Continuous Cucumber Research Articles

Response of soil microbial community diversity to continuous cucumber cropping in facilities along the Yellow River irrigation area.

Cucumber is an important cash crop; however, continuous cropping obstacles readily occur within the intensive production processes of facility horticulture. This study aimed to determine the effects of continuous cropping on soil quality and the microbial community in the rhizosphere soil of cucumbers. Rhizosphere soil of cucumber planted continuously for 4, 8, and 12 years was investigated, and soil that was not continuously planted was used as the control. Soil physicochemical properties, enzyme activity, microbial diversity, and richness were determined. The results showed that with the increase in continuous cropping years (0, 4, 8, and 12 years), soil total salt content continuously increased, while the pH value significantly decreased. Compared with the control, soil organic matter, alkali-hydrolyzed nitrogen, available phosphorus, available potassium, and nitrate nitrogen contents increased significantly after 4 and 8 years of continuous cropping. Spearman correlation analysis showed that pH was negatively correlated with sucrase or sucrose and available phosphorus was positively correlated with alkaline phosphatase. Compared with the control, the diversity and abundance of bacterial and fungal communities in cucumber rhizosphere soil decreased after 4 and 12 years of continuous cropping. Continuous cropping led to a significant increase in the richness of the dominant phylum of cucumber rhizosphere soil. Principal coordinates analysis showed that, compared with the control, the soil microbial community structure was significantly separated after 4, 8, and 12 years of continuous cropping, and the microbial community structure was most similar after 4 and 8 years of continuous cropping. In addition, redundancy analysis showed that pH was the main driver of soil microbial dominance. In conclusion, continuous cropping of cucumber along the Yellow River irrigation area has led to the deterioration of soil nutrients and microbial communities in that region. This experiment provides a theoretical foundation for addressing the challenges associated with continuous cropping in cucumber cultivation.

Changes in rhizospheric microbiome structure and soil metabolic function in response to continuous cucumber cultivation.

With the increasing reliance on intensive arable agriculture, analysis of the problems associated with continuous cropping has become a global research focus. Here, high-throughput sequencing and nontargeted metabolomics were used to evaluate the responses of soil microbial community structure and soil metabolic function to continuous cucumber cultivation (from 1 to 18 years of continuous cultivation) in greenhouses. Continuous cucumber cropping resulted in increased soil nutrient concentrations, but decreased concentrations of available nutrients. The abundance of several bacterial genera associated with nutrient cycling, such as Bacillus and Sphingomonas, was reduced by continuous cucumber cultivation. The abundance of several beneficial fungal genera, including pathogen antagonists (e.g. Chaetomium, Mortierella, Aspergillus, and Penicillium), were found to gradually decrease in response to the increased duration of continuous cropping. 3-amino-2-naphthoic acid and L-valine increased initially and then decreased as the cropping continued, which were related to fatty acid metabolism and amino acid biosynthesis. We also confirmed a close association between microbial community structure and soil metabolites. This study linked the changes in microbial community structure and metabolites in the rhizosphere soil and provided new insights into soil-microbial interactions in continuous cucumber culture systems.

Impact of bambara seed residue biochar and NPK on soil fertility, aggregate carbon and nitrogen concentrations and yield of cucumber

The mechanisms of biochar effects on soil and crop yield are still elusive. Assessing the influence of biochar on total carbon (TC) and total nitrogen (TN) concentrations in hierarchical soil aggregates could provide an explanation. In a randomized complete block design were control, bambara seed residue biochar (BSB), NPK and NPK + BSB treatments superimposed on a two-year bambara seed residue amended Ultisols, in a four-year continuous cucumber cultivation. The effects of the treatments on optimizing cucumber yield and soil sustainability parameters, particularly the aggregate- (4.75-2.00, 1.00-2.00, 0.25-1.00 and < 0.25 mm) associated TC and TN concentrations were studied. The BSB and NPK + BSB treatments significantly (p ≤ 0.05) increased the concentrations of TC by 113.79 and 104.60%; TN by 100 and 87.50%; and available P by 172% and 415%, respectively. Furthermore, both treatments significantly reduced exchangeable Al3+ but increased Mg2+ and soil moisture content 4-6 weeks after planting. Exchangeable K+ was significantly increased by BSB. The BSB and NPK + BSB significantly improved TC and TN in all aggregate fractions with minimal effect in the 0.25-1.00 mm fraction. However, the overall percentile TC and TN increase by these treatments was more in the macro- (4.75-0.25 mm) than in the micro (< 0.25 mm) aggregates. Application of BSB and NPK + BSB significantly improved cucumber fruit weight by 12- and 24-fold, respectively, compared to NPK treatment. The study demonstrated that BSB enhanced soil fertility, while NPK + BSB further improved cucumber productivity. In addition, these treatments have the potential to substantially sequester carbon and nitrogen more in macro- than micro- aggregates.

Cover Plants-Mediated Suppression of Fusarium Wilt and Root-Knot Incidence of Cucumber is Associated With the Changes of Rhizosphere Fungal Microbiome Structure-Under Plastic Shed System of North China.

Cover crops are known to alleviate the adverse effects of continuous cropping by influencing plant health and changing host fungal-microbiome structures. However, insight into the shift of rhizomicrobiota composition and their effects on plant growth performance and resistance mechanism is still limited under plastic shed cultivation (PSC). Four leafy vegetable rotations namely spinach rotation (SR), non-heading Chinese cabbage rotation (NCCR), coriander rotation (CR), and leafy lettuce rotation (LLR) were used as cover crops in 7-years of continuous cucumber planted soil (CC). Their ecological impacts were studied for plant growth performance, replant diseases incidence rate, and rhizosphere fungal microbiome. Compared to CC, SR showed a highly suppressive effect on fusarium wilt, i.e., by 13.2% in the spring season, while NCCR decreased the root-knot nematode incidence rate by 8.9% in the autumn season. Such protective effects caused a significant increase of shoot and fruit biomass and thus sustained the fruit quality of cucumber. High-throughput sequencing revealed that the CR, SR, and NCCR treatments altered the fungal community composition by increasing the abundance of the beneficial fungal genera, decreasing pathogenic taxa, and fostering the saprotrophic and symbiotic functions. However, the relative abundance of most of the potentially pathogenic fungal genera increased in CC and LLR cropping. There were 8 potential pathogens and 10 beneficial or biocontrol fungi characterized. It was found that Paecilomyces, Chaetomium, Cladorrhinum, Zopfiella, Purpureocillium, and Metarhizium were the putative biocontrol microbes that positively affected plant growth and replanted diseases inhibition. The characterized Fusarium, Dactylonectria, Alternaria, Gibberella, and Aspergillus were the key pathogenic fungal agents found to be negatively associated with plant growth characters, suggesting that rhizomicrobiome may play an important role in the occurrence of disease incidence of cucumber plants. Considering the ecological potential of some cover plants, this study suggested that rotation with spinach, non-heading Chinese cabbage, or coriander can enhance rhizosphere immunity by triggering the development of plant-protective fungal microbiomes under plastic shed cucumber cultivation.

Relationship between accumulation of autotoxins and soil fertility factors under long-term continuous cropping of cucumber in solar greenhouse

In this study, we investigated the effects of long-term continuous cucumber cropping on phenolic acids in rhizosphere soil, as well as their link to soil chemical characteristics, enzyme activities, and microbiological activities, using rhizosphere soil from the 2nd, 6th, 10th, 14th, 18th, 20th, 24th, and 26th round of cucumber cultivation in solar greenhouse. The results showed that contents of phenolic acids increased significantly with increasing continuous cropping rounds. The increase amount per round of total phenolic acid was significantly higher in the early stage (0-2 rounds) and late stage (20-26 rounds) than middle stage (10-14 rounds) of continuous cropping. Soil nutrient contents were enriched, while invertase enzyme activity and microbial activities were decreased. Redundancy analysis showed that organic matter, total phosphorus, total nitrogen, available nitrogen, microbial biomass carbon and microbial metabolic entropy were main soil fertility factors correlating with the accumulation of phenolic acids. Results of structural equation model showed that soil phosphorus enrichment directly led to the accumulation of phenolic acids, and that nitrogen enrichment indirectly facilitated the accumulation of phenolic acids by altering the activity of microorganisms. As a result, proper nitrogen and phosphorus fertilizers application would reduce the accumulation of phenolic acids and alleviate the cucumber continuous cropping obstacles.

Arbuscular mycorrhizal inoculum coupled with organic substrate induces synergistic effects for soil quality changes, and rhizosphere microbiome structure in long-term monocropped cucumber planted soil

The integrated soil biological amendments of mycorrhizal inoculation and organic substrate can be additive, synergistic, or antagonistic under plant-soil-microbe interaction. Underlying mechanisms of associated soil quality changes and microbiota structure are, however, less understood. To probe into this, consecutive greenhouse experiments (2016–2018) were conducted to study the effects of mycorrhizal inoculum (AMF: Diversispora epigaea L.) and soil organic substrate (GS: garlic stalk) were used as single and combined applications. In this study, a high-throughput sequencing approach was used to evaluate the rhizosphere microbiome structure of bacteria in the replanted substrate of 7-years of continuous cucumber cropping. From the two years of treatment, we found that co-amended GS + AMF significantly altered the soil quality changes through increasing soil organic matter, soil nutrient contents, and enzyme activities. Our 16 S rRNA amplicon revealed a distinct impact on alpha diversity and bacterial community. The observed species richness index (OTUs, Chao1, and ACE) and community diversity index (Shannon) were increased due to GS-amended soil and GS + AMF inoculation, respectively. Soil amendments also had apparent effects by altering bacterial community compositions at the phylum level, which were mostly associated with the higher abundance of Proteobacteria, Planctomycetes, Gemmatimonadetes, Actinobacteria and Bacteroidetes. Furthermore, correlation analyses revealed that the soil pH and enzyme activities emerged as the major determinants of the key microbial attributes. Our results suggest that GS + AMF treatment can directly regulate the soil environmental attributes or induce compositional shifts of microbes in the continuous cucumber cropping substrates. However, their co-inoculation impact was the shift of the key soil-microbiota consortium. Therefore, the study provides new insight into ways that can reduce the adverse effect of continuous cropping stress and eco-friendly contribute to the stable and healthy micro-ecological development in protected cultivation.

Effects of continuous cucumber cropping on crop quality and soil fungal community.

Long-term continuous cropping is a common practice in facility vegetable production, which has an adverse effect on cucumber yield and quality. Soil fungi are of great significance for creating a normal soil ecological environment. However, the impact of continuous cropping on cucumber quality and soil fungal community has yet to be understood. In this study, we evaluated the effects of continuous cropping on cucumber using high-throughput sequencing technology. The results showed that the extension of continuous cropping would increase nitrate and total acidity of cucumber, while the contents of vitamin C (VC), soluble sugar, and protein were decreased. The increase of continuous cropping duration also reduced the fungal diversity of the cucumber soil. For example, the activity of three dominant fungal phylums, Ascomycota, Aphelidiomycota, and Basidiomycota, decreased with the extension of planting years. The relative abundance of the two fungi species (Remersonia_thermophila, Mortierella_oligospora) was negatively correlated with the contents of available phosphorus and available potassium (P < 0.05). Redundancy analysis (RDA) found that soil electrical conductivity (EC), available phosphorus (AP), and pH accounted for the top three major factors of fungal community structure changes. The soil fungal community was changed during the continuous cucumber cultivation, which might be the result of the combined cultivation period of cucumber and excessive application of chemical fertilizers (nitrogen fertilizer, phosphate fertilizer, etc.). Our study provides a theoretical basis for the understanding of the impact of continuous cropping in cucumber facilities.

Impact of Intercropping on the Diazotrophic Community in the Soils of Continuous Cucumber Cropping Systems.

Diazotrophs are important soil components that help replenish biologically available nitrogen (N) in the soil and contribute to minimizing the use of inorganic N fertilizers in agricultural ecosystems. However, there is little understanding of how diazotrophs respond to intercropping and soil physicochemical properties in cucumber continuous cropping systems. In this study, using the nifH gene as a marker, we have examined the impacts of seven intercropping plants on diazotrophic community diversity and composition compared to a cucumber continuous cropping system during two cropping seasons. The results showed that intercropping increased the abundance of the nifH gene, which was negatively correlated with available phosphorous in the fall. Diazotrophic diversity and richness were higher in the rape–cucumber system than in the monoculture. Multivariate regression tree analysis revealed that the diversity of the diazotrophic communties was shaped mainly by soil moisture and available phosphorous. Skermanella were the dominant genera in all of the samples, which increased significantly in the mustard–cucumber system in the fall. There was no effect of intercropping on the structure of the diazotrophic community in this case. Non-metric multidimensional scaling analysis showed that cropping season had a greater effect than intercropping on the community structure of the diazotrophs. Overall, our results suggest that intercropping altered the abundance and diversity rather than the structure of the diazotrophic community, which may potentially affect the N fixation ability of continuous cropping systems.

Dominant hyphae-associated bacteria of Fusarium oxysporum f. sp. cucumerinum in different cropping systems and insight into their functions

Serious cucumber fusarium wilt (CFW) caused by the pathogenic fungus Fusarium oxysporum f. sp. cucumerinum (Foc) frequently occurs during continuous cultivation. The soil bacteria colonized in Foc hyphosphere are supposed to be related to Foc performance and cucumber health. In the present study, culture-independent approach was used to examine the Foc hyphae-associated bacterial communities in different cucumber cropping systems. It was found that the assembly of Foc hyphae-associated bacterial communities was mainly affected by the continuous cucumber practice followed by the pathogen colonization. Proteobacteria, Actinobacteria and Bacteroidetes accounted for 89–93% of the Foc hyphae-associated bacteria, and their abundance changed along with cucumber growth and Foc presence. The abundance of dominant Achromobacter was driven by cucumber cultivation, while the abundance of Rhizobium increased with continuous cucumber cultivation but decreased by Foc spiking. Bioassay tests of cultivable bacterial strains showed that the proportion of Rhizobium and Achromobacter played a key role in the occurrence of CFW, i.e. decreased Rhizobium and increased Achromobacter in the bacterial mixtures led to the decline of Foc suppression. This study indicates the relationship of Foc hyphae-associated bacterial community and cropping systems, and reveals the roles of some specific assembly of dominant bacteria colonizing Foc hyphae in CFW suppression.

Long-Term Greenhouse Cucumber Production Alters Soil Bacterial Community Structure

Long-term intensive greenhouse production commonly leads to continuous cropping obstacles and therefore declines the productivity of greenhouse system, soil microbiological mechanisms behind which remain poorly understood so far. Here, based on a continuous greenhouse cucumber cropping system, the differences in bacterial community structure of the soils with different cucumber cultivation history were assessed through high-throughput sequencing. The β diversity of bacterial community, but not α diversity, significantly changed as consecutive cucumber cultivation and also positively linked to cucumber yield. As for bacterial community members, at phylum level, prolonged cucumber cultivation increased average relative abundances of Chloroflexi and Gemmatimonadetes while decreasing average relative abundance of Nitrospirae; at genus level, continuous cucumber cultivation decreased average relative abundances of some beneficial microbes (i.e. Bacillus, Solirubrobacter, and Rubrobacter) and N-cycling related microbes (i.e. Nitrospira and Azoarcus) while increasing average relative abundance of some functional microbes (i.e. Agromyces, Thermomicrobium, Desulfotomaculum, Sphaerobacter, and Mycobacterium). Soil available phosphorus and organic carbon contents were the most important contributors to the shifts of bacterial community structure. Co-occurrence network analysis indicated long-term greenhouse cucumber cultivation weakened the interaction of species within bacterial community and led to less complex and connected organization among bacterial taxa. Overall, our results suggested that soil bacterial community structure and the interactions of bacterial taxa may play the important roles in the occurrence of continuous cropping obstacles in a long-term intensive greenhouse production system.

Long-term effects of bio-organic fertilizer application on soil organic carbon pool and enzyme activity of cucumber continuous cropping.

The combination of field trial and indoor incubation experiment were conducted to examine the long-term effects of one-time application of bio-organic fertilizer on soil organic carbon (C) components, organic C mineralization, and enzyme activity in cucumber continuous cropping. Compared with CK, bio-organic fertilizer application significantly increased the content of soil organic C, activated C pool, slow-release C pool and inert C pool during four continuous cucumber planting seasons. With the increases of the number of consecutive crops, the proportion of soil inert carbon gradually increased. After four continuous seasons of cucumber planting, the cumulative and daily mineralization rate of soil organic C in the bio-organic fertilizer treatment increased by 17.3%-31.0% and 7.8%-43.0%, respectively. In the stage of cucumber ripening, bio-organic fertilizer application increased the activities of continuous soil urease, catalase, sucrose and neutral phosphatase by 10.5%-62.1%, 4.8%-25.5%, 3.9%-21.4% and 4.6%-66.4%. The activities of those four enzymes increased with the increases of the application amount of organic fertilizer. Results from the correlation and path analysis showed that the activity of the four enzymes were significantly correlated with the dynamics of organic carbon components in soil cucumber continuous cropping process. Soil urease and invertase activities significantly affected organic carbon mineralization during the continuous cropping process of cucumber. Application of bio-organic fertilizer could increase soil organic carbon content and enzyme activity, improve inert carbon ratio of soil organic carbon pools, cumulative and mineralization rate of organic carbon in continuous cropping process, thereby enhance soil carbon sequestration capacity.

Hiseq Base Molecular Characterization of Soil Microbial Community, Diversity Structure, and Predictive Functional Profiling in Continuous Cucumber Planted Soil Affected by Diverse Cropping Systems in an Intensive Greenhouse Region of Northern China.

Cover crops are key determinants of the ecological stability and sustainability of continuous cropping soils. However, their agro-ecological role in differentially reshaping the microbiome structure and functioning under a degraded agroecosystem remains poorly investigated. Therefore, structural and metabolic changes in soil bacterial community composition in response to diverse plant species were assessed. Winter catch leafy vegetables crops were introduced as cover plants in a cucumber-fallow period. The results indicate that cover crop diversification promoted beneficial changes in soil chemical and biological attributes, which increased crop yields in a cucumber double-cropping system. Illumina high-throughput sequencing of 16S rRNA genes indicated that the bacterial community composition and diversity changed through changes in the soil properties. Principal component analysis (PCA) coupled with non-metric multidimensional scaling (NMDS) analysis reveals that the cover planting shaped the soil microbiome more than the fallow planting (FC). Among different cropping systems, spinach–cucumber (SC) and non-heading Chinese cabbage–cucumber (NCCC) planting systems greatly induced higher soil nutrient function, biological activity, and bacterial diversity, thus resulting in higher cucumber yield. Quantitative analysis of linear discriminant analysis effect size (LEfSe) indicated that Proteobacteria, Actinobacteria, Bacteroidetes, and Acidobacteria were the potentially functional and active soil microbial taxa. Rhizospheres of NCCC, leaf lettuce–cucumber (LLC), coriander–cucumber (CC), and SC planting systems created hotspots for metabolic capabilities of abundant functional genes, compared to FC. In addition, the predictive metabolic characteristics (metabolism and detoxification) associated with host–plant symbiosis could be an important ecological signal that provides direct evidence of mediation of soil structure stability. Interestingly, the plant density of non–heading Chinese cabbage and spinach species was capable of reducing the adverse effect of arsenic (As) accumulation by increasing the function of the arsenate reductase pathway. Redundancy analysis (RDA) indicated that the relative abundance of the core microbiome can be directly and indirectly influenced by certain environmental determinants. These short-term findings stress the importance of studying cover cropping systems as an efficient biological tool to protect the ecological environment. Therefore, we can speculate that leafy crop diversification is socially acceptable, economically justifiable, and ecologically adaptable to meet the urgent demand for intensive cropping systems to promote positive feedback between crop–soil sustainable intensification.

Changes in soil microbial diversity and control of Fusarium oxysporum in continuous cropping cucumber greenhouses following biofumigation

Soil biofumigation with Brassia plant parts has been demonstrated to suppress soil-borne pathogens. This effect has been attributed to the bactericidal effect of their glucosinolate degradation products. However, little is known regarding the effect of biofumigation on the microbial community structure and control of Fusarium oxysporum in continuous cropping cucumber systems. Field and pot experiments were performed to study the effect of biofumigation with brassica crops of different glucosinolate contents on the microbial diversity and control of Fusarium oxysporum during the cucumber growth period in a continuous cropping culture system. Samples collected from biofumigation and control treatments differed in the number of soil bacterial bands observed by denaturing gradient gel electrophoresis (DGGE) profiling, suggesting that biofumigation changed the soil microbial diversity. Compared with control and chemically-fumigated (HY) soils, the biofumigated soil exhibited significantly higher Shannon-Weaver diversity indices for bacteria and fungi. Cluster analysis and principal component analysis revealed that soil bacteria communities were different in the hymexazol (HY)-treated soils compared with the communities before biofumigation (BB) and those in the no fumigation (CK) groups. This was true for the mustard containing high glucosinolates (MHG), mustard containing low glucosinates (MLG), mustard (MU), and turnip (TU) groups. Pot experiments demonstrated that the amounts of Fusarium oxysporum in MHG- and HY-treated soils were significantly lower than those in other biofumigation treatments. These results demonstrate the potential utility of Brassica crops in the control of Fusarium wilt in continuous cucumber cropping systems, and the control effect of MGH was the best compared with other treatments, which could effectively reduce Fusarium oxysporum in soil by more than 60%.

Applications of nitrate and ammonium fertilizers alter soil nematode food webs in a continuous cucumber cropping system in Southwestern Sichuan, China

Nitrate (NO 3 - -N) and ammonium (NH 4 + -N) fertilizers are the main forms of chemical inorganic nitrogen fertilizers that are widely used in agro-ecosystem for high yield. However, the responses of soil nematode food web to different forms and rates of inorganic nitrogen fertilizers are not well understood. The objective of this study was to determine the responses of soil nematode food web to the applications of inorganic nitrogen fertilizers in a continuous cucumber ( Cucumis sativus L.) cropping system. Nitrate (NaNO 3 ) and ammonium (NH 4 HCO 3 ) fertilizers were applied to cucumber plants at the nitrogen (N) rate of 0, 67.5, 135.0 and 202.5 kg N hm - 2 before planting. It was conducted in a randomized complete block design with 4 replications at Huaizi village, Leshan district, Sichuan province, Southwestern China. The effects were analyzed at the stages of seedling, blooming and fruiting, respectively. The results indicated that the numbers of nematodes were significantly higher in soils with the addition of 67.5 kg N hm -2 than the control at the seedling and blooming stages. Nematode number strongly increased at the seedling stage and decreased at the blooming and fruiting stages in nitrate-treated soils compared to the ammonium-treated. The percentage of herbivores to total nematodes significantly decreased while that of bacterivores increased with a fertilizer rate less than 135 kg N hm - 2 at the seedling and fruiting stages. Nitrate significantly reduced the percentage of herbivores, and increased that of bacterivores to total nematodes by comparison with ammonium at the blooming and fruiting stages. The application of nitrate significantly increased nematode diversity and evenness, and decreased dominance at the blooming stage relative to ammonium. Nitrate significantly decreased the values of channel index at the blooming stage and maturity index at the seedling stage in comparison with ammonium, respectively. Enrichment index and structural index strongly increased at the seedling stage, and decreased at the blooming and fruiting stages under the treatment of nitrate relative to ammonium. The results suggested responses of nematode food web dependent on the rates and forms of inorganic nitrogen fertilizers and stages of cucumber growth.

Effects of single-root-grafting, double-root-grafting and compost application on microbial properties of rhizosphere soils in Chinese protected cucumber (Cucumis sativus L.) production systems

The grafting and compost application generally have positive effects on plant growth in continuous cropping systems, which may be related to root-associated microbial properties that are important for plant growth. A field study was conducted to investigate the effects of grafting and compost application on improvement of degraded soil in a continuous cucumber cropping system in Beijing, China. Self-root (SR), single-root-grafted (SRG) and double-root-grafted (DRG) seedlings were respectively transplanted to the soils treated with the chicken manure (CM) or CM compost (CMC), and rhizosphere soil microbial properties, plant biomass and fruit yields were determined in two cropping seasons after treatments. Rhizosphere soil microbial properties were evaluated with a combination of microbial populations measured by quantitative PCR, microbial community composition analyzed by denaturing gradient gel electrophoresis and 454 pyrosequencing, and sole-carbon utilization capacity by microbial communities. In general, DRG increased microbial (bacterial and fungal) abundance but decreased microbial diversity compared to SR, and increased total fruit yield compared to SRG. SRG decreased microbial abundance and diversity, but increased total dry matter compared to SR. When compared to CM, CMC increased bacterial abundance, microbial diversity and cucumber fruit yield, but decreased fungal abundance and microbial diversity in the early-spring (ES) season. Reverse trends were found in the autumn–winter (AW) season. The highest total fruit yield was found under the treatment DRG-CMC. Principal component (PC) analysis of soil microbial properties showed that both PC1 and PC2 were significantly correlated with TDM (both P<0.01). These results suggest that DRG-CMC is a beneficial practice for increasing cucumber yields. In addition, there are close but complex relationships between rhizosphere soil microbial properties and total dry matter.

Effects of intensified corn stalk degradation by biocontrol agents on soil microbial community in continuous cucumber cropping

tunted crop growth,yield decline and disease susceptibility have been associated with monoculture cropping.Soil borne diseases have emerged as the main obstacle to continuous cropping,which current biological techniques have failed to overcome.In recent years,however,intensified corn stalk degradation by biocontrol agents has been a widely used technique in winter greenhouses in North China.This technique combining application of crop stalk and biocontrol agents,which can improve soil quality,reduce soil diseases,increase crop productivity,etc.Thus this study aimed to investigate what effects this technique has on soil microbial community in continuous cucumber cropping.The dynamics of fungi,bacteria,actinomycetes,biocontrol agents and pathogens in cucumber fields were determined using both the plate culture counting and terminal-restriction fragment length polymorphism(T-RFLP) methods.The results showed that intensified corn stalk degradation by biocontrol agents significantly influenced soil microbial community in cucumber fields.After treatment,the number of fungi in soils of the second crop(6.33×104 CFU·g-1) was lower than that in the first crop(1.81×105CFU·g-1) while bacteria and actinomycetes showed the reverse trend.Bacteria to fungi(B/F) ratio increased from 222.30 at the end of the first crop to 667.16 at the end of the second crop.The contents of biocontrol agents,Purpureocillium lilacinum and Bacillus subtilis,remained stable in soils under continuously cropped cucumber.Although insignificantly,the amount of pathogen Fusarium oxysporum f.sp.cucumerinum decreased.On the other hand,soil bacteria diversity significantly increased.This somehow promoted beneficial bacteria TRF139 propagation while inhibiting harmful bacteria TRF341 and TRF501.Moreover,the technique improved cucumber yield by 25.9% under continuous cropping and reduced root-knot nematode disease index by 71.4% at the end of the third crop.Thus the combination of corn stalk and biocontrol agents positively influenced soil microbes and their community structures,promoted biocontrol agent colonization within a few crops,inhibited the growth of pathogens and subsequently improved the health of soil microenvironment.

Effects of Arbuscular Mycorrhizal Fungi Communities on Soil Quality and the Growth of Cucumber Seedlings in a Greenhouse Soil of Continuously Planting Cucumber

A pot experiment was performed to determine the effects of arbuscular mycorrhizal fungi (AMF) communities on soil properties and the growth of cucumber seedlings in a degraded soil that had been used for continuous cucumber monoculture in a greenhouse for 15 years. In the experiment, AMF communities (created by combining various AMF species that were found to be dominant in natural farm soil) were inoculated into the degraded soil, and then the soil was planted with cucumber. Inoculation with AMF communities did not affect soil pH but increased soil aggregate stability and decreased the concentrations of salt ions and electrical conductivity (EC) in the soil. Inoculation with AMF communities increased the numbers of culturable bacteria and actinomycetes but reduced the number of fungi. AMF communities increased plant growth, soluble sugar content, chlorophyll content, and root activity compared to non-mycorrhizal or a single AMF species treatments. Improvements of soil quality and plant growth were greatest with the following two communities: Glomus etunicatum + G. mosseae + Gigaspora margarita + Acaulospora lacunosa and G. aggregatum + G. etunicatum + G. mosseae + G. versiforme + G. margarita + A. lacunosa. The results suggested that certain AMF communities could substantially improve the quality of degraded soil.

Effects of continuous cucumber cropping and alternative rotations under protected cultivation on soil microbial community diversity

The diversity of soil microbial communities as affected by continuous cucumber cropping and alternative rotations under protected cultivation were evaluated using community level physiological profiles (CLPP) and random amplified polymorphic DNA (RAPD) analysis. The soils were selected from six cucumber cropping systems, which cover two cropping practices (rotation and continuous cropping) and a wide spectrum for cucumber cropping history under protected cultivation. Shannon–Weaver index and multivariate analysis were performed to characterize variations in soil microbial communities. Both CLPP and RAPD techniques demonstrated that cropping systems and plastic-greenhouse cultivation could considerably affect soil microbial functional diversity and DNA sequence diversity. The open-field soil had the highest Shannon–Weaver index (3.27 for CLPP and 1.50 for RAPD), whereas the lowest value occurred in the 7-year continuous protected cultivation soil (3.27 for CLPP and 1.50 for RAPD). The results demonstrated that continuous plastic-greenhouse cultivation and management can cause the reduction in the species diversity of the biota. Higher Shannon–Weaver index and coefficients of DNA sequence similarity were found in soils under rotation than those under continuous cropping. Cluster analysis also indicated that microbial community profiles of continuous cultivation soils were different from profiles of rotation soils. The reduction in diversity of microbial communities found in continuous cultivation soils as compared with rotation soils might be due to the differences in the quantity, quality and distribution of soil organic matter.