Continuous Cropping Obstacles Research Articles

Correlation between rhizospheric microorganisms distribution and alkaloid content of Fritillaria taipaiensis

In order to reveal the relationship between the amount of soil microorganisms and the quality of Fritillaria taipaiensis, both cultivated and wild F. taipaiensis were collected from Chongqing, Wuxi at different stages of their growth as objects of the research. The mycorrhizal infection rate and colonization intensity, peimisine and total alkaloid content in bulbs, the amount of microorganisms and biomass carbon content in rhizospheric soil were all determined using common methods. The results showed that the typical arbuscular-vesicle roots were formed after the AM fungi infected the F. taipaiensis roots which were collected from different origins. The mycorrhizal infection rates were ranged from 78.74% to 98.68% and the colonization intensities were ranged from 13.29% to 37.06%. The rhizospheric microorganisms of F. taipaiensis showed abundant resources. The distribution rule of them in the rhizospheric soil was as follows: the amount of bacteria>the amount of actinomycetes>the amount of fungi. The rhizospheric bacteria, decomposition inorganic phosphorus bacteria, decomposition organic phosphorus bacteria, actinomycetes amount and the total number of microbes increased first and then decreased with the increase of years, while decomposition potassium bacteria showed decreasing trend and fungi showed gradual increasing trend. The soil microbial flora content in the soil changed from "bacterial type" with a high fertility to "fungal type" with a low fertility. The mass fraction of peimisine and total alkaloid content increased first and then decreased with the increase of over the years, the same trend of culturable rhizosphere soil bacteria and actinomycetes indicated that the growth years affected the quality of soil and medicinal materials on different levels. Therefore, the diversity of microbial communities in rhizosphere soil reduced with the increase of years leading to the continuous cropping obstacles and the destruction of medicinal quality of F. taipaiensis.

Ecological effects of three phenolic acids on formation of continuous cropping obstacle in peanut（Arachis hypogaea L.）

Ecological effects of three phenolic acids on formation of continuous cropping obstacle in peanut（Arachis hypogaea L.）

Effects of three phenolic compounds on mitochondrial function and root vigor of cotton (Gossypium hirsutum L.) seedling roots

Continuous cropping of cotton causes accumulation of allelochemicals in soil that results in substantial crop yield and quality losses. To elucidate the physiological mechanism of the effects of allelochemicals on cotton root growth, and solve the problem of continuous cropping obstacles, hydroponics experiments were carried out to study the effects of three allelochemicals (p-hydroxybenzoic acid (PHBA), phloroglucinol, and ferulic acid) at different concentrations (0.8, 4.0, and 20.0 mmol L−1) on the production of reactive oxygen species, antioxidant enzyme activities, and mitochondrial function of cotton seedling roots. All three phenolic compounds suppressed cotton root growth, decreased the activity of antioxidant enzymes (superoxide dismutase, catalase and peroxidase) and H+-ATPase in root mitochondria, and increased generation of O2− and the content of H2O2. They also increased the degree of openness of mitochondria permeability transition pores, and decreased the membrane fluidity of mitochondria, and the ratio of cytochrome (Cyt) c/a, thus resulting in the damage of mitochondrial structure and overall function of the root system. Ferulic acid at 20.0 mmol L−1 inhibited cotton root growth more than the other treatments. Above all, all three kinds of allelochemicals inhibited antioxidant enzyme activity and mitochondrial function in cotton seedling roots, and the inhibition depended on the dose of phenolic compounds. Compared to PHBA and phloroglucinol, ferulic acid was a stronger inhibitor of cotton seedling root growth.

Effects of biochar on soil nutrition and microbial community diversity under continuous cultivated cucumber soils in greenhouse

In this study, we examined the effects of biochar addition on the soil nutrition and microbial community diversity in continuous cultivated cucumber soils, using 95% soils of planting cucumbers for 6 and 10 years mixed with 5% biochar as treatment and no biochar addition as control, all plants cultivated in the pots. The results showed that adding biochar increased per plant yield of cucumber by 11.4% and 62.8% compared with continuous cropping soil of 6 years and 10 years, respectively. Biochar addition significantly decreased two continuous cropping soils bulk density, increased the content of soil organic matter, available P content, cation exchange capacity (CEC) and soil pH. Meanwhile, biochar addition remarkably improved the abundance of bacteria, ratio of bacteria/fungi, but reduced the abundance of fungi and fusarium oxysporum, which made fungal type soil turn to bacterial type soil. For 10 years continuous cropping soils of adding biochar, the abundance of soil bacteria and bacteria/fungi ratio were 2.00 and 3.64 times to that in the control, respectively, and the abundance of fungi and fusarium oxysporum were decreased by 54.8% and 55.9%, respectively. Biochar addition significantly enhanced soil microbial activities, soil microbial Shannon and McIntosh indexes of 10 years soil by 1.50, 2.14 and 1.31 times, respectively. For continuous cropping soil of 10 years, biochar addition significantly increased microbial utilization abilities of carbohydrate, amino acid, phenolic acid and amine by 1.62, 1.81, 1.74 and 1.93 times, respectively. There were remarkable influences of soil bulk density, available P content, CEC, and pH value to changes of soil microbial community. In conclusion, biochar addition optimized the riphzosphere environment, increased cucumber yield, and alleviated continuous cropping obstacles by improving soil physical and chemical properties, as well as soil microbial community.

A plant growth-promoting bacterium alters the microbial community of continuous cropping poplar trees' rhizosphere.

We aimed to develop a biological agent that regulates the microbial community structure of the poplar rhizosphere and alleviates the effects of continuous poplar cropping. Poplar rhizosphere soils were treated with or without Paenibacillus polymyxa CP-S316 microbial fermentation medium. Real-time polymerase chain reaction was performed to measure bacteria and fungi in both groups, and microbial communities were analysed by metabarcoding. In fungi, the operational taxonomic units, abundance-based coverage estimator and Chao index of the CP-S316-treated group were significantly lower than those in the control check (CK) group. In bacteria, the proportions of Bacillus in the CP-S316 and CK groups were 5·20 and 2·38%, respectively, whereas those of Rhizoctonia were 2·20 and 5·82% respectively. The diameter at breast height, culturable bacteria and total bacteria of poplars treated with CP-S316 exceeded those in the CK group. Our data confirmed that CP-S316 could improve the microbial community structure of poplar rhizosphere and promote the growth of poplars. Research aimed at alleviating continuous cropping obstacles and promoting poplar growth via biocontrol agents is uncommon. We analysed the community structures of bacteria and fungi in rhizosphere soil to illustrate the use of CP-S316 for poplar cropping for improving plant health in the continuous cropping of poplar trees.

GC-MS-based identification and statistical analysis of liposoluble components in the rhizosphere soils of Panax notoginseng.

Continuous cropping obstacle, mainly caused by microorganisms and organic components in soil, has become a serious problem for the plantation of Panax notoginseng (Araliaceae) due to the rapidly increased demands of this famous herbal medicine in recent decades. The rhizosphere soils cultivated with 3-year-old healthy and ill notoginseng were chemically investigated by gas chromatography-mass spectrometry (GC-MS) and compared with the corresponding soils without the plantation of notoginseng. Totally 47 liposoluble components were identified. Furthermore, the multiple statistical analysis showed that these constituents were qualitatively and quantitatively associated with the differences between the cultivated soil with P. notoginseng and the uncultivated soil. Among them, neophytadiene (4), d-α-tocopherol (38), (3β,22E,24S)-ergosta-5,22-dien-3-ol (39), (3β,24R)-ergost-5-en-3-ol (40), stigmasta-5,22-dien-3-ol (41), stigmast-4-en-3-one (44) and (5α)-stigmastane-3,6-dione (47) contributed most to the significant differences between the cultivated and uncultivated soils, whereas cyclopentadecane (3), octadecanoic acid methyl ester (16), docosanoic acid ethyl ester (31), nonacosane (34), 38 and 39 were found in much higher amount in the soils with ill P. notoginseng as compared to the case of those with the healthy P. notoginseng. On the other hand, liposoluble components in different cultivation areas were of great diversity; however, they were able to remain relatively consistent across the overall trend of differential substances.

Effects of yam/leguminous crops intercropping on soil chemical and biological properties of yam field.

We investigated the effects of yam/leguminous crops intercropping on soil chemical and biological properties as well as soil comprehensive fertility in a field experiment. Results showed that compared with the monoculture, both yam/alfalfa and yam/clover intercropping increased the concentrations of nitrate nitrogen (N), available phosphorus (P) and available potassium (K) in the 0-20 cm and 20-40 cm soil layers, while reduced soil pH and electrical conductivity (EC) in early growth period and rhizome rapid expansion period of yam. Intercropping with leguminous crops enhanced the activities of urease, alkaline phosphatase and catalase, and also enhanced soil basal respiration in the 0-20 cm and 20-40 cm soil layers during the whole growth period of yam. There was no influence of intercropping on soil sucrase activity and dehydrogenase activity. The effects of intercropping with leguminous crops on soil fertility at yam harvest were further analyzed by combining the membership function model and principal component analysis. Results showed that intercropping with leguminous crops could significantly increase the soil comprehensive fertility in the 0-20 cm and 20-40 cm soil layers. Therefore, it might be an effective measure to improve soil fertility and environmental quality, as well as alleviate continuous cropping obstacles of yam by yam/leguminous crops intercropping through enhancing soil biological diversity.

The Alleopathic Compound Luteolin from Peanut Litter Affects Peanut Nodule Formation and the Rhizosphere Microbial Community

Core Ideas Flavonoid luteolin can accumulate in consecutively monocultured peanut fields. Luteolin treatment changes the rhizosphere microbial community of peanut. Flavonoid luteolin in peanut residues may cause continuous cropping obstacles. The flavonoid luteolin is a common flavone released from peanut (Arachis hypogaea L.) residues. Luteolin accumulates in consecutively monocultured soil and affects the growth and nodulation of continuously cropped peanut. A microcosm experiment was performed to determine the effects of luteolin released from peanut residue on peanut nodule formation and on the rhizosphere soil microbial community. Luteolin reached a maximum concentration of 0.42 μg g−1 soil in litterbag experiments, and the half‐life of luteolin at 2.5 to 40 μg g−1 soil varied from 1.13 to 2.91 d. Results from pot experiments indicate that soil with luteolin treatment inhibited peanut seedling nodulation and growth, soil dehydrogenase activity, microbial biomass carbon content, biofilm formation, and chemotactic response of Rhizobium sp. and changed the microbial community structures and abundances at concentration of luteolin as low as 0.42 μg g−1 in soil. This might explain why peanut performs poorly with continuous consecutive monocropping.

Deciphering the bacterial composition in the rhizosphere of Baphicacanthus cusia (NeeS) Bremek

Rhizobacteria is an important ingredient for growth and health of medicinal herbs, and synthesis of pharmacological effective substances from it. In this study, we investigated the community structure and composition of rhizobacteria in Baphicacanthus cusia (NeeS) Bremek via 16S rRNA amplicon sequencing. We obtained an average of 3,371 and 3,730 OTUs for bulk soil and rhizosphere soil samples respectively. Beta diversity analysis suggested that the bacterial community in the rhizosphere was distinctive from that in the bulk soil, which indicates that B.cusia can specifically recruit microbes from bulk soil and host in the rhizosphere. Burkholderia was significantly enriched in the rhizosphere. Burkholderia is a potentially beneficial bacteria that has been reported to play a major role in the synthesis of indigo, which was a major effective substances in B. cusia. In addition, we found that Bacilli were depleted in the rhizosphere, which are useful for biocontrol of soil-borne diseases, and this may explain the continuous cropping obstacles in B. cusia. Our results revealed the structure and composition of bacterial diversity in B. cusia rhizosphere, and provided clues for improving the medicinal value of B. cusia in the future.

Stereoscopic cultivation of Panax notoginseng: A new approach to overcome the continuous cropping obstacle

Stereoscopic cultivation (SC) of Panax notoginseng was a technique that plant P. notoginseng in the three-layer vertical placed seedbeds (with upper, middle, and lower layers) in a greenhouse. The cultivation environment of greenhouse and culture medium of seedbed are artificially prepared. The feasibility of using SC to solve the continuous cropping obstacle (CCO) of P. notoginseng was investigated in this study. The results showed that because the light and air temperature conditions of SC were inferior to those of field cultivation (FC), net photosynthetic efficiency was in the order of FC > upper > middle > lower layers. Soil microbial biomass values in the upper, middle, and lower layers were all significantly lower than those observed under FC. Soil urease, invertase, and neutral phosphatase activities increased gradually from the lower layer to the upper layer. Neutral phosphatase activity in each layer was significantly higher than that in the FC, and invertase activity in the upper and middle layers was significantly lower than that under FC, whereas urease and cellulase activities did not change significantly. Soil nitrogen and potassium contents were in the order of upper > middle layer > FC > lower layer, while the phosphorus content under SC was significantly higher than that in FC. The proportion of N and P in underground organs (rhizome, root tuber, and hair roots) of the upper layer increased, while it decreased in the middle and lower layers. Of the three layers, the proportion of K decreased significantly in the underground organs. The root biomass yield and saponin content in the same SC planting area was in the order of upper > middle > lower layer, which were all significantly lower than those of FC. However, total root biomass and saponin yield per unit floor area were 1.8 times that of FC. In conclusion, P. notoginseng grew normally under SC, and it was feasible to apply to solve the CCO. The yield and quality of P. notoginseng herbs can be further improved by perfecting the SC environment.

Prevention and Control of Continuous Cropping Obstacle of Watermelon by Reductive Soil Disinfestation (RSD)

This study aimed to explore whether reductive soil disinfestation (RSD) is an effective method of controlling continuous cropping obstacle of watermelon. Samples of watermelon continuous cropping soils were treated by RSD in laboratory tests and pot experiments in August 2015 and from December 10, 2016 to April 10, 2017. The soil samples for the laboratory test were divided into 16 groups, and each group comprised three parallel samples of 100 g (dry soil weight). Except for the original and control (CK) samples, the 14 other groups of soil samples were treated with different combinations of 1% or 3% alfalfa powder, 1% or 3% ammonia (NH3) water, and 1% or 3% acetic acid. The soil samples were placed inside size-five self-styled plastic bags and incubated in a constant-temperature biochemical incubator at 35°C for 14 days after blending, flooding, and sealing. Seven groups of soil samples were designed for the pot experiments based on the laboratory test results. Each group consisted of 30 parallel samples of 3 kg (dry soil weight). These samples were incubated outdoors for 4 months after mixing with alfalfa powder and/or NH3 and/or acetic acid according to the experimental design, blending, flooding, and sealing. Watermelon seedlings were planted in the air-dried soil samples from May to July in 2017. The results showed that the pH of the soil samples treated by RSD were elevated except for those samples with acetic acid. In addition, the electrical conductivities of the soil samples treated by RSD were effectively adjusted. The presence of soil-borne pathogenic Fusarium oxysporum f.sp. niveum was significantly suppressed (p < 0.05) in soil samples treated by RSD, and the incidence and mortality rate of watermelons planted in these samples were remarkably lower than those planted in the CK and flooded CK soil samples. Therefore, continuous cropping obstacle of watermelon can be controlled by RSD.

Effects of microbial fertilizer on soil improvement and fruit quality of kiwifruit in old orchard.

The continuous cropping obstacles caused by the increase of kiwifruit planting period resulted in imbalance of soil microbial community structure, and decrease of soil enzyme activity and physicochemical indicators, which substantially reduced both the quality and yield of kiwifruit. Under the field conditions, the traditional fertilization of fruit farmers was used as a control (CK) to study the effects of two different microbial fertilizers, JF and KF, which had been verified the growth promotion of kiwifruit aseptic seedlings test, on soil microbial community structure, soil enzyme activities, soil physicochemical characters during different growth periods of kiwifruit (germination period, florescence period, fruit enlargement period, fruit ripening period and next year germination period), as well as fruit quality. The results showed that both fertilizers significantly increased the ratio of bacteria with fungi and the ratio of actinomycetes with fungi in the kiwifruit orchard soil, indicating that they could improve and balance the soil microbial community structure. The enzymes activity in kiwifruit orchard soil with the addition of both fertilizers were significantly higher than that in CK, and among which sucrose, urease, phosphatase and polyphenol oxidase were increased by 17.9%-83.5%, 7.9%-83.0%, 7.3%-45.4% and 8.1%-140.3%, respectively. JF and KF increased soil fertility (the concentrations of available nitrogen, phosphorus, potassium, total nitrogen, total phosphorus, total potassium, and organic matter content significantly increased) and decreased soil pH (a decrease of 0.29 to 0.34). After application of microbial ferti-lizer, the content of vitamin C, soluble sugar, soluble protein and other contents of kiwifruit increased, and the titratable acid content decreased. Therefore, the application of both fertilizers could balance soil microbial community structure, enhance soil fertility, and improve the fruit quality of kiwifruit. Our results provide robust theoretical basis for the application of microbial fertilizers in the old-aged kiwifruit orchards.

Long-term greenhouse vegetable cultivation alters the community structures of soil ammonia oxidizers

Continuous cropping obstacles derived from long-term intensive cultivation has severely affected the healthy development of greenhouse vegetable industry in China. The alterations in soil microbial communities are commonly thought to be the important reasons behind continuous cropping obstacles. However, little attention is focused on soil functional microorganisms, such as soil ammonia oxidizers, which convert NH3 to NO2− in soils and play an important role in terrestrial ecosystem N cycling. With the help of quantitative real-time PCR and high-throughput sequencing methods, this study investigated the effects of consecutive greenhouse vegetable cultivation on the abundances and community structures of ammonia-oxidizing archaea (AOA) and bacteria (AOB). Continuous greenhouse production significantly affected soil physicochemical properties but slightly influenced on soil biochemical properties. Long-term greenhouse production significantly decreased soil potential nitrification rates. The abundances of AOA and AOB were insensitive to continuous greenhouse cultivation, whereas their community structures were significantly altered. A significant increase in average relative abundance of Nitrososphaerales Clade B4 in AOA community was observed after long-term greenhouse cultivation but just the opposite for Nitrososphaerales Clade Nitrososphaera. Increasing greenhouse cultivation years decreased the average relative abundance of Nitrosospira in AOB community, and their ecological niches were gradually occupied by Nitrosomonas; consequently, Nitrosomonas dominated AOB community under long-term greenhouse vegetable cultivation. Soil physicochemical properties, but not biological activity, were directly linked to the shifts of community structures of ammonia oxidizers. Moisture and total nitrogen significantly regulated AOA community structure, whereas organic matter and salinity mediated that of AOB. Our results demonstrated that consecutive greenhouse production obviously affected soil N turnover through altering community structures of nitrifiers, and soil functional microorganisms should be taken more attention when exploring the mechanisms for continuous cropping obstacles of greenhouse vegetable. The current study also highlights the fast adaptation of both AOA and AOB communities to complexly varied soil physicochemical environments.

Suicide attempts by jumping and length of stay in general hospital

American ginseng is a medicinal plant with large market demands, however, its producing areas are shrinking because of the continuous cropping obstacles in China. Therefore, it is urgent to establish a suitable model to determine the new producing areas. Here we evaluated and predicted the suitable areas of American ginseng using the maximum entropy model (MaxEnt).Based on the 37 environmental variables over thirty years from 1970 to 2000 and 226 global distribution points of American ginseng, MaxEnt was used to determine the global ecological suitable areas for American ginseng. The Receiver Operating Curve (ROC) was used to evaluate the model prediction accuracy. Meanwhile, an innovative ecological variable, the precipitation–temperature ratio, was established to indicate the climate characteristic in the American ginseng suitable areas based on the monthly precipitation and temperature.The potential ecological suitable areas of American ginseng were primarily in Appalachian Mountain in America and Changbai Mountain in China, about in the range of 35°N–50°N, 60°W–120°W and 35°N–50°N, 110°E–145°E, respectively, including the United States, Canada, China, North Korea, South Korea, Russia and Japan. South Korea and Japan were the potential producing regions. The precipitation–temperature ratios were stable at (0.22, 0.56) of the vigorous growth period (April–October) in the best suitable areas of American ginseng, serving as characteristic parameters to optimize the prediction model. The model showed that the common soil parameters were pH 4.5–7.2, Base Saturation (BS) above 80%, Cation Exchange Capacity (CEC) 10–20 cmol/kg, organic carbon (OC) < 1.4%, and the soil types were sandy loam or loam.An optimized MaxEnt model was established to predict the producing area for American ginseng that needed to be validated by a field test.

Precision Irrigation Scheduling Using ECH2O Moisture Sensors for Lettuce Cultivated in a Soilless Substrate Culture

Soilless culture has become an effective technique to avoid continuous cropping obstacles in protected horticulture. The reliable measurement of substrate moisture and a rational irrigation are difficult tasks because of the low water-holding capacity of the substrate. Our objectives were to study the irrigation scheduling based on the ECH2O moisture sensor(EC-5), using a matched model of wetting pattern and lettuce root zone in the substrate under drip irrigation. The EC-5 sensor was designed to connect to a controller, and a threshold value of 0.14 cm3/cm3 was set for irrigation scheduling. The controller turned on the irrigation system via communication with a solenoid valve on the irrigation line and with the EC-5 sensor in response to a threshold value and stopped when the overlap area of the wetting pattern and crop root zone was more than 90%. The EC-5 sensors were installed at a horizontal distance from each plant and depth of 3 and 4 cm, respectively, under the substrate surface to the check substrate moisture for lettuce cultivation, and at (3,15) cm or (6,15) cm to monitor leakage. These parameters were determined by simultaneously considering the distance from the plants, the depths of effective root water extraction, and the region of substrate wetted volume under drip irrigation. Leakage occurred during each irrigation process, but the leakage ratewas15.7% lower than that of conventional irrigation, as a result of irrigation scheduling in the presence of the EC-5 sensors.

Mechanisms by which organic fertilizer and effective microbes mitigate peanut continuous cropping yield constraints in a red soil of south China

Red soils are acid soils which occupy about one fifth of the total area of tropical and subtropical soils in China. Peanut (Arachis hypogaea L.) is regarded as the main oil and cash crop in the red soil region. However, yields of peanut have gradually but significantly declined under continuous cropping. We conducted a field experiment in Jiangxi province, south China from 1996 to investigate the mitigation of the peanut continuous cropping constraint. Three types of fertilizer (chemical, organic, and organic fertilizer with effective microbes) were applied in the field. After 20 years of cropping the continuous cropping constraint was found to be more severe where chemical fertilizers were applied and was mitigated where the fields were amended with organic fertilizer or organic fertilizer with effective microbes. Soil properties and the rhizosphere bacterial community structure were determined in 2016. Long-term application (20 years) of organic fertilizer increased the plant available phosphorus in the rhizosphere soil. Phosphorus is known to be one of the most limiting factors for peanut growth in red soils and peanut yield was promoted as the soil phosphorus status increased. Organic fertilizer and effective microbes also optimized the rhizobacteria of peanut to mitigate the continuous cropping obstacle. The bacterial wilt pathogen (Ralstonia) decreased in abundance in the rhizosphere and bacterial wilt disease of peanut declined significantly. Moreover, beneficial bacteria in the rhizosphere capable of promoting peanut growth increased in abundance.

Comparison of Photosynthetic Physiological Characteristics and Yield of Watermelon Varieties with Different Resistance to Fusarium Wilt

With the continuous development of facilities and horticulture, the area of vegetable planting in facilities increased year by year. Watermelon (Citrullus vulgaris Schrad) as the main cultivars within the facility, the continuous cropping problem is very serious, resulting in continuous cropping obstacles become increasingly obvious, the incidence of fusarium wilt increased year by year. Grafted watermelon roots developed to improve the growth of grafted roots of the conditions, resulting in robust plant growth. At the same time, the use of different purposes of the rootstock can make watermelon in different soil conditions under normal growth, such as the use of low temperature, drought, salt tolerance, barren and other characteristics of the rootstock. Secondly, the rootstock of the strong absorption of water absorption capacity, to promote the growth of grafted watermelon plants strong, large watermelon fruit, high yields. In addition, grafted watermelon seedlings grow fast early, for early maturing cultivation and overcome the seedless watermelon early growth slow defects is extremely favorable. So the use of pumpkin as a watermelon grafting rootstock, can effectively improve the effect of watermelon resistance to Fusarium wilts. And provide the theoretical basis and scientific basis for the further study of photosynthetic characteristics, disease resistance breeding and effective control of watermelon. In this experiment, the watermelon varieties with different resistance to fusarium wilt were selected, and the anti-fusarium wilt watermelon was studied systematically. There are changes in physiological characteristics during growth and development. In conclusion, grafting promotes the growth of watermelon and physiological characteristics of the index rose. KEYWORDS: watermelon; fusarium wilt; growth period; physiological characteristics

Analysis of the succession of structure of the bacteria community in soil from long-term continuous cotton cropping in Xinjiang using high-throughput sequencing.

The present study aimed to identify the structural succession of the bacteria community in soil during long-term continuous cotton cropping and its relationship with continuous cropping obstacles in Xinjiang, China. High-throughput sequencing was used to analyze and compare the composition of the bacterial community in the soil at the cotton root zone after years of continuous cotton cropping and crop rotation over 30years of cultivation. Cotton cultivation increased the structural diversity of the bacterial community, among which the populations of Actinobacteria, Acidobacteria, Firmicutes, Nitrospirae, and Chloroflexi changed considerably. A 0-year sample and samples after continuous short- and long-term cropping, along with some with crop rotation, were gathered into three individual clusters. The findings of the rotation sample were similar to those of the sample of continuous long-term cropping. Cropping is the main cause of changes in the structure of the bacteria community; however, the new structure formed under continued duress of both long-term cotton cultivation and the associated farming methods gradually stabilizes after 10years of repeated fluctuations. Crop rotation can lead to the rapid recovery of some species of soil bacteria.

Effects of Tobacco Pathogens and Their Antagonistic Bacteria on Tobacco Root Exudates

The research on relationship between rhizosphere microbes and root exudates has a great significance on discussion of interaction between rhizosphere microbes and plants, as well as control of soil-borne diseases and insect pest. GC-MS was used to analyze changes of tobacco root exudates under the antagonistic action of tobacco bacterial wilt and black shank. It turned out that when pathogens of tobacco bacterial wilt and black shank in tobacco root microorganisms increase, tobacco root exudates augmented rapidly among of which organic acids have the biggest growth, followed by amines. When the pathogens of tobacco bacterial wilt and black shank are inhibited by the active substance of antagonistic antibacterial, 20 - 23 kinds of root exudates are added; besides, the content of 7 substances was reduced to 0. Another inter-esting finding was that the fluctuations of phthalic acid, isophthalic acid and benzoic acid, which have caused continuous cropping obstacles, were very dis-tinct. The results of this study have provided novel clues for the exploration of continuous tobacco cropping obstacles and soil-borne diseases.

Mechanisms of earthworms to alleviate continuous cropping obstacles through regulating soil microecology

Mechanisms of earthworms to alleviate continuous cropping obstacles through regulating soil microecology