Straw return is an effective strategy to alleviate soil-borne diseases. Though watermelon Fusarium wilt is a severe soil-borne disease, the effect of wheat straw on the disease remains unclear. Thus, we investigated the effects of wheat straw on soil bacterial and fungal communities by adding wheat straw to consecutive watermelon soil in the greenhouse condition. The microbiome changes were further investigated using network analysis based on 16S rDNA and internal transcribed spacer deep sequencing. Wheat straw addition increased the fungal community diversity, whereas the bacterial diversity was not affected. Compared to the control group, the relative abundance of some bacteria, including Actinobacteria , Chloroflexi , and Saccharibacteria , was increased with wheat straw addition. For fungi, the relative abundance of Fusarium was decreased with wheat straw addition. Microbial network analysis demonstrated that the fungal community has a more complex connection than the bacterial community. In addition, redundancy analysis indicated that the Fusarium genera were significantly related to the disease index. Taken together, the addition of wheat straw might affect the microbial community through increasing the relative abundance of phylum Actinobacteria , decreasing the relative abundance of Fusarium, and increasing the fungal network complexity to enhance the defense of watermelon against Fusarium wilt disease.

Soil C‐N‐P stoichiometry offers an effective way to explore the balance, limitation, cycling, and distribution of chemical elements in Chinese fir plantations. This research aimed to explore how soil organic C (Corg), total N (Ntot), and total P (Ptot) contents and stocks, together with their stoichiometric ratios vary with stand age (3, 9, 17, and 26 years) as well as soil layer (0–10, 10–20, 20–30, and 30–40 cm) at aggregate scales in Chinese fir plantations from Guangxi, China. For Chinese fir plantations of diverse ages, soil aggregate stability, Corg, Ntot, and Ptot contents and stocks, together with C/N, C/P, and N/P ratios, remarkably declined when soil depth increased. Stand age could influence C‐N‐P stoichiometric characteristics in soil, but such effect was more obvious in soil depth of 0–30 cm in comparison to that of 30–40 cm. In 0–30 cm soil layer, Corg and Ntot contents and stocks, together with C/P and N/P ratios, first rose and then reduced during Chinese fir planting; meanwhile, the highest levels could be observed in the 17‐year‐old Chinese fir plantations. However, Ptot content and stock, together with C/N ratio, were not related to the stand age. Overall, the present research helped to understand soil C, N, and P dynamics within a chronosequence of Chinese fir plantations. Also, it provided supplementary information for soil ecological stoichiometry in global terrestrial ecosystems.

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BackgroundWheat straw is a rich resource worldwide. Straw return is an effective strategy to alleviate soil-borne diseases on monoculture watermelon. Previous studies focus on soil structure, physical and chemical properties; however, little is known about the molecular responses on host plant.ResultsNo significant difference on the population of Fusarium oxysporum f.sp. niveum race 1(Fon1) in rhizosphere soil was found between control (no addition of wheat straw) and the treated groups (addition of 1% (T1) or 2% (T2) wheat straw). RNA-Seq analysis showed that 3419 differentially expressed genes were clustered into 8 profiles. KEGG analysis revealed that phenylpropanoid biosynthesis and plant hormone signal transduction were involved in wheat straw induced response in monoculture watermelon. Genes in lignin biosynthesis were found to be upregulated, and the lignin and auxin contents were higher in T1 and T2 compared to the control. Lignin was also enriched and the Fon1 population decreased in watermelon roots treated with wheat straw. The enzyme activities of phenylalanine ammonia-lyase and peroxidase were increased.ConclusionsOur data suggest that the addition of wheat straw enhances the defense response to Fon1 infection in watermelon through increasing lignin and auxin biosynthesis.

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Crop rotation affects soil properties and soil microbial diversity and structure. Currently, it is not well understood how soil microbial diversity changes following different crop rotation systems of industrial hemp, an ancient and economically important crop. Therefore, these changes were analyzed in this study. Our results showed that different rotation systems significantly affected the wilt disease incidence, plant height, yield, soil physicochemical properties and soil microbial communities in the greenhouse. The rotation systems used in this study significantly reduced the plant mortality and increased the yield compared with a monoculture system. The levels of alkaline hydrolysis and available phosphorus in the soil decreased significantly compared with a monoculture cropping system. Using MiSeq high-throughput sequencing, we showed that the soil diversity and number of bacteria and fungi were significantly higher for rotation systems and controls compared to the monoculture system. The relative abundance of pathogens increased with a monoculture system. Redundancy analysis suggests that soil properties may also affect the soil microbial composition. Taken together, different rotation systems used in this study significantly decreased the disease incidence, increased plant yields and increased soil microbial diversity compared with monoculture for industrial hemp. We believe that applying these rotation systems is an efficient and eco-friendly approach to control soil borne pathogenic diseases and increase floral yields.

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