[Effects of Combined Stress of High Density Polyethylene Microplastics and Chlorimuron-ethyl on Soybean Growth and Rhizosphere Bacterial Community].

With the vigorous development of agriculture in China， plastic mulch film and pesticides are widely used in agricultural production. However， the accumulation of microplastics （formed by the degradation of plastic mulch film） and pesticides in soil has also caused many environmental problems. At present， the environmental biological effects of microplastics or pesticides have been reported， but there are few studies on the combined effects on crop growth and the rhizosphere soil bacterial community. Therefore， in this study， the high density polyethylene microplastics （HDPE， 500 mesh） were designed to be co-treated with sulfonylurea herbicide chlorimuron-ethyl to study their effects on soybean growth. In addition， the effects of the combined stress of HDPE and chlorimuron-ethyl on soybean rhizosphere soil bacterial community diversity， structure composition， microbial community network， and soil function were investigated using high-throughput sequencing technology， interaction network， and PICRUSt2 function analysis to clarify the combined toxicity of HDPE and chlorimuron-ethyl to soybean. The results showed that the half-life of chlorimuron-ethyl in soil was prolonged by the 1% HDPE treatment （from 11.5 d to 14.3 d）， and the combined stress of HDPE and chlorimuron-ethyl had more obvious inhibition effects on soybean growth than that of the single pollutant or control. The HiSeq 2 500 sequencing showed that the rhizosphere bacterial community of soybean was composed of 20 phyla and 312 genera under combined stress， the number of phyla and genera was significantly less than that of the control and single pollutant treatment， and the relative abundances of bacteria with potential biological control and plant growth-promoting characteristics （such as Nocardioides and Sphingomonas） were reduced. Alpha diversity analysis showed that the combined stress significantly reduced the richness and diversity of the soybean rhizosphere bacterial community， and Beta diversity analysis showed that the combined stress significantly changed the structure of the bacterial community. The dominant flora of the rhizosphere bacterial community were regulated， and the abundances of secondary functional layers such as amino acid metabolism， energy metabolism， and lipid metabolism were reduced under combined stress by the analysis of LEfSe and PICRUSt2. It was inferred from the network analysis that the combined stress of HDPE and chlorimuron-ethyl reduced the total number of connections and network density of soil bacteria， simplified the network structure， and changed the important flora species to maintain the stability of the network. The results above indicated that the combined stress of HDPE and chlorimuron-ethyl significantly affected the growth of soybean and changed the rhizosphere bacterial community structure， soil function， and network structure. Compared with that of the single pollutant treatment， the potential risk of combined stress was greater. The results of this study can provide guidance for evaluating the ecological risks of polyethylene microplastics and chlorimuron-ethyl and for the remediation of contaminated soil.

[Effects of Microplastic High-density Polyethylene on Cotton Growth, Occurrence of Fusarium wilt, and Rhizosphere Soil Bacterial Community].

Plastic mulch, especially polyethylene mulch, is widely used in agricultural production in China, but the microplastics formed by its degradation gradually have accumulated in soil, causing a series of environmental problems. At present, there have been many reports on the environmental biological effects of microplastics in farmland soil, but studies on the effects of microplastics on crop growth, disease occurrence, and rhizosphere soil bacterial communities are still lacking. In the previous study, it was found that 1% high-density polyethylene (HDPE, 500 mesh) could increase the incidence rate of cotton Fusarium wilt (33.3%) and inhibit growth, but this phenomenon was not found after soil sterilization. It was speculated that HDPE could affect the growth and occurrence of Fusarium wilt by regulating the soil microbial community. Therefore, high-throughput sequencing technology, combined with network and FAPROTAX function analysis, were used to investigate the effects of HDPE on the bacterial community structure, interaction network, and soil function in cotton rhizosphere in order to analyze the mechanism of HDPE. NovaSeq sequencing showed that the bacterial community of HDPE-treated cotton rhizosphere soil was composed of 54 phyla and 472 genera; the number of phyla and genera was higher than that in untreated soil. The α and ß diversity and ANOSIM/Adonis analyses showed that HDPE significantly reduced the richness of the bacterial community and changed the composition of the community structure. Based on a T-test species difference analysis, HDPE significantly reduced the relative abundance of bacteria with biological control, pollutant degradation, and antifungal drug synthesis (such as Kribbella, Massiliam, Hailiangium, and Ramlibacter).The change in the bacterial community will lead to the change in soil bacterial function. Further analysis of FAPROTAX function revealed that HDPE weakened some biochemical functions of bacteria in the cotton rhizosphere soil, such as aerobic chemoheterotrophy, fermentation, and nitrate reduction. The correlation network at the genus level showed that HDPE treatment weakened the interaction between rhizosphere bacteria, reduced the number of positive correlation connections, increased the number of negative correlation connections, simplified network structure, and changed the key flora. The above results showed that HDPE could reduce the cotton growth and the occurrence of Fusarium wilt by changing the bacterial community, interaction, and functional metabolism in rhizosphere soil, which can provide guidance for evaluating the ecological risk of polyethylene microplastics and the remediation of contaminated soil.

The Prevention of Bio-Organic Fertilizer Fermented from Cow Manure Compost by Bacillus sp. XG-1 on Watermelon Continuous Cropping Barrier.

The continuous cropping barrier is an important factor leading to the decline of watermelon quality and yield. In this study, we focused on a bio-organic fertilizer prepared with one bacterial strain, Bacillus sp. XG-1, to prevent the occurrence of the continuous cropping barrier. The strain XG-1 was isolated from watermelon rhizosphere soil, and promoted the growth of watermelon by producing phytase (0.19 U/mL), indole-3-acetic acid (IAA, 7.31 mg/L), and gibberellins (GA3, 2.47 mg/L). In addition, the strain also possessed a strong antagonistic effect against the pathogen Fusarium oxysporum f. sp. niveum (Fon) by inhibiting conidia germination with an inhibition ratio of 85.3% and mycelium growth. The bio-organic fertilizer fermented by XG-1, based on cow manure compost and rapeseed meal (85:15, w/w) under optimal conditions, was mixed in soil (watermelon had been planted for two consecutive years). After the cultivation of watermelon for 50 d, a higher density of XG-1 (9.79 × 105 colony-forming units (CFU)/g) and one order of magnitude lower of Fon (1.29 × 103 copies/g) were detected in the rhizosphere soil compared with soils without bio-organic fertilizer (7.59 × 104 copies/g for Fon), leading to an 86.4% control efficiency of watermelon caused by Fusarium wilt. The application of bio-organic fertilizer enriched soil nutrients, including the organic matter (13.2%), total nitrogen (13.9%), total phosphorus (20.5%), and total potassium (3.77%), adjusted the soil pH from 6.69 to 7.01, and significantly improved the watermelon growth in terms of the seedling height, root length, fresh weight of seedling and root with increase of 78.8%, 72.2%, 84.6%, and 96.4%, respectively. This study regarded the watermelon continuous cropping soil as the research point, and focused on inhibiting Fon, regulating soil properties and enhancing watermelon growth to eliminate the continuous cropping barrier through a combination of compost and functional strains, demonstrating the potential application value in watermelon production.