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.

BACKGROUND Most allelochemicals are secondary products released from root excretions or plant residues that accumulate in continuous cropping systems and cause severe decline in peanut yield. Resveratrol is a plant‐derived stilbene that is released from peanut residues and accumulates in the soil; however, its allelopathic effects on peanut production are overlooked. Effective management solutions need to be developed to relieve allelopathy caused by soil resveratrol. Here, the biodegradation of resveratrol by the fungal endophyte Phomopsis liquidambari was investigated in a mineral salt medium and a soil trial. Resveratrol and its metabolites (produced by degradation by P. liquidambari) were detected by high‐performance liquid chromatography–mass spectrometry (HPLC‐MS). RESULTS Resveratrol released from peanut residues reached a maximum concentration of 0.18 μg g−1 soil in litterbag experiments. Exogenous resveratrol inhibited peanut growth, nodule formation, and soil dehydrogenase activity, and reduced the soil microbial biomass carbon content and bacterial abundance, indicating an allelopathic role in peanut growth. More than 97% of the resveratrol was degraded within 72 and 168 h by P. liquidambari in pure culture and soil conditions, respectively. Resveratrol was first cleaved to 3,5‐dihydroxybenzaldehyde and 4‐hydroxybenzaldehyde, which were subsequently oxidized into 3,5‐dihydroxybenzoic acid and 4‐hydroxybenzoic acid, respectively. Fungal resveratrol cleavage oxygenase and the related gene expression were enhanced when P. liquidambari was induced by the resveratrol during the incubation. CONCLUSION Our results indicate that the practical application of the fungal endophyte P. liquidambari has strong potential for biodegrading soil resveratrol, which can cause allelopathy in peanut continuous cropping systems. © 2019 Society of Chemical Industry

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We monitored the dynamics of Trichoderma spp. communities in a cucumber monocropping system. Trichoderma spp. community structure and abundance were analyzed with PCR-denaturing gradient gel electrophoresis and quantitative PCR, respectively. Results showed that long-term monocropping did not affect the Trichoderma spp. community structure as indicated by the number of bands, Shannon-Wiener index and evenness index of the PCR-denaturing gradient gel electrophoresis profile. Trichoderma spp. community structure abundance was the highest in the first cropping of cucumber. Our results suggested that changes in Trichoderma spp. communities may not be the causal agent of soil sickness in cucumber monocropping.