Specific responses in soil metabolite alteration and fungal community decline to the long-term monocropping of lisianthus

Continuous cropping obstacle (CCO) is becoming a serious threat to the quality production of lisianthus (Eustoma grandiflorum). However, investigations of the causal mechanism of CCO in lisianthus are still lacking. To this end, soil biotic dynamics and metabolites alterations were illuminated using metagenomic sequencing and metabolomic profiling along a chronosequence that has cultivated lisianthus from 2 weeks to 6 years. Soil EC and nutrient contents increased significantly as the cultivation duration prolonged. Fungal community has undergone significant decline in their diversity and biomass. Nevertheless, no apparent accumulation of pathogenicity- related microbes was observed along the investigated chronosequence. The alterations of soil metabolites along the chronosequence reflect the decline of microbial activity, the accumulation of phytotoxic compounds and the loss of metabolite involved in beneficial plant-microbe interactions. As a result, lisianthus plants in the longer continuous cropping soil experienced stressful condition as evidenced by the increasing trend of stress responsive metabolites and the overall soil function deterioration as indicated by soil enzymes. Hierarchical partitioning analysis showed that the investigated factors can explain a total of 92.25 % of the variations in the soil function degradation. Of which, soil metabolite alteration was the most important factor in explaining the CCO development, covering 24.55 % of the explainable variations. Spearman's correlation results further implied that soil metabolite alteration is the main driver in the development of CCO in lisianthus, especially by mediating the plant-microbes interactions. Our findings revealed a general pattern of soil biotic and abiotic response to the continuous monocropping of lisianthus and suggest that the overcome of the CCO in lisianthus requires further studies focusing on the crucial metabolites and their interactions with microbes.