Effect of Casuarina Crushed Nodules, Rhizospheric Soil and Leaves Compost on Salt Tolerance of <i>Casuarina equisetifolia</i>L. and <i>Casuarina obesa</i>Miq.

Soil salinization is one of the major causes of land degradation. In Senegal, this phenomenon continues to grow, making soils unsuitable for agriculture. To rehabilitate salty lands, one of the recommended strategies is the use of salt-tolerant plants. Among them, plants of Casuarinaceae family form a relationship with symbiotic microorganisms such as arbuscular mycorrhizal fungi and nitrogen fixing bacteria. It has been shown that symbiotic microorganisms play an important role in the establishment of tolerant plants in saline conditions (Djighaly et al., 2018). They improve plant performance and reduce transplant shock under salt stress conditions (Diagne et al., 2014). These microorganisms can be used as biofertilizers. However, inocula containing symbiotic microorganisms are either too expensive or unavailable in many developing countries. The aim of this study is to test alternatively affordable and low-tech solutions to promote symbiotic interactions such as Casuarina crushed nodule, Casuarina rhizosphere soil and Casuarina leaves compost that may contain symbiotic microorganisms and also nutrients such as N and phosphorus. Two species of Casuarina (Casuarina equisetifolia L. and Casuarina obesa Miq.) were grown in the greenhouse on sterile soil to which an amendment was added (Casuarina crushed nodules, Casuarina Rhizospheric soil or Casuarina leaves compost). Plants were subjected to saline stress. After four months of cultivation, they were harvested and morphological and physiological parameters were determined. Results showed that inoculation with Casuarina crushed nodules, Casuarina rhizospheric soil and Casuarina leaves compost improved growth, total dry biomass, total chlorophyll and proline contents of C. equisetifolia and C. obesa plants in salt stress condition. These positive effects were more important in C. obesa plants amended with Casuarina leaves compost. This study shows that Casuarina leaves compost can play an important role in the rehabilitation of saline soils by improving Casuarina trees performance in saline conditions.

Effects of Consecutively Monocultured Rehmannia glutinosa L.on Diversity of Fungal Community in Rhizospheric Soil

Continuous monoculture problems, or replanting diseases, are one of the key factors affecting productivity and quality of Chinese medicinal plants. The underlying mechanism is still being explored. Most of the studies on continuous monoculture ofRehmannia glutinosa L. are focused on plant nutritional physiology, root exudate, and its autotoxieity. However, the changes in the diversity of microflora in the rhizosphere mediated by the continuous monoculture pattern have been remained unknown. In this study, terminal restriction fragment length polymorphism （T-RFLP） technique was used for fingerprinting fungal diversity in the rhizosphere soil sampled from the fields ofR. glutinosa monocultured for 1 and 2 yr. The results showed that the structure of fungal community in consecutively moncultured rhizosphere soil was different from that in control soil （no cropping soil）, and varied with the consecutive monoeulture years （1 and 2 yr）. The comprehensive evaluation index （D） of fungal community estimated by principal component analysis of fragment number, peak area, Shannon-Weiner index, and Margalef index was higher in 1 yr monoculture soil than that in 2 yr monoculture soil, suggesting that consecutive monoculture of R. glutinosa could be a causative agent to decrease the diversity of fungal community in the rhizosphere soil.

Nutrient coordination mechanism of tiger nut induced by rhizosphere soil nutrient variation in an arid area, China

Tiger nut is a bioenergy crop planted in arid areas of northern China to supply oil and adjust the planting structure.However,in the western region of Inner Mongolia Autonomous Region,China,less water resources have resulted in a scarcity of available farmland,which has posed a huge obstacle to planting tiger nut.Cultivation of tiger nut on marginal land can effectively solve this problem.To fully unlock the production potential of tiger nut on marginal land,it is crucial for managers to have comprehensive information on the adaptive mechanism and nutrient requirement of tiger nut in different growth periods.This study aims to explore these key information from the perspective of nutrient coordination strategy of tiger nut in different growth periods and their relationship with rhizosphere soil nutrients.Three fertilization treatments including no fertilization(N:P(nitrogen:phosphorous)=0:0),traditional fertilization(N:P=15:15),and additional N fertilizer(N:P=60:15)were implemented on marginal land in the Dengkou County.Plant and soil samples were collected in three growth periods,including stolon tillering period,tuber expanding period,and tuber mature period.Under no fertilization,there was a significant correlation between N and P contents of tiger nut roots and tubers and the same nutrients in the rhizosphere soil(P<0.05).Carbon(C),N,and P contents of roots were significantly higher than those of leaves(P<0.05),and the C:N ratio of all organs was higher than those under other treatments before tuber maturity(P<0.05).Under traditional fertilization,there was a significant impact on the P content of tiger nut tubers(P<0.05).Under additional N fertilizer,the accumulation rate of N and P was faster in stolons than in tubers(P<0.05)with lower N:P ratio in stolons during the tuber expansion period(P<0.05),but higher N:P ratio in tubers(P<0.05).The limited availability of nutrients in the rhizosphere soil prompts tiger nut to increase the C:N ratio,improving N utilization efficiency,and maintaining N:P ratio in tubers.Elevated N levels in the rhizosphere soil decrease the C:N ratio of tiger nut organs and N:P ratio in stolons,promoting rapid stolon growth and shoot production.Supplementary P is necessary during tuber expansion,while a higher proportion of N in fertilizers is crucial for the aboveground biomass production of tiger nut.

Effect of slope position on leaf and fine root C,N and P stoichiometry and rhizosphere soil properties in Tectona grandis plantations

Little is known about C-N-P stoichiometries and content in teak(Tectona grandis)plantations in South China,which are mostly sited on hilly areas with lateritic soil,and the effect of slope position on the accumulation of these elements in trees and rhizosphere soils.Here we analyzed the C,N,P content and stoichiometry in leaves,fine roots and rhizosphere soils of trees on the upper and lower slopes of a 12-year-old teak plantation.The Kraft classification system of tree status was used to sample dominant,subdominant and mean trees at each slope position.The results showed that the C,N and P contents in leaves were higher than in fine roots and rhizosphere soils.The lowest C/N,C/P and N/P ratios were found in rhizosphere soils,and the C/N and C/P ratios in fine roots were higher than in leaves.Nutrient accumulation in leaves,fine roots and rhizosphere soils were significantly influenced by slope position and tree class with their interaction mainly showing a greater effect on rhizosphere soils.Leaf C content and C/N ratio,fine root C and P contents,and C/N and C/P ratios all increased distinctly with declining slope position.The contents of organic matter(SOM),ammonium(NH4+-N),nitrate-nitrogen(NO3--N)and available potassium(AK)in rhizosphere soils were mainly enriched on upper slopes,but exchange calcium(ECa),available phosphorus(AP),and pH were relatively lower.Variations in the C,N and P stoichiometries in trees were mainly attributed to the differences in rhizosphere soil properties.N and P contents showed significant positive linear relationships between leaf and rhizosphere soil,and C content negative linear correlation among leaves,fine roots and rhizosphere soils.Chemical properties of rhizosphere soils,particularly C/N and NH4+-N,had significant effects on the leaf nutrients in trees on the upper slope.Correspondingly,rhizosphere soil properties mainly influenced fine root nutrients on the lower slope,and soil AK was the major influencing factor.Overall,these results offer new insights for the sustainability and management of teak plantations in hilly areas.

Isolation of phloridzin-degrading,IAA-producing bacterium Ochrobactrum haematophilum and its effects on the apple replant soil environment

We isolated and identified a bacterium that could produce IAA and degrade phloridzin in the rhizosphere soil of healthy replanted apple(the rootstock is M9T337 and the scion is Yanfu 3),providing a theoretical basis for reducing the obstacles associated with apple replant disease(ARD).Isolates were screened using Salkowski colorimetry and screening medium for phloridzin.The isolate of interest(W6)was identified as Ochrobactrum haematophilum based on morphological analysis,physiological and biochemical tests,and 16S rDNA sequencing.In a laboratory experiment,W6 produced auxin and promoted the growth of Arabidopsis thaliana roots,and its degradation rate of 100 mg.L^(-1 )phloridzin was 62.0%.In a pot experiment,W6 significantly reduced the phenolic acid contents of replanted soil,lowered the abundance of the harmful fungus Fusarium solani,and increased soil enzyme activities,thereby improving the micro-ecological environment of replant soil.W6 increased the root antioxidant enzyme activity and leaf photosynthetic pigment content of replanted Malus hupehensis Rehd.seedlings,effectively alleviating the decrease in net photosynthetic rate,transpiration rate and stomatal conductance caused by ARD.In a field experiment,W6 also promoted the growth of replanted apple(the rootstock is M9T337 and the scion is Yanfu 3)saplings.Therefore,W6 can promote apple growth and degrade phenolic acids,and it can be used as an effective treatment for the reduction of ARD.

Rhizosphere Soil Fungal Diversity and Soil Physicochemical Properties of Different Vegetations in Tundra of Changbai Mountain

By studying the diversity and community structure of rhizosphere soil fungi of different plants in the tundra on the northern slope of Changbai Mountain, it provides theoretical support for the restoration of environmental degradation and in-depth study of fungal diversity in the tundra of Changbai Mountain. High-throughput sequencing technology was used to determine the ITS1 region of fungal amplicons, so as to analyze the diversity of fungal communities in the rhizosphere soil of six plants in the tundra of Changbai Mountain, and to analyze the correlation between the environment and the diversity and richness of fungal communities in combination with relevant soil physical and chemical factors. The diversity and richness of fungal community in the rhizosphere soil of six plants in Changbai Mountain tundra were different. The Simpson and Shannon indexes of Saxifraga stolonifera Curt were the highest, and the richness of fungal community in Dryas octopetala was the highest. The analysis of fungal community composition showed that the fungal colonies in plant rhizosphere soil samples mainly belonged to Ascomycota and Basidiomycota, which were the main dominant phyla. Mortierella, Fusarium and Sordariomycetes are common fungal genera in the rhizosphere soil of six plants, but their abundances are different among different plants. Water content was negatively correlated with fungal diversity, and TP was positively correlated with fungal community diversity. There were some differences in the composition and diversity of rhizosphere soil fungal communities of six plants in Changbai Mountain tundra. Ascomycota and Basidiomycota were the main soil fungal phyla in the rhizosphere of six plants in Changbai Mountain tundra. The results could provide theoretical guidance for ecological protection of Changbai Mountain tundra.

The Preliminary Study on Screening and Application of Phthalic Acid-Degrading Bacteria

Phthalic acid is a main pollutant, which is also an important reason for the continuous cropping effect of tobacco. In order to degrade the phthalic acid accumulated in the environment and relieve the obstacle effect of tobacco continuous cropping caused by the accumulation of phthalic acid in the soil. In this study, phthalate degrading bacteria B3 is screened from continuous cropping tobacco soil. The results of biochemical identification and 16sDNA comparison show that the homology between degrading bacterium B3 and Enterobacter sp. is 99%. At the same time, the growth of Enterobacter hormaechei subsp. B3 and the degradation of phthalic acid under different environmental conditions are studied. The results show that the environment with a temperature of 30˚C, PH of 7, and inoculation amount of not less than 1.2%, which is the optimal growth conditions for Enterobacter sp. B3. In an environment with a concentration of phthalic acid not exceeding 500 mg/L, Enterobacter sp. B3 has a better effect on phthalic acid degradation, and the degradation rate can reach 77% in 7 d. The results of indoor potting experiments on tobacco show that the degradation rate of phthalic acid by Enterobacter B3 in the soil is about 45%, which can reduce the inhibitory effect of phthalic acid on the growth of tobacco seedlings. This study enriches the microbial resources for degrading phthalic acid and provides a theoretical basis for alleviating tobacco continuous cropping obstacles.

Effect of long-term continuous cropping of strawberry on soil bacterial community structure and diversity

Long-term monoculture leads to continuous cropping （CC） problems, which complicate agricultural production, both locally and abroad. This study contrasted the different bacterial community compositions, physicochemical properties and enzyme activities of strawberry soil subjected to CC, CC rhizosphere （CCR）, non-CC （NCC） and non-CC rhizosphere （NCCR） treatments. The soil physicochemical properties and enzyme activities were significantly reduced after long-term CC. In addition, five variation trends were observed for the 11 major bacterial genera in the soil. Sphingomonas was the only stable group among all treatments. The proportions of Novosphingobium, Rhodoplanes, Povalibacter, Cellvibrio and Stenotrophobacterdecreased after CC. The relative abundances of Pelagibius, Thioprofundum and AIIokutzneria increased only in the CC treatment. Nitrospira were more abundant in rhizosphere soil than in non-rhizosphere soil. The relative abundance of Bacillus increased after CC. Redundancy analysis revealed that Bacillus, Pelagibius and AIIokutzneria had significant negative correlations with the soil physicochemical properties and enzyme activities. Therefore, these genera may be the key bacteria influenced by the physicochemical properties and enzyme activities altered by replanting. These results indicate that long-term CC of strawberry leads to less favourable rhizosphere soil conditions, which can be understood as a stress-induced response of the bacterial community diversity. Further research is needed to determine how the quality of soil is reduced by the shift in the diversity of the soil bacterial community.

Effects of reduced nitrogen and suitable soil moisture on wheat(Triticum aestivum L.) rhizosphere soil microbiological,biochemical properties and yield in the Huanghuai Plain,China

Soil management practices affect rhizosphere microorganisms and enzyme activities, which in turn influence soil ecosystem processes. The objective of this study was to explore the effects of different nitrogen application rates on wheat(Triticum aestivum L.) rhizosphere soil microorganisms and enzyme activities, and their temporal variations in relation to soil fertility under supplemental irrigation conditions in a fluvo-aquic region. For this, we established a split-plot experiment for two consecutive years(2014–2015 and 2015–2016) in the field with three levels of soil moisture: water deficit to no irrigation(W1), medium irrigation to(70±5)% of soil relative moisture after jointing stage(W2), and adequate irrigation to(80±5)% of soil relative moisture after jointing stage(W3);and three levels of nitrogen: 0 kg ha^–1(N1), 195 kg ha^–1(N2) and 270 kg ha^–1(N3). Results showed that irrigation and nitrogen application significantly increased rhizosphere microorganisms and enzyme activities. Soil microbiological properties showed different trends in response to N level;the highest values of bacteria, protease, catalase and phosphatase appeared in N2, while the highest levels of actinobacteria, fungi and urease were observed in N3. In addition, these items performed best under medium irrigation(W2) relative to W1 and W3;particularly the maximum microorganism(bacteria, actinobacteria and fungi) amounts appeared at W2, 5.37×10^7 and 6.35×10^7 CFUs g^–1 higher than those at W3 in 2014–2015 and 2015–2016, respectively;and these changes were similar in both growing seasons. Microbe-related parameters fluctuated over time but their seasonality did not hamper the irrigation and fertilization-induced effects. Further, the highest grain yields of 13 309.2 and 12 885.7 kg ha^–1 were both obtained at W2 N2 in 2014–2015 and 2015–2016, respectively. The selected properties, soil microorganisms and enzymes, were significantly correlated with wheat yield and proved to be valuable indicators of soil quality. These results clearly demonstrated that the combined treatment(W2 N2) significantly improved soil microbiological properties, soil fertility and wheat yield on the Huanghuai Plain, China.

Rhizosphere and bulk soil enzyme activities in a Nothotsuga longibracteata forest in the Tianbaoyan National Nature Reserve,Fujian Province,China

The rhizosphere, distinct from bulk soil, is defined as the volume of soil around living roots and influenced by root activities. We investigated protease, invertase, cellulase, urease, and acid phosphatase activities in rhizosphere and bulk soils of six Nothotsuga longibracteata forest communities within Tianbaoyan National Nature Reserve, including N. longibracteata ＋ either Phyllostachys pubescens, Schima superba, Rhododendron simiarum, Cunninghamia lanceolata, or Cyclobalanopsis glauca, and N. longibracteata pure forest. Rhizosphere soils possessed higher protease, invertase, cellulase, urease, and acid phosphatase activities than bulk soils. The highest invertase, urease, and acid phosphatase activities were observed in rhizosphere samples of N. longibracteata ＋ S. superba. Protease was highest in the N. longibracteata ＋ R. simiarum rhizosphere, while cellulase was highest in the pure N. longibracteata forest rhizosphere. All samples exhibited obvious rhizosphere effects on enzyme activities with a significant linear correlation between acid phosphatase and cellulase activities （p 〈 0.05） in rhizosphere soils and between protease and acid phosphatase activities （p 〈 0.05） in bulk soils. A principal component analysis, correlating 13 soil chemical properties indices relevant to enzyme activities, showed that protease, invertase, acid phosphatase, total N, and cellulase were the most important variables impacting rhizosphere soil quality.

Role of the different planting age of seabuckthorn forests to soil amelioration in coal mining subsidence land

To investigate the effects of seabuckthorn(Hippophae rhamnoides)on soil amelioration,using the space replacement method,soil physical and chemical indexes as well as the microorganism quantity and soil enzyme activities were analyzed.The results showed that:the soil bulk density of surface soil decreased and soil porosity and field capacity increased after afforestation with seabuckthorn.The plant was found to effectively reduce the soil pH,increase the soil conductivity,soil organic matters and available nutrients.Soil microorganism quantity,soil enzyme activities were both higher in 0-20 cm layer than in 20-40 cm layer.With the increase years of remediation with seabuckthorn,the quantity of soil microorganism and enzyme activities were increasing to a higher level 5 to 8 years later.Our study indicates that seabuckthorn can effectively improve soil physical and chemical properties,increase the quantity of soil microorganisms and enzyme activities,which is of great significance for the ecosystem restoration in mining areas.

Nitrogen application and intercropping change microbial community diversity and physicochemical characteristics in mulberry and alfalfa rhizosphere soil

Intercropping of mulberry(Morus alba L.)and alfalfa(Medicago sativa L.)is a new forestry-grass compound model in China,which can provide high forage yields with high protein.Nitrogen application is one of the important factors determining the production and quality of this system.To elucidate the advantages of intercropping and nitrogen application,we analyzed the changes of physicochemical properties,enzyme activities,and microbial communities in the rhizosphere soil.We used principal components analysis(PCA)and redundancy discriminators analysis to clarify the relationships among treatments and between treatments and environmental factors,respectively.The results showed that nitrogen application significantly increased pH value,available nitrogen content,soil water content(SWC),and urea(URE)activity in rhizosphere soil of monoculture mulberry.In contrast,intercropping and intercropping+N significantly decreased pH and SWC in mulberry treatments.Nitrogen,intercropping and intercropping+N sharply reduced soil organic matter content and SWC in alfalfa treatments.Nitrogen,intercropping,and intercropping+N increased the values of McIntosh diversity(U),Simpson diversity(D),and Shannon-Weaver diversity(H’)in mulberry treatments.However,PC A scatter plots showed clustering of monoculture mulberry with nitrogen(MNE)and intercropping mulberry without nitrogen(M0).Intercropping reduced both H’and D but nitrogen application showed no effect on diversity of microbial communities in alfalfa.There were obvious differences in using the six types of carbon sources between mulberry and alfalfa treatments.Nitrogen and intercropping increased the numbers of sole carbon substrate in mulberry treatments where the relative use rate exceeded 4%.While the numbers declined in alfalfa with nitrogen and intercropping.RDA indicated that URE was positive when intercropping mulberry was treated with nitrogen,but was negative in monoculture alfalfa treated with nitrogen.Soil pH and SWC were positive with mulberry treatments but were negative with alfalfa treatments.Intercropping with alfalfa benefited mulberry in the absence of nitrogen application.Intercropping with alfalfa and nitrogen application could improve the microbial community function and diversity in rhizosphere soil of mulberry.The microbial community in rhizosphere soil of mulberry and alfalfa is strategically complementary in terms of using carbon sources.

Screening of Actinomycetes from Medicinal Plant Rhizosphere Soils for Industrial Enzymes and Antimicrobial Activity

This study aimed to investigate the production of some metabolites （i.e., antibiotics, amylases and cellulases） of terrestrial actinomycetes isolated from medicinal plant rhizosphere soils. Initially, the soil samples were collected from Camellia sinensis （L） Okuntze., Peuraria mirifca Airy Shaw Suvatabandhua., Ananus comosus Merr., Elephantopus scaber Linn., Orthosiphon grandiforus Bolding., Jatropha multifda Linn. and Senna siamea. To screen and isolate actinomycetes, the soil samples were pretreated by air-drying and subsequent heat incubation. The bacterial isolates exhibiting actinomycetes features were then randomly screened for their production of amylases, cellulases and antibiotics. It was found that 130 isolates （from 136） could produce amylases; 40 （from 107） produced cellulases; and seven （from 45） exhibited antimicrobial activity. The data of this study were preliminary, and yet demonstrated a rich diversity of rhizo-actinomycetes from medicinal plants. Besides, these organisms could be an untapped source for discovering of biotechnologically useful metabolites.

Research Progress on Effects of Continuous Cropping on Soil Microbial Florae and Its Restoration

Continuous cropping has become a common form of agricultural production at present, but with the increase of continuous cropping years, continuous cropping obstacles such as soil-borne diseases and plant growth potential decline are becoming more and more common. At present, the causes of continuous cropping obstacles and continuous cropping restoration have become a hot issue in agricultural research. This paper summarized the effects of continuous cropping obstacles on soil microbial community structure and main technical methods to repair continuous cropping obstacles, such as agricultural measure management, microbial balance adjustment and soil improvement, aiming to provide theoretical reference for protecting the sustainable utilization of soil ecosystem and ensuring the stability of crop production.

Restoration potential of pioneer plants growing on lead-zinc mine tailings in Lanping, southwest China

This study focused on the restoration potential of ten pioneer plants (Artemisia roxburghiana, Artemisia tangutica, Carex inanis, Cyperaceae hebecarpus, Plantago depresa, Cynoglossum lanceolatum, Potentilla saundesiana, Coriaria sinica, Oxyria sinensis, and Miscanthus nepalensis) during the early phase of Pb-Zn mine tailings phytostabilization, in Lanping, China. The concentrations of heavy metals (Pb, Zn, and Cu) and soil fertility (the available N, P, K, and organic matter) in the rhizosphere of these spe...

Biodiversity of arbuscular mycorrhizal fungi in different trees of madhupur forest, Bangladesh

Roots and rhizosphere soils of Acacia auriculiformis A. Cunn. ex Benth., A. mangium Wild., Artocarpus heterophyUus Lamk. C., Dalbergia sissoo Roxb. ex A. P. D., Eucalyptus camaldulensis Dehnn., Hevea brasiliensis （Wild. ex Juss） Muell. Arg., Swietenia macrophylla King. and Tectona grandis L. were collected from different locations of Madhupur forest area to study the biodiversity of Arbuscular Mycorrhizal （AM） fungal colonization and spore population. All the plants showed AM colonization. Out of eight selected plants, mycelial colonization was lowest in the roots of A. heterophyllus （22%） and the highest was in the roots of H. brasiliensis （78%）. Mycelial intensity was observed poor （25%-77%） and moderate （23%-57%） in all plants species and abundant （11%-40%） was in most of the plant species. Vesicular colonization was observed in five plant species. The lowest was recorded in E. camaldulensis （4%） and the highest was in H. brasiliensis （21%）. Poor （24%-56%）, moderate （16%-100%） and abundant （11%-40%） type of vesicular intensity were observed. Arbuscular colonization was observed in three plants. The highest was in A. mangium （72%） and the lowest was in S. macrophylla （17%）. Arbuscular intensity was recorded as poor （12%-44%）, moderate （22%-100%） and abundant （4%-47%）. The highest AM fungal spore population was in A. auriculiformis （714） and the lowest was in D. sissoo （102）. Five AM fungal genera were recorded. Glomus was found to be dominant. A few spores remained unidentified. Significant correlation was observed between percent coloniza- tion and spore population. The results of the present study indicate the occurrence of AM fungi and the mycotrophism of the plants of Madhupur forest area and the applicability of AM technology in the forest management of Madhupur forest.

Effects of different rotation patterns on the occurrence of clubroot disease and diversity of rhizosphere microbes

Clubroot disease, caused by Plasmodiophora brassicae, is one of the most destructive soil-borne diseases in cruciferous crops worldwide. New strategies are urgently needed to control this disease, as no effective disease-resistant varieties or chemical control agents exist. Previously, we found that the incidence rate and disease index of clubroot in oilseed rape decreased by 50 and 40%, respectively, when oilseed rape was planted after soybean. In order to understand how different rotation patterns affect the occurrence of clubroot in oilseed rape, high-throughput sequencing was used to analyze the rhizosphere microbial community of oilseed rape planted after leguminous (soybean, clover), gramineous (rice, maize) and cruciferous (oilseed rape, Chinese cabbage) crops. Results showed that planting soybeans before oilseed rape significantly increased the population density of microbes that could inhibit P. brassicae (e.g., Sphingomonas, Bacillus, Streptomyces and Trichoderma). Conversely, consecutive cultivation of cruciferous crops significantly accumulated plant pathogens, including P. brassicae, Olpidium and Colletotrichum (P<0.05). These results will help to develop the most effective rotation pattern for reducing clubroot damage.

Biochar pyrolyzed at low temperature enhanced acidophilous plant growth by promoting rhizospheric microbes in a slightly alkaline urban soil

Biochar has been considered as a potential way to enhance acidophilous plant growth in alkaline soils.However,whether such enhancements are closely linked with biochar pyrolysis temperature and its improvements in rhizospheric soil fertility and microbial activities remains largely unknown.We performed a pot experiment to investigate changes in azalea(Rhodo-dendron)morphology and physiology,as well as its rhizosphere soil chemical and biological properties in a slightly alkaline urban soil under the amendment of biochars that pyrolyzed at three temperatures(i.e.,350,550 and 700°C).Our results showed that the effects of biochars on plant growth and soil properties depended on pyrolysis temperature.In comparison with the non-amended control,350 and 550°C biochars showed significant promotions on the azalea growth in terms of photosynthetic characteristics,biomass,root morphology,and N and P uptake.Whereas,700°C biochar showed an inhibi-tion effect on them.350°C biochar decreased soil pH and increased soil available P and K contents and the activities ofα-glucosidase,N-β-glucosaminidase,phosphatase and sulfatase.In addition,350°C biochar significantly enhanced bacterial 16S rRNA and fungal 18S rRNA gene abundances in the rhizosphere soil of azalea and mycorrhizal infection.Correlation analysis indicated that soil pH,available nutrients and fungal abundance had positive associations with the enhanced plant growth parameters.Therefore,our findings suggest that biochar produced at low temperature could be a feasible strategy for enhancing acidophilous azalea growth and improving urban soil quality.

Comparison of rhizosphere and endophytic microbial communities of Chinese leek through high-throughput 16S rRNA gene Illumina sequencing

Chinese leek（Allium tuberosum Rottler ex Sprengel） is a common vegetable in China. In our previous study, Chinese leek in rotation was found to have significant antifungal and nematicidal activity. This study＇s aim was to investigate the potential antifungal and nematicidal activity associated with rhizosphere or endophytic microbes of Chinese leek. Thus, a total of 79 261 high-quality sequences were obtained from Chinese leek rhizosphere soil, leaf and root samples. In the rhizosphere soil, the bacterial community comprised five dominant phyla： Proteobacteria（37.85%）, Acidobacteria（10.99%）, Bacteroidetes（8.24%）, Cyanobacteria（7.79%） and Planctomycetes（7.1%）. The leaf and root bacterial communities comprised two dominant phyla： Cyanobacteria（83.42% in leaf and 75.44% in root） and Proteobacteria（14.75% in leaf and 21.04% in root）. Microbial diversity, richness and evenness in the rhizosphere soil bacterial community were higher than that in the endophytic bacterial communities. The rhizosphere bacterial community was significantly different from the endophytic bacterial communities. The endophytic bacterial communities from the leaf and the root were slightly, but not significantly different from each other. This study＇s findings would contribute to the isolation and identification of nematicidal and antifungal bacterial communities in Chinese leek.

Influencing factors and partitioning methods of carbonate contribution to CO_(2)emissions from calcareous soils

In calcareous soils,recent studies have shown that soil-derived CO_(2)originates from both soil organic carbon(SOC)decomposition and soil inorganic carbon(SIC)dissolution,a fact often ignored in earlier studies.This may lead to overestimation of the CO_(2)emissions from SOC decomposition.In calcareous soils,there is a chemical balance between precipitation and dissolution of CaCO_(3)-CO_(2)-HCO_(3),which is affected by soil environmental factors(moisture,temperature,pH and depth),root growth(rhizosphere effect)and agricultural measures(organic materials input,nitrogen fertilization and straw removal).In this paper,we first introduced the contribution of SIC dissolution to CO_(2)emissions from calcareous soils and their driving factors.Second,we reviewed the methods to distinguish two CO_(2)sources released from calcareous soils and quantify the 13C fractionation coefficient between SIC and SIC-derived CO_(2)and between SOC and SOC-derived CO_(2),and to partition three CO_(2)sources released from soils with plants and organic materials input.Finally,we proposed methods for accurately distinguishing three CO_(2)sources released from calcareous soils.This review helps to improve the accuracy of soil C balance assessment in calcareous soils,and also proposes the direction of further investigations on SIC-derived CO_(2)emissions responses to abiotic factors and agricultural measures.