Effects of lead pollution on soil microbial community diversity and biomass and on invertase activity

Lead(Pb)pollution is one of the most widespread and harmful environmental problems worldwide.Determination of changes in soil properties and microbial functional diversity due to land use is needed to establish a basis for remediation of soil pollution.This study aimed to investigate soils contaminated by Pb from different sources and to analyze the functional diversity and metabolism of soil microbial communities using Biolog technology.Pb pollution(>300 mg kg-1)significantly influenced the diversity and metabolic functions of soil microbial communities.Specifically,Pb contamination significantly reduced soil microbial biomass carbon(C)and nitrogen(N)levels and catalase activity while increasing invertase activity.Furthermore,Biolog EcoPlate assays revealed that Pb pollution reduced the general activities of soil microorganisms,suppressing their ability to utilize C sources.In Pb-contaminated areas lacking vegetation cover,Shannon,Simpson,and McIntosh diversity indices of soil microorganisms were significantly reduced.The microbial diversity and biomass C and N levels were affected by land use and soil properties,respectively,whereas soil enzyme activity was primarily affected by the interaction between land use and soil properties.Our results provide a reference and a theoretical basis for developing soil quality evaluation and remediation strategies.

Interactions between phosphorus availability and microbes in a wheat–maize double cropping system:A reduced fertilization scheme

Mechanisms controlling phosphorus(P) availability and the roles of microorganisms in the efficient utilization of soil P in the wheat–maize double cropping system are poorly understood.In the present study,we conducted a pot experiment for four consecutive wheat–maize seasons(2016–2018) using calcareous soils with high(30.36 mg kg^(–1)) and low(9.78 mg kg^(–1)) initial Olsen-P content to evaluate the effects of conventional P fertilizer application to both wheat and maize(Pwm) along with a reduced P fertilizer application only to wheat(Pw).The microbial community structure along with soil P availability parameters and crop yield were determined.The results showed that the Pw treatment reduces the annual P input by 33.3% without affecting the total yield for at least two consecutive years as compared with the Pwm treatment in the high Olsen-P soil.Soil water-soluble P concentrations in the Pw treatment were similar to those in the Pwm treatment at the 12-leaf collar stage when maize requires the most P.Furthermore,the soil P content significantly affected soil microbial communities,especially fungal communities.Meanwhile,the relative abundances of Proteobacteria and alkaline phosphatase(ALP) activity of Pw were significantly higher(by 11.4 and 13.3%) than those of Pwm in soil with high Olsen-P.The microfloral contribution to yield was greater than that of soil P content in soil with high Olsen-P.Relative abundances of Bacillus and Rhizobium were enriched in the Pw treatment compared with the Pwm treatment.Bacillus showed a significant positive correlation with acid phosphatase(ACP) activity,and Rhizobium displayed significant positive correlations with ACP and ALP in soil with high Olsen-P,which may enhance P availability.Our findings suggested that the application of P fertilization only to wheat is practical in high P soils to ensure optimal production in the wheat and maize double cropping system and that the soil P availability and microbial community may collaborate to maintain optimal yield in a wheat–maize double cropping system.

Straw-returning reduces the contribution of microbial anabolism to salt-affected soil organic carbon accumulation over a salinity gradient

●In low-salinity soil,straw-returning did not change necromass contribution to SOC.●In medium-salinity soil,straw-returning reduced necromass contribution to SOC.●Straw-returning reduced POC contribution to SOC in low-salinity soil.●Straw-returning increased POC contribution to SOC in medium-salinity soil.●Salinity affects the contribution of microbial-derived and plant-derived C to SOC.Salinization affects microbial-mediated soil organic carbon(SOC)dynamics.However,the mechanisms of SOC accumulation under agricultural management practices in salt-affected soils remain unclear.We investigated the relative contribution of microbial-derived and plant-derived C to SOC accumulation in coastal salt-affected soils under straw-returning,by determining microbial necromass biomarkers(amino sugars)and particulate organic C(POC).Results showed that,straw-returning increased necromass accumulation in low-salinity soil but did not change its contribution to SOC.In medium-salinity soil,straw-returning did not increase necromass accumulation but decreased its contribution to SOC.In low-and medium-salinity soils,the contribution of POC to SOC showed the opposite direction to that of the necromass.These results suggest that under straw-returning,the relative contribution of microbial-derived C to SOC decreased with increasing salinity,whereas the reverse was true for plant-derived C.Our results highlighted that straw-returning reduces the contribution of microbial anabolism to SOC accumulation in salt-affected soils with increasing salinity.

Three dimensional BC/rGA aerogel:preparation,characterization,and adsorption of Cr(Ⅵ)

Graphene-based composite aerogel doped with other low-cost materials can reduce the cost and promote the use in water treatment.This work prepared ball-milled biochar/reduced graphene oxide aerogel(BC/rGA)using GO and low-cost ball-milled biochar(BC)in a certain proportion with the freeze-thawing technique and sol-gel method,and applied BC/rGA on the Cr(Ⅵ)removal from aquatic environments.The characterization results showed that aerogel had a honeycomb briquette three-dimension(3D)and mesoporous structure with interconnected pores,and proved the preparation progress of aerogel in principle.Compared with GO,rGA and BC/rGA had better adsorption performance with 3D structure and well-developed pores,and BC/rGA with the mixture ratio of BC and GO of 1:4 was more appropriate.The adsorption kinetics data of rGA and BC/rGA_((1:4))were fitting well with the pseudo-second-order model(R^(2)>0.951),and the isotherm adsorption results were fitting the Langmuir model well(R^(2)>0.974).The results demonstrated that the adsorption process was monolayer and endothermic adsorption involving chemisorp-tion.Additionally,the adsorption capacities of rGA and BC/rGA_((1:4))at solution pH 2 were 3.71 and 3.89 times greater than those at solution pH 8,respectively.High background ion strength and low temperature slightly inhibited the adsorption of Cr(Ⅵ)by both rGA and BC/rGA_((1:4)).The adsorption mechanisms of Cr(Ⅵ)on rGA and BC/rGA_((1:4))were electrostatic interaction,reduction and ion exchange.The use of BC/rGA could reduce the cost and promote the green reuse of agricultural waste.Overall,BC/rGA could be used as a promising green adsorbent alternative for the feasible treatment of heavy metal contaminated water.

植物促生芽孢杆菌中新型脂肪酸通过两组分调控系统OmpS/R和毒素转运蛋白介导的“嗜食同类”机制促进生物被膜的形成

当单细胞繁殖进入多细胞水平时,为了应对环境压力,细菌必须进化出维持其群体稳定的作用机制.“嗜食同类”是芽孢杆菌应对环境营养缺乏的一种策略,维持了芽孢杆菌的生存.作为芽孢杆菌的模式种群,枯草芽孢杆菌的“嗜食同类”行为已被广泛研究,但其他芽孢杆菌的“嗜食同类”机制仍然未知.生物被膜是一种被胞外基质包裹的多细胞群体,维持细菌在自然环境中的生存.本研究报道了由贝莱斯芽孢杆菌SQR9合成的新型次级代谢物杆菌酸(bacillunoic acids,BAs)介导的“嗜食同类”行为及机制,以及它对菌株SQR9生物被膜形成的促进作用.菌株SQR9细胞群体分化为两个亚群,一个亚群合成BAs并通过两组分调控系统OmpS-OmpR激活相应免疫基因bnaAB的表达,而不能合成BAs的亚群对该物质敏感.因而,群体中合成BAs的亚群通过该物质裂解部分不合成BAs的同类,由此释放的胞外DNA促进了生物被膜的形成.该研究结果阐明了菌株SQR9群体中的一些细胞如何牺牲自己,从而使群体中其它细胞有更好的机会在环境中存活下来.因此,菌株SQR9群体受益于“嗜食同类”系统.