Improving the adsorption performance of wetland fillers is of great significance for enhancing pollutant removal in constructed wetlands. Currently, limited by complex preparation processes and high costs, large numbers of high adsorption fillers studied in lab are difficult to be applied in practical engineering. In this study, a newly low-cost and efficient phosphorus removal composite wetland filler (CFB) is prepared by using industrial and agriculture waste (steel slag and oyster shells) and natural ore (volcanic rock) as raw materials. The results show that phosphorus removal efficiency was largely enhanced by synergistic effects of steel slag, oyster shells, and volcanic rock, and it was mainly influenced by the proportion of each component of CFB. Based on the fitting of the classical isothermal equation, the adsorption capacity of CFB is 18.339 mg/g. The adsorption of phosphorus by CFB is endothermic and spontaneous, and there are heterogeneous surfaces and multi-layer adsorption processes, as well as pH value and temperature, are free from the influence on CFB phosphorus removal. During the practical wastewater application experiments, the phosphorus removal rate of the CFB-filled constructed wetland apparatus (CW-A) can reach 94.89% and is free from the influence on the removal of other pollutants (COD, TN, and NH3-N) by the system. Overall, the prepared CFB is of excellent decontamination effect, an extremely simple preparation process, low cost, and sound practical engineering application potential, providing new ideas and approaches for enhancing the phosphorus removal capacity and waste resource utilization of constructed wetland systems.

Long-term fertilization is considered as the most effective practice in organic C accrual in intensively managed paddy soils. However, the contribution and mechanism of microbial necromass C for soil organic C accrual, and the effective incremental component in paddy soils under the different fertilization remain unclear. To address the knowledge gap, we collected soils from a 31-year long-term fertilization paddy field including no fertilization (control), mineral fertilizers alone (NPK), mineral fertilizers plus rice straw incorporation (NPK + S), and mineral fertilizers plus manure incorporation (NPK + M). Living microbial biomass and their necromass were quantified by the biomarker analysis of phospholipid fatty acids and amino sugars, respectively. Results showed that the three fertilization treatments significantly increased the bacterial and fungal biomass in both 0-10 and 10-20 cm layers, which were universally greatest in NPK + M. The microbial necromass C was little affected by 31-year mineral fertilization; however, mineral combined organic fertilizers incorporation greatly stimulated microbial necromass C accumulation. Besides, soil treated with NPK + M showed 3.55 +/- 0.12 g kg(-1) higher accumulation of microbial necromass C than NPK + S, because manure application increased the abundance of Gram-positive r -strategy bacteria (mainly Firmicutes and Actinobacteria), and enriched filamentous fungi (Ascomycota). Compared to the control, the increase in the microbial necromass C contribution to SOC was lowest in NPK and highest in NPK + M, mainly derived from the variation in the contribution of bacterial necromass. Consequently, this study suggested long-term mineral combined manure application in subtropical paddy fields could effectively increase soil C sequestration by strengthening microbial necromass accumulation. Bacterial and fungal necromass C accrual was closely associated with living microbial biomass and their community structure. Given the C sequestration potential of manure in paddy soil, as the crucial resource of livestock and poultry waste in this region, it should be incorporated into subtropical agricultural ecosystems.

Intercropping is a powerful practice to alter the allocation of photosynthetic carbon (C) to belowground ecosystems via promotion of diversified plant communities. The feedback of soil C stability to intercropping is controlled by microbial C use efficiency (CUE). Despite its significance, there is currently insufficient evidence to decipher how soil microbial CUE reacts to intercropping. By combining a 10-year-long intercropping experiment with a substrate-independent 18O-H2O labelling approach and high-throughput sequencing, we elucidated the performance of intercropping on soil C pool and microbial metabolic traits as well as their relationships with soil microbial communities. Compared with monoculture, maize intercropping with peanut and soybean significantly increased soil C storage, soil mineral-associated organic C (MAOC), soil dissolved organic (DOC), and soil microbial biomass (MBC) contents at maize four growth stages. Soil microbial CUE increased significantly, especially at maize flowering and mature stages, as a consequence of enhanced microbial growth and biomass turnover rate after maize intercropping with peanut and soybean. Soil C storage and accessibility indicators (e.g., MAOC, DOC, and MBC contents) could significantly predict the changes of soil microbial diversity and core taxa. Meanwhile, the beta-diversity (community composition) of soil bacteria, fungi, saprotroph and protists, as well as rare fungal taxa were positively correlated with soil microbial CUE, and these indicators showed a high prediction of the microbial CUE. Soil C storage and accessibility indicators directly and indirectly influenced soil microbial CUE by regulating microbial diversity and key taxa. Soil microbial diversity and core taxa directly and indirectly influenced microbial CUE by mediating microbial respiration, growth, biomass, and enzyme activity, which mediated by soil C storage and accessibility. These findings provide an evidence for the associations between microbial diversity, CUE, and soil C stability, highlighting the importance of intercropping-driven soil microbiome to enhance soil microbial CUE.

Both natural revegetation and cropping have great impact on long-term soil carbon (C) sequestration, yet the differences in their underlying mechanisms remain unclear. In this study, we investigated trends in soil organic C (SOC) accumulation during natural revegetation (VR) and cropping processes over 24 years, and explored the contributions of microbial necromass and plant-derived C to SOC formation and their primary controls. Over the course of 24 years of land use/cover change (LUCC) from 1995, SOC content exhibited a more substantial increase in VR (0.31 g kg(-1) a(-1) ) than in cropland (0.14 g kg(-1) a(-1) ) during Stage II (>10 y after LUCC), and recalcitrant organic carbon explained more of the SOC variation than easily oxidizable carbon. The higher SOC content in VR was attributed to a greater contribution of plant-derived C (14-28 %) than that in cropland (3-11 %) to SOC and a consistently lower ratio of cinnamyl (C)- to vanillyl (V)-type phenols in VR across all the assessed years. Although there were higher proportion of microbial necromass of SOC (41-84 %) in cropland than in VR, the differences were not significant. The dominant bacterial phylum of Chloroflexi and soil nitrogen content were the primary biotic and abiotic factors regulating microbial-derived and plant-derived C in both cropland and VR. However, soil phosphorus content was the main factor in cropland, while climatic factors such as mean annual precipitation were more important in VR. These results provided evidence that long-term natural revegetation enhanced SOC sequestration by greater contribution of plant-derived C to SOC formation compared to cropping. These findings underscore the synergistic contribution of vegetation and microorganisms to longterm SOC sequestration, offering insights into the different mechanisms of carbon formation during VR and cropping processes, and providing support for optimizing land management to achieve global carbon neutrality goals.

Intercropping can increase soil carbon (C) sequestration and utilization by planting a variety of plants on a same land. However, the main plant and microbial-driven pathways leading to the increased C sequestration in intercropping soils are rarely studied. Therefore, it is important to reveal the distinct contributions of plant- and microbe-derived C to soil organic C (SOC) for understanding the regulation of intercropping in global C storage. Herein, two widely accepted sets of bio-markers, namely, amino sugars and lignin phenols, were employed to compare the distribution of plant- and microbe-derived C as well as their contributions to SOC in maize monoculture and intercropping systems, based on a field experiment established in 2013; meanwhile, the associations of soil physicochemical properties and microbial physiological traits with plant- and microbe-derived residues were disclosed via correlation and model analysis. Compared with the monoculture, maize intercropping significantly increased soil amino sugar and microbial necromass C contents as well as their contributions to SOC in maize mature stage; maize inter-planted with gingelly or soybean significantly increased these variables in the elongation stage; meanwhile, maize inter-planted with gingelly significantly increased soil lignin phenol content and its contribution to SOC in the mature stage. In all treatments and growth stages, microbial necromass C contributed more to SOC than lignin phenols, and fungal necromass C contributed more to SOC than bacterial necromass. The contribution of microbial necromass C to SOC was mainly influenced by amino sugar content, microbial C use efficiency, dissolved organic C content, and microbial biomass C content. The contribution of plant-derived C to SOC was mainly influenced by lignin phenol content, pH, and NH4+-N content. These results demonstrate the distinct regulations of maize intercropping on plant- and microbe-derived C to soil C pool by influencing soil physicochemical properties and microbial physiological traits, and meanwhile, highlight the potential of intercropping in global C storage.

The type VI secretion system (T6SS) is a bacterial weapon capable of delivering antibacterial effectors to kill competing cells for interference competition, as well as secreting metal ion scavenging effectors to acquire essential micronutrients for exploitation competition. However, no T6SS effectors that can mediate both interference competition and exploitation competition have been reported. In this study, we identified a unique T6SS-1 effector in Yersinia pseudotuberculosis named TepC, which plays versatile roles in microbial communities. First, secreted TepC acts as a proteinaceous siderophore that binds to iron and mediates exploitative competition. Additionally, we discovered that TepC has DNase activity, which gives it both contact-dependent and contact-independent interference competition abilities. In conditions where iron is limited, the iron-loaded TepC is taken up by target cells expressing the outer membrane receptor TdsR. For kin cells encoding the cognate immunity protein TipC, TepC facilitates iron acquisition, and its toxic effects are neutralized. On the other hand, nonkin cells lacking TipC are enticed to uptake TepC and are killed by its DNase activity. Therefore, we have uncovered a T6SS effector, TepC, that functions like a "Trojan horse" by binding to iron ions to provide a valuable resource to kin cells, whereas punishing cheaters that do not produce public goods. This lure-to-kill mechanism, mediated by a bifunctional T6SS effector, may offer new insights into the molecular mechanisms that maintain stability in microbial communities.

Incorporating rice straw into upland has been adopted as a strategy to increase crop productivity and decrease poisoning to rice from reducing substances accumulation as well as mitigate methane emission from paddy fields in South China. However, the mechanism underlying long-term ex situ incorporation of rice straw in upland on soil organic carbon (SOC) and crop yields through microbial metabolism remains unclear. Hence, a field experiment was established to investigate the response mechanism of SOC and crop yields underlying microbe-mediated carbon dynamics with nutrient stoichiometry by ex situ incorporation of rice straw in upland. The results showed that the treatment of cropping with chemical fertilizers plus rice straw (SCF) had the highest SOC accumulation rate (0.14 ± 0.03 g C kg−1 yr−1) during the 22-year experimental period. The mean yields of rapeseed and sweet potato were increased by 5.0

Straw addition markedly affects the soil aggregates and microbial community structure. However, its influence on the profile of antibiotic resistance genes (ARGs), which are likely associated with changes in bacterial life strategies, remains unclear. To clarify this issue, a soil microcosm experiment was incubated under aerobic (WS) or anaerobic (AnWS) conditions after straw addition, and metagenomic sequencing was used to characterise ARGs and bacterial communities in soil aggregates. The results showed that straw addition shifted the bacterial life strategies from K- to r-strategists in all aggregates, and the aerobic and anaerobic conditions stimulated the growth of aerobic and anaerobic r-strategist bacteria, respectively. The WS decreased the relative abundances of dominant ARGs such as QnrS5, whereas the AnWS increased their abundance. After straw addition, the macroaggregates consistently exhibited a higher number of significantly altered bacteria and ARGs than the silt+clay fractions. Network analysis revealed that the WS increased the number of aerobic r-strategist bacterial nodes and fostered more interactions between r-and K-strategist bacteria, thus promoting ARGs prevalence, whereas AnWS exhibited an opposite trend. These findings provide a new perspective for understanding the fate of ARGs and their controlling factors in soil ecosystems after straw addition.Environmental implicationsStraw soil amendment has been recommended to mitigate soil fertility degradation, improve soil structure, and ultimately increase crop yields. However, our findings highlight the importance of the elevated prevalence of ARGs associated with r-strategist bacteria in macroaggregates following the addition of organic matter, particularly fresh substrates. In addition, when assessing the environmental risk posed by ARGs in soil that receives crop straw, it is essential to account for the soil moisture content. This is because the species of r-strategist bacteria that thrive under aerobic and anaerobic conditions play a dominant role in the dissemination and accumulation of ARG.

Biochar contains biotoxic aromatic compounds, and their influence on nitrogen-fixing cyanobacteria, the critical nitrogen fixer in paddy soil, has never been tested. Here, the physiological, metabolomic, and transcriptomic analyses of Nostoc sp. PCC7120 in response to biochar leachate were performed. The results suggested that biochar leachate inhibited the efficiency of photosynthesis, nitrogen fixation, and nitrate assimilation activities of nitrogen-fixing cyanobacteria. Biochar leachate containing aromatic compounds and odd- and long-chain saturated fatty acids impaired the membrane structure and antenna pigments, damaged the D1 protein of the oxygen evolution complex, and eventually decreased the electron transfer chain activity of photosystem II. Moreover, the nitrogen fixation and nitrate assimilation abilities of nitrogen-fixing cyanobacteria were inhibited by a decrease in photosynthetic productivity. A decrease in iron absorption was another factor limiting nitrogen fixation efficiency. Our study highlights that biochar with relatively high contents of dissolved organic matter poses a risk to primary nitrogen assimilation reduction and ecosystem nitrogen loss. Further evidence of the potential negative effects of biochar leachates on the fixation and assimilation capacity of nitrogen by soil microbes is needed to evaluate the impact of biochar on soil multifunctionality prior to large-scale application.

Soil sickness a severe problem in tobacco production, leading to soil-borne diseases and reduce in tobacco yield. This occurs as a result of the interaction between root exudates and rhizosphere microorganisms, which is however, little studied until now. By combining the field investigation and pot experiment, we found the output yield consistently decreased during the first 10 years of continuous cropping in a tobacco field, but increased at the 15th year (15Y). The root exudate and rhizosphere bacterial community was further analyzed to reveal the underlying mechanism of the suppressive soil formation. Root exudate of 15Y tobacco enriched in amino acids and derivatives, while depleted in the typical autotoxins including phenolic acids and alkaloids. This was correlated to the low microbial diversity in 15Y, but also the changes in community composition and topological properties of the co-occurrence network. Especially, the reduced autotoxins were associated with low Actinobacteria abundance, low network complexity and high network modularity, which significantly correlated with the recovered output yield in 15Y. This study revealed the coevolution of rhizosphere microbiota and root exudate as the soil domesticated by continuous cropping of tobacco, and indicated a potential role of the autotoxins and theirs effect on the microbial community in the formation of suppressive soil.

Despite the widespread use of anaerobic soil disinfestation (ASD) to improve soil health, its impact on soil antibiotics, human pathogenic bacteria (HPB) and antibiotic resistance genes (ARGs) remains unclear. To address this knowledge gap, we conducted an incubation study in manure -amended soil with three treatments: no treatment (CK), crop straw only (CS), and CS combined with water flooding and plastic covering (ASD). The results showed that ASD increased the concentrations of tetracycline by 27 % and 8-lactam by 22 %, while depleting macrolide by 51 %. Furthermore, ASD increased the numbers of potential HPB species and genes by 4.1 % and 23 %, respectively. Co -occurrence network analysis demonstrated intensified cooperation and competition among HPB and HNPB (human non-pathogenic bacteria) species under ASD, favoring the prevalence of HPB species such as Escherichia coli, Streptococcus equi, Clostridium tetani, and Bacillus anthracis. Potential HPB species in Proteobacteria exhibited negative correlations with macrolide and 8-lactam antibiotics, whereas those in Firmicutes showed positive correlations with tetracycline antibiotics, suggesting that specific bacterial taxa contributed to the production and degradation of antibiotics in response to ASD. Interestingly, CS mitigated the presence of ARGs in soil, while ASD further amplified this reduction, almost eliminating nalC, acrB, OXA-60, VIM -7, tetL, and tetQ. The variation in ARG profiles (91.7 %) could be explained by antibiotics, HPB, and HNPB species, indicating their collective contribution to reducing soil ARGs under ASD. Moreover, host prediction and network analysis revealed that, compared with CK, where potential HPB species were the main carriers of ARGs, soil ARGs were less frequently carried by potential HPB species after ASD, indicating a reduction in the collaborative dissemination of HPB and ARGs in manured soil. In conclusion, ASD provides a promising strategy for mitigation of soil biologic contamination, which can have profound significance for environmental safety and agricultural sustainability.

The regulatory gate hypothesis suggests that the mineralization of soil organic matter (SOM) is controlled by carbon accessibility due to microbial redundancy. However, this opinion is contentious because the extensively high available carbon released during the fumigation in these studies strongly stimulated microbial activity, which is unlikely to occur in real soil and would compensate for the effect of reduced microbial abundance. In this study, natural soil was moderately diluted with mineral complexes in varying proportions to obtain soils with a gradient of microbial abundance and low carbon availability. The results revealed that despite minimal changes in the dissolved organic carbon content (DOC), the CO2 emission rate and activity of SOM hydrolysis significantly decreased with decreasing microbial abundance. Regression analysis and the random forest model highlighted microbial abundance as the primary factor influencing carbon decomposition, which was more fundamental than DOC and microbial diversity. These findings underline the crucial role of microbes in soil carbon turnover and the importance of maintaining microbial abundance to preserve the soil carbon cycling capacity.

Atmospheric trace gases, such as H-2 and CO, are important energy sources for microbial growth and maintenance in various ecosystems, especially in arid deserts with little organic substrate. Nonetheless, the impact of soil organic C availability on microbial trace gas oxidation and the underlying mechanisms are unclear at the community level. This study investigated the energy and life-history strategies of soil microbiomes along an organic C gradient inside and out of Hedysarum scoparium islands dispersed in the Mu Us Desert, China. Metagenomic analysis showed that with increasing organic C availability from bare areas into "fertile islands", the abundance of trace gas oxidizers (TGOs) decreased, but that of trace gas nonoxidizers (TGNOs) increased. The variation in their abundance was more related to labile/soluble organic C levels than to stable/insoluble organic C levels. The consumption rates of H-2 and CO confirmed that organic C addition, especially soluble organic C addition, inhibited microbial trace gas oxidation. Moreover, microorganisms with distinct energy-acquiring strategies showed different life-history traits. The TGOs had lower 16 S rRNA operon copy numbers, lower predicted maximum growth rates and higher proportions of labile C degradation genes, implying the prevalence of oligotrophs. In contrast, copiotrophs were prevalent in the TGNOs. These results revealed a mechanism for the microbial community to adapt to the highly heterogeneous distribution of C resources by adjusting the abundances of taxa with distinct energy and life-history strategies, which would further affect trace gas consumption and C turnover in desert ecosystems.

Although soil ecological stoichiometry is constrained in natural ecosystems, its responses to anthropogenic perturbations are largely unknown. Inputs of inorganic fertilizer and crop residue are key cropland anthropogenic managements, with potential to alter their soil ecological stoichiometry. We conducted a global synthesis of 682 data pairs to quantify the responses of soil carbon (C), nitrogen (N), and phosphorus (P) and grain yields to combined inputs of crop residue plus inorganic fertilizer compared with only inorganic fertilizer application. Crop residue inputs enhance soil C (10.5%-12%), N (7.63%-9.2%), and P (2.62%-5.13%) contents, with an increase in C:N (2.51%-3.42%) and C:P (7.27%-8.00%) ratios, and grain yields (6.12%-8.64%), indicating that crop residue alleviated soil C limitation caused by inorganic fertilizer inputs alone and was able to sustain balanced stoichiometry. Moreover, the increase in soil C and C:N(P) ratio reached saturation in similar to 13-16 years after crop residue return, while grain yield increase trend discontinued. Furthermore, we identified that the increased C, N, and P contents and C:N(P) ratios were regulated by the initial pH and C content, and the increase in grain yield was not only related to soil properties, but also negatively related to the amount of inorganic N fertilizer input to a greater extent. Given that crop residual improvement varies with soil properties and N input levels, we propose a predictive model to preliminary evaluate the potential for crop residual improvement. Particularly, we suggest that part of the global budget should be used to subsidize crop residue input management strategies, achieving to a win-win situation for agricultural production, ecological protection, and climate change mitigation.

Plantation forests are essential in driving global biogeochemical cycling and mitigating climate change. Biodiversity and environmental factors can shape multiple forest ecosystem functions simultaneously (i.e., multifunctionality). However, their effect on multifunctionality when pure plantations are converted into two-aged plantations remains underexplored. Therefore, we assessed above- and below-ground biodiversity and environmental factors and 11 ecosystem functions in different plantation types in subtropical China. The two-aged mixed plantations exhibited higher multifunctionality than did a pure plantation, primarily due to soil fungal diversity and secondarily due to tree diversity, based on the coefficient of variation for tree diameter at breast height (CVD) and community-weighted specific leaf area (CWMSLA). Further analysis revealed saprotrophy as the key soil fungal trophic mode in maintaining multifunctionality. Moreover, structural equation modeling confirmed that soil environmental factors, namely the soil water content and pH, had no direct association with multifunctionality, but were indirectly related to multifunctionality via elevated CVD and CWMSLA, respectively. Our results indicate that the tree and soil fungal diversity, as well as soil environmental factors, resulting from the conversion of pure plantations to two-aged mixed plantations, can enhance multifunctionality, and provide a better comprehensive understanding of the driving mechanisms of multifunctionality, leading to the sustainable management of subtropical plantation forest ecosystems.

Addition of organic amendments, such as manure and straw, to arable fields as a partial substitute for mineral phospho-rus (P), are a sustainable practice in high-efficiency agricultural production. Different organic inputs may induce var-ied soil organic carbon (OC) stability and phoD harboring microbes, subsequently regulate P behavior, but the underlying mechanisms are poorly understood. A 11-year field experiment examined P forms by 31P-nuclear magnetic resonance (NMR), OC chemical composition by 13C NMR, and biologically-based P availability methods, phoD bacte-rial communities, and their co-occurrence in soils amended with chemical P fertilizer (CF), chemical P partly substituted by organic amendments including pig manure (CM), a mixture of pig manure and corn straw (CMS), and corn straw (CS), with equal P input in all treatments. Organic amendments significantly increased soil labile Pi (CaCl2-P, citrate-P, 2.91-3.26 and 1.16-1.32 times higher than CF) and Po (enzyme-P, diesters, 4.08-7.47 and 1.71-2.14 times higher than CF) contents and phosphatase activities, while significantly decreased aromaticity (AI) and recalcitrance indexes (RI) of soil C, compared with CF. The keystone genera in manured soils (Alienimomas and Streptomyces) and straw-applied soils (Janthinobacterium and Caulobacter) were significantly correlated with soil enzyme-P, microbial biomass P (MBP), diesters, and citrate-P. Soil AI and RI were significantly correlated with the phoD keystone and soil P species. It suggested that the keystone was impacted by soil OC stability and play a role in regulating P redistribution in amended soils. This study highlights how manure and straw incorporation altered soil OC stability, shaped the phoD harboring community, and enhanced soil P biological processes promoted by the keystone taxa. The partial substitution of mineral P by mixture of manure and straw is effectively promote soil P avail-ability and beneficial for environmental sustainability.

Continuous cropping leads to the development of serious fungal diseases in tobacco plants and depleted yield of tobacco ( Nicotiana tabacum ), which can be mitigated by organic fertilization. Yet, we know little about how organic fertilizers affect the fungal community of continuous cropping tobacco soil. In this study, we investigated the soil fungal community after 11 years of tobacco planting with chemical fertilization (CF) or chemical fertilization combined with organic fertilizers obtained from plant or animal origin, including oil cake (CFO), straw (CFS), and farmyard fertilizer (CFM). The predominant phyla of Ascomycota (70%) and Mortierellomycota (15%) were identified in all the treatments. A significantly higher proportion of Pyrenochaetopsis and lower relative abundance of Sordariomycetes were observed in the CFM group compared to the controls. Compared to CF and non-fertilized control (CK), CFO and CFS led to higher species richness ( P < 0.05), while CFM led to a less uniform fungal community, indicated by lower Shannon and higher Simpson diversity indices ( P < 0.05). Pearson’s correlation and redundancy analysis suggested that fertilizations primarily influenced the fungal community by altering the soil nutrient conditions, among which soil organic carbon and total phosphorus significantly correlated with the fungal diversity and community composition ( P < 0.05). Notably, FUNGuild annotation suggested that while other treatments showed no significant effect on the fungal trophic modes, CFM strongly increased the abundance of saprotrophic fungi by more than 30% ( P < 0.05), thus preventing the prevalence of potential pathotypes and symbionts. The results suggest that the type of organic fertilizers is essential to the long-term effects of organic application on the fungal community, and the animal-origin manure seems to be a better choice than plant-origin materials in continuous cropping tobacco fields.

Phosphorus (P) limitation to microorganisms is increasingly recognized in soils, but how the limitation mediates the metabolic processes of microbes driving soil carbon (C) release remains unclear. Here, we performed a 60-day incubation experiment adding two C-13-labeled organic C sources (glucose and straw) at five inorganic P addition levels in loess with low available P from the Loess Plateau, China. The nutrient limitations of microbes were quantified by enzymatic vector analysis, associated with soil respiration, microbial metabolic quotient (qCO(2)), C use efficiency (CUE) and priming effect (PE) at both early (10 days) and late (60 days) stages of incubation. Results showed that reducing microbial P limitation increased CO2 release from soils by 19-26% and from labeled glucose and straw by 12% and 29%, respectively. This indicated that soil P limitation overall constrains rather than promotes microbial C metabolism. A negative relationship between relative C and P limitations at the first 10-day incubation further indicated that added P (decreased P-acquiring enzyme activities) stimulated microbial C metabolism (increased C-acquiring enzyme activities) under enough C source. Whereas a positive relationship at 60-day incubation suggested that high microbial heterotrophic respiration under high P addition alleviate their C limitation. Furthermore, both multiple regression and partial least squares path models indicated that an increase in CO2 release with P and C additions at early incubation was due to two processes, i.e., increasing available P promoted decomposition of native soil organic C due to PE as well as decay of added organic C by increasing qCO(2) and decreasing CUE. At late incubation, however, P addition increasing decomposition of native soil C via PE is the dominated control on CO2 release under C limitation. We conclude that microbes are dominant by maintenance rather than growth metabolism in loess with low phosphorus availability, whereas the pathways of the metabolism driving C release depend on soil C availability. Our findings suggest that microbial P limitation has considerable positive effects on soil C sequestration in these ecosystems with low soil P availability.

Improving nitrogen (N) acquisition by crops from soil is essential to reduce fertilization rates whilst maintaining yields. Plants can adapt their nutrient acquisition strategies according to N availability, which also affects soil microbial community structure, functions and activities and relies on the supply of carbon (C) for energy. We hypothesized that N deprivation would create hotspots of N- and C-acquiring hydrolase activities in maize rhizosphere through the effects of altered root exudation on the rhizosphere bacterial community. We grew maize under three N fertilization rates and combined soil zymography with the identification of rhizosphere microbial communities and non-targeted metabolic profiling of root exudates to explore enzyme hotspot formation. The rhizosphere extents of β-1,4-glucosidase (BG) and β-N-acetylglucosaminidase (NAG) activities decreased after N fertilization, narrowing by 48% and 39%, respectively, under typical field N application rates compared to zero application. Rhizosphere extents of enzyme activities were more sensitive to altered N supply than changes in the rates of enzyme activities: BG activity decreased by ∼10%, while NAG activity was unaffected. Decreases in the activities of both hydrolases and their rhizosphere extents caused by N addition correlated with reduced abundances of oligotrophs. The relative abundances of oligotrophic bacteria (e.g., Acidobacteria) decreased, while copiotrophs (e.g., Pseudomonadota and Patescibacteria) increased under the highest N application rate. Co-occurrence networks of the rhizosphere bacterial community revealed that functional units increased with BG activity, while an efficient and denser co-occurrence network supported expansion of its rhizosphere extent. The metabolic profiles of root exudates changed according to the N application rate, suggesting that their chemistry was regulated by the plant in response to N supply. The composition of root exudates and dissolved organic C and nitrate contents explained the largest variations in NAG hotspots in the rhizosphere. In summary, maize actively adjusts the composition of root exudates to increase interactions with rhizosphere bacteria, thereby stimulating hydrolase production and activities, and altering their rhizosphere extents to mobilize N and energy (C) in a larger soil volume, under conditions of N deficiency.

A paddy soil, with microbial biomass considerably reduced by chloroform fumigation, was treated with low-crystalline ferrihydrite and high-crystalline goethite and with 13C-labeled acetate. In the first 10 days of the incubation, CH4 was produced mainly from the added acetate (56‒91%). After day 30, however, 3‒11% of the total CH4 emissions originated from the added acetate. Chloroform fumigation reduced the microbial biomass by 43‒87%, leading to the decrease in the CH4 emission from the fumigated soil for 352‒1127 times compared to that from the unfumigated soil. Acetate only contributed to 0‒6% of the total CH4 emission from the fumigated soil during the entire incubation period. Thus, chloroform fumigation largely reduced the abundance of methanogens, and the reduction in the abundance of acetotrophic methanogens was high. Iron oxide additions reduced CH4 emissions from the added acetate and from other sources. The reduction was stronger in the fumigated soil compared to that in the unfumigated soil because the lower abundance of methanogens in the fumigated soil decreased the competition for substrates with iron reducers. The effect of ferrihydrite on CH4 emission from non-acetate sources was stronger than that of goethite before day 6; however, this effect became weaker thereafter, because of the reduced number of reactive sites after acetate sorption by ferrihydrite. We conclude that the marked reduction in the microbial biomass, and especially methanogens, decreased the methane production, changed the CH4 sources, and increased the relative effects of iron oxides on CH4 production.