作物茬口对黑土农田土壤反硝化细菌数量及群落结构的影响

  【目的】  反硝化作用导致农田土壤氮素损失和温室气体N₂O的排放。研究不同作物茬口对土壤反硝化细菌群落结构的影响,旨在揭示作物茬口影响N₂O排放的相关机制。  【方法】  定位试验位于黑龙江省海伦市前进乡光荣村(47°23′N,126°51′E),种植方式包括玉米连作(CC)、大豆连作(SS)以及玉米–大豆轮作,每年一季。取样时,轮作体系玉米已倒茬三次、大豆两次。采集CC、SS以及轮作体系中的大豆茬口(SSC)和玉米茬口(CSC)的表层土壤(0—15 cm)样品,利用实时定量PCR (qPCR)和高通量测序技术,分析土壤中的nirS和nirK型反硝化细菌丰度和群落组成。  【结果】  在4个作物茬口土壤中,CC处理的反硝化速率最高,玉米–大豆轮作体系中SSC和CSC处理的反硝化速率显著高于SS处理。轮作体系两个茬口SSC和CSC处理的nirS和nirK型反硝化细菌基因丰度多显著高于SS处理,而与CC处理多差异不显著。PCoA结果显示,SSC和CSC处理的nirS型反硝化细菌群落间差异显著,而CC和SS处理的nirK型反硝化细菌群落间存在显著差异。RDA分析结果表明,NO₃–-N和C/N分别是nirS和nirK型反硝化细菌群落分异的最主要驱动因子。SEM分析结果显示,nirS型反硝化细菌群落与反硝化速率呈显著正相关(R2=0.92),而nirS和nirK型基因丰度与土壤反硝化速率无显著相关关系。  【结论】  作物茬口显著影响黑土农田土壤反硝化细菌群落和丰度组成。反硝化细菌群落组成而非反硝化细菌丰度是反硝化速率变化的决定性因素,nirS型反硝化细菌对土壤反硝化作用贡献更大。     

富氧灌溉池塘中反硝化细菌丰度昼夜垂直变化特征分析

为了探讨农用灌溉池塘蓄积的生活污水在富氧条件下反硝化细菌丰度变化及其与水质参数的相关性,应用实时荧光定量聚合酶链式反应技术对富氧灌溉池塘水体不同深度水层中(上层10~30 cm、中层90~110 cm、和下层150~170 cm)反硝化功能基因丰度昼夜变化特征进行了研究。结果表明:水质参数中溶解氧(dissolved oxygen,DO)浓度、p H值、水温、光照度及NO3--N浓度均具有垂向分层效应,随水层的加深而逐渐降低,NH4+-N及PO43--P浓度则呈现与前者相反的趋势,随水层加深而逐渐升高;nir K,nir S和nos Z 3类反硝化基因受DO浓度和p H值调节作用显著,均表现为白天丰度高,晚间丰度低的时间效应;3类反硝化基因丰度整体表现为表层水体中的基因丰度高,其次为中层水体,底层水体中的丰度最低的趋势,即同样表现出垂向分层效应。nir S基因丰度总是比nir K基因丰度高,说明nir S型反硝化细菌更能适应富氧灌溉池塘水质环境。3类反硝化基因丰度与环境参数中的DO浓度和p H值呈显著正相关(P0.01)。综上,富氧条件下灌溉池塘水质参数尤其是DO浓度昼夜垂向变化促使nir K,nir S和nos Z 3类反硝化细菌丰度变化具有一定的时间效应和垂直空间分层效应,说明在自然条件下也可能有大量的好氧反硝化细菌存在,并且因为长时间受富氧条件驯化,导致反硝化细菌丰度受DO浓度变化影响较大,可能会促使不同深度水层断面发生的氮转化过程及其强度具有差异。进而为原位状态下好氧反硝化脱氮的可能性提供了更有利的佐证。该研究为富氧污水在用于农田灌溉使用时提供背景参数。     

亚热带土壤亚铁与厌氧反硝化

本文就亚热带土壤亚铁参与反硝化的可能性进行了探讨。研究结果表明:厌氧还原条件下加入KNO3的处理中,Fe2+浓度随培养时间延长而下降,且Fe2+浓度的降低和NO3–-N浓度的降低呈显著正相关。预培养结束后的亚铁浓度(In-Fe2+)和厌氧培养期间Fe2+浓度降低速率与反硝化势表征指标k、b、v7,以及与无定形铁氧化物(活性铁)含量的显著正相关性初步证明,活性铁通过不同价态铁离子(Fe2+和Fe3+)之间的转化,参与了反硝化的电子传递过程。当有机碳等电子供体受限时,Fe2+可作为电子供体参与反硝化还原NO3–-N。这一结果表明,NO3–-N作为电子受体参与厌氧条件下Fe2+氧化成Fe3+的反应可能在铁氧化物含量丰富的亚热带土壤中普遍存在。     

两种水分含量下生物质炭对黑土N2O排放及硝化反硝化基因丰度的影响

生物质炭对土壤结构改良、土壤肥力提升和农田温室气体排放具有重要意义。本研究以吉林省梨树县典型黑土为研究对象，通过培育实验，研究不同土壤水分含量（40%WHC和100%WHC）下，生物质炭种类（玉米秸秆生物质炭和稻壳生物质炭）和施加量（0%、1%和4%（w/w））对黑土N2O排放及硝化反硝化功能基因丰度的影响。结果表明，随着秸秆生物质炭施加量的增加，土壤N2O排放呈下降趋势，4%高量秸秆生物质炭添加下，土壤N2O排放量仅为1%低量秸秆生物质炭添加下的33.9%。同时土壤NO- 3-N也表现出一致性规律，4%高量生物质炭添加下土壤NO- 3-N含量显著低于1%低量生物质炭。在100%WHC土壤水分状况下，玉米秸秆生物质炭显著增加了土壤N2O排放，而稻壳生物质炭则显著降低了土壤N2O排放。高土壤水分显著促进了土壤N2O排放，进一步为实时荧光定量PCR结果所证实，高土壤水分通过增加nirS基因丰度进而促进了土壤反硝化作用过程，而4%高量稻壳生物质炭添加下nosZ基因丰度显著高于玉米秸秆生物质炭添加，表现出更强的N2O还原潜力。尽管amoA-AOA基因丰度在不同生物质炭添加量下并未发生显著变化，但amoA-AOB基因丰度在高量玉米秸秆生物质炭添加下显著下降。结果说明，土壤水分和生物质炭通过影响土壤硝化反硝化微生物的营养底物和代谢过程，进而影响土壤N2O排放特征。     

江苏句容水库农业流域农田土壤反硝化作用的研究

2008年6月、8月、12月和2009年3月,在江苏句容水库农业流域采集农田原状土壤样品,使用乙炔抑制实验室培养法测定土壤的反硝化速率,同时测定土壤的含水率、铵态氮（NH2-N）和硝态氮（NO_3-N）的含量,研究农田土壤反硝化速率变化、影响因素及其对流域氮损失的贡献。结果显示,旱地土壤反硝化速率范围在0．13-51．96kgN·hm^-2a^-1之间,水田土壤的反硝化速率范围在3．16-12．29kgN·hm^-2a^-1之间。相关分析表明,反硝化速率与土壤硝态氮（NO_3-N）浓度、铵态氮（NH2-N）浓度之间不具有显著相关关系;在12月和3月,反硝化速率与土壤含水率之间有显著相关关系,其他月份无显著相关关系。流域内农田土壤反硝化损失的总氮量为31．93tN·a^-1低于流域施氮总量的3．19％,可见,反硝化作用不是该流域氮损失的主要途径。     

种植行距和品种对玉米根际反硝化菌群丰度和功能的影响

反硝化是根际氮素损失重要途径,作物品种和行距改变是否会对根际反硝化产生影响尚不清楚。本研究比较了不同玉米品种和种植行距间根际土壤反硝化菌群丰度和功能的差异,为降低根际反硝化损失和提高氮肥利用效率提供科学依据。通过两个独立的田间试验,利用生物化学和分子微生物学方法,分别研究‘浚单20’、‘安农8号’、‘郑单958’、‘品玉18’和‘隆平206’5个玉米品种以及20 cm、30 cm、40 cm、50 cm种植行距对根际土壤反硝化能力、反硝化菌群丰度、N_2O/(N_2O+N_2)产物比和土壤呼吸等指标的影响。‘浚单20’、‘安农8号’、‘郑单958’根际反硝化能力显著低于其他两个品种;随着行距减少,反硝化能力有显著增加趋势。‘隆平206’和‘品玉18’的nir S型反硝化菌群丰度显著高于其他品种,而nir K和nosZ型菌群的丰度以‘浚单20’和‘安农8号’最高;行距20 cm的nir S和nir K型菌丰度显著高于其他行距处理,但nosZ型菌丰度以40 cm行距丰度最大。品种对N_2O/(N_2O+N_2)产物比有一定影响,其中‘安农8号’最低,但行距对产物比没有显著影响。相关分析表明反硝化能力与土壤呼吸和nirS型菌群丰度均极显著正相关,但与nos Z和nir K型菌群未呈现这种关系,由此表明nirS型菌丰度和根际有机碳差异可能是造成反硝化能力不同的主导因子。品种和种植行距会对玉米根际反硝化过程产生一定影响,根际低反硝化损失品种的筛选、选育和根际反硝化过程调控是减少根际反硝化损失,提高氮肥利用效率的有效途径。     

水分和温度对旱地红壤硝化活力和反硝化活力的影响

采集第四纪红色粘土发育和第三纪红砂岩发育的红壤,分别在4C冰箱内保存(O),室温下湿润(M)和淹水(F)培养110天后测定硝化细菌、反硝化细菌、硝化势、反硝化势和反硝化酶活性。结果表明,低温有利于保持硝化细菌和反硝化细菌的数量,但显著抑制它们的硝化和反硝化活力。湿润有利于保持硝化细菌的硝化活力,而淹水则有利于保持反硝化细菌的反硝化活力,但均不利于硝化细菌和反硝细菌的存活。由此说明,不同的研究目的和需要测定的项目,应采用不同的土壤样本保存方法。     

转基因水稻秸秆还田对土壤硝化反硝化微生物群落的影响

转基因作物可能通过根系分泌物和植株残体组成的改变及外源基因的转移释放令土壤微生物群落产生变化,影响土壤微生物的生态功能。氨氧化细菌和反硝化细菌是驱动土壤硝化和反硝化过程的关键微生物,其群落结构的变化直接关系土壤氮素的转化与利用。本研究利用荧光定量PCR和PCR-DGGE技术分析了转cry1Ac/cpti双价抗虫基因水稻‘Kf8’秸秆还田降解过程中,土壤氨氧化细菌和反硝化细菌群落丰度与组成的变化,探讨转基因水稻是否存在影响稻田土壤氮素转化与N2O排放的可能。结果显示:无论是氨氧化细菌amo A基因还是反硝化细菌nirS基因,其丰度在转基因水稻‘Kf8’与非转基因水稻‘Mh86’的秸秆还田土壤中都没有显著差异;转基因水稻‘Kf8’和非转基因水稻‘Mh86’秸秆还田降解过程中0~10 cm土层中的amo A基因丰度均显著高于10~20 cm及20~30 cm土层(P0.05);各深度土层中的nirS基因丰度均存在随秸秆还田时间延长而增加的趋势。水稻秸秆还田降解过程中,转基因水稻‘Kf8’的土壤氨氧化细菌和反硝化细菌的群落多样性指数及组成,均与非转基因水稻‘Mh86’没有显著差异。相关分析结果表明土壤氨氧化细菌和反硝化细菌群落组成均与水稻秸秆还田时间存在显著相关性(P=0.002),反硝化细菌群落组成还与土层深度显著相关(P=0.024)。本研究表明转cry1Ac/cpti抗虫基因水稻秸秆还田对稻田土壤硝化和反硝化关键微生物群落不会产生明显影响。就土壤微生物群落而言,转cry1Ac/cpti抗虫基因水稻秸秆还田不存在影响土壤氮素转化与N2O排放的可能。     

长期施肥对土nirS型反硝化细菌的影响及其与N2O排放的关系

土壤反硝化作用是土壤N₂O产生的重要过程,亚硝酸盐还原酶(NIR)催化的亚硝态氮(NO^-₂)还原为一氧化氮(NO)是反硝化作用的关键环节,研究长期施肥对反硝化微生物的影响及其与N₂O排放的关系对于全面理解土壤反硝化过程具有重要意义。基于28年的旱作雨养长期施肥试验,通过常规监测、定量PCR和高通量测序等探讨了长期不同施肥(不施肥CK、偏施肥的单施氮肥N和氮钾配施NK、以及氮磷钾平衡施肥NPK)下土N₂O排放和nirS反硝化细菌群落特征及两者之间的关系。结果表明:长期化肥施用(N,NK和NPK)均显著提高了N₂O累积排放量,其中平衡施肥(NPK)最高。长期化肥施用对nirS基因丰度和nirS型反硝化细菌的α-多样性无显著影响,但长期平衡施用化肥提高了uncultured_bacterium_2303和Rhodanobacter_sp._D206a的相对丰度,降低了unclassified_k_norank_d_Bacteria和unclassified_p_Proteobacteria的相对丰度,从而改变了nirS型反硝化细菌的群落结构组成。雨养旱作条件下,土壤有机碳(SOC)、全氮(TN)、有效磷(AP)和pH等土壤性质是土nirS型反硝化细菌群落结构组成变化的主要影响因素。土nirS型反硝化细菌群落结构组成对土壤N₂O排放具有显著影响,而nirS基因丰度和nirS型反硝化细菌多样性并没有显著影响。     

有机和无机肥配比对黄褐土硝化和反硝化微生物丰度及功能的影响

【目的】 土壤硝化与反硝化作用是氮循环的两个关键环节,本文研究不同比例的有机、无机肥配施对硝化和反硝化进程产生的影响,为高效施肥提供理论基础。 【方法】 在安徽农业大学农翠园试验基地的黄褐土上进行了小麦–玉米轮作田间试验。试验以不施氮肥为对照 (CK),在小麦、玉米总施氮量相同的条件下,设置5个处理,分别为单施无机肥 (T1)、无机肥∶有机肥 = 2∶1 (T2)、无机肥∶有机肥 = 1∶1 (T3)、无机肥∶有机肥 = 1∶2 (T4)、单施有机肥 (T5)。在小麦拔节期,取0—20 cm土壤样品,利用荧光定量PCR技术测定反硝化和氨氧化微生物丰度,并结合反硝化能力、N₂O/(N₂O+N₂) 产物比、土壤呼吸、硝化势和氨氧化细菌 (AOB) 与古菌 (AOA) 对硝化势相对贡献率的测定,分析江淮地区长期有机和无机肥配施对黄褐土硝化、反硝化微生物丰度及其功能的影响。 【结果】 单施无机肥或有机肥处理的硝化势均高于不同配比处理。与添加有机肥相比,增施无机肥会显著增加AOA的丰度和硝化贡献率。在反硝化方面,反硝化能力和土壤呼吸随着有机肥投入量的增加而增加,单施有机肥处理显著高于其它处理。nirS和nosZ型反硝化菌丰度随着有机肥的增加而增加,而nirK型反硝化菌丰度呈减少趋势。相关分析表明,反硝化能力与nirS型、nosZ型反硝化菌丰度、有机质和可溶性有机碳含量极显著正相关,与nirK相关性不强。 【结论】 与单施无机肥或有机肥处理相比,有机和无机肥适当配施可降低土壤硝化势,并能调控AOA和AOB在硝化过程中的作用,有效地降低土壤反硝化损失。      

Effects of long-term manure applications on the occurrence of antibiotics and antibiotic resistance genes (ARGs) in paddy soils: Evidence from four field experiments in south of China

Most studies of the effects of manure amendment on the occurrence of antibiotics and antibiotic resistance genes (ARGs) in soil employ the investigation of grab samples or short-term laboratory studies. However, the effects of long-term manure applications on antibiotics, ARGs and their vertical distribution in paddy soil in field experiments are lacking. We assessed the concentrations of antibiotics, ARGs and their vertical distribution in paddy soil receiving long-term manure applications in four field experiments. High concentrations of tetracyclines were detected in most manured soils, while sulfonamides were not detectable. Long-term manure amendments generally increased the antibiotic concentrations and ARGs abundances in the paddy soil over decades. However, in some sites such significant trends of ARGs could not be observed. The abundance of ARGs was statistically correlated with antibiotics and soil properties including pH and soil organic matter (SOM), indicating their importance in the selection of resistance genes. Tetracyclines could be detected in soil at different depths and the concentrations of tetracyclines and abundance of ARGs generally decreased with increasing soil depths.     

铜和强力霉素复合污染对土壤微生物与酶活性的影响

当前土壤环境中重金属和抗生素的广泛共存及二者复合存在所诱导出的细菌抗性,与单一物质的污染相比,均能够加剧对土壤质量和作物安全的破坏。在在实验室模拟培养条件下,向土壤中加入不同浓度的重金属(铜)和抗生素(强力霉素),探讨抗生素和重金属复合污染对土壤微生物呼吸、脲酶、蔗糖酶和过氧化氢酶活性和四环素抗性基因的丰度等土壤微生物指标的影响。结果显示,在整个培养期(30 d)内,铜和强力霉素单一及复合污染均会显著抑制土壤微生物呼吸强度,对脲酶活性主要表现为促进作用,对蔗糖酶、过氧化氢酶活性主要为抑制作用,对过氧化氢酶活性的抑制强度明显大于蔗糖酶。综合而言,铜和强力霉素的复合污染相对于单一污染对上述微生物指标的影响较大,强力霉素的加入可以促进铜对微生物呼吸或酶活性的初始影响。此外,该研究还表明添加为400mg·kg~(–1)铜可以提高强力霉素在土壤培养中后期诱导的抗性基因相对丰度的能力水平。本研究从微生物角度定量探讨铜与强力霉素单一及复合污染对土壤微生物指标的影响程度,以期为重金属与抗生素协同污染的土壤构建微生物预警体系,并为土壤修复和风险评估工作提供理论依据。     

Effects of 3,4-dimethylpyrazole phosphate (DMPP) on the abundance of ammonia oxidizers and denitrifiers in two different intensive vegetable cultivation soils

Purpose

Nitrification and denitrification in the N cycle are affected by various ammonia oxidizers and denitrifying microbes in intensive vegetable cultivation soils, but our current understanding of the effect these microbes have on N₂O emissions is limited. The nitrification inhibitor, 3,4-dimethylpyrazole phosphate (DMPP), acts by slowing nitrification and is used to improve fertilizer use efficiency and reduce N losses from agricultural systems; however, its effects on nitrifier and denitrifier activities in intensive vegetable cultivation soils are unknown.

Materials and methods

In this study, we measured the impacts of DMPP on N₂O emissions, ammonia oxidizers, and denitrifying microbes in two intensive vegetable cultivation soils: one that had been cultivated for a short term (1 year) and one that had been cultivated over a longer term (29 years). The quantitative PCR technique was used in this study. Three treatments, including control (no fertilizer), urea alone, and urea with DMPP, were included for each soil. The application rates of urea and DMPP were 1800 kg ha^?1 and 0.5% of the urea-N application rate.

Results and discussion

The application of N significantly increased N₂O emissions in both soils. The abundance of ammonia-oxidizing bacteria (AOB) increased significantly with high rate of N fertilizer application in both soils. Conversely, there was no change in the growth rate of ammonia-oxidizing archaea (AOA) in response to the applied urea despite the presence of larger numbers of AOA in these soils. This suggests AOB may play a greater role than AOA in the nitrification process, and N₂O emission in intensive vegetable cultivation soils. The application of DMPP significantly reduced soil NO₃^?-N content and N₂O emission, and delayed ammonia oxidation. It greatly reduced AOB abundance, but not AOA abundance. Moreover, the presence of DMPP was correlated with a significant decrease in the abundance of nitrite reductase (nirS and nirK) genes.

Conclusions

Long-term intensive vegetable cultivation with heavy N fertilization altered AOB and nirS abundance. In vegetable cultivation soils with high N levels, DMPP can be effective in mitigating N₂O emissions by directly inhibiting both ammonia oxidizing and denitrifying microbes.

     

氮肥对稻田土壤反硝化细菌群落结构和丰度的影响

以氮肥田间定位试验为研究对象,利用PCR-DGGE(聚合酶链反应变性梯度凝胶电泳)和荧光定量PCR(real-time PCR)技术,通过对反硝化细菌nirS基因的检测,分析了定位试验第2年稻田反硝化细菌群落结构和丰度的变化。DGGE图谱及依据其条带位置和亮度数字化数值进行的主成分分析(PCA)结果均显示:在氮肥定位试验第2年,与不施肥对照(CK)比较,在水稻各个生育期(分蘖期、齐穗期和成熟期)内,施用氮肥[150kg(N)·hm-2]的稻田根层土或表土中的反硝化细菌群落结构均无明显变化;且稻田根层土或表土中的反硝化细菌群落结构在水稻各个生育期间也均无明显差异。荧光定量PCR结果显示,在水稻生长发育过程中,施用氮肥的稻田根层土或表土中的反硝化细菌nirS基因拷贝数始终显著(P<0.05)高于其对应的不施肥对照。此外,无论施用氮肥与否,根层土中的反硝化细菌nirS基因拷贝数在水稻成熟期时都会显著(P<0.05)降低;但表土中的nirS基因拷贝数在水稻各生育期间无明显变化;且水稻成熟期时施用氮肥和不施肥的稻田表土中nirS基因拷贝数都显著(P<0.05)高于根层土。同时,与对照比较施用氮肥可促进水稻增产44%。研究表明,短期定位试验中施用氮肥能够显著提高稻田土壤反硝化细菌的丰度,但对其群落结构没有明显影响。     

汉江流域不同土地利用方式下土壤反硝化率及其控制因素研究

Land-use patterns can affect various nutrient cycles in stream ecosystems, but little information is available about the effects of urban development on denitrification processes at the watershed scale. In the presented study, we investigated the controlling factors of denitrification rates within the streams of the Han River Basin, Korea, with different land-use patterns, in order to enhance the effectiveness of water resource management strategies. Ten watersheds were classified into three land-use patterns （forest, agriculture and urban） using satellite images and geographic information system techniques, and in-situ denitrification rates were determined using an acetylene blocking method. Additionally, sediment samples were collected from each stream to analyze denitrifier communities and abundance using molecular approaches. In-situ denitrification rates were found to be in the order of agricultural streams （289.6 mg N20-N m-2 d-1） 〉 urban streams （157.0 mg N20-N m-2 d-1） 〉 forested streams （41.9 mg N20-N m-2 d-l）. In contrast, the average quantity of denitrifying genes was the lowest in the urban streams. Genetic diversity of denitrifying genes was not affected by watershed land-use pattern, but exhibited stream-dependent pattern. More significance factors were involved in denitrification in the sites with higher denitrification rates. Multiple linear regression analysis revealed that clay, dissolved organic carbon and water contents were the main factors controlling denitrification rate in the agricultural streams, while dissolved organic carbon was the main controlling factor in the urban streams. In contrast, temperature appeared to be the main controlling factor in the forested streams.     

广东西枝江-东江流域抗生素抗性基因污染特征研究

抗生素抗性基因（Antibiotics Resistance Genes,ARGs）污染已成为全球性环境问题之一。于枯水季对广东西枝江一东江流域的淡水河、西枝江、东江干流上120多公里河段范围采样,共10个点,每个点同步采集水样和沉积物样品,采用实时荧光定量PCR方法,测定了3种代表性磺胺类耐药基因（sul1、sul2、sul3）及2种代表性整合酶基因（int1、int2）的存在及其丰度。结果显示,水样及沉积物样品中sul1、su12、sul3和int1、int2均具有100％检出率,表明西枝江一东江流域水环境受到这5种抗生素抗性基因的污染。sull和sul2在水样和沉积物中的绝对丰度和相对丰度最高,为优势抗性基因。抗性基因丰度在水体和沉积物间,具有较好的相关性（R2—0．54）。无论水体和沉积物,一些抗性基因之间也存在显著的正相关：sul1和int1（R2〉0．95,P=0．000〈0．01）,sul1和sul2（R^2〉0．8,P=0．002〈0．01）,sul2和int1（R^2〉0．8,P=-0．004〈0．01）。西枝江一东江流域的不同采样点的丰度水平并没有明显峰值,从支流到干流抗性基因丰度未随着水量的增加而削减,反而随着微生物繁殖和新的污染源排放而不断富集。     

粪肥施用土壤抗生素抗性基因来源、转移及影响因素

随着新型抗生素开发速度的不断下降以及抗性基因(Antibiotic resistant genes,ARGs)的快速出现和传播,细菌抗药性和ARGs对公共健康存在威胁,被公认为当前全球亟待解决的难题。虽然土壤本底存在ARGs,但畜禽粪便施用等人类活动加速了ARGs在土壤环境中的扩散和传播。粪肥施入土壤后,其对土壤微生物的抗性选择压力及基因水平转移导致的ARGs扩散转移将持续存在。畜禽粪便中的抗性细菌所携带的ARGs、土壤中抗生素累积导致微生物产生的ARGs和粪肥刺激含有ARGs微生物的繁殖等均为土壤中ARGs的主要来源。土壤中ARGs可以向水体和农作物传移,并随着食物链向动物及人类传播。自然因素(温度、降水、时间和土壤类型)和人为因素(抗生素的含量和种类、粪便种类和处理方式、重金属含量及生物质炭添加)均会影响土壤中ARGs的持久和扩散。目前,粪肥施用土壤中ARGs污染对环境质量及健康的潜在影响并不完全清楚,建议加强模型建立、溯源、生物地理分布、从污染源向环境介质的转移规律、削减措施和机制等方面研究,以有效遏制ARGs在环境中的污染,真正做到畜禽粪便资源化、无害化利用。     

Differentiation of nitrogen and microbial community in the littoral and limnetic sediments of a large shallow eutrophic lake (Chaohu Lake,China)

Purpose

Nitrogen (N) is one of the major elements causing eutrophication in freshwater lakes, and the N cycle is mainly driven by microorganisms. Lake littoral zones are found to be “hotspots” for N removal from both the basin and receiving waters. However, the environmental factors that drive the distribution of microorganisms are diverse and unclear. Here, we examined the differentiation of nitrogen and microbial community between the littoral and limnetic sediments to explore their interactions.

Materials and methods

Sediment samples were collected in the littoral and limnetic zones of Chaohu Lake in winter (ca. 7 °C) and autumn (ca. 22 °C). Abundances of the bacterial and archaeal genes amoA (ammoxidation), nirS and nirK (denitrification), hzsB (anaerobic ammonium oxidation; anammox), and nrfA (dissimilatory nitrate reduction to ammonium; DNRA) were measured via quantitative real-time polymerase chain reaction (qPCR). Clone libraries were constructed for further phylogenetic analysis to study the community composition.

Results and discussion

We observed significant higher concentration values in terms of sedimentary NH₄⁺-N and NO₃^?-N in the limnetic zone than littoral zone (p?<?0.05; n?=?12). In general, abundance values of the above six genes in the littoral zone were all higher than those in the limnetic zone, while higher in winter (7 °C) than in autumn (22 °C) (p?<?0.05; n?=?6). The spatial heterogeneity had the most significant effect on the distribution of ammonia-oxidizing archaea (AOA) and anammox bacteria abundance. Both temporal (temperature) and spatial heterogeneity affected the abundance of ammonia-oxidizing bacteria (AOB). The variation in the abundance of denitrifying bacteria and DNRA bacteria mainly reflected the temporal (temperature) heterogeneity.

Conclusions

The six N-cycle-related microorganisms were affected by different environmental factors and presented different distribution patterns. The lower nitrogen content and the higher microbial abundance and diversity showed that the littoral zone was the “hotspot” of N-cycling-related microorganisms in a large, eutrophic, and turbid lake. It is suggested that increasing the area and restoring the ecological function of the littoral zone was effective and significant in eutrophic lake management.

     

稻虾共作对稻田土壤nirK反硝化微生物群落结构和多样性的影响

稻虾共作是水稻种植与克氏螯虾共作形成的互利共生的稻田种养复合生态模式。目前对稻虾共作模式稻田反硝化微生物多样性和群落结构的影响尚不清楚。本研究以江汉平原常规中稻模式(MR)为对照,设置连续3年(2014—2016年)稻虾共作模式(CR)为处理,通过特异引物提取中稻抽穗期稻田土壤nirK基因,采用Illumina Miseq高通量测序技术,探讨稻虾共作模式对稻田土壤nirK反硝化微生物多样性和群落结构的影响。结果表明:稻虾共作模式显著提升水稻抽穗期稻田土壤中硝态氮、全氮及全碳的含量,对土壤碳氮比、碱解氮和铵态氮含量没有显著影响。稻虾共作模式显著增加稻田土壤nirK基因微生物的丰富度指数,但对nirK基因微生物的多样性指数影响不显著。稻虾共作模式改变了nirK基因微生物在目、科、属、种水平的群落组成,较常规中稻模式,稻虾共作模式在各分类水平组成类群均减少;稻虾共作模式较常规中稻模式改变了目的种类,对共有目相对丰度没有显著性改变。RDA分析表明稻虾共作模式对土壤nirK基因菌群的群落结构有一定的改变,但稻虾共作模式与常规中稻模式在群落结构上仍保留着一定的相似性。硝态氮含量是影响nirK反硝化细菌群落结构的主效因子。可见,稻虾共作模式对微生物多样性指数没有显著影响,但显著增加了微生物丰富度指数,改变了稻田土壤nirK反硝化微生物在目、科、属、种的群落结构。     

Nitrogen removal and metabolic profiling of a cold-adaptive and biofilm producing paddy soil bacterium Cupriavidus sp. PDN31

To assess the physiology and low temperature adaptability of the key players of nitrification and denitrification, denitrifying bacteria were isolated and characterized from the selected paddy fields. Bacterial strains belonging to Cupriavidus and Ochrobactrum sp. were explored through the selective screening of heterotrophic nitrifying and aerobic denitrifying bacteria. The direct implication of nitrate removal in the natural sample was estimated by taking the nitrate supplemented soil as well as the enriched culture. A more prominent cold-adaptive bacterium was identified as Cupriavidus sp. PDN31. The utilization of ammonium, nitrate, and nitrite and the presence of nitrous oxide reductase (nosZ) gene, catalyses the first step of the denitrification conferred its heterotrophic nitrification and aerobic denitrification ability. The ammonium, nitrate, and nitrite removal efficiency of PDN31 was found to be 92.1%, 93.5%, and 99.8%, respectively. The functional traits, evaluated from metabolizing various nitrogen substrates (Biolog) suggested its ability to utilize some sources as L-arginine, L-asparagine, L-cysteine, L-glutamic Acid, L-glutamine, L-histidine, L-citrulline and N-acetyl-L glutamic acid. The adaptive behaviour of PDN31 with its ability to remove nitrogen and induced biofilm production under low temperature regime makes it a suitable candidate among the plethora of microorganism resided in any agriculture environment.