The Abatement Mechanism Of Pseudostellaria Heterophlla's Continuous Cropping Obstacles Under Different Rotation Cropping Modes

This study focused on the abatement effect of Pseudostellaria heterophlla's continuouscropping obstacles under different rotation cropping modes by assessing the production andquality of Radix Pseudostell, measuring its biochemical indicators, and appraising the autotoxicsubstances and autotoxicity potential of the soil. The soil enzyme activity and T-RFLP techniqueswere used to investigate the soil's Micro-ecological functional regulation that related to theabatement mechanism of P. heterophlla's continuous cropping obstacles. The main findings areas follows:Continuous cropping leads to a significant decline in the production and quality in medicineof Radix Pseudostell, the output of P. heterophlla from the continuous cropping was only57.46%(P <0.05) of the main cropping, polysaccharides and saponins content were only81.5%(P <0.05)and73.7%(P <0.05) respectively. The measurement of physiological indices showed thatcompared with newly planted, continuous cropping caused the reduction of P. heterophlla'schlorophyll content, photosynthetic rate, intercellular CO₂and other photosynthetic parameters.The photosynthesis was suppressed; biomass reduced; the activity of protective enzymes SOD,POD and CAT increased; the degree of membrane lipid and the malondialdehyde content bothincreased. Therefore, the growth and development of P. heterophlla was retarded, indicating thecropping obstacle phenomenon. The test of Allelopathic autotoxicity potential showed that theallelopathic autotoxicity potential of the liquid extracted from the P. heterophlla continuouscropping soil was stronger than that from the main cropping soil. Such allelopathic autotoxicitysubstances were first separated by the ADS series of macroporous resin of different polarity. Thenthe component with the strongest allelopathic autotoxicity potential (ADS-7, the polarity of theadsorption surface) was appraised by GC-MS. The results showed that the P. heterophllarhizosphere soil contained a great amount of acids, alcohols, aldehydes and ketones, and theconcentration of these substances increased with the P. heterophlla planting years. The test of soilenzymatic activity indicated that compared with the main cropping soil, the activity of invertase,urease, polyphenol oxidase in the continuous cropping soil decreased significantly, but the activityof acid phosphomonoesterase and catalase increased. The results of colony T-RFLP analysis of theP. heterophlla rhizosphere soil showed that the amount of colony in the continuous cropping soil decreased, the biodiversity also decreased significantly. Further analysis found that in thecontinuous cropping soil, the species and quantity of probiotics that relate to the nutrient cycling;both autotoxic substance degradation and soil texture improvement declined or even disappeared.On the contrary, the pathogen content, such as streptococcus, helicobacter and little pear-shapedgenus, all increased.The study on the abatement mechanism of P. heterophlla's continuous cropping obstaclesunder different rotation cropping modes found that under the rice-P. heterophlla rotation croppingmode, the production, polysaccharide content and total saponin content of P. heterophlla reached92.29%and116%,86.8%, of the main cropping; under the bean-P. heterophlla rotation croppingmode, the production, polysaccharide content and total saponin content of P. heterophllaamounted to64.79%,90.4%,134.6%, of the main cropping. The abatement effect is especiallyremarkable under the rice-P. heterophlla rotation cropping mode.The measurement of physiological indices showed that under the two rotation croppingmodes, P. heterophlla's chlorophyll content, photosynthetic rate, intercellular CO₂and otherphotosynthetic parameters were all higher than that of the continuous cropping; Compared withthe continuous cropping, the suppression of photosynthesis was weakened; the biomass increased;the activity of protective enzymes, such as SOD, POD and CAT, all decreased; the degree ofmembrane lipid and the malondialdehyde content both decreased. These effects were particularlyremarkable on the rice-P. heterophlla rotation cropping mode.Further analysis on the allelopathic autotoxicity potential of the liquid extracted from the soilof the continuous and rotation cropping showed that of the soil allelopathic autotoxicity potentialunder these two rotation cropping modes were both lower than that of the continuous cropping.The soil allelopathic autotoxicity potential under rice-P. heterophlla rotation cropping mode wasthe weakest. The appraisal of autotoxic substances indicated that under the rice-P. heterophllarotation cropping mode, the acids, alcohols, aldehydes and ketones content in the RadixPseudostell rhizosphere soil all decreased slightly, but the content of benzoquinone substancesincreased slightly; under the bean-P. heterophlla rotation cropping mode, the acids, alcohols,aldehydes and ketones content in the P. heterophlla rhizosphere soil all decreased slightly, but thecontent of benzoquinone substances increased significantly. The results of soil enzymatic activity test showed that under these two rotation croppingmodes, the activity of invertase, urease and polyphenol oxidase in the P. heterophlla rhizospheresoil were all higher than that of the continuous cropping. Under the rice-P. heterophlla rotationcropping mode, the activity of soil invertase enzyme and polyphenol oxidase enzyme were bothhigher than that of the bean-P. heterophlla rotation cropping, but the urease activity was lowerthan that of the bean-P. heterophlla rotation cropping. The acid phosphomonoesterase activityin the continuous cropping soil was higher than that of the bean-P. heterophlla rotation cropping,but slightly lower than that of the rice-P. heterophlla rotation cropping. The catalase activityshowed no difference among these three cropping modes.The T-RFLP analysis of the colony in the P. heterophlla rhizosphere soil under differentcropping modes indicated that compared with the continuous cropping, the amount of the colonyin the P. heterophlla rhizosphere soil increased under the two rotation cropping modes, thebiodiversity level rised significantly. The microbial functional analysis found that, compared to therhizosphere soil in continuous cropping, the species and quantity of probiotics that relate to thenutrient cycling, autotoxic substance degradation and soil texture improvement both exhibited anincreasing trend under the rice-P. heterophlla rotation cropping mode, while the species andquantity of pathogen decreased slightly. Under the bean-P. heterophlla rotation cropping mode,the species and quantity of probiotics that relate to the nutrient cycling, autotoxic substancedegradation and soil texture improvement also increased slightly, but at the meantime the speciesand quantity of pathogen increased significantly.From the above, the P. heterophlla continuous cropping led to the accumulation of toxicsubstances in soil, which selected and promoted specific species of Microorganism causing theimbalance and graceful degradation of the Micro-ecosystem in the soil, resulting in P.heterophlla's continuous cropping obstacles,eventually lead to the declined of its yield and qualitycharacteristics. This study also explores the abatement effect and the function mechanism ofP.heterophlla continuous cropping obstacles under rice-P.heterophlla's and bean-P.heterophlla's.Under the rice-P. heterophlla rotation cropping mode the acids, alcohols, aldehydes and ketonescontent in the P.heterophlla rhizosphere soil all decreased; the species and quantity of probioticsthat relate to the nutrient cycling, autotoxic substance degradation and soil texture improvementboth exhibited an increasing trend, while the species and quantity of pathogen decreased slightly; the activity of invertase, urease and polyphenol oxidase were all rised, soil ecological functionimproved. Therefore, regulated and recovered the microorganism diversity in soil by adoptingmethods such as biodiversity cropping, could reduce the accumulation of toxic substances,improved the diversity of microbial community in soil, thus restored the ecological systemfunctioning, overcomed the crop cropping problems by simplification cultivation,achieved thepurpose of Chinese herbal high yield, good quality, ecological and security.