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Purpose: Understanding the interactions among soil microbial communities, soil multifunctionality, and soil-borne pathogens are important for ecological prevention and control of soil-borne diseases. In this study, we aimed to compare the differences in microbial communities and multifunctionality between healthy and Alternaria solani-infected potato rhizosphere soils. Additionally, we investigated the relationships among soil microbial communities, soil multifunctionality, and potato early blight incidence. Methods: We collected healthy and Alternaria solani-infected potato rhizosphere soil samples from a potato field in Ningbo, Zhejiang, China. Amplicon sequencing was used to detect changes in soil microbial communities. The Z scores (standard scores) of soil chemical properties, soil enzyme activities, and potato yield were averaged to obtain soil multifunctionality. Results: We found significantly reduced potato yield, soil multifunctionality, and bacterial richness under diseased conditions. Additionally, there were significant differences between healthy and diseased rhizosphere soil microbial communities. Specific microbial taxa including Kaistobacter, Candidatus Koribacter, Candidatus Solibacter, Rhodoplanes, Bradyrhizobium, Gynumella, Massilia, Alicyclobacillus, Mycochlamys, and Conocybe were enriched in diseased rhizosphere soils. The complexity of microbial co-occurrence networks decreased. The proportion of positive correlations among microbial taxa decreased, whereas the proportion of negative correlations increased in diseased rhizosphere soils. These changes were strongly associated with decreased soil multifunctionality. Conclusion: Our results increased our comprehension of the interactions among soil microbial communities, multifunctionality, and potato early blight, thus providing important implications for the design and implementation of control strategies against soil-borne diseases in the future. [ABSTRACT FROM AUTHOR]

In China, soil-borne viruses transmitted by the root parasite Polymyxa graminis have caused significant yield loss in winter wheat for many years. At present, it is believed that two main soil-borne RNA viruses, namely wheat yellow mosaic virus (WYMV) and Chinese wheat mosaic virus (CWMV) are responsible for such losses. The molecular characteristics and infection processes of these two viruses have been intensively investigated and described substantially in detail, following the complete sequencing of their respective genomes. In this review, we highlight our recent findings on the distribution of WYMV and CWMV in China, the associated crop damage, the biological functions of WYMV and CWMV proteins as well as the viral temperature sensitivities. We also describe the characteristics of the resistance genes and discuss the novel virus–plant arms race strategies in hope of enlarging our understanding on the theme of virus-plant interactions. Finally, we compare current disease-management options and suggest the application of biotechnology-based genetic resistance to develop more cost-effective countermeasures for controlling soil-borne virus diseases in the future. [ABSTRACT FROM AUTHOR]

Paddy soils make up the largest anthropogenic wetlands on earth, and are characterized by a prominent potential for organic carbon (C) sequestration. By quantifying the plant‐ and microbial‐derived C in soils across four climate zones, we identified that organic C accrual is achieved via contrasting pathways in paddy and upland soils. Paddies are 39%–127% more efficient in soil organic C (SOC) sequestration than their adjacent upland counterparts, with greater differences in warmer than cooler climates. Upland soils are more replenished by microbial‐derived C, whereas paddy soils are enriched with a greater proportion of plant‐derived C, because of the retarded microbial decomposition under anaerobic conditions induced by the flooding of paddies. Under both land‐use types, the maximal contribution of plant residues to SOC is at intermediate mean annual temperature (15–20°C), neutral soil (pH~7.3), and low clay/sand ratio. By contrast, high temperature (~24°C), low soil pH (~5), and large clay/sand ratio are favorable for strengthening the contribution of microbial necromass. The greater contribution of microbial necromass to SOC in waterlogged paddies in warmer climates is likely due to the fast anabolism from bacteria, whereas fungi are unlikely to be involved as they are aerobic. In the scenario of land‐use conversion from paddy to upland, a total of 504 Tg C may be lost as CO2 from paddy soils (0–15 cm) solely in eastern China, with 90% released from the less protected plant‐derived C. Hence, preserving paddy systems and other anthropogenic wetlands and increasing their C storage through sustainable management are critical for maintaining global soil C stock and mitigating climate change. [ABSTRACT FROM AUTHOR]

Biological nitrogen (N2) fixation as a source of new N input into the soil by free-living diazotrophs is important for achieving sustainable rice agriculture. However, the dominant environmental drivers or factors influencing N2 fixation and the functional significance of the diazotroph community structure in paddy soil across a climatic gradient are not yet well understood. Thus, we characterized the diazotroph community and identified the ecological predictors of N2 fixation potential in four different climate zones (mid-temperate, warm-temperate, subtropical, and tropical paddy soils) in eastern China. Comprehensive nifH gene sequencing, functional activity detection, and correlation analysis with environmental factors were estimated. The potential nitrogenase activity (PNA) was highest in warm-temperate regions, where it was 6.2-, 2.9-, and 2.2-fold greater than in the tropical, subtropical, and mid-temperate regions, respectively; nifH gene abundance was significantly higher in warm-temperate and subtropical zones than in the tropical or mid-temperate zones. Diazotroph diversity was significantly higher in the tropical climate zone and significantly lower in the mid-temperate zone. Non-metric multidimensional scaling and canonical correlation analysis indicated that paddy soil diazotroph populations differed significantly among the four climate zones, mainly owing to differences in climate and soil pH. Structural equation models and automatic linear models revealed that climate and nutrients indirectly affected PNA by affecting soil pH and diazotroph community, respectively, while diazotroph community, C/P, and nifH gene abundance directly affected PNA. And C/P ratio, pH, and the diazotroph community structure were the main predictors of PNA in paddy soils. Collectively, the differences in diazotroph community structure have ecological significance, with important implications for the prediction of soil N2-fixing functions under climate change scenarios. [ABSTRACT FROM AUTHOR]

Mean residence time (MRT) of carbon (C) in soil is the most important parameter of C sequestration and stability and crucial for CO 2 removal from the atmosphere. Climate and soil properties controls of MRT of upland soils are well known, but the drivers of C stability in paddies were never summarized. Here, we estimated MRT of paddies across monsoon Asia using the stock-over-flux method, i.e., soil organic C (SOC) stock over organic matter input considering the net primary production (NPP), and determined the main factors affecting SOC turnover. The average MRT of paddy soils in monsoon Asia ranges between 19 and 50 yr, depending on straw management. These estimates are similar to recent estimates for the global average MRT across all soils, but longer than for upland croplands. Tropical regions have the shortest MRT for rice paddies (16–42 yr), while the MRT of C in soils of temperate and subtropical regions are longer (20–56 yr). Across a wide range of environmental factors, MRT was most strongly affected by temperature. We estimate that 2 °C warming decreases MRT by 7% on average, with the strongest decreases in the western Indonesian islands and north-east China. Because C stocks per area in paddy soils are larger and the MRT is longer than in corresponding upland cropland soils, paddies play a key role in the global C cycle. Our results emphasize the need for management practices that retain stable soil C input rates to reduce possible positive feedbacks for global warming. • Mean residence time (MRT) of C in paddies ranges 19–50 yr. • MRT was shortest in tropics, while similar in temperate and subtropics. • MAT influenced C turnover more than other environmental factors. • MRT of C in paddies is declining at an average rate of 7% to 2 °C warming. [ABSTRACT FROM AUTHOR]

Background and aims: Paddy field abandonment has become a major concern in China, particularly among traditional rice-cultivation regions. Abandonment results in the alteration of many processes affecting C sequestration and turnover, but the final effects on C stocks remain unknown. Methods: To examine the effects of paddy abandonment on topsoil organic C (SOC) content and stocks, a long-term experiment was performed in subtropical China, examining an abandoned paddy field with different pre-abandonment fertilization history (from 1991 to 2006 years) and SOC gradients (from 19.2 to 22.0 g C kg). Results: Paddy field abandonment significantly reduced the topsoil SOC content and stock (0-20 cm). Eight years after cultivation ceased, SOC content and C stock had decreased by 9.9-20.9% and 10.2-20.8%, respectively, yielding a mean annual loss rate of 0.30-0.60 g C kg·yr. and 0.50-1.15 t C ha·yr., respectively. Soils with higher initial SOC content were more sensitive to abandonment than soils with low SOC levels. Dissolved organic C (DOC) was more sensitive to abandonment, as evidenced by the faster decrease of DOC than SOC. The rapid reduction of SOC content, combined with a strong decrease in DOC, indicates that post-abandonment C inputs into the soil were far lower than the concurrent SOC mineralization. The SOC content decreases was likely because of the shift from anaerobic to aerobic conditions. This change leads to faster litter decomposition and SOC mineralization, accompanied with decreasing SOC retention or stabilization by soil aggregates, mineral or Fe redox processes. Conclusion: Abandonment of paddy soils leads to switch from a C sink to a C source, resulting in high C losses. The succession of grasses in abandoned fields did not compensate for the losses of soil C stocks. [ABSTRACT FROM AUTHOR]

Autotrophic microorganisms, which can fix atmospheric CO 2 to synthesize organic carbon, are numerous and widespread in soils. However, the extent and the mechanism of CO 2 fixation in soils remain poorly understood. We incubated five upland and five paddy soils from subtropical China in an enclosed, continuously 14 CO 2 -labeled, atmosphere and measured 14 CO 2 incorporated into soil organic matter (SOC 14 ) and microbial biomass (MBC 14 ) after 110 days. The five upland soils supported dominant crops soils (maize, wheat, sweet potato, and rapeseed) in the region, while all paddy soils were cultivated in a regime consisting of permanently-flooded double-cropping rice cultivation. The upland and paddy soils represented typical soil types (fluvisols and ultisols) and three landforms (upland, hill, and low mountain), ranging in total carbon from low (<10 g kg −1 soil organic carbon) to medium (10–20 g kg −1 ) to high (>20 g kg −1 ). Substantial amounts of 14 CO 2 were fixed into SOC 14 (mean 20.1 ± 7.1 mg C kg −1 in upland soil, 121.1 ± 6.4 mg C kg −1 in paddy soil) in illuminated soils (12 h light/12 h dark), whereas no 14 C was fixed in soils incubated in continuous darkness. We concluded that the microbial CO 2 fixation was almost entirely phototrophic rather than chemotrophic. The rate of SOC 14 synthesis was significantly higher in paddy soils than in upland soils. The SOC 14 comprised means of 0.15 ± 0.01% (upland) and 0.65 ± 0.03% (paddy) of SOC. The extent of 14 C immobilized as MBC 14 and that present as dissolved organic C (DOC 14 ) differed between soil types, accounting for 15.69–38.76% and 5.54–18.37% in upland soils and 15.57–40.03% and 3.67–7.17% of SOC 14 in paddy soils, respectively. The MBC 14 /MBC and DOC 14 /DOC were 1.76–5.70% and 1.69–5.17% in the upland soils and 4.23–28.73% and 5.65–14.30% in the paddy soils, respectively. Thus, the newly-incorporated C stimulated the dynamics of DOC and MBC more than the dynamics of SOC. The SOC 14 and MBC 14 concentrations were highly significantly correlated ( r = 0.946; P < 0.0001). We conclude that CO 2 uptake by phototrophic soil microorganisms can contribute significantly to carbon assimilation in soil, and so warrants further future study. [ABSTRACT FROM AUTHOR]

Purpose: Free amino acids (FAAs) and peptides, and dissolved organic nitrogen (DON) comprise key pools in terrestrial soil carbon (C) and nitrogen (N) cycles. A comparative study of organic and conventional arable farming systems was conducted in Shanghai, China to determine the influence of management practices on characterization of AA and peptide dynamics. Materials and methods: Soils from an accredited organic farm (OS), transitional farm (TS), and neighboring conventionally managed farm (CS) were sampled from agricultural areas in Shanghai, China, and the AA and peptide behavior of top soils were evaluated by C labeled techniques. Results and discussion: Results showed that organic management resulted in significant increases ( P < 0.05) in AA and peptide rate acquisition, possibly due to higher soil organic C (SOC) and soil respiration in OS, compared to TS and CS. The half-life of valine (Val), valine-proline-proline (Val-Pro-Pro), glutamate (Glu), and glutamate-phenylalanine (Glu-Phe) averaged across the three soils (OS, TS, and CS) was 10.6 ± 2.3, 9.4 ± 2.2, 7.1 ± 1.9, and 6.7 ± 1.5 h, respectively. The relative AA and peptide C amounts partitioned into respiration (15-32% of total) versus biomass production (68-85% of total C) was also affected by management strategy and generally followed the order CS>TS>OS; OS was significantly different from TS and CS; however, a significant difference was not detected between TS and CS. We hypothesize that AA and peptide mineralization acts as a purely biological process, as CHCl fumigation and autoclaving resulted in no observable mineralization. Results showed that AA and peptide addition to soil resulted in rapid N mineralization and subsequent NO-N production, which followed a progression based on soil N mineralization rate of OS>TS>CS. AAs and peptides were only weakly sorbed onto the soil solid phase; however, our results suggested that this did not limit soil bioavailability. Conclusions: The results of our study indicated that soil management regimes have a substantial effect on AA and peptide behavior (mineralization, microbial uptake, and sorption, among other attributes) in horticultural production systems. Therefore, we propose that SOC and total microbial activity are likely key determinants governing AA and peptide behavior in horticultural soils. [ABSTRACT FROM AUTHOR]

Soil soluble organic nitrogen plays a significantly important role in nitrogen biogeochemical cycling. The aim of this study was to investigate the amount of soluble organic and inorganic nitrogen pools extracted by water, salt solutions, and centrifugal-drainage technique from different horticultural management system soils. Approximately 5.4-16.6, 4.4-46.5, 7.1-18.2, 8.8-27.8, 1.8-5.6, and 1.7-4.4 mg kg - 1 soluble organic nitrogen were obtained by 1M KCl, 0.5M K2SO4, 10 mM CaCl2, 1/15 mM phosphate buffer (pH 7.0), water, and centrifugal-drainage technique, respectively, in the 0-20 cm horticultural soils. Large variation in soluble organic nitrogen pools was observed across the sites in the present study and the volumes of soluble organic nitrogen pools generally followed the order: organic production system soil > conventional production system soil > transitional production system soil. In relative contrast to soluble organic nitrogen, organic management, known primarily for the absence of artificial fertilizers and pesticides, resulted in significantly lower levels of both soluble inorganic nitrogen and total soluble nitrogen in the soil. The degree of soluble inorganic nitrogen recovery appears highly dependent on the different chemical extractants and generally followed the series: phosphate buffer (pH 7.0) > KCl≈K2SO4 > CaCl2 > water > centrifugal-drainage technique. The soluble organic carbon and nitrogen in all soil extracts were all positively related to soil total carbon, total nitrogen, and electric conductivity value. This suggested that soil total carbon and nitrogen played a central role in the retention of soluble organic nitrogen in soils. Further studies on investigating the soluble organic nitrogen degradation pathway and its bottleneck are warranted. [ABSTRACT FROM AUTHOR]

Continuous nitrogen (N) loading alters plant growth and subsequently has the potential to impact soil organic carbon (SOC) accumulation in salt marshes. However, the knowledge gap of photosynthesized carbon (C) allocation in plant-soil-microbial systems hampers the quantification of C fluxes and the clarification of the mechanisms controlling the C budget under N loading in salt marsh ecosystems. To address this, we conducted an N fertilization field observation combined with a 5 h 13C-pulse labeling experiment in a salt marsh dominated by Suaeda. salsa (S. salsa) in the Yellow River Delta (YRD), China. N fertilization increased net 13C assimilation of S. Salsa by 277.97%, which was primarily allocated to aboveground biomass and SOC. However, N fertilization had little effect on 13C allocation to belowground biomass. Correlation analysis showed that 13C incorporation in soil was significantly and linearly correlated with 13C incorporation in shoots rather than in roots both in a 0 N (0 g N m−2 yr−1) and +N (20 g N m−2 yr−1) group. The results suggested that SOC increase under N fertilization was mainly due to an increased C assimilation rate and more efficient downward transfer of photosynthesized C. In addition, N fertilization strongly improved the 13C amounts in the chloroform-labile SOC component by 295.26%. However, the absolute increment of newly fix 13C mainly existed in the form of residual SOC, which had more tendency for burial in the soil. Thus, N fertilization enhanced SOC accumulation although C loss increased via belowground respiration. These results have important implications for predicting the carbon budget under further human-induced N loading. • Newly fixed carbon allocation and turnover in a salt marsh were quantified in situ. • Nitrogen fertilization enhanced photosynthetic carbon fixation in salt marshes. • Increased newly fixed carbon in +N group mainly allocated in shoot and soil organic carbon. • Soil organic carbon accumulation was mainly benefited by greater shoot growth. • Nitrogen fertilization improved residual soil organic carbon and is favor for carbon sequestration. [ABSTRACT FROM AUTHOR]

Dissolved organic nitrogen (DON) is a significant nitrogen (N) pool in most soils and isconsidered to be important for N cycling. Increasing evidence suggests that not only aminoacids but also small peptides are potential direct nutrient sources for both soil microorganismsand plants. However, current understanding of turnover and underlying mechanismsof those low molecular weight DON (LMW DON) compounds in soils remainsincomplete. In this study, we aimed to investigate mineralization of LMW DONcompounds in a paddy soil from different depths under different N fertilisationpractices; and to test the linkages between soil characteristics and LMW DONturnover. To accomplish this, we collected soils from different depths (i.e., 0-10, 1020, 20-30 and 30-40 cm) in a paddy field under long-term different fertilisationpractices (i.e., control without fertiliser, chemical fertiliser and organic fertiliseralone and their combination) in southern China. We measured soil physiochemicalproperties and abundance and structure of soil microbial communities after long-termfertilisation management. In 14C mineralization assay (7 days at 22 oC), we used theamino acid L-alanine and its peptide tri-L-alanine as model L-enantiomer substratesto investigate the rates of LMW DON mineralisation in paddy soils. Overall, adouble first-order kinetic model conformed very well to the experimental data ofamino acid and peptide mineralization. For both form of LMW DON, the poolsizes of both catabolic and anabolic processes were significantly affected by Nfertiliser, soil depth, and their interaction (P &#x003C;0.0001), thus contributing to pronounceddifferences in microbial C use efficiency among treatments. However, microbial uptakerates of peptide but not amino acid were significantly affected by N fertiliser, soildepth, and their interaction (all P &#x003C;0.05). Results of canonical correspondenceanalysis suggest that microbial C use efficiency of both LMW DON was positivelycorrelated with soil pH, while microbial uptake rates were predominately associatedwith other soil biochemistry properties (e.g. soil and microbial C and N indices). [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) is a key component of the carbon (C) cycle, and its accumulation is influenced by the stoichiometry of C: nitrogen (N): phosphorus (P), as well as microbial metabolism. However, the mechanisms driving SOC accumulation in agricultural and natural soils remain unclear. Therefore, this study aimed to investigate the impact of soil and microbial biomass (MB) C:N:P stoichiometry and microbial metabolic limitation on SOC accumulation in agricultural and natural soils. A survey of soils from 277 locations in eastern China was conducted, revealing that agricultural soils (paddy and upland soils) had 1.74-times higher SOC content than that of natural soils (wasteland and woodland soils). SOC showed a significant positive correlation with microbial C use efficiency (CUE), which in turn promoted SOC accumulation in agricultural soils. CUE was higher in agricultural soils (0.38–0.41) than in natural soils (0.25–0.31), which was attributed to reduced microbial metabolic limitation in agricultural soils. Increased nutrient supply was evident in agricultural soils, indicated by high SOC:TP, dissolved organic C:dissolved organic N, MBC:MBN, and MBC:MBP ratios, which alleviated microbial C and P limitations. However, in natural soils, low nutrient availability and enzyme activities resulted in significant microbial C and P limitations, thereby hindering SOC accumulation. Our results indicate that microbial metabolic limitation regulated by C:N:P stoichiometry stimulates SOC accumulation in agricultural soils, offering novel insights into SOC storage and emphasizing the importance of ecological stoichiometry and microbial metabolic limitation in SOC storage. [Display omitted] • Agricultural soils store more soil organic carbon than natural soils. • Carbon use efficiency was positively correlated with soil organic carbon. • Microbial C and P limitations negatively affected carbon use efficiency. • Decrease of the C:N:P stoichiometric ratios increased carbon use efficiency. [ABSTRACT FROM AUTHOR]

A decrease in C inputs from the return of crop residues to soil has occurred in many regions worldwide in recent years. The effects of this decline in C inputs could provide valuable information for assessing the long-term impact of litter C inputs on soil organic C (SOC) in rice paddy soils. The present study aimed to evaluate the response of rice paddy SOC accumulation to changes in actual C inputs in subtropical China, with emphasis on the response of C accumulation to declining C inputs. For this, we used a long-term field experiment on paddy soil in a rice-rice ( Oryza sativa L.) cropping system running from 1990 to 2014. The four treatments were CK (control, no fertilizer), OM (organic matter application), NPK (N, P, and K fertilizer application), and NPKOM (NPK and organic matter application). Organic matter application for the OM and NPKOM treatments included rice straw and green manure that were left in the field after harvest and chopped, along with rice residues with stubbles and roots. In all treatments, C sequestration showed an increasing trend (from 0.207 to 0.880 g kg −1 yr −1 ) in the early and middle stages of the experiment (1990–2006) followed by a decreasing trend (from −0.429 to −0.064 g kg −1 yr −1 ) in the late stage (2007–2014). The trends were more pronounced for the OM and NPKOM treatments than for their CK and NPK counterparts. The changes in SOC stocks were consistent with changes in C inputs ( p < 0.01). During the late stage, yield and litter inputs from crop residues and green manure decreased, quickly affecting SOC stock in paddy soils. This declining trend in annual rice yields was mainly caused by the decline in first rice yields, accounting for 42.3–91.5% of the decrease in annual C inputs. Insufficient P or N and K supply and unfavorable climatic factors (decreases in sunshine duration and both maximum and minimum temperatures) are possible reasons for the decline in first rice yields and green manure biomass in the late stage. Collectively, the results suggest that C stocks in high-productivity paddy soils respond very sensitively to a decline in C inputs. This raises the risk of loss of C stock in paddy soil if, in the long run, a large return of C to soil with crop residues or by other sources, e.g., green manure, cannot be achieved. [ABSTRACT FROM AUTHOR]

Reclamation has been widely used to alleviate the degradation of cultivated upland and support the increasing grain demand. However, the response of soil ecosystem functioning and soil health to the reclamation of coastal wetlands remains unclear. A reclaimed soil chronosequence over 1000 years in Hangzhou Bay, China, was analyzed to assess two key approaches to evaluate soil health. We used the minimum data set along with the soil quality index (SQI) area and the sensitivity–resistance approaches. The physicochemical properties of the reclaimed soils changed drastically at the initial stage (during the first 60 years) but only marginally thereafter. Owing to continuous freshwater irrigation, plant cultivation, fertilization, and desalination, from natural tidal flats converted to vegetable fields, the SQI and soil multifunctional index increased along the reclamation chronosequence. The soil properties sensitive to the reclamation of coastal wetlands (electrical conductivity, exchangeable potassium, and enzyme activities) explained most of the variation in the SQI area, followed by the resistance indicators. This suggests that small changes in the sensitivity indicators might have considerable impacts on the improvement of soil quality. The most resistant properties with the slowest changes included pH and physical characteristics—water content, bulk density, and aggregate size classes. The quality indicators identified for reclaimed soils in Hangzhou Bay based on the SQI area and sensitivity–resistance approaches can be useful for soil health evaluation for soils affected by natural and anthropogenic factors. These approaches and indicators can be effectively used to evaluate soil quality and develop sustainable agriculture. [Display omitted] • Soil quality indexes (SQI) were used and analyzed in a chronosequence of tidal flat reclamation. • SQI area and sensitivity–resistance approaches were useful for soil health evaluation. • Tidal flat reclamation increased soil quality and multifunctionality in Hangzhou Bay. • Sensitive parameters explained more variability of SQI area index than resistant soil properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • Soil P limitation constrains rather than promotes microbial C metabolism. • Removal of microbial P limitation by P addition increases CO 2 release from soils by 19%–26% • Negative or positive relationship of microbial C and P limitations depend on soil C availability. • Alleviated microbial P limitation promotes soil C release via q CO 2 and priming effect under C sufficiency. • Soil native C decomposition via priming effect dominates soil C release under C limitation. 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 13C-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 (q CO 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 CO 2 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 CO 2 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 q CO 2 and decreasing CUE. At late incubation, however, P addition increasing decomposition of native soil C via PE is the dominated control on CO 2 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. [ABSTRACT FROM AUTHOR]

Abstract: Soil organic matter (SOM) content in paddy soils is higher than that in upland soils in tropical and subtropical China. The dissolved organic matter (DOM) concentration, however, is lower in paddy soils. We hypothesize that soil moisture strongly controls the fate of DOM, and thereby leads to differences between the two agricultural soils under contrasting management regimens. A 100-day incubation experiment was conducted to trace the fate and biodegradability of DOM in paddy and upland soils under three moisture levels: 45%, 75%, and 105% of the water holding capacity (WHC). 14C labeled DOM, extracted from the 14C labeled rice plant material, was incubated in paddy and upland soils, and the mineralization to 14CO2 and incorporation into microbial biomass were analyzed. Labile and refractory components of the initial 14C labeled DOM and their respective half-lives were calculated by a double exponential model. During incubation, the mineralization of the initial 14C labeled DOM in the paddy soils was more affected by moisture than in the upland soils. The amount of 14C incorporated into the microbial biomass (2.4–11.0% of the initial DOM-14C activity) was less affected by moisture in the paddy soils than in the upland soils. At any of the moisture levels, 1) the mineralization of DOM to 14CO2 within 100days was 1.2–2.1-fold higher in the paddy soils (41.9–60.0% of the initial DOM-14C activity) than in the upland soils (28.7–35.7%), 2) 14C activity remaining in solution was significantly lower in the paddy soils than in the upland soils, and 3) 14C activity remaining in the same agricultural soil solution was not significantly different among the three moisture levels after 20days. Therefore, moisture strongly controls DOM fate, but moisture was not the key factor in determining the lower DOM in the paddy soils than in the upland soils. The UV absorbance of DOM at 280nm indicates less aromaticity of DOM from the paddy soils than from the upland soils. At any of the moisture levels, much more labile DOM was found in paddy soils (34.3–49.2% of the initial 14C labeled DOM) compared with that in upland soils (19.4–23.9%). This demonstrates that the lower DOM content in the paddy soil compared with that in the upland soil is probably determined by the less complex components and structure of the DOM. [Copyright &y& Elsevier]

Denitrification is important for nitrogen balance in agricultural ecosystems. It is well established that the abundance and structure of denitrifier are strongly influenced by environmental factors. However, knowledge of how nirS - and nirK -harboring microbial communities vary in paddy soils of different climatic regions is lacking, along with how these microbes are associated with denitrification potential. In this study, forty paddy soils from tropical, sub-tropical, warm-temperate, and mid-temperate climate zones were collected. The results showed that soils from the sub-tropical zone had the highest denitrification rates. The abundances of nirS and nirK had a strong negative association with C/N ratio and clearly varied among the four climate zones. Variation in nirS- and nirK- containing communities existed across sampling sites from each climate zone in terms of α- and β-diversity. Soil pH and climate factors significantly affected community diversity. Network analysis revealed that different climate regions had similar keystone taxa like Azospira , and Achromobacter , which were significantly related to denitrification rates. Structural equation modeling indicated that the differences in denitrifying enzyme activity among the four climate zones were mostly explained by climate factors, soil pH, and nirS biodiversity. Specifically, the biodiversity of nirS was more important than that of nirK in regulating potential denitrification activity in paddy soil, suggesting that nirS- type denitrifiers may have high activity under anaerobic conditions. Our results allow a deeper insight into the relative contribution of nirS- and nirK- containing communities to the soil denitrification activity in paddy soils across climate zones. This study highlighted the need of manipulation experiment to explain how denitrifier biodiversity affect potential denitrification activity in the future. • Soils from the sub-tropical zone have the highest denitrification rates. • nirS and nirK gene abundances show clear variations among the four climate zones. • nirS and nirK gene abundances have strong negative associations with C/N ratio. • The pH, C/N and climate factor significantly affected the community structure. • nirS gene biodiversity is important to regulate denitrification rates in paddy soil. [ABSTRACT FROM AUTHOR]

• Upland decreased soil C, but increased soil P. • Paddy increased soil C, N and P, but N and P increases exceeded that of C. • Both paddy and upland decreased the soil C:N:P stoichiometric ratios. • Responses of soil C:N:P stoichiometry across all climatic zones were similar in direction. • Effects of agricultural use on C:N:P stoichiometry were greater in warmer and wetter zones. Agricultural land use profoundly alters soil carbon (C), nitrogen (N), and phosphorus (P) contents, impacting crop productivity, environmental quality, and soil C sequestration. However, how the soil C:N:P stoichiometry is affected by upland and paddy cropping over broad geographical scale remains largely unknown. The objective of this study is to examine the soil C:N:P stoichiometry in woodland (as control), agricultural upland and paddy from four climate zones (tropics, subtropics, warm temperate, and mid-temperate) across eastern China. 720 surface soil samples were collected from 240 sites with adjacent woodland, upland, and paddy at a depth of 0–15 cm. Total C, N, and P contents and their ratios were determined. Among climate zones, C and N contents and C:N ratios decreased in the order of mid-temperate > tropics > subtropics > warm temperate, whereas C:P and N:P ratios followed the order of subtropics > mid-temperate and tropics > warm-temperate. Compared to woodland, upland agriculture decreased the C content by 4.0–6.4 g kg−1, but increased P content by 0.2–0.5 g kg−1, resulting in the decreases of C:N, C:P, and N:P ratios by 1.4–5.1, 3.4–91.5, and 1.6–4.1, respectively. Hence, uplands are relatively limited by C and N but enriched with P, particularly in warm temperate zone. By contrast, the C, N, and P contents in paddy soils were all increased compared to woodland soils, but larger N and P increase leads to the decreases in C:N and C:P ratios. The higher P content, and consequently lower C:N:P ratios in both agricultural soils are the consequences of intensive fertilization. As a whole, the direction of soil C, N, and P contents and their stoichiometric ratios in response to agricultural use was similar in the four climate zones: P increased, but C:N:P ratios decreased. The more intensive agricultural practices and stronger biological and geochemical processes with higher temperature and precipitation in warmer and wetter zones lead to more pronounced differences of soil C, N, and P contents and their stoichiometric ratios among land-use types than those in cooler and drier climates. [ABSTRACT FROM AUTHOR]

The microbial community within the root system, the rhizosphere closely connected to the root, and their symbiotic relationship with the host are increasingly seen as possible drivers of natural pathogen resistance. Resistant cultivars have the most effective strategy in controlling the Chinese wheat yellow mosaic disease, but the roles of the root and rhizosphere microbial interactions among different taxonomic levels of resistant cultivars are still unknown. Thus, we aimed to investigate whether these microbial community composition and network characteristics are related to disease resistance and to analyze the belowground plant-associated microflora. Relatively high microbial diversity and stable community structure for the resistant cultivars were detected. Comparison analysis showed that some bacterial phyla were significantly enriched in the wheat root or rhizosphere of the resistant wheat cultivar. Furthermore, the root and rhizosphere of the resistant cultivars greatly recruited many known beneficial bacterial and fungal taxa. In contrast, the relative abundance of potential pathogens was higher for the susceptible cultivar than for the resistant cultivar. Network co-occurrence analysis revealed that a much more complex, more mutually beneficial, and a higher number of bacterial keystone taxa in belowground microbial networks were displayed in the resistant cultivar, which may have been responsible for maintaining the stability and ecological balance of the microbial community. Overall, compared with the susceptible cultivar, the resistant cultivar tends to recruit more potential beneficial microbial groups for plant and rhizosphere microbial community interactions. These findings indicate that beneficial rhizosphere microbiomes for cultivars should be targeted and evaluated using community compositional profiles. KEY POINTS: • Different resistance levels in cultivars affect the rhizosphere microbiome.. • Resistant cultivars tend to recruit more potential beneficial microbial groups. • Bacteria occupy a high proportion and core position in the microflora network., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Microorganisms play an essential role in nitrogen cycling and greenhouse gas emissions in soils and sediments. The recently discovered oxygenic denitrifiers are proposed to reduce nitrate and nitrite via nitric oxide dismutation directly to N 2 and O 2 . So far, the ecological role of these microbes is not well understood. The only available tool for a targeted study of oxygenic denitrifiers is their respective maker gene, nitric oxide dismutase (nod). Here, we established the use of PacBio long-read sequencing of nod gene amplicons to study the diversity and community structure of oxygenic denitrifiers. Two distinct sets of environmental samples, agricultural soil and lake sediment, were investigated as examples. The circular consensus sequences (ca 1.0 kb) obtained covered most substitution characteristic of NO dismutase and allowed for reliable classification of oxygenic denitrifiers. Distinct nod gene pools and community structure were revealed for the different habitats, with most sequence types affiliated to yet unidentified environmental nod lineages. The abundance of nod genes ranged 2.2 × 10 6 -3.2 × 10 7 gene copies g -1 soil or sediment, accounting for up to 3% of total bacterial 16S rRNA gene counts. This study indicates that nod-gene-targeted long-read sequencing can be a powerful tool for studying the ecology of these novel microbes, and the results also suggest that oxygenic denitrifiers are prevalent and abundant in different terrestrial samples, where they could play an important, but yet overlooked role in nitrogen transformations.

Phosphorus (P), despite being an essential nutrient element for plants growth in agricultural ecosystem, the low utilization rate of soil P and the environmental problems caused by soil P losses are serious. Therefore, scoping knowledge of the possible sources and utilization extent of soil P by microorganisms is very helpful for better understanding of promoting P utilization for sustainable agriculture. Oxygen isotope of phosphate technology is an effective tool to trace the sources of P. In this study, P contents and oxygen isotope composition of inorganic phosphate (δ 18 O P ) of different pools (H 2 O-P, NaHCO 3 -P, NaOH-P, and HCl-P) in typical agricultural soil from Northeast China and Central China were analyzed and quantified. The results showed that fertilizer and land use were important factors influencing the contents of H 2 O-P t and NaHCO 3 -P t and the soil TP contents from different types of soils were greatly affected by soil weathering degree. The δ 18 O P of different P pools indicated that the difference in utilization extent of different P fractions by microorganisms and the δ 18 O P values of different P fractions could be due to accumulation of multiple factors. The results will provide effective information for further study on sources and effective utilization of different P fractions in soil., (Copyright © 2019 Elsevier Ltd. All rights reserved.)