Soybean(Glycine max)rhizosphere organic phosphorus recycling relies on acid phosphatase activity and specific phosphorusmineralizing-related bacteria in phosphate deficient acidic soils

Bacteria play critical roles in regulating soil phosphorus(P) cycling. The effects of interactions between crops and soil P-availability on bacterial communities and the feedback regulation of soil P cycling by the bacterial community modifications are poorly understood. Here, six soybean(Glycine max) genotypes with differences in P efficiency were cultivated in acidic soils with long-term sufficient or deficient P-fertilizer treatments. The acid phosphatase(AcP) activities, organic-P concentrations and associated bacterial community compositions were determined in bulk and rhizosphere soils. The results showed that both soybean plant P content and the soil AcP activity were negatively correlated with soil organic-P concentration in P-deficient acidic soils. Soil P-availability affected the ɑ-diversity of bacteria in both bulk and rhizosphere soils. However, soybean had a stronger effect on the bacterial community composition, as reflected by the similar biomarker bacteria in the rhizosphere soils in both P-treatments. The relative abundance of biomarker bacteria Proteobacteria was strongly correlated with soil organic-P concentration and AcP activity in low-P treatments. Further high-throughput sequencing of the phoC gene revealed an obvious shift in Proteobacteria groups between bulk soils and rhizosphere soils, which was emphasized by the higher relative abundances of Cupriavidus and Klebsiella, and lower relative abundance of Xanthomonas in rhizosphere soils. Among them, Cupriavidus was the dominant phoC bacterial genus, and it was negatively correlated with the soil organic-P concentration. These findings suggest that soybean growth relies on organic-P mineralization in P-deficient acidic soils, which might be partially achieved by recruiting specific phoCharboring bacteria, such as Cupriavidus.

Morphological Characterization of Arbuscular Mycorrhizal Fungi Associated with the Rhizosphere According to the Age of Xanthosoma sagittifolium L. Schott Plants in the Field

The objective of this work was to carry out a morphological characterization of arbuscular mycorrhizal fungi in the rhizosphere of Xanthosoma sagittifolium L. Schott plants. The plant material used was the white and red cultivars of X. sagittifolium, belonging to age intervals of 3 - 6, 6 - 9, and 9 - 12 months. Three harvest sites were chosen in the Central Region of Cameroon. In each site, soil from the rhizosphere and plant roots was collected in a randomized manner. In the field, the agronomic parameters were evaluated. The physicochemical characteristics of the soils, the mycorrhization index, and the morphological characterization of the mycorrhizal types of each site were carried out. The results obtained show that the agronomic growth parameters varied significantly using the Student Newman and Keuls Test depending on the harvest sites. The soils’ pH in all sites was acidic and ranged between 4.6 and 5.8. The Nkometou site has a loamy texture while the Olembe and Soa sites have loam-clay-sandy and loam-clay textures respectively. The highest mycorrhization frequencies appeared at the Nkometou site, with 75 and 87.33% of the white and red cultivars plant roots at 6 - 9 and 3 - 6 months. The relative abundance of AMF arbuscular mycorrhizal fungal spores in the rhizosphere of X. sagittifolium plants varied with age and cultivar. There were 673 spores between 9 - 12 months in Nkometou in the red cultivar. Six AMF genera were identified in all the different soils collected: Acaulospora sp., Funneliformis sp., Gigaspora sp., Glomus sp., Scutellospora sp., and Septoglomus sp. The genus Glomus sp. was the most present at all age intervals in both cultivars.

Changes in the activities of key enzymes and the abundance of functional genes involved in nitrogen transformation in rice rhizosphere soil under different aerated conditions

Soil microorganisms play important roles in nitrogen transformation. The aim of this study was to characterize changes in the activity of nitrogen transformation enzymes and the abundance of nitrogen function genes in rhizosphere soil aerated using three different methods(continuous flooding(CF), continuous flooding and aeration(CFA), and alternate wetting and drying(AWD)). The abundances of amoA ammonia-oxidizing archaea(AOA) and ammonia-oxidizing bacteria(AOB), nirS, nirK, and nifH genes, and the activities of urease, protease, ammonia oxidase, nitrate reductase, and nitrite reductase were measured at the tillering(S1), heading(S2), and ripening(S3) stages. We analyzed the relationships of the aforementioned microbial activity indices, in addition to soil microbial biomass carbon(MBC) and soil microbial biomass nitrogen(MBN), with the concentration of soil nitrate and ammonium nitrogen. The abundance of nitrogen function genes and the activities of nitrogen invertase in rice rhizosphere soil were higher at S2 compared with S1 and S3 in all treatments. AWD and CFA increased the abundance of amoA and nifH genes, and the activities of urease, protease, and ammonia oxidase, and decreased the abundance of nirS and nirK genes and the activities of nitrate reductase and nitrite reductase, with the effect of AWD being particularly strong. During the entire growth period, the mean abundances of the AOA amoA, AOB amoA, and nifH genes were 2.9, 5.8, and 3.0 higher in the AWD treatment than in the CF treatment, respectively, and the activities of urease, protease, and ammonia oxidase were 1.1, 0.5, and 0.7 higher in the AWD treatment than in the CF treatment, respectively. The abundances of the nirS and nirK genes, and the activities of nitrate reductase and nitrite reductase were 73.6, 84.8, 10.3 and 36.5% lower in the AWD treatment than in the CF treatment, respectively. The abundances of the AOA amoA, AOB amoA, and nifH genes were significantly and positively correlated with the activities of urease, protease, and ammonia oxidase, and the abundances of the nirS and nirK genes were significantly positively correlated with the activities of nitrate reductase. All the above indicators were positively correlated with soil MBC and MBN. In sum, microbial activity related to nitrogen transformation in rice rhizosphere soil was highest at S2. Aeration can effectively increase the activity of most nitrogen-converting microorganisms and MBN, and thus promote soil nitrogen transformation.

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.

Different genotypes regulate the microbial community structure in the soybean rhizosphere

The soybean rhizosphere has a specific microbial community,but the differences in microbial community structure between different soybean genotypes have not been explained.The present study analyzed the structure of the rhizosphere microbial community in three soybean genotypes.Differences in rhizosphere microbial communities between different soybean genotypes were verified using diversity testing and community composition,and each genotype had a specific rhizosphere microbial community composition.Co-occurrence network analysis found that different genotype plant hosts had different rhizosphere microbial networks.The relationship between rhizobia and rhizosphere microorganisms in the network also exhibited significant differences between different genotype plant hosts.The ecological function prediction found that different genotypes of soybean recruited the specific rhizosphere microbial community.These results demonstrated that soybean genotype regulated rhizosphere microbial community structure differences.The study provides a reference and theoretical support for developing soybean microbial inoculum in the future.

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.

Rhizosphere bacterial communities and soil nutrient conditions reveal sexual dimorphism of Populus deltoides

Sexual dimorphism of plants shapes the diff erent morphology and physiology between males and females.However,it is still unclear whether it infl uences belowground ecological processes.In this study,rhizosphere soil of male and female Populus deltoides and bulk soil were collected from an 18-year plantation(male and female trees mix-planted)and grouped into three soil compartments.Soil carbon(C),nitrogen(N)and phosphorus(P)levels were determined,and soil bacterial communities were analyzed by high-throughput sequencing.The results showed the less total carbon and total organic carbon,the more nutrients(available phosphorus,nitrate nitrogen and ammonium nitrogen)available in the rhizosphere soils of female poplars than soils of males.However,α-diversity indices of the rhizosphere bacterial communities under male plants were signifi-cantly higher.Principal component analysis showed that the bacterial communities were signifi cantly diff erent between the male and female soil compartments.Further,the bacterial co-occurrence network in soil under male trees had more nodes and edges than under females.BugBase analysis showed the more functional bacteria taxa related to biofi lm formation and antioxidation under males.The results indicate that soils under male poplars had more diverse and more complex co-occurrence networks of the rhizosphere bacterial community than soils under female trees,implying that male poplars might have better environmental adaptability.The study provides insight into the diff erent soil-microbe interactions of dioecious plants.More details about the infl uencing mechanism of sexual dimorphism on rhizosphere soil bacterial communities need to be further studied.

Correction to:Effect of slope position on leaf and fi ne root C,N and P stoichiometry and rhizosphere soil properties in Tectona grandis plantations

During production process,the below mentioned errors appeared in the original article and inadvertently published with error.The corrections are as given below.

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.

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.

Changes in fungal community and diversity in strawberry rhizosphere soil after 12 years in the greenhouse

Soil fungi play a very important role in the soil ecological environment. In agricultural production, long-term monoculture and continuous cropping lead to changes in fungal community diversity. However, the effects of long-term monoculture and continuous cropping on strawberry plant health and fungal community diversity have not been elucidated. In this study, using high-throughput sequencing(HTS), we compared the fungal community and diversity of strawberry rhizosphere soil after various durations of continuous cropping(0, 2, 4, 6, 8, 10 and 12 years). The results showed that soil fungal diversity increased with consecutive cropping years. Specifically, the soil-borne disease pathogens Fusarium and Guehomyces were significantly increased after strawberry continuous cropping, and the abundance of nematicidal(Arthrobotrys) fungi decreased from the fourth year of continuous cropping. The results of correlation analysis suggest that these three genera might be key fungi that contribute to the changes in soil properties that occur during continuous cropping. In addition, physicochemical property analysis showed that the soil nutrient content began to decline after the fourth year of continuous cropping. Spearman's correlation analysis showed that soil pH, available potassium(AK) and ammonium nitrogen(NH_4^+-N) were the most important edaphic factors leading to contrasting beneficial and pathogenic associations across consecutive strawberry cropping systems.

Wheat, maize and sunflower cropping systems selectively influence bacteria community structure and diversity in their and succeeding crop's rhizosphere

Wheat and maize are increasingly used as alternative crops to sunflower monocultures that dominate the Hetao Irrigation District in China.Shifts from sunflower monocultures to alternate cropping systems may have significant effects on belowground microbial communities which control nutrient cycling and influence plant productivity.In this research,rhizosphere bacterial communities were compared among sunflower,wheat and maize cropping systems by 454 pyrosequencing.These cropping systems included 2 years wheat(cultivar Yongliang 4) and maize(cultivar Sidan 19) monoculture,more than 20 years sunflower(cultivar 5009) monoculture,and wheat-sunflower and maize-sunflower rotation.In addition,we investigated rhizosphere bacterial communities of healthy and diseased plants at maturity to determine the relationship between plant health and rotation effect.The results revealed taxonomic information about the overall bacterial community.And significant differences in bacterial community structure were detected among these cropping systems.Eight of the most abundant groups including Proteobacteria,Bacteroidetes,Acidobacteria,Gemmatimonadetes,Chloroflexi,Actinobacteria,Planctomycetes and Firmicutes accounted for more than 85%of the sequences in each treatment.The wheat-wheat rhizosphere had the highest proportion of Acidobacteria,Bacteroidetes and the lowest proportion of unclassified bacteria.Wheat-sunflower cropping system showed more abundant Acidobacteria than maize-sunflower and sunflower monoculture,exhibiting some influences of wheat on the succeeding crop.Maize-maize rhizosphere had the highest proportion of γ-Proteobacteria,Pseudomonadales and the lowest proportion of Acidobacteria.Sunflower rotation with wheat and maize could increase the relative abundance of the Acidobacteria while decrease the relative abundance of the unclassified phyla,as was similar with the health plants.This suggests some positive impacts of rotation with wheat and maize on the bacterial communities within a single field.These results demonstrate that different crop rotation systems can have significant effects on rhizosphere microbiomes that potentially alter plant productivities in agricultural systems.

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.

Rhizosphere Aeration Improves Nitrogen Transformation in Soil, and Nitrogen Absorption and Accumulation in Rice Plants

Two rice cultivars(Xiushui 09 and Chunyou 84)were used to evaluate the effects of various soil oxygen(O2)conditions on soil nitrogen(N)transformation,absorption and accumulation in rice plants.The treatments were continuous flooding(CF),continuous flooding and aeration(CFA),and alternate wetting and drying(AWD).The results showed that the AWD and CFA treatments improved soil N transformation,rice growth,and N absorption and accumulation.Soil NO3–content,nitrification activity and ammonia-oxidising bacteria abundance,leaf area,nitrate reductase activity,and N absorption and accumulation in rice all increased in both cultivars.However,soil microbial biomass carbon and pH did not significantly change during the whole period of rice growth.Correlation analysis revealed a significant positive correlation between the nitrification activity and ammonia-oxidising bacteria abundance,and both of them significantly increased as the total N accumulation in rice increased.Our results indicated that improved soil O2 conditions led to changing soil N cycling and contributed to increases in N absorption and accumulation by rice in paddy fields.

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.

Rhizosphere soil bacterial community composition in soybean genotypes and feedback to soil P availability

Soil with low phosphorus (P) availability and organic matter contents exists in large area of southwest of China, but some soybean genotypes still show well adaptations to this low yield farmland. However, to date, the underlying mechanisms of how soybean regulates soil P availability still remains unclear, like microbe-induced changes. The objective of the present study was to compare the differences of rhizosphere bacterial community composition between E311 and E109 in P-sufficiency (10.2 mg kg^-1) and P-insufficiency (5.5 mg kg^-1), respectively, which then feedback to soil P availability. In P-sufficiency, significant differences of the bacterial community composition were observed, with fast-growth bacterial phylum Proteobacteria, genus Dechloromonas, Pseudomonas, Massilia, and Propionibacterium that showed greater relative abundances in E311 compared to E109, while in P-insufficiency were not. A similar result was obtained that E311 and E109 were clustered together in P-insufficiency rather than in P-sufficiency by using principal component analysis and hierarchical clustering analysis. The quadratic relationships between bacterial diversity and soil P availability in rhizosphere were analyzed, confirming that bacterial diversity enhanced the soil P availability. Moreover, the high abundance of Pseudomonas and Massilia in the rhizosphere of E311 might increased the P availability. In the present study, the soybean E311 showed capability of shaping rhizosphere bacterial diversity, and subsequently, increasing soil P availability. This study provided a strategy for rhizosphere management through soybean genotype selection and breeding to increase P use efficiency, or upgrade middle or low yield farmland.

Effects of intercropping on rhizosphere soil microorganisms and root exudates of Lanzhou lily(Lilium davidii var.unicolor)

Both yield and quality of Lanzhou lily(Lilium davidii var. unicolor) are seriously affected by continuous cropping. We attempted to understand the effects of intercropping on the obstacles associated with continuous cropping of Lanzhou lily(Lilium davidii var. unicolor). The changes of rhizosphere microbial biomass and diversity in interplanting and monoculturing systems were studied by using the Illumina Hi Seq sequencing technique. The contents and composition of lily root exudates were measured by gas chromatography–mass spectrometer(GC–MS). The intercropping results of Lanzhou lily showed:(1) There was no difference in the composition of the rhizosphere soil microbes at the phylum level, but the relative abundance of the microbes decreased; and the relative abundance of harmful fungi such as Fusarium sp. increased. The relative abundance of Pleosporales sp. and other beneficial bacteria were reduced. After OTU(operational taxonomic unit)clustering, there were some beneficial bacteria, such as Chaetomium sp., in the lily rhizosphere soil in the interplanting system that had not existed in the single-cropping system. We did not find harmful bacteria that had existed in the single-cropping systm in the rhizosphere soil of interplanting system. The above results indicated that the changes of relative abundance of soil fungi and bacteria in lily rhizosphere soil was not conducive to improving the ecological structure of rhizosphere soil microbes. At the same time, the microbial composition change is very complex—beneficial and yet inadequate at the same time.(2) Root exudates provide a matrix for the growth of microorganisms. Combined with the detection of root exudates, the decrease in the composition of the root exudates of the lily was probably the reason for the decrease of the relative abundance of microbes after intercropping. At the same time, the decrease of the relative content of phenolic compounds, which inhibit the growth of microorganisms, did not increase the relative content of rhizosphere soil microorganisms. Changes in amino acids and total sugars may be responsible for the growth of Fusarium sp.. The results showed that the intercropping pattern did not noticeably alleviate the obstacle to continuous cropping of Lanzhou lily, and the change of microbial biomass and diversity was even unfavorable. However, the emergence of some beneficial bacteria, the disappearance of harmful fungi, and other changes with intercropping are in favor of alleviation of obstacles to continuous cropping of Lanzhou lily.

Wheat straw biochar amendment suppresses tomato bacterial wilt caused by Ralstonia solanacearum: Potential effects of rhizosphere organic acids and amino acids

Complex interactions based on host plant, rhizosphere microorganisms and soil microenvironment are presumed to be responsible for the suppressive properties of biochar against soil-borne diseases, although the underlying mechanisms are not well understood. This study is designed to evaluate the efficacy of biochar amendment for controlling tomato bacterial wilt caused by Ralstonia solanacearum, and to explore the interactions between biochar-induced changes in rhizosphere compound composition, the pathogen and tomato growth. The results showed that biochar amendment decreased disease incidence by 61–78% and simultaneously improved plant growth. The positive ‘biochar effect' could be associated with enhanced microbial activity and alterations in the rhizosphere organic acid and amino acid composition. Specifically, elevated rhizosphere citric acid and lysine, but reduced salicylic acid, were induced by biochar which improved microbial activity and rendered the rhizosphere unsuitable for the development of R. solanacearum. In addition, nutrients which were either made more available by the stimulated microbial activity or supplied by the biochar could improve plant vigor and potentially enhance tomato resistance to diseases. Our findings highlight that biochar's ability to control tomato bacterial wilt could be associated with the alteration of the rhizosphere organic acid and amino acid composition, however, further research is required to verify these ‘biochar effects' in field conditions.

Physiological and biochemical appraisal for mulching and partial rhizosphere drying of cotton

Water is the main factor for the healthy life of plant.One of the main negative effects of climate change is the increasing scarcity of water that is lethal for plant.Globally,for water deficit regions(arid and semi-arid),drought is the main factor responsible for low production of agriculture,especially for cotton.Great efforts have been and are being made to find alternatives to water saving practices.This study aimed to examine the effects of partial rhizosphere drying(PRD,half of the root system irrigated at one event,and the other half irrigated in the next event,and so on)with and/or without various mulching treatments on physiological and biochemical traits of cotton.To explore this objective,we laid out experiments in completely randomized design with factorial arrangement in the Islamia University of Bahawalpur,Pakistan in 2016.Two factors included were four mulching treatments(M0,no mulching;M1,black plastic mulching;M2,wheat straw mulching;and M3,cotton sticks mulching)and two irrigation levels(I0,control(full irrigation);and I1,PRD).Fisher's analysis of variance among means of treatments was compared using least significant difference test at 5% probability level.Results revealed that the maximum plant height,leaf area,leaf gas exchange(photosynthetic rate and stomata conductance),chlorophyll,proline and total sugar contents,and enzyme activities were higher under M2 than under other three mulching treatments.As for irrigation levels,higher values of plant height,photosynthesis and water related parameters(leaf water potential,leaf osmotic potential,leaf turgor potential,etc.)were recorded.Contents of total sugar and proline and activities of antioxidant enzymes were significantly higher in PRD-treated plants than in control plants.It was concluded that combined application of PRD and mulching was more effective than the rest of the treatments used in the experiment.Similar study can be conducted in the field by applying irrigation water in alternate rows in semi-arid regions.

Microbial Diversity in Rhizosphere Soil of Cotinus coggygria Based on High Throughput Sequencing

In order to reveal the influence of different plant configurations on the microbial community structure and diversity in rhizosphere soil of Cotinus coggygria in Fragrant Hills park,the ITS+5.8S rDNA gene and 16S rDNA gene V3-V4 region sequencing analysis for fungi and bacteria,respectively,were conducted by high throughput sequencing(Illumina MiSeq).The results showed that the fungal diversity in the rhizosphere soil samples of C.coggygria in Fragrant Hills park in 2018 was significantly higher than that in 2016,and it was higher in the rhizosphere soil of healthy C.coggygria in Xunlupo than that in diseased ones in 2018.Verticillium dahliae,which is the causal agent of C.coggygria wilt,was detected in five soil samples.In 2018,the bacterial diversity in the rhizosphere soil of diseased C.coggygria in Xunlupo was the lowest,while it was the highest in the rhizosphere soil of healthy C.coggygria under Platycladus orientalis in Langfengting.