Polychlorinated biphenyls (PCBs) are typical pollutants in soil. Nanoscale zero-valent iron (nZVI) can effectively dechlorinate high-chlorinated PCBs into low-chlorinated PCBs which can be more easily degraded by microorganisms. In this study, soil samples contaminated by PCBs were collected from an e-waste recycling site in Taizhou, Zhejiang Province. The remediation of combined nZVI and PCBs-degrading strain Rhodococcus pyridinovorans R04 was carried out to investigate the removal effect of PCBs in soil. The results showed that the combined treatment of nZVI and degrading strain R04 had better effects than the treatment of nZVI or R04 alone in removing PCBs or various chlorinated PCB congeners in soil. After combined treatment with nZVI and degrading strain R04 for 32 d, the removal rate of PCBs in soil reached 59.4%, which was higher than 46.1% of nZVI treatment and 34.4% of degrading strain R04 treatment (P＜0.05). Therefore, the combination of nZVI and degrading bacteria in the remediation of PCBs contaminated soil has good application potential.
Under the iron-deficiency condition, roots of graminaceous plants secrete mugineic acids into the soil. To determine the effects of rice root exudate 2′-deoxymugineic acid (DMA) on rhizosphere and root endosphere bacterial community, wild type rice named as Nipponbare and osbhlh156 and iro2 mutant rices that loss the ability to secrete DMA were used as experimental materials in this study. The rhizosphere and root endosphere microorganisms were sampled for DNA extraction and 16S rRNA gene amplicon sequencing and data analysis. The results showed that soil types and cultivation conditions had significant impacts on rhizosphere and root endosphere bacterial community composition. In contrast, the root exudate DMA had relatively less impact, but not negligible. The bacterial species and diversity decreased from rhizosphere to root endosphere, which confirmed that the root endosphere bacteria were gradually selected and colonized inside root by interacting with plants. Nine microbial taxa, including Bradyrhizobium and Dictyobacter, etc., were selected as biomarkers, to distinguish whether there is DMA secretion in the rice rhizosphere. Through functional prediction, it was found that the bacterial taxa with adenosine triphosphate-binding cassette (ABC) transporter function may be involved in plant iron transport and related function. This study clarifies the effects of DMA on the composition of rhizosphere and root endosphere bacterial community of rice and provides data support for the comprehensive analysis of the role of microorganisms in response to iron deficiency in rice.
As a processing technology that can rapidly fabricate customized products in small batches, three-dimensional (3D) printing has great application potential in horticultural gardens. On the basis of existing studies on controlled releasing materials for 3D printing, the carrier materials for solo nutrition were developed after a range of formulation screening. The new formulations were suitable for material extrusion 3D printing and the single-material carrier formulation fertilizer contained sodium alginate or xanthan gum as a binder, mannitol as a filler, ethanol/water with fixed ratio as a solvent, sepiolite as a thickening agent, and urea as the core fertilizer. It was confirmed that the maximum adding ratio of urea could reach 1∶4 [m (urea)∶V (solvent)] when using sodium alginate as a binder, while the maximum adding ratio could reach 3∶4 [m (urea)∶V (solvent)] when using xanthan gum as a binder. It was confirmed that the developed formulation could also be used as the carrier of other types of nutrients including KCl, K2HPO4, and ZnSO4. This work also demonstrated that it was possible to combine different nutrients and achieve element couplings by using multi-material extrusion 3D printing technology. Through the printing parameter adjustment experiment, the optimal printing was achieved when the printing speed was 200 mm/min, and the extrusion speed was 0.02 mm/s, and the extrusion height was 1 mm, and the nozzle diameter was 1 mm. The controlled release period of different formulations were further studied by the sand column leaching method. There were significant differences between the controlled release period of single-material carrier formulation fertilizers under different formulations and their post-treatments. The modified formulation with sepiolite can obviously change the release rate of single-material carrier formula fertilizer and the longest controlled release period reached 30 d.
Bacterial leaf blight in rice is a significant disease, and understanding the effects of straw burning on pathogens and antibiotic resistance genes (ARGs) in paddy fields is crucial. Soil and rice stubble samples were collected from bacterial leaf blight outbreak areas in Ningbo City of Zhejiang Province, and these samples were subjected to high-throughput metagenomic sequencing to investigate the effects of straw burning. The results indicated that the relative abundance of pathogens in the rice stubble was significantly higher than that in the soil. After straw burning, except for the significant increase in available potassium content, there were no significant changes in the other physicochemical properties of the soil. Overall, there were no significant differences in pathogen community diversity after straw burning, but straw burning led to a sharp decrease in the relative abundance of Xanthomonas oryzae in the rice stubble. The relative abundances of ARGs in the soil and rice stubble increased after straw burning, but there were no significant differences compared with those before straw burning (P＞0.05), while the relative abundance of mobile genetic elements (MGEs) in the rice stubble decreased significantly after straw burning (P＜0.05). The proportion of positively correlated links in the coexisting networks of pathogens-ARGs decreased after straw burning. Mantel analysis revealed that the water content (r=0.642, p＜0.01), pH value (r=0.582, p＜0.05), total organic carbon content (r=0.325, p＜0.05), total nitrogen content (r=0.570, p＜0.01), and available phosphorus content (r=0.311, p＜0.05) were closely related to the soil ARG subtypes; the dissolved organic carbon (DOC) content (r=0.275, p＜0.05) and available potassium content (r=0.312, p＜0.05) were correlated with the ARG subtypes, and the DOC content (r=0.201, p＜0.05) significantly affected the pathogen community structure in the rice stubble. In summary, straw burning can reduce the relative abundance of X. oryzae in the rice stubble, which suggests that it may be a viable option for preventing and controlling rice bacterial leaf blight; moreover, a reduction in the positive correlation ratio of pathogens-ARGs and in the relative abundance of MGEs after straw burning may inhibit the formation of potentially resistant pathogens. However, given the complexity of soil biological compound pollution, the effects of straw burning on pathogens and ARGs in paddy fields need to be further explored by long-term location experiments.
In the highly acidic soil pilot area contaminated by cadmium (Cd) in Yongkang City of Zhejiang Province, we screened low-Cd-accumulating rice cultivars and soil passivators in the field and performed the combined effect tests for two consecutive years to explore the safe utilization technology model suitable for local Cd-polluted paddy fields. The results showed that ‘Xiushui 519’ (XS519), ‘Zhenuo 106’ (ZN106), ‘Zhongzheyou 1’ (ZZY1H) and ‘Zhongjia 8’ (ZJ8H) could be recommended as low-Cd-accumulating rice cultivars suitable for local planting. Among them, ‘Xiushui 519’ had the lowest and most stable Cd accumulation ability, and the average bioconcentration factors (BCFs) of Cd in the rice grains in the two years were 0.090 and 0.159, respectively; in the screening tests of passivators, the improvement effect of lime (L) on soil pH was significant. Lime, iron-modified biochar (FeC) and calcium-magnesia phosphate fertilizer (CaMgP) could reduce soil available Cd contents to a certain extent (passivation rates were 14.8%, 7.1% and 6.9%, respectively). In addition, 1 800 kg/hm2 iron-modified biochar and 2 400 kg/hm2 soil conditioner had better effects on reducing the Cd content in the rice grains of ‘Zhongjia 8’, which decreased by 32.2% and 29.0%, respectively, after application. According to the results of the combination tests of the low-Cd-accumulating cultivars and passivators, both the application of 2 250 kg/hm2 iron-modified biochar and 2 250 kg/hm2 soil conditioner increased obviously the soil pH values at the tillering stage and filling stage, the soil conditioner of which had a better improvement effect. The Cd contents in the rice grains of ‘Xiushui 519’ and ‘Zhenuo 106’ were extremely significant correlations with the soil pH values (5.19-5.61) at the mature stage. Within the range of soil pH values involved in the test, except for the combination of ‘Xiushui 519’ and the 1 500 kg/hm2 soil conditioner, the Cd content in the rice grains increased with increasing application amount of passivators. Therefore, planting ‘Xiushui 519’ (a low-Cd cultivar) directly is the best choice for the safe utilization of Cd-contaminated paddy fields in this area, which is both economical and convenient.
Non-flooding plastic film mulching cultivation (PM) for rice is a comprehensive and innovative technology that utilizes plastic film covering as the core to achieve water-saving rice production. However, after mulching with plastic film, nitrogen (N) fertilizer can only be applied once as a basal fertilizer before transplanting, which will lead to excessive vegetative growth at the early stage and potential N deficiency at the late growth stage, thereby limiting the high yield of rice. Polymer coated urea (CR) is a controlled release N fertilizer that has become one of the best management measures for improving crop yield and N use efficiency under a traditional flooding cultivation (TF) pattern, but it has not been evaluated in a long-term positioning test under the PM pattern. In this study, taking the high-yielding and medium-maturing indica hybrid rice cultivar ‘Liangyoupeijiu’ as a test material, the effects of applying CR and urea (UR) on rice yield, N use efficiency and soil nutrient contents were compared under the PM and TF patterns. The results showed that, compared with applying UR, applying CR under the TF and PM patterns improved the N use efficiency by 9.2% and 15.4%, respectively (P＜0.05), and increased the rice yield by 8.6% and 15.0%, respectively (P＜0.05). Compared with the TF pattern, the PM pattern accelerated the decomposition of soil organic matter and reduced the contents of total N and alkali-hydrolyzable N in the soil. Compared with applying UR, applying CR under the PM pattern alleviated the decrease of the total N and alkali-hydrolyzable N contents in the soil and increased the economic benefits by 16.8%. In summary, applying CR is an effective way to solve the problem of N deficiency at the late growth stage of rice under the PM pattern.
To understand the community structure composition and dynamic change characteristics of human pathogenic bacteria (HPB) in soils after manure application, laboratory cultivation experiments were conducted on agricultural soils with long-term application of chicken manure, pig manure, or chemical fertilizer in five regions of Hangzhou, Jiaxing, Quzhou, Jinhua, and Longyou in Zhejiang Province, and the community compositions of the soil bacteria and HPB were analyzed by high-throughput sequencing and sequence alignment methods. The results showed that a total of 75 HPB were detected in 160 soil samples and two manure samples, and the dominant HPB were Bacillus_megaterium_QM_B1551 (24.2%) and Clostridium_beijerinckii_NCIMB_8052 (23.1%). The Shannon indexes of bacteria and HPB in the soils decreased after the application of pig manure, while the diversities of bacteria and HPB in the soils with the application of chicken manure or chemical fertilizer had no significant changes. The results of the principal coordinate analysis showed that there was a significant difference in the bacterial community composition of soils between the manure treatment and the unfertilized control, especially in the pig manure treatment (P＜0.001); 22.7% of all HPB were shared among the soil samples; and the relative abundance of most HPB in the soils treated with manure was higher than that in the unfertilized control, and it decreased continuously with the extension of cultivation time. The results of the variance partitioning analysis showed that soil physicochemical properties, bacterial communities, and their interactions were important factors contributing to the variation of HPB in the soils. In summary, the HPB variation characteristics in soils treated with manure are influenced mainly by manure types, soil types, soil physicochemical properties, and inherent bacterial communities.
