| Objective:The continuous cropping obstacle will lead to the serious diseases and insects of Curcuma kwangsiensis S.G·Lee et C·F.Liangand the decrease of yield and quality,which seriously restricts the sustainable development of C.kwangsiensis.To study the occurrence mechanism and countermeasures of continuous cropping obstacles in C.kwangsiensis is the key issue to ensure the sustainable developent of C.kwangsiensis.Therefore,this study measured continuous and non continuous C.kwangsiensis quality and yield,soil physicochemical properties,p H value,rhizosphere soil microbial diversity,and C.kwangsiensis allelopathy test.Preliminary reveal the mechanism of continuous cropping obstacles in C.kwangsiensis,providing scientific basis for standardized cultivation and improvement of medicinal material quality.Methods:(1)The contents of moisture,ash and leachate of C.kwangsiensis were determined with reference to the general rules of Part IV of the Pharmacopoeia of the People’s Republic of China,2020 edition(hereinafter referred to as "Chinese Pharmacopoeia").(2)Referring to Appendix XD of the Chinese Pharmacopoeia 2020 edition,the volatile oil of C.kwangsiensis was extracted and analyzed by GC-MS.(3)Analysis of physicochemical properties of continuous and non-continuous C.kwangsiensis soils: soil p H was determined by electrode method;organic matter content by low-temperature external heat potassium dichromate oxidation-colorimetric method;total N content by Kjeldahl method;phosphorus content by colorimetric method;potassium content by flame photometer method.Exploring the role of soil physicochemical properties in crop succession barriers.Soil microbial population indicators were measured by dilution plate method,and Illumina Mi Seq sequencing technology was applied to study and analyze the structure and diversity of inter-root soil bacterial community and fungal community of C.kwangsiensis in continuous and non-continuous cropping.(4)By chemosensory experiments with C.kwangsiensis inter-root soil extracts,root secretions.Exploring the role of chemosensory autotoxicity of C.kwangsiensis in continuous crop barriers;and the isolation and identification of chemosensory autotoxic substances of C.kwangsiensis.Results:(1)The moisture,total ash,and volatile oil contents in the rhizomes of C.kwangsiensis from different production areas were significantly higher than those of C.kwangsiensis from continuous crop.C.kwangsiensis yield and quality were significantly reduced by continuous crop,with an overall decrease of 47.29% in yield and an overall decrease of 33.29% and 27.47% in total ash and leachate in quality,respectively,and a serious yield reduction of C.kwangsiensis.(2)The unique components in the volatile oil of C.kwangsiensis in continuous cropping group included Diethylcyanamide;Benzene;1-ethyl-2,4-dimethyl-,Furan;2-ethyl-5-methyl-;and so on.(3)After comparing the continuous crop group with the non-continuous crop in the three production areas,the abundance of Actinomycetes and Ascomycetes in the soil of C.kwangsiensis in the Bingyang production area decreased by 36.54% and10.13% in the three years of continuous crop.The abundance of Actinomycetes and Ascomycetes in the soil of C.kwangsiensis decreased by 4.74% and 8.34%in three years of continuous crop in the Nanning production area.The abundance of Actinomycetes,Proteobacteria,Chloroflexi,and Basidiomycota decreased by 20.18%,40.21%,20.18%,and 18.99% in the soil of C.kwangsiensis for three years of continuous crop in Qinzhou production area.Redundancy analysis(RDA)showed that the changes of total phosphorus,available potassium,total potassium and p H value in soil physicochemical properties were the main factors affecting the microbial community of C.kwangsiensis.(4)The soil water extract of C.kwangsiensis root system had a significant autotoxic effect on radish and cabbage seeds,with increasing concentrations producing a significant inhibition of radish and cabbage seed embryonic root and germ,with embryonic root length reduced by 21.83%-54.00% and germ length reduced by 9.71%-50.52% compared to the control.The non-continuous C.kwangsiensis root soil extract showed a "high inhibition and low promotion" phenomenon on the growth of radish and cabbage seeds.The root secretion of C.kwangsiensis had a significant inhibitory effect on the growth of radish and cabbage seeds,while the root secretion of non-continuous C.kwangsiensis showed a "high inhibition and low promotion" phenomenon on the growth of radish and cabbage seeds.The above phenomena suggest that continuous cropping of C.kwangsiensis has a significant self-toxic effect.By GC-MS analysis,39 and 36 allelopathic substances were identified in chloroform,petroleum ether and ethyl acetate from rhizosphere soil and root secretory fluid of C.kwangsiensis.It is speculated that dibutyl phthalate and palmitic acid may be allelopathic substances that cause continuous cropping obstacle of C.kwangsiensis.Conclusions:(1)Continuous cropping resulted in decreased yield and quality of C.kwangsiensis.(2)The compositions of volatile oil in C.kwangsiensis were different between continuous cropping and non-continuous cropping.(3)Continuous cropping of C.kwangsiensis resulted in the decrease of soil p H value,serious soil acidification,excessive enrichment of P and Zn,and the decrease of K,Fe,Mn and Cu.These changes in soil physical and chemical properties significantly reduced the diversity and evenness of functional groups,and showed obvious dominance concentration,which may be one of the main causes of C.kwangsiensis continuous cropping disorder(4)C.kwangsiensis continuous cropping rhizosphere soil extract and root secretion inhibited the growth of radish and Chinese cabbage seeds obviously.These results indicate that allelopathic substances may exist in the rhizosphere soil extract and root secretions of C.kwangsiensis,which hinder the growth and development of C.kwangsiensis,and thus lead to the continuous cropping obstacle of C.kwangsiensis.Identification results of allelopathic substances in soil extract and root secretion of C.kwangsiensis showed that there were differences in the types and amounts of allelopathic substances in continuous cropping and non-continuous cropping.Dibutyl phthalate and palmitic acid are allelopathic substances causing continuous cropping disorder of C.kwangsiensis.Based on the above results,there may be three reasons for continuous cropping obstacles.First,the change of soil physical and chemical properties and the loss of trace elements;The change of microbial community structure.The accumulation of allelopathic substances in soil may lead to autotoxicity,resulting in the decline of yield and quality. |
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