Effects of exogenous organic acids on the growth, edaphic factors, soil extracellular enzymes, and microbiomes predict continuous cropping obstacles of Panax notoginseng from the forest understorey.

Aims: The accumulation of organic acids in soil can trigger autotoxicity, resulting in the continuous cropping obstacles (CCOs) for Panax notoginseng under conventional management systems. However, limited information is available about the threshold value of organic acids representing the CCOs in the soil of P. notoginseng from the forest understorey. Methods: In this study, mixed organic acids at different concentrations were exogenously applied to simulate the P. notoginseng CCO. The plant growth, edaphic factors, soil extracellular enzyme activity, and bacterial/fungal abundances and diversity in the rhizospheric soil were assessed in the P. notoginseng from the forest understorey. Results: High concentrations (>150 mg/kg) rather than low concentrations (<150 mg/kg) of organic acid decreased the dry and fresh weight of plants (1.99%-1.98%), edaphic properties (2.75%-1.03%) and soil extracellular enzyme activities (3.38%-1.05%). Under high organic acid concentrations, the fungal abundance increased by 2.37%, whereas the bacterial abundance decreased by 4.56%. Moreover, the abundance of Pseudomonadales, Xanthomonadales, and Ilyonectria as pathogenic bacteria tended to increase. Compared to bacteria, the fungal community structure varied significantly, and the fungal core flora was more abundant. The SEM results showed that the direct and indirect factors affecting the α-diversity in the rhizosphere of P. notoginseng were increased under the high organic acid concentrations. Conclusion: Organic acid concentrations greater than 150 mg/kg in P. notoginseng soils are detrimental to the relationships among plant growth, soil environment, and microbiomes, which implies the occurrence of the CCOs in P. notoginseng; and therefore, we recommend that P. notoginseng should not be planted again. [ABSTRACT FROM AUTHOR]