Ammonium,Nitrate and Nitrite Nitrogen and Nitrate Reductase Enzyme Activity in Groundnut (Arachis hypogaea L.) Fields After Diazinon,Imidacloprid and Lindane Treatments

Impacts of diazinon (O,O-diethyl O-2-isopropyl-6-methylpyrimidin-4-yl phosphorothioate), imidacloprid [1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine] and lindane (1,2,3,4,5.6-hexachlorocyclohexane) treatments on ammonium, nitrate, and nitrite nitrogen and nitrate reductase enzyme activities were determined in groundnut (Arachis hypogaea L.) field for three consecutive years (1997 to 1999). Diazinon was applied for both seed- and soil-treatments but imidacloprid and lindane were used for seed treatments only at recommended rates. Diazinon residues persisted for 60 days in both the cases. Average half-lives (t_1/2) of diazinon were found 29.3 and 34.8 days respectively in seed and soil treatments. In diazinon seed treatment, NH₄ ⁺, NO₃ ^?, and NO₂ ^? nitrogen and nitrate reductase activity were not affected. Whereas, diazinon soil treatment indicated significant increase in NH₄ ⁺-N in a 1-day sample, which continued until 90 days. Some declines in NO₃ ^?N were found from 15 to 60 days. Along with this decline, significant increases in NO₂ ^?N and nitrate reductase activity were found between 1 and 30 days. Imidacloprid and lindane persisted for 90 and 120 days with average half-lives (t_1/2) of 40.9 and 53.3 days, respectively. Within 90 days, imidacloprid residues lost by 73.17% to 82.49% while such losses for lindane residues were found 78.19% to 79.86 % within 120 days. In imidacloprid seed-treated field, stimulation of NO₃ ^?N and the decline in NH₄ ⁺NO₂ ^?-N and nitrate reductase enzyme activity were observed between 15 to 90 days. However, lindane seed treatment indicated significant increases in NH₄ ⁺-N, NO₂ ^?-N and nitrate reductase activity and some adverse effects on NO₃ ^?N between 15 and 90 days.     

Spore inhibition-based enzyme substrate assay for monitoring of aflatoxin M1 in milk

A spore germination-based concept and its transformation into a field level prototype for monitoring aflatoxin M₁ (AFM₁) in milk was developed. Initially, 15 strains of Bacillus spp. procured from different culture collection were screened for AFM₁ sensitivity using spot assay and marker strain showing inhibition at 0.5 ppb was selected based upon maximum zone of inhibition. The selected strain B. megaterium 2949 was further screened for different enzymes activities and subsequently its spores were produced to an extent of 73.13% ± 3.197% in newly developed sporulation medium containing beef extract (0.0075% ± 0.0004%), yeast extract (0.015% ± 0.001%), peptone (0.0375% ± 0.0016%), and sodium chloride (0.0375% ± 0.0018%). A spore germination-based concept/ assay was optimized by immobilizing spores in eppendorf with pretreated milk (80°C/15 min) containing germinant and chromogenic substrate followed by incubation at 37°C. The appearance of sky blue color within real time of 45 min indicated spores germination and release of specific marker enzyme such as acetyl esterase and its specific action on chromogenic substrate which demonstrates absence of AFM₁ in milk. However, if there was no color change, presence of AFM₁ at 0.5 ppb MRL was denoted by Codex. The developed concept on AFM₁ detection was validated and a correlation of 0.97 was established with AOAC approved Charm 6602 and ELISA at Codex MRL with minimal false positive and negative results. The cost effective test has potential application in dairy farms, manufacturing, and R&D units for routine monitoring of AFM₁ in milk.     

三峡库区消落带落羽杉人工林土壤细菌群落结构多样性及动态变化

消落带是连接陆地与水域的交错地带,具有重要的生态功能,其适生木本植物的种植对消落带土壤的生物地球化学循环起着重要的作用.为探究适生植物对三峡库区消落带环境的适应机制,采用高通量测序技术对消落带退水后适生植物落羽杉(Taxodium distichum)不同生长时期(T1:5月、 T2:7月和T3:9月)的土壤细菌群落组成及多样性进行研究,同时采用PICRUSt2对细菌功能进行预测.结果表明,土壤pH值、硝态氮、铵态氮、土壤蔗糖酶、磷酸酶和脲酶等理化指标随时间变化显著(P<0.05);土壤细菌多样性、丰富度和结构也随时间变化而变化,除Chao1以外,根际土壤细菌的α多样性均表现为：T1>T2>T3,非根际土壤细菌α多样性则表现为：T3>T1>T2. RDA分析表明,影响细菌群落的理化指标主要有土壤pH值、脲酶、铵态氮和硝态氮.所有土壤样本中共检测到细菌60门,其中以变形菌门和酸杆菌门为优势细菌门.根据PICRUSt2预测,代谢是落羽杉土壤细菌群落中普遍存在的基本功能,与C、 N和P有关的各代谢途径存在一定的时间差异.以上研究结果有助于加深对三峡消落带植被修复...     

牡蛎壳粉和石灰改良酸性水稻土对磷有效性、形态和酶活性的影响

我国南方粮食主产区土壤酸化治理是提升耕地地力促进粮食增产的重要内容,目的是探究酸化土壤改良剂牡蛎壳粉和石灰对水稻土酸度、磷有效性和形态以及酶活性和相关功能基因的影响.盆栽试验设计2种改良剂的3个施用量（0.05%、0.10%和0.15%）,以水稻为试验作物.结果表明：①牡蛎壳粉和石灰均显著提高土壤pH,降低土壤交换性酸,且改良效果随着改良剂用量增加而提高,相同用量下石灰对土壤酸性的改良效果高于牡蛎壳粉;② 4种有效磷提取剂提取的土壤有效磷测定结果表明,牡蛎壳粉和石灰显著提高H₂SO₄-P、Bray-1 P和Olsen-P含量,其中Olsen-P含量随改良剂用量的增加而提高.③土壤中不同形态无机磷含量表现为：Fe-P>Al-P>Ca-P,石灰和牡蛎壳粉显著提高Al-P和Fe-P含量,分别提高26.3%~37.4%和7.9%~23.7%;0.15%改良剂显著增加Ca-P含量;④石灰和牡蛎壳粉对土壤DHA、ALP、IPP活性和phoD基因拷贝数具有提高作用,而对土壤ACP活性、phoC和pqqC拷贝数表现为降低;⑤改良剂（0.10%和0.15%）显著提高水稻产量,0.15%用量的石灰和牡蛎壳粉分别提高水稻产量34.2%和46.8%,但对秸秆生物量无显著影响.相关分析表明,土壤无机磷和有效磷含量与pH和ALP活性呈显著正相关,改良剂通过消除土壤酸化和提高土壤磷酸酶活性来改善土壤磷营养状况,这对促进作物产量具有积极作用.     

生物炭施用对黄壤土壤养分及酶活性的影响

生物炭因其具有特殊的理化性质,作为土壤改良剂或调理剂被广泛应用于改善土壤质量;土壤养分与土壤酶活性是表征土壤质量化学性质和生物学性质的重要指标.采用大田试验,研究生物炭不同施用水平：0（CK）、5（B5）、10（B10）、20（B20）和50（B50） t·hm^-2对黄壤养分和土壤酶活性的影响,运用结构方程模型（SEM）定量分析生物炭处理对土壤养分和酶活性的直接或间接影响及其作用大小.结果表明,生物炭显著增加土壤pH值、电导率、有机碳、碱解氮、有效磷和速效钾（P<0.05）;随生物炭施用量的增加,土壤过氧化氢酶和脲酶活性先增加后降低,磷酸酶和蔗糖酶活性增加（P<0.05）;B10处理下,土壤过氧化氢酶、脲酶和磷酸酶的活性均达到最大值,蔗糖酶活性也相对较高.随生物炭作用时间增加,土壤pH值、碱解氮、有效磷和速效钾含量均增加,而电导率和有机碳与之相反;过氧化氢酶活性降低,脲酶和磷酸酶活性升高,蔗糖酶活性无明显变化规律.SEM结果显示,生物炭施用对过氧化氢酶具有直接的负效应;通过提升pH、电导率、有机碳和碱解氮含量间接影响过氧化氢酶活性,通过提升pH和电导率间接促进蔗糖酶活性,通过提高电导率以及碱解氮和有效磷含量间接增加磷酸酶活性.综上,生物炭施用量及作用时间显著影响土壤养分含量,进而间接作用于土壤酶活性;酸性黄壤施用10 t·hm^-2的生物炭较为适宜.     

甲苯对土壤芳基硫酸酯酶活性的影响

甲苯作为土壤酶测定的前处理试剂及许多有机污染物在环境中降解的中间产物,有关其对土壤酶的影响研究在土壤酶学和环境科学领域具有重要意义.因此,采用模拟方法,较系统地研究了不同剂量甲苯和处理时间下芳基硫酸酯酶活性的变化规律.结果表明,甲苯对纯酶具有明显的抑制作用,酶活性降幅最大达到45.5%;灭菌土壤对溶液中的纯酶有很强的吸附能力;极微量的甲苯即可完成对土壤中酶活性的激活作用,酶活性增幅为109%～298%;随着甲苯剂量的增加,土壤酶活性的变化幅度逐渐趋缓,并可用Langmuir模型较好地拟合,由此获得了最大表观酶活性Umax,发现其与土壤性质显著相关,说明甲苯主要是通过杀死土壤中的微生物来影响土壤酶活性的.此外,初步探讨了不同土壤中胞外酶量与胞内酶量的关系,发现在供试土样中土壤芳香硫酸酯酶胞外酶和胞内酶分别占54.4%和45.6%.本研究可为后续土壤酶测定质量的完善和提高提供依据.     

镉和乙草胺复合污染对玉米生理特性的影响

采用盆栽试验,研究了镉与乙草胺复合污染对玉米幼苗MDA含量和抗氧化酶活性的影响。结果表明,镉单独处理,低浓度下MDA的含量变化不大,当镉浓度大于30 mg/kg时,MDA的含量急剧上升;超氧化物歧化酶SOD、CAT在浓度为30 mg/kg时活性达到最高,之后随浓度的增大,其活性逐渐降低;POD的活性随着镉浓度的增大逐渐升高,且100 mg/kg时达到最高。镉与乙草胺复合处理,低镉浓度下MDA的含量与对照组CK相比差异显著,处理浓度越大,MDA含量越高;SOD、CAT的活性变化趋势与单镉处理时相类似,但变化幅度更加明显;POD的活性则随着浓度的增大继续升高。镉与乙草胺复合处理对玉米幼苗的毒害程度要大于单镉处理,并且施加乙草胺的浓度越大,玉米受毒害程度越深。     

四环素类抗生素对不同蔬菜生长的影响及其富集转运特征

本研究探讨了四环素类抗生素(TCs)对两种蔬菜生长的影响及其在蔬菜体内的富集和转运特征,以期为四环素类抗生素的植物毒性和对人体健康的风险评价提供理论基础.采用土培试验研究了不同水平(0、50和150 mg·kg-1)的四环素类抗生素(四环素TC、土霉素OTC、金霉素CTC)对生菜和小白菜生长、抗生素含量及其富集转运特征的影响.结果表明,TCs总体上抑制了生菜的生长,地上部和地下部鲜重分别较CK降低了1.56%~26.84%和17.36%~51.04%,小白菜地上部和地下部鲜重反而较对照提高了3.7%~7.3%和3.1%~82.2%.TCs在一定程度上增加了生菜和小白菜的气孔导度(Gs)和蒸腾速率(Tr),抑制了生菜的净光合速率(Pn),Pn在TCs为150 mg·kg-1时较CK降低了32.43%~82.43%.TCs还抑制了生菜和小白菜的SOD活性,较CK降低了29.17%~223.12%,以OTC的抑制作用最强.生菜和小白菜的MDA含量在TCs为150mg·kg-1时达到最大值(生菜地上部除外).小白菜地上部和地下部TCs的含量均高于生菜,以CTC处理的小白菜和生菜TCs含量较高.种植生菜的土壤TCs残留量高于小白菜土壤,以OTC处理的土壤TCs残留量最高.小白菜对TCs的富集系数和转运系数分别是生菜的1.07~7.35倍和1.15~2.25倍.3种四环素类抗生素中以OTC和CTC的生态风险较大.     

微生物-生物促生剂协同修复河道底泥——促生剂投量对修复效果的影响

采用5个110L的模拟河道反应器,在投加菌剂的基础上（底泥稳定后向底泥和水中分别注射浓度为0.09%和0.03%的菌剂）,生物促生剂投量分别设计为0.08,0.09,0.10和0.11g/L,单独投加菌剂组作为空白实验.通过为期四十余天的实验研究微生物与促生剂协同作用时的修复效果.结果表明,促生剂投量为0.10g/L时,上覆水COD去除率69%高于其余各组;各协同修复组上覆水中NO₃^--N基本无积累,且促生剂投量为0.11g/L时NO₃^--N去除率最高,可达96%;40d内各组底泥TOC,TN含量变化不显著,延长反应时间至84d,各协同修复组底泥TOC,TN去除率均有明显提升.各协同修复组脲酶活性均波动下降,蛋白酶活性在15d左右时达到峰值,增幅可达106%~237%.通过高通量测序技术发现,43d时Desulfuromonas,Pseudomonas,Treponema_2,Blvii28_wastewater-sludge_group等主要功能菌群的相对丰度与空白实验组相比均增加,且促生剂投量为0.10g/L可使微生物群落向更适宜降解去除氮素及有机质的方向演替,有效改善底泥环境.协同修复对底泥,上覆水水质及微生物群落有良好改善效果,且促生剂投量为0.1g/L时整体修复情况更为理想.     

黄土旱塬24 a不同秸秆还田土壤碳、氮、磷和胞外酶计量特征

探索黄土旱塬区农田土壤碳、氮和磷生物地球化学循环特征,可为农作物高效生产和土地可持续利用提供科学依据和技术支撑.以山西寿阳24 a玉米旱作试验田为对象,研究长期秸秆覆盖还田、直接还田、过腹还田和不还田对土壤元素和胞外酶活性化学计量比的影响,并计算向量角度和长度用于指示微生物面临的资源限制情况,向量角大于45°和小于45°分别表示微生物受磷限制和氮限制,偏离45°越大表示限制程度越大,向量长度越长表示微生物受碳限制越严重.结果表明：(1)长期秸秆还田土壤C/N和C/P分布在9.81～14.28和14.58～21.92之间,均值分别为12.36和17.51,分别较试验初期降低了6.0%和4.2%;土壤N/P分布在1.27～1.57之间,均值为1.42,较初期提高了2.2%.土壤C/N和C/P均呈现出先降低后升高的变化趋势,土壤N/P基本呈现出持平趋势,且不同秸秆还田处理之间土壤元素计量比均无显著性差异.(2)相比24 a长期不还田处理,长期秸秆覆盖还田处理土壤β-1,4-葡萄糖苷酶(BG)和β-1,4-N-乙酰葡糖氨糖苷酶(NAG)活性显著提高了134.4%和107.5%(P<0.0...