The microbial community,nutrient supply and crop yields differ along a potassium fertilizer gradient under wheat-maize double-cropping systems

Soil microorganisms play critical roles in ecosystem function.However,the relative impact of the potassium(K)fertilizer gradient on the microbial community in wheat-maize double-cropping systems remains unclear.In this long-term field experiment(2008-2019),we researched bacterial and fungal diversity,composition,and community assemblage in the soil along a K fertilizer gradient in the wheat season(K0,no K fertilizer;K1,45 kg ha^(-1) K_(2)O;K_(2),90 kg ha^(-1)K_(2)O;K3,135 kg ha^(-1)K_(2)O)and in the maize season(K0,no K fertilizer;K_(1),150 kg ha^(-1) K_(2)O;K_(2),300 kg ha^(-1)K_(2)O;K_(3),450 kg ha^(-1)K_(2)O)using bacterial 16S rRNA and fungal internally transcribed spacer(ITS)data.We observed that environmental variables,such as mean annual soil temperature(MAT)and precipitation,available K,ammonium,nitrate,and organic matter,impacted the soil bacterial and fungal communities,and their impacts varied with fertilizer treatments and crop species.Furthermore,the relative abundance of bacteria involved in soil nutrient transformation(phylum Actinobacteria and class Alphaproteobacteria)in the wheat season was significantly increased compared to the maize season,and the optimal K fertilizer dosage(K2 treatment)boosted the relative bacterial abundance of soil nutrient transformation(genus Lactobacillus)and soil denitrification(phylum Proteobacteria)bacteria in the wheat season.The abundance of the soil bacterial community promoting root growth and nutrient absorption(genus Herbaspirillum)in the maize season was improved compared to the wheat season,and the K2 treatment enhanced the bacterial abundance of soil nutrient transformation(genus MND1)and soil nitrogen cycling(genus Nitrospira)genera in the maize season.The results indicated that the bacterial and fungal communities in the double-cropping system exhibited variable sensitivities and assembly mechanisms along a K fertilizer gradient,and microhabitats explained the largest amount of the variation in crop yields,and improved wheat?maize yields by 11.2-22.6 and 9.2-23.8%with K addition,respectively.These modes are shaped contemporaneously by the different meteorological factors and soil nutrient changes in the K fertilizer gradients.

Effect of allelochemicals sustained-release microspheres on the ingestion, incorporation, and digestion abilities of Daphnia magna Straus

Allelochemicals sustained-release microspheres(ACs-SMs)exhibited great inhibition effect on algae,however,few studies have focused on ACs-SMs toxicity on invertebrate.In this study,the effects of single high-concentration ACs(15 mg/L,SH-ACs),repeated lowconcentration ACs(3×5 mg/L,RL-ACs)and ACs-SMs containing 15 mg/L ACs exposure on the ingestion,incorporation,and digestion of Daphniamagna Straus(DS)were investigated by stable isotope 15N labeling method.Meanwhile,the diversity and abundance of microflora in DS guts were determined by 16S rRNA genes and cloning methods.The results showed that SH-ACs exposure caused 50%and 33.3%death rates for newborn and adult DS,while RL-ACs exposure caused 10%death rate for newborn DS and no obvious effect on the activity of adult DS.And ACs-SMs exposure did not diminish the motility of both newborn and adult DS,indicating the lower acute toxicity of ACs-SMs.Furthermore,SH-ACs inhibited the ingestion(-6.45%),incorporation(-47.1%)and digestion(-53.8%)abilities of DS and reduced the microbial abundance(-27.7%)in DS guts.Compared with SH-ACs,RL-ACs showed relatively low impact on the ingestion(-3.23%),incorporation(-5.89%)and digestion(-23.9%)abilities of DS.Interestingly,ACs-SMs enhanced the ingestion(+9.68%),incorporation(+52.9%)and digestion(+51.3%)abilities of DS and increased the microbial abundance(+10.7%)in DS guts.Overall ACs and ACs-SMs reduced the diversity of microflora in DS guts.In conclusion,ACs-SMs can release ACs sustainably and prolong the sustained release time,which not only effectively reduce the toxicity of ACs,but also had positive effects on DS.

Occurrence and migration of microplastics and plasticizers in different wastewater and sludge treatment units in municipal wastewater treatment plant

Microplastics(MPs)and plasticizers,such as phthalate esters(PAEs),were frequently detected in municipal wastewater treatment plants(MWTP).Previous research mainly studied the removal of MPs and PAEs in wastewater.However,the occurrence of MPs and PAEs in the sludge was generally ignored.To comprehensively investigate the occurrence and the migration behaviors of MPs and PAEs in MWTP,a series of representative parameters including the number,size,color,shape of MPs,and the concentrations of PAEs in wastewater and sludge were systematically investigated.In this study,the concentrations of MPs in the influent and effluent were 15.46±0.37 and 0.30±0.14 particles/L.The MP removal efficiency of 98.1%was achieved and about 73.8%of MPs were accumulated in the sludge in the MWTP.The numbers of MPs in the sludge before and after digestion were 4.40±0.14 and 0.31±0.01 particles/g(dry sludge),respectively.Fourier Transform Infrared Spectroscopy(ATR FT-IR)analysis showed that the main types of MPs were polyethylene terephthalate(PET),polypropylene(PP),polyethylene(PE),and polystyrene(PS).Six PAEs,including phthalate(DMP),diethyl phthalate(DEP),diisobutyl phthalate(DIBP),ortho dibutyl phthalate(DBP),butyl benzyl phthalate(BBP),and bis(2-ethyl)hexyl phthalate(DEHP),were detected in the MWTP.The concentrations of total PAEs(ΣPAEs)in the influent and effluent were 76.66 and 6.28μg/L,respectively.The concentrations ofΣPAEs in the sludge before and after digestion were 152.64 and 31.70μg/g,respectively.In the process of thermal hydrolysis,the number and size of MPs decreased accompanied by the increase of the plasticizer concentration.

Removal efficiencies of natural and synthetic progesterones in hospital wastewater treated by different disinfection processes

Progesterones are ubiquitous in hospital wastewater(HWW)with concentrations much higher than those of estrogens and androgens.To ensure that these water systems are safe to use,disinfection is crucial during HWW treatment by providing"front line"defense against biological contaminations.Here,five disinfection processes,namely,chlorine(Cl_(2)),chlorine dioxide(ClO_(2)),ozone(O_(3)),ultraviolet(UV)),and UV/chlorine(UV/Cl_(2)),were selected to investigate their removal efficiencies for progesterones in primary filtration and secondary biological treatment effluents.There were 61 natural and synthetic progesterones detected in HWW,with the natural progesterones being the main components with a concentration of 845.51 ng/L and contributing to 75.08%of the total proge-sterones.The primary filtration treatment presented insignificant removal effects on the progesterones,while the secondary biological treatment significantly reduced the progesterone content by biode-gradation.The order of removal efficiencies of total progesterones by different disinfection processes was UV/Cl_(2)>Cl_(2)>O_(3)>ClO_(2)>UV.UV/Cl_(2)showed the highest removal efficiency against progesterones mainly due to the activation of Cl_(2)by ultraviolet(UV)photolysis,which helps open the heterocyclic,aromatic,and phenolic rings,thus accelerating progesterone degradation.In addition,the removal efficiencies of natural progesterones in the five disinfection processes were higher than those of synthetic progesterones(progesterone derivatives,19-nortestosterone derivatives,and 17α-hydroxyprogesterone derivatives).

Characteristics of typical dissolved black carbons and their influence on the formation of disinfection by-products in chlor(am)ination

Dissolved black carbon(DBC)released from biochar can be one of the potential disinfection by-products(DBPs)precursors in the dissolved organic matter pool.However,the physiochemical and structural properties of DBC and the effects on the development of DBPs and DBP formation potential(DBPFP)during the disinfection process remain unclear.In this study,the characteristics of two kinds of DBC,namely,animal-derived DBC(poultry litter DBC,PL-DBC)and plant-derived DBC(wheat straw DBC,WS-DBC),were investigated.The effects of different kinds of DBC on the evolution of DBPs and DBPFP in chlorine and chloramine disinfection processes were compared with natural organic matter(NOM).The results showed that the total DBPs concentrations derived from PL-DBC,WS-DBC and NOM were similar during chlorination(i.e.,61.23µg/L,64.59µg/L and 64.66µg/L,respectively)and chloramination(i.e.,44.63µg/L,44.42µg/L and 45.58µg/L,respectively).The lower total DBPs and DBPFP concentrations in chloramination could be attributed to the fact that the introduction of ammonia in chloramine inhibited the breaking of the bond between the disinfectant and the active group of the precursor.Additionally,DBC presented much lower total DBPFP concentrations than NOM in both chlorination and chloramination.However,both kinds of DBC tended to form more monochloroacetic acids and haloacetamides than NOM,which could result from the higher organic strength,higher protein matter,and nitrogen-rich soluble microbial products of DBC.