in P bioavailability may be the key drivers maintaining rice productivity and P utilization under the context of reduced P loading.

Effects of warming and isolation from precipitation on the soil carbon, nitrogen, and phosphorus, and their stoichiometries in an alpine meadow in the Qinghai–Tibet Plateau: A greenhouse warming study

Introduction

In the Qinghai–Tibet Plateau (QTP), alpine meadows are among the most noticeable reflection of global climate change. However, effects of global warming on soils hosting alpine meadows in the QTP, such as reduced moisture because of low precipitation, remain unclear.

Methods

Here, the soil moisture content (SMC), pH, dissolved organic carbon (DOC), ammonium nitrogen (NH4+–N), nitrate nitrogen (NO3−–N) and available phosphorus (AP) contents in the QTP were analyzed. The changes in and stoichiometries of total carbon, nitrogen, and phosphorus (TC, TN, and TP), microbial biomass carbon, nitrogen, and phosphorus (MBC, MBN, and MBP), β-1,4-glucosidase (BG), β-1,4-N-acetylglucoaminosidase (NAG), leucine aminopeptidase (LAP), and acid phosphatase (ACP) in the 0–30 cm layer of soils associated with warming in a greenhouse in the QTP from 2015 to 2020 were characterized.

Results

We found that warming in the greenhouse significantly decreased the SMC, NO3−–N, MBC, MBN, MBP, BG, LAP, ACP, and enzymatic C:N ratio. The warming increased the DOC, NH4+–N, AP, MBC:MBN, and enzymatic N:P ratios noticeably. The pH, TC, TN, TP, C:N, C:P, N:P, MBC:MBP, MBN:MBP, and enzymatic C:P ratios were minimally affected.

Conclusion

The results showed that warming and isolation from precipitation promoted mineralization of N and P in the soil but did not significantly alter the cycling of elements in soils in an alpine meadow.

Effects of microplastics on nitrogen and phosphorus cycles and microbial communities in sediments

Sediments are the long-term sinks of microplastics (MPs) and nutrients in freshwater ecosystems. Therefore, understanding the effect of MPs on sediment nutrients is crucial. However, few studies have discussed the effects of MPs on nitrogen and phosphorus cycles in freshwater sediments. Herein, 0.5% (w/w) polyvinyl chloride (PVC), polylactic acid (PLA), and polypropylene (PP) MPs were added to freshwater sediments to evaluate their effects on microbial communities and nitrogen and phosphorus release. The potential biochemical functions of the bacterial communities in the sediments were predicted and assessed via 16S rRNA gene sequencing. The results showed that MPs significantly affected the microbial community composition and nutrient cycling in the sediments. PVC and PP MPs can promote microbial nitrification and nitrite oxidation, while PP can significantly promote alkaline phosphatase (ALP) activity and the abundance of the phosphorus-regulation (phoR) gene. PLA MPs had the potential to promote the abundance of microbial phosphorus transporter (ugpB), nitrogen fixation (nifD, nifH, and nifX), and denitrification (nirS, napA, and norB) genes and inhibit nitrification, resulting in massive accumulation and release of ammonia nitrogen. Although PLA MPs inhibited the activity of ALP and the abundance of the organophosphorus mineralization (phoD) gene, it could enhance dissimilatory iron and sulfite reduction, which may promote the release of sedimentary phosphorus. Our findings may help understand the mechanisms of nitrogen and phosphorus cycles and microbial communities driven by MPs in sediments and provide a basis for future assessments of the environmental behavior of MPs in freshwater ecosystems.

Effect of grazing exclusion on emission of greenhouse gases and soil organic carbon turnover in alpine shrub meadow

Grazing exclusion (GE) is a management option used widely to restore degraded grassland and improve grassland ecosystems. However, the impacts of GE on soil properties and greenhouse gas emissions of alpine shrub meadow are still unclear, especially long-term GE of more than ten years. To fill part of this gap, we examined the effects of long-term GE of alpine shrub meadow on soil nutrients, soil properties, greenhouse gas emissions (CO₂ and CH₄) and soil organic carbon (SOC) turnover. When compared to grazed grassland (GG), long-term GE resulted in: 1) greater SOC, nitrogen (N), and phosphorous (P) content, especially in the 20-30 cm soil layer; 2) greater soil C:N, C:P and N:P ratios in the 20-30 cm depth; 3) greater soil CO₂, but lesser CH₄ emission during the growing season; and 4) much faster SOC turnover time (0-30 cm). GE of more than ten years can increase grassland C reserves and improve the C sequestration capacity of the ecosystem. Results from this study can have important implications in developing future grassland management policies on soil nutrient balances, restoration of degraded grassland and controlling shrub expansion.

Effects of Bradyrhizobium Co-Inoculated with Bacillus and Paenibacillus on the Structure and Functional Genes of Soybean Rhizobacteria Community

Plant growth-promoting rhizobacteria (PGPR) are widely used to improve soil nutrients and promote plant growth and health. However, the growth-promoting effect of a single PGPR on plants is limited. Here, we evaluated the effect of applying rhizobium Bradyrhizobium japonicum 5038 (R5038) and two PGPR strains, Bacillus aryabhattai MB35-5 (BA) and Paenibacillus mucilaginosus 3016 (PM), alone or in different combinations on the soil properties and rhizosphere bacterial community composition of soybean (Glycine max). Additionally, metagenomic sequencing was performed to elucidate the profile of functional genes. Inoculation with compound microbial inoculant containing R5038 and BA (RB) significantly improved nodule nitrogenase activity and increased soil nitrogen content, and urease activity increased the abundance of the nitrogen cycle genes and Betaproteobacteria and Chitinophagia in the rhizosphere. In the treatment of inoculant-containing R5038 and PM (RP), significant changes were found for the abundance of Deltaproteobacteria and Gemmatimonadetes and the phosphorus cycle genes, and soil available phosphorus and phosphatase activity were increased. The RBP inoculants composed of three strains (R5038, BA and PM) significantly affected soybean biomass and the N and P contents of the rhizosphere. Compared with RB and RP, RBP consistently increased soybean nitrogen content, and dry weight. Overall, these results showed that several PGPR with different functions could be combined into composite bacterial inoculants, which coordinately modulate the rhizosphere microbial community structure and improve soybean growth.

Biocrusts increase the resistance to warming-induced increases in topsoil P pools

Ongoing global warming and alterations in rainfall patterns driven by climate change are known to have large impacts on biogeochemical cycles, particularly on drylands. In addition, the global increase in atmospheric nitrogen (N) deposition can destabilize primary productivity in terrestrial ecosystems, and phosphorus (P) may become the most limiting nutrient in many terrestrial ecosystems. However, the impacts of climate change on soil P pools in drylands remain poorly understood. Furthermore, it is unknown whether biocrusts, a major biotic component of drylands worldwide, modulate such impacts.Here we used two long-term (8-10 years) experiments conducted in Central (Aranjuez) and SE (Sorbas) Spain to test how a ~2.5°C warming, a ~30% rainfall reduction and biocrust cover affected topsoil (0-1 cm) P pools (non-occluded P, organic P, calcium bound P, occluded P and total P).Warming significantly increased most P pools-except occluded P-in Aranjuez, whereas only augmented non-occluded P in Sorbas. The rainfall reduction treatment had no effect on the soil P pools at any experimental site. Biocrusts increased most soil P pools and conferred resistance to simulated warming for major P pools at both sites, and to rainfall reduction for non-occluded and occluded P in Aranjuez. Synthesis. Our findings provide novel insights on the responses of soil P pools to warming and rainfall reduction, and highlight the importance of biocrusts as modulators of these responses in dryland ecosystems. Our results suggest that the observed negative impacts of warming on dryland biocrust communities will decrease their capacity to buffer changes in topsoil P driven by climate change.

The effectiveness of reed-biochar in mitigating phosphorus losses and enhancing microbially-driven phosphorus dynamics in paddy soil

Biochar is a promising novel material for mitigating phosphorus (P) loss and enhancing P retention in chemical-amended agricultural soils. However, the optimal application rate for aforesaid effectiveness and potential drivers of the process are not well understood. Herein, a column-based pot experiment was carried out to investigate how and to what extent reed-biochar is effective in positively triggering P loss and availability in paddy soils treated by chemical fertilizer. Compared with chemical-only treatment, the accumulated leakage of total P, dissoluble P, and particulate P in chemical fertilizer coupled with 1-4% reed-biochar treatment decreased by 5.3-13.3%, 8.3-10.4%, and 3.0-15.4%, respectively. The accumulated leakage of total P and dissoluble P in 6-8% rate treatments was increased by 5.6-7.5% and 18.3-32.9%, respectively. Increasing reed-biochar rate from 1% to 8% caused an enhancement in soil total P and available P content and P activation coefficient, and the 4% rate achieved a similar effectiveness to the higher rate. Reed-biochar application increased the abundance and diversty of soil phoD-harboring microbes (P < 0.05), while the increment had little to do with the application rate. Soil phoD-harboring community composition and total C content were the main predictors of the P leaching losses, and meanwhile, the total C content was the dominated predictor of soil P retention and availability. These results suggest that adding 1-4% reed-biochar was more beneficial to mitigate paddy P loss and to enhance soil P availability. This study highlights the importance of understanding how microbial populations mediate P transformation to decipher the biochar-driven improvement of soil P utilization.

Elemental Stoichiometry (C, N, P) of Soil in the Wetland Critical Zone of Dongting Lake, China: Understanding Soil C, N and P Status at Greater Depth

Earth’s critical zone is defined as a plant–soil–water system, which covers a wide area and has a large vertical thickness, but the soil elemental stoichiometry characteristics of the critical zone at different depths are still unclear. In this study, the spatial distribution of soil carbon (C), nitrogen (N) and phosphorus (P) in the critical zone of a typical wetland in Dongting Lake, China, and their ecological chemometric characteristics were analyzed. The results indicated that: (1) the average C, N and P contents were 18.05, 0.86 and 0.52 g/kg, respectively, with a decreasing trend from the surface to the deeper layers. The soil is relatively rich in C and P, while N is the main element limiting plant growth and development. (2) The mean values of soil C/N, N/P and C/P were 21.1, 1.7 and 35.4 respectively, with the C/N ratio and C/P ratio showing a trend of increasing and then decreasing in the vertical direction and reaching a maximum at a depth of 2–5 m below ground. (3) According to the correlation results, C, N and P in soils are coupled and influenced by each other (p < 0.001), and pH, infiltration coefficient and human activities are closely related to the spatial distribution of C, N and P. (4) Stable Redfield ratios (1:1.6:35.4) may exist in lake wetland soils, and future studies should be conducted for complete systems of the same type of wetlands. The results of the study will provide a theoretical basis for the sustainable development and scientific management of lake wetlands.

Carbon-Phosphorus Coupling Governs Microbial Effects on Nutrient Acquisition Strategies by Four Crops

Plants adjust root morphological and/or exudation traits in response to phosphorus (P) mobilization mediated by microorganisms. We hypothesized that straw application coupled with P fertilization would influence microbial P and then root nutrient-acquisition strategies related to crop growth. Root morphological (length and average diameter) and exudation traits (acid phosphatase and carboxylates) of Brassica chinensis, Solanum lycopersicum, Lactuca sativa, and Vigna unguiculata in response to microbial P dynamics were characterized in no-P and P-fertilized soil with/without straw addition. Straw addition increased the growth of fungi and bacteria, stimulating microbial P immobilization at day 24. The high microbial abundance was associated with four tested crops having short roots in straw-amended compared with no-straw soil at day 24. In straw-amended soil, B. chinensis and S. lycopersicum shifted toward root P-acquisition strategies based on fast elongation and strong carboxylate exudation from days 24 to 40. Such effective root P-acquisition strategies together with microbial P release increased shoot P content in S. lycopersicum in straw-amended compared with those without straw at day 40. Conversely, L. sativa and V. unguiculata produced short roots in response to the stable (or even increased) microbial P after straw addition till day 40. In straw-amended soil, high P application stimulated root elongation and carboxylate exudation in L. sativa and V. unguiculata, whereas carboxylate exudation by S. lycopersicum was decreased compared with the straw-amended but non-fertilized treatment at day 40. In summary, root P-acquisition strategies in response to microbial P differed among the tested crop species. Phosphorus fertilization needs to be highlighted when returning straw to enhance P-use efficiency in vegetable cropping systems.

Spatial Patterns and Composition Traits of Soil Microbial Nitrogen-Metabolism Genes in the Robinia pseudoacacia Forests at a Regional Scale

Microbial-driven processes related to the nitrogen-metabolism (N-metabolism) in soil are critical for ecosystem functioning and stability. There are spatial patterns of microbial-mediated nitrogen processes, but we still lack an overview of the soil N-metabolism genes of single nitrogen-fixing tree species pure forests at a regional scale. Here, we investigated the spatial variation and drivers of microbial N-metabolism genes in the rhizosphere soil of Robinia pseudoacacia on the Loess Plateau by metagenomic technology. We found that the distance-decay of soil N functional gene similarities in Robinia pseudoacacia forests on the Loess Plateau spanning a geographic distance of 230 km was significant (p < 0.001). The gene composition and co-occurrence patterns in the process of soil microbial N-metabolism were very different, and they were mainly driven by soil pH and MAP (mean annual precipitation). The proportion of positive links and edges co-occurrence networks between N functional genes increased with increasing pH, suggesting that increasing pH promoted connections between functional genes. The relative frequencies of N-metabolism pathways were consistent on the Loess Plateau, the abundance of ammonia assimilation pathway was highest, and the abundance of the nitrogen fixation pathway was the lowest; only the abundance of the nitrogen fixation pathway was not significantly different. The bacterial and archaeal communities involved in soil nitrogen metabolism were significantly different. Structural equation modeling showed that decreases in soil pH and MAP mainly affected the increase in nitrogen functional gene abundance through an increase in the diversity of N-metabolism microorganisms. In conclusion, this study provides a baseline for biogeographic studies of soil microbe functional genes.

Distinct Elevational Patterns and Their Linkages of Soil Bacteria and Plant Community in An Alpine Meadow of the Qinghai-Tibetan Plateau

Soil microbes play important roles in determining plant community composition and terrestrial ecosystem functions, as well as the direction and extent of terrestrial ecosystem feedback to environmental changes. Understanding the distribution patterns of plant and soil microbiota along elevation gradients is necessary to shed light on important ecosystem functions. In this study, soil bacteria along an elevation gradient in an alpine meadow ecosystem of the Qinghai−Tibetan Plateau were investigated using Illumina sequencing and GeoChip technologies. The community structure of the soil bacteria and plants presented a continuous trend along the elevation gradient, and their alpha diversity displayed different distribution patterns; however, there were no linkages between them. Beta diversity of the soil bacteria and plants was significantly influenced by elevational distance changes (p < 0.05). Functional gene categories involved in nitrogen and phosphorus cycling had faster changes than those involved in carbon degradation, and functional genes involved in labile carbon degradation also had faster variations than those involved in recalcitrant carbon degradation with elevational changes. According to Pearson’s correlation, partial Mantel test analysis, and canonical correspondence analysis, soil pH and mean annual precipitation were important environmental variables in influencing soil bacterial diversity. Soil bacterial diversity and plant diversity had different distribution patterns along the elevation gradient.

Divergent responses of soil microbial functional groups to long-term high nitrogen presence in the tropical forests

A massive rise in atmospheric nitrogen deposition (ND) has threatened ecosystem health through accelerating soil nitrogen (N) cycling rates. While soil microbes serve a crucial function in soil N transformation, it remains poorly understood on how excess ND affects microbial functional populations regulating soil N transformation in tropical forests. To address this gap, we conducted 13-year N (as NH₄NO₃) addition experiments in one N-rich tropical primary forest (PF) and two N-poor tropical reforested forests (rehabilitated and disturbed) in South China. Based on our data, 13-year N introduction markedly enhanced soil N₂O generation in all forests, regardless of soil N status, but microbial functional groups showed divergent responses to excess N addition among the studied forests. In the PF, long-term N introduction markedly decreased presence of bacterial 16S rRNA gene, nitrifier (amoA) and denitrifier genes (nirK, nirS and nosZ) and bacteria/fungi ratio, which could be attributed to the decreases in soil pH, dissolved organic carbon to N ratio and understory plant richness. In the two reforested forests, however, long-term N introduction generally did neither alter soil properties nor the abundance of most microbial groups. We further found that the elevated N₂O generation was related to the increased soil N availability and decreased nosZ abundance, and the PF has the highest N₂O generation than the other two forests. Overall, our data indicates that the baseline soil N status may dominate response of microbial functional groups to ND in tropical forests, and N-rich forests are more responsive to excess N inputs, compared to those with low-N status. Forests with high soil N status can produce more N₂O than those with low-N status. With the spread of elevated ND from temperate to tropical zones, tropical forests should merit more attention because ecosystem N saturation may be common and high N₂O emission will occur.

Linkages of nitrogen-cycling microbial resistance and resilience to soil nutrient stoichiometry under dry-rewetting cycles with different fertilizations and temperatures in a vegetable field

Multiple dry-rewetting (DRW) cycles occur in intensively managed vegetable fields due to frequent tillage and irrigation. Soil nitrogen (N) cycling depends on the resistance and resilience of related microbial populations to DRW cycles, which could be closely related to soil nutrient status. However, the linkage of N-cycling microbial resistance and resilience and soil nutrient stoichiometry remains unknown in vegetable field. Here, we established four fertilization treatments in a four-year greenhouse vegetable field: no N fertilization, synthesized N fertilization, substituting 50% of chemical N with organic fertilizer or biofertilizer. Then, we set up an 85-day DRW-cycling incubation at 15, 25 and 35 °C including a 55-day fluctuating moisture for microbial resistance and then a 30-day constant moisture for microbial resilience. The results showed that microbial resistance was high (resistance index = 0.87- 0.99) in response to DRW cycles, but microbial resilience was generally low (resilience index = -0.36- 0.76), especially in 50% organic substitution or 15 °C. N-cycling microbes showed an important trade-off between their resistance and resilience to DRW cycles. Furthermore, most treatments showed microbial carbon limitation and N abundance during DRW cycles and recovered gradually to the undisturbed state. Microbial resistance was significantly related to the soil nutrient stoichiometry of carbon, N and phosphorus, while microbial resilience was mainly correlated with carbon-related indicators. In conclusion, N-cycling microbes presented good stability with oligotrophic strategy to frequent DRW cycles, which was linked to not only the historical legacy effect of DRW cycles but also soil nutrient stoichiometry in the vegetable field.

Understanding how reed-biochar application mitigates nitrogen losses in paddy soil: Insight into microbially-driven nitrogen dynamics

Biochar application to chemical-amended paddy soils has been proposed as a potential strategy to enhance nitrogen (N) retention and nitrogen use efficiency (NUE) by crops. However, optimal concentrations for these enhancements and the potential drivers are not well understood. Herein, a column-based pot experiment was carried out to investigate the impacts of reed-biochar application rate on N losses and dynamics in paddy soils treated by chemical fertilizer, and particularly, to explore the dominant factors of the processes. The addition of 2-4% reed-biochar had the most significant effects on mitigating N loss by leaching. Reed-biochar amendment increased soil total N and mineral N (NH₄⁺-N and NO₃^--N) content, and denitrifying gene abundance, and the increments of those variables were positively related to the application rate. Soil treated with 1-4% reed-biochar at harvest period showed higher gene abundances of ammonia-oxidizing and dissimilatory nitrate reduction to ammonium (DNRA) and higher activity of β-1,4-N-acetyl-glucosaminidase (NAG) and leucine aminopeptidase compared with the 4-8% application rate. The amoA-AOA gene abundance, NAG activity, and total carbon (C) content were the main predictors of total N and mineral N accumulated leakage. Total C content was the main predictor of soil total N and mineral N content, followed by the pH and NAG activity. These results suggest that adding 2-4% reed-biochar was more beneficial to mitigate N loss and thus enhance soil N storage and availability. This study highlights the importance of understanding how microbial populations mediate N transformation to decipher biochar-driven NUE enhancement in paddy soils.

Tea plantation intercropping green manure enhances soil functional microbial abundance and multifunctionality resistance to drying-rewetting cycles

Climate change leads to more serious drying-rewetting alternation disturbance, which furtherly affects soil ecosystem function and agriculture production. Intercropping green manure, as an ancient agricultural practice, can improve the physical, chemical, and biological fertility of soil in tea plantation. However, the effects of intercropping green manure on soil multifunctional resistance to drying-rewetting disturbance in tea plantation has not been reported. In this study, the effects of different green manure practices over four years (tea plant monoculture, tea plant and soybean intercropping, tea plant and soybean + milk vetch intercropping) on soil multifunctionality resistance to drying-rewetting cycles, and the pivotal influencing factors were investigated. We used quantitative PCR array and analysis of multiple enzyme activities to characterize the abundance of functional genes and ecosystem multifunctionality, respectively. Compared with tea plantation monoculture, tea plant intercropping soybean and soybean + milk vetch significantly increased multifunctionality resistance by 12.07% and 25.86%, respectively. Random forest analysis indicated that rather than the diversity, the abundance of functional genes was the major drive of multifunctionality resistance. The structure equation model further proved that tea plantation intercropping green manure could improve the abundance of C cycling related functional genes mediated by soil properties, and ultimately increased multifunctionality resistance to drying-rewetting disturbance. Therefore, tea plantation intercropping green manure is an effective approach to maintain the multifunctionality resistance, which is conducive to maintain the soil nutrient supply capacity and tea production under the disturbance of drying-rewetting alternation.

Deciphering the diversity and functions of plastisphere bacterial communities in plastic-mulching croplands of subtropical China

Considering the inhomogeneity of plastisphere and surrounding soil, it is plausible that the microbial community colonizing it also varies, affecting soil services and sustainability. Herein, we analyzed the soil and film residue from fifty-five plastic-mulching croplands in the subtropical areas of China. Based on the outcomes of this analysis, we explored the diversity and functions of the associated bacterial communities. Alpha-diversity and phylogenetic diversity of the plastisphere bacterial community was significantly lower than the surrounding soil. The average net relatedness and net nearest taxa indices of samples were less than zero. Four phyla and twenty genera were enriched in the plastisphere compared to the surrounding soil. Ecological networks of the plastisphere community showed multiple nodes, but fewer interactions, and the members of Bradyrhizobium, Rhodospirillaceae, and Bacillus were indicated as the hub species. Predicted pathways related to human disease, as well as the metabolisms of cofactors, vitamins, amino acids, and xenobiotic biodegradation, were reinforced in the plastisphere, and meanwhile, accompanied by an increase in abundance of genes related to carbon, nitrogen, and phosphorus cycles. These results demonstrated the diversity and functions of the plastisphere microbiome and highlighted the necessity for exploring the ecological and health risks of plastic residue in croplands.

Deciphering Rhizosphere Microbiome Assembly of Castanea henryi in Plantation and Natural Forest

Based on the importance and sensitivity of microbial communities to changes in the forest ecosystem, soil microorganisms can be used to indicate the health of the forest system. The metagenome sequencing was used to analyze the changes of microbial communities between natural and plantation Castanea henryi forests for understanding the effect of forest types on soil microbial communities. Our result showed the soil microbial diversity and richness were higher in the natural forests than in the plantation. Proteobacteria, Actinobacteria, and Acidobacteria are the dominant categories in the C. henryi rhizosphere, and Proteobacteria and Actinobacteria were significantly enriched in the natural forest while Acidobacteria was significantly enriched in the plantation. Meanwhile, the functional gene diversity and the abundance of functions in the natural forest were higher than that of the plantation. Furthermore, we found that the microbial network in the natural forests had more complex than in the plantation. We also emphasized the low-abundance taxa may play an important role in the network structure. These results clearly showed that microbial communities, in response to different forest types, provide valuable information to manipulate microbiomes to improve soil conditions of plantation.

Contrasting effects of carbon source recalcitrance on soil phosphorus availability and communities of phosphorus solubilizing microorganisms

Carbon (C) additions to soil interact through chemical and microbiological processes to cause changes in soil phosphorus (P) availability. However, the response of soil P transformations and relevant microbial communities to C additions having different degrees of recalcitrance remains uncertain. We studied the effects of glucose, hemicellulose and lignin addition on soil P availability, P transformation processes and relevant microbial activity and communities in a P-deficient flooded soil. Lignin significantly increased soil available P concentrations, which was attributed to chemical release of inorganic P and increased alkaline phosphatase activity. Glucose and hemicellulose additions stimulated microbial metabolism of C thereby enhancing microbial demand for P, with increased soil P availability especially in the early incubation period. Glucose or hemicellulose addition changed soil microbial diversity and community composition, leading to enhanced growth and interactions of P solubilizing microorganisms such as Desulfitobacterium, Bacillus and Desulfosporosinus. Our results infer the importance of pH alteration and competitive sorption between PO₄ and functional groups of recalcitrant C (e.g., lignin) with Fe/Al (hydr) oxides in regulating soil P availability. Further, the microbial response to labile C additions led to increased P availability in the P-deficient soil. This study provides important mechanistic information to guide microbially-regulated soil P management in agricultural ecosystems.

Metagenomic insights into nitrogen and phosphorus cycling at the soil aggregate scale driven by organic material amendments

The soil microbiome, existing as interconnected communities closely associated with soil aggregates, is the key driver in nutrient cycling. However, the underlying genomic information encoding the machinery of the soil microbiome involved in nutrient cycling at the soil aggregate scale is barely known. Here comparative metagenomics and genome binning were applied to investigate microbial functional profiles at the soil aggregate scale under different organic material amendments in a long-term field experiment. Soil samples were sieved into large macroaggregates (>2 mm), macroaggregates (0.25-2 mm) and microaggregates (<0.25 mm). Microbial taxonomic and functional alpha diversity were significantly correlated to soil NO₃^- and SOC. The highest abundance of nasB, nirK, and amoA genes, which are responsible for denitrification and ammonia oxidizers driving nitrification, was observed in microaggregates. Both manure and peat treatments significantly decreased the abundance of napA and nrfA that encode enzymes involved in dissimilatory nitrate reduction to ammonium (DNRA). As a biomarker for soil inorganic P solubilization, the relative abundance of gcd was significantly increased in macroaggregates and large macroaggregates. Three nearly complete genomes of Nitrososphaeraceae (AOA) and seven bacterial genomes were shown to harbor a series of genes involved in nitrification and P solubilization, respectively. Our study provides comprehensive insights into the microbial genetic potential for DNRA and P-solubilizing activity across different soil aggregate fractions and fertilization regimes.