生物硝化抑制剂(BNI)在提高农业生产系统中氮利用率方面的研究进展

施肥是提高农业生产率的主要手段之一,提高氮肥利用率是化肥施用的核心问题之一。硝化和反硝化作用引起的硝态氮淋失和一氧化二氮(N2O)排放是氮肥利用率低的主要原因,N2O是一种导致全球气温急剧升高的温室气体。生物硝化抑制是指从植物根部释放具有抑制硝化作用的天然化合物的能力,释放的天然化合物称为生物硝化抑制剂(biological nitrification inhibitor,BNI),其特异性抑制土壤硝化中微生物的活性。生物硝化抑制剂可显著提高水稻(Oryza sativa)、玉米(Zea mays)等作物产量5%~10%,可使玉米对氮素的利用率提高3.1%,还能减少温室气体N2O的排放;与不产生BNI的植物相比,其释放的N2O降低量可达90%。臂形草(Brachiaria humidicola)释放的名为“brachialactone”的BNI在其抑制硝化过程中抑制效果占总抑制作用的60%~90%。综上可知,生物硝化抑制剂在抑制硝化作用、提高氮素利用率及作物产量、减少温室气体排放等方面起着重要的作用。本文综述了已知释放生物硝化抑制的植物和能够抑制土壤硝化作用的植物,并进一步讨论了生物硝化抑制在农业系统中的重要作用。     

不同利用方式对内蒙古羊草草原氨氧化微生物丰度的影响

草地利用方式变化会显著改变草地的氮素循环,进而影响草原生态系统功能。土壤硝化作用是土壤氮素循环的重要环节,由氨氧化微生物驱动的氨氧化过程是硝化作用的限速步骤,在土壤氮素可利用性等方面起着关键作用。目前,土壤氨氧化微生物对于羊草（Leymus chinensis）草原利用方式变化响应的研究仍然欠缺。本研究应用定量PCR的方法,对内蒙古羊草草原不同利用方式（放牧和围封）下氨氧化微生物丰度及其与硝化潜势的关系进行研究。结果表明：放牧和围封样地的氨氧化古菌（Ammonia-Oxidizing Archaea,AOA）丰度均明显高于氨氧化细菌（Ammonia-Oxidizing Bacteria,AOB）丰度,土壤AOA-amoA和AOB-amoA基因丰度范围分别为每克干土（1.82~3.40）×10⁸个拷贝数和（1.05~1.17）×10⁶个拷贝数;长期围封后,AOA丰度显著下降,下降了46.5%,AOB丰度则无显著变化;长期围封后,羊草草原的硝化潜势显著降低,硝化潜势与AOA丰度呈显著正相关关系,与AOB丰度没有显著性相关。与AOB相比,AOA丰度对于草地利用方式的改变更敏感,可能是影响土壤硝化潜势的优势种群。该研究为理解内蒙古羊草草原硝化过程的微生物机制提供科学依据。     

猪场污水异养硝化-好氧反硝化菌筛选及性能研究

高氨氮含量是猪场污水达标处理的一大难点,传统生物脱氮工艺是在不同的工艺条件下分别进行硝化或反硝化作用,设施成本高且占地面积大,因此并不适合应用于猪场污水的处理.异养硝化-好氧反硝化(HN-AD)菌作为一类能同时进行硝化反应和反硝化反应的细菌,能较好解决硝化和反硝化不能同存一池的问题.本研究以猪场污水处理系统兼性塘中长期...     

西南地区pH影响紫色土硝化作用机制研究

硝化作用是一个对pH高度敏感的典型过程,但pH影响土壤硝化作用的机制尚不完全明了。本研究以西南地区3种发育于同一母质的不同pH的紫色土(酸性紫色土 pH=5.7,中性紫色土 pH=7.3,石灰性紫色土 pH=8.0)作为供试材料,研究pH对紫色土硝化强度及氨氧化微生物的长期效应;通过人为添加酸(H₂SO₄)或碱(NaOH)短期改变土壤pH的方法,研究pH对紫色土硝化作用强度、氨氧化微生物活性及丰度的短期效应。结果表明,pH的短期改变对酸性与石灰性紫色土的硝化作用无显著影响(P>0.05),但对中性紫色土的硝化速率影响显著(P<0.05);氨氧化古菌(AOA)的amoA基因在酸性土壤环境中的表达更高(3.04×10⁸/g干土,AOA/AOB=31.8),而氨氧化细菌(AOB)则更适应于石灰性紫色土环境(2.35×10⁸/g干土,AOA/AOB=0.07)。研究表明,紫色土的硝化作用强度受pH的影响显著,且在不同pH土壤中其作用机制各不相同。硝化微生物群落和活性主导了酸性和石灰性紫色土中的硝化作用,而中性紫色土中的硝化作用则是由底物浓度所主导。研究推测长期稳定的pH是影响硝化微生物群落和活性的关键因素,而pH的短期改变则主要影响硝化反应的底物有效性。     

单步硝化作用与全程氨氧化微生物研究进展

单步硝化作用,即由一种微生物(全程氨氧化微生物)单独完成将NH₃氧化为NO3-的整个硝化过程,于2015年底被发现。该发现终结了传承百年的两步硝化作用的经典理论,并引发了众多关于全球氮素循环的重要科学问题。就单步硝化作用及全程氨氧化微生物发现后两年来的研究进展进行概述。目前已确定的全程氨氧化微生物均属于硝化螺菌门谱系Ⅱ(Nitrospira spp. Linage Ⅱ),包括两个分支A和B(Clade A和Clade B);广泛分布于农业土壤、森林土壤、稻田水域、淡水等自然环境中。全程氨氧化细菌(Nitrospira inopinata)比大多数可培养的氨氧化细菌(AOB)以及氨氧化古菌(AOA)物种对氨具有更高的亲和力,能够更好地适应极低氨浓度环境。此外,全程氨氧化微生物具有不同的碳氮代谢途径,可能具有和其他氨氧化微生物不同的生态位点。单步硝化作用的相对贡献与全程氨氧化微生物的生态位分化是今后的重要研究方向。     

应用N~(15)研究桑园氮素平衡的初步结果

<正> 随着蚕业生产的发展,桑园氮肥施用量迅速增加,研究氮肥施入土壤后的氮素平衡状况,对于了解氮肥的增产效果,提高氮肥的利用率及制订合理施肥技术措施都是极为重要的。氮肥施入土壤后,一部分被桑树吸收,一部分残留在土壤中,一部分则通过不同途径而损失(如氮素的硝化淋失,反硝化作用损失及氨的挥发等)。这几个部分构成了桑园的“氮素平衡”。气候、土壤、耕作和栽培技术,以及氮肥的种类,施肥时间和施肥方法等因素,都对氮肥的氮素平衡状况产生显著的影响。因此,吸收、残留、损失的三部分氮素占施入氮素总量的比例也会有很大     

Meta分析放牧对中国草地土壤氮素矿化和硝化作用的影响

氮素矿化和硝化作用对草地土壤氮素转化过程具有重要影响。放牧干扰影响草地土壤氮素矿化和硝化作用。本研究基于Meta分析方法，对已开展的59个放牧影响中国草地土壤氮素矿化作用、55个放牧影响中国草地土壤氮素硝化作用影响的试验结果进行整合分析。结果表明：放牧降低草地土壤氮素矿化、硝化作用，平均效应值分别为—0.09和—0.08,降幅分别为8.61%和7.69%,但均未达到显著性检验水平；不同放牧强度对草地土壤氮素矿化作用和硝化作用平均效应值的影响呈现出轻度放牧>重度放牧>中度放牧；土壤全氮含量显著影响矿化作用平均效应值，可解释4.91%的效应值变异；土壤有机碳和全氮含量显著影响硝化作用平均效应值，分别可以解释18.35%和19.17%的效应值变异。本研究旨在为明晰放牧草地氮素循环提供理论基础。     

多年冬种紫云英对两种典型双季稻田土壤肥力及硝化特征的影响

以湖南紫潮泥和江西黄泥田两种典型稻田下的绿肥定位试验为依托,分析了晚稻收获后两种土壤的养分性状、硝化强度、硝化势及氨氧化细菌(AOB)和氨氧化古菌(AOA)的amoA基因丰度,探讨多年冬种紫云英对两类稻田土壤肥力、硝化作用及氨氧化微生物的影响。两地试验处理一致,包括:1)不施肥不种紫云英(CK);2)冬种紫云英不施化肥(GM);3)不种紫云英单施化肥(CF);4)冬种紫云英配施化肥(GM+CF)。结果表明,冬种紫云英可以改善两种典型稻田土壤pH,即提高江西酸性土壤pH、降低湖南碱性土壤pH;提高土壤全氮、有机质、无机氮和有效磷含量。两种典型水稻土的硝化能力不同,江西黄泥田的硝化强度及硝化势均明显低于湖南紫潮泥。在湖南紫潮泥中,各处理硝化强度在0.269~0.325 μg/(g·h)之间,处理间差异不显著;硝化势在培养第5周达到10.25%,紫云英配施化肥在一定程度上抑制了紫潮泥的硝化作用。江西黄泥田中,各处理硝化强度在0.010~0.021 μg/(g·h)之间,硝化势从培养第3周开始上升,在培养第5周达到5.41%;单独种植翻压紫云英相对于不施肥对照提高了土壤硝化强度及硝化势,与施用化肥处理效果相当,绿肥配施化肥对硝化作用的促进最强。AOA在紫潮泥和黄泥田中均占优势地位,紫潮泥中AOA-amoA基因丰度显著高于黄泥田,冬种紫云英对紫潮泥中AOA-amoA和AOB-amoA基因丰度均无明显影响,而显著提高了黄泥田中AOA-amoA和AOB-amoA基因丰度,与冬种紫云英对硝化强度和硝化势的影响一致。     

氮沉降影响草地生态系统土壤氮循环过程的研究进展

人类活动及化石燃料应用的加剧增加了大气中的氮沉降，对陆地生态系统氮素循环过程造成了显著影响，从而影响生态系统生产力及稳定性。草地作为陆地生态系统的重要组成部分，常因为人们的过度利用及保护意识不强，造成资源损失、养分失衡，严重限制了畜牧业的发展。探究氮沉降对草地生态系统氮循环的影响对提高草地生产力，合理开发与利用草地资源具有重要意义。通过追踪国内外已有的研究成果发现，大部分氮添加抑制了生物固氮过程，促进了土壤的硝化作用、反硝化作用和矿化作用，并抑制了固氮微生物活性，增加了硝化功能微生物氨氧化细菌（AOB）、反硝化微生物功能基因nirK、nirS、narG、nosZ的丰度。但是因为草地本底氮营养差异及施氮措施的不同导致少数研究中土壤氮循环对氮沉降的响应出现不同结果。通过总结已有研究发现：1）土壤本底营养及氮吸收阈值的不同造成氮沉降对氮循环的影响存在差异；2）微生物作为土壤氮素循环的重要参与者，对不同施氮时间、频率、数量等的响应存在差异；3）土壤中氮循环的各环节紧密耦联，相互影响，但现有的研究大多只针对某一环节开展，研究结果不具有全面性。因此，在未来的研究中，应针对不同营养水平的草地，加强氮控制条件下土壤氮循环微生物变化的研究，关注多环节的耦联关系，对于提高草地生态系统功能，并减轻氮素损失对环境造成的威胁意义重大。     

不同土壤水分条件下松嫩草地土壤呼吸及其组分对氮添加和放牧的响应

量化土壤呼吸的时间变化（包括热时刻）并阐明不同土壤水分条件下（“干旱”和“湿润”）氮沉降增加和放牧干扰对自养呼吸和异养呼吸的影响,有助于准确估算区域生态系统的CO2通量。本研究于2016年在松嫩草甸草原进行了氮添加和放牧处理试验,于2020年6～8月对土壤呼吸及其组分进行连续测定,并同步测定了土壤理化性质、土壤微生物特征和植物生物量。研究发现,在观测期间的“湿润”时期,所有处理的土壤呼吸和自养呼吸均高于“干旱”时期。各处理对土壤呼吸的影响受土壤水分条件调控,即在“干旱”条件下,放牧处理以及氮添加和放牧共同处理显著降低了土壤呼吸,而氮添加显著增加了土壤呼吸和自养呼吸,对异养呼吸无显著影响。在“湿润”条件下,放牧以及氮添加和放牧共同处理增加了土壤呼吸,单独氮添加对土壤呼吸及其组分均无显著影响。研究结果阐明了氮沉降增加和放牧干扰对自养呼吸和异养呼吸影响的水分条件依赖性。     

Inducible nitric oxide synthase and nitrotyrosine in listeric encephalitis: a cross-species study in ruminants

Listeria monocytogenes (LM) is a Gram-positive facultative intracellular bacterium that causes fatal meningoencephalitis in humans and ruminants. A current paradigm predicts that intracellular bacteria are controlled by nitric oxide (NO) whose synthesis is catalyzed by inducible nitric oxide synthase (iNOS). The ability of macrophages (Mphi) to express iNOS shows extreme interspecies variability. Here the expression of iNOS and synthesis of NO was studied in listeric encephalitis of cattle, sheep, and goats. iNOS was expressed by a subset of Mphi in cerebral microabscesses in all three species. The level of iNOS expression and the density of cells per lesion expressing iNOS was highest in cattle, intermediate in sheep, and lowest in goats. The accumulation of nitrotyrosine (NT), an indicator of local NO synthesis, was observed in lesions of cattle but not in those of small ruminants. The density of iNOS-expressing cells in lesions was inversely correlated with the number of bacteria. No species differences were observed in regard to reactive oxygen intermediate (ROI) production by stimulated granulocytes, using the flow cytometric dihydrorhodamine-123 (DHR) method indicating ROI generation. Thus, the marked species differences in iNOS expression, NT accumulation, and LM content in lesions of ruminants with listeric encephalitis are explained by different amounts of ROI produced. It suggests that variations in the ability of Mphi to synthesize NO are of pathophysiological significance in listeriosis.     

不同乳酸菌添加剂对天然牧草青贮品质的影响

以内蒙古半干旱山地草原天然混合牧草为原料,通过添加不同的乳酸菌添加剂进行青贮对比试验,探讨不同乳酸菌添加剂对天然牧草青贮饲料品质的影响,筛选适宜的乳酸菌添加剂.结果表明:5种添加剂均能不同程度地改善天然牧草青贮品质,经过感官评定,乳酸菌添加剂青贮饲料优于对照组;青贮饲料的发酵品质和营养价值综合分析表明,在提高乳酸含量,降低氨态氮含量、pH值、酸性洗涤纤维等方面表现最佳的是中农1号乳酸菌,其次是中农3号,中农2号、4号和8号添加剂青贮效果改善不明显.     

The role of nitric oxide in Listeria encephalitis of ruminants and in rats intracisternally infected with Listeria monocytogenes

Listeria monocytogenes is a Gram-positive facultative intracellular bacteria which infects a wide range of hosts. In ruminants, infection with L. monocytogenes frequently causes encephalitis, which is usually fatal in sheep and goat, while cattle often recover with antibiotic therapy. Since the role of NO in the control of Listeria is controversial, we have studied the expression of iNOS in the brains of cattle, sheep and goats which had succumbed to listeria encephalitis. iNOS was demonstrated in decreasing intensity in the M phi of microabscesses from cattle, sheep and goat. iNOS expression was accompanied by NT in the microabscesses of cattle, but was only present to a low degree in sheep and was absent in goats. This is indirect evidence for differences in the ability to produce NO in the three species. Presence of iNOS and NT were inversely correlated with the numbers of bacteria. While microabscesses of goats contained high amounts of L. monocytogenes they occurred only rarely in cattle. To corroborate our hypothesis that NO is involved in the control of listeria encephalitis a new animal model was developed. Eleven day old infant rats were infected intracisternally with a low dose of L. monocytogenes. This resulted in a transient meningoencephalitis with moderate clinical signs and low mortality. Listeria proliferated strongly in the inflammatory lesions during the first days of infection, reached a peak at day 4 and were eliminated until day 7. The presence of bacteria was closely accompanied by high numbers of iNOS-expressing M phi and the formation of NT. Administration of the iNOS inhibitor L-NIL or the radical scavenger PBN resulted in rapid death of the treated animals. However, the increase in bacterial numbers was one order of magnitude higher for animals treated with PBN compared with L-NIL administration. This shows that NO plays an important role in the control of a brain infection with Listeria, but suggests that reactive oxidants other than NO are also involved. In conclusion, our findings point to a possible involvement of the differences in the ability to express iNOS and subsequent NO production in the different clinical outcome of listeria encephalitis in cattle and small ruminants.     

Effects of bovine mammary secretion during the early nonlactating period and antibiotics on polymorphonuclear neutrophil function and morphology.

The effect of bovine mammary secretion during the early nonlactating period and of antibiotic preparations on bovine polymorphonuclear neutrophil (PMN) phagocytic function and morphology were evaluated in a series of in vitro multifactorial experiments. Benzathine cloxacillin (CL), benzathine cephapirin (CE), sodium novobiocin (NO), and a combination of dihydrostreptomycin with procaine penicillin G (DP) were prepared in the presence and absence of a peanut oil aluminum monostearate vehicle. The PMN were isolated from bovine blood, and the effect of each antibiotic preparation on PMN function and morphology was evaluated in a buffer, fat, skin, and a combination of fat with skim from bovine mammary secretion during the nonlactating period. The fat and skim were diluted with buffer to approximate their concentration in mammary secretion. Phagocytic functions of PMN were monitored by fluorescent microscopy, which made it possible to estimate both ingestion and intracellular killing of bacteria by PMN. Changes in PMN morphology were monitored by transmission electron microscopy. The ability of PMN to ingest and kill Staphylococcus aureus ATCC 25923 was significantly decreased by fat, skim, CL, CE, NO, and DP. Effects of some antibiotics on ingestion and killing of bacteria by PMN were influenced by the addition of vehicle and by interactions with mammary secretion. Neutrophil morphology was altered by fat, skim, CL, CE, NO, and DP. The detrimental effects of CL, CE, NO, and DP on PMN morphology were influenced (some significantly) by the presence of vehicle and interactions with mammary secretion. There were significant correlations among secretion- and antibiotic-induced changes in PMN ingestion of bacteria, PMN killing of bacteria, and PMN morphology.     

Significance of nitric oxide concentration in plasma and uterine secretes with puerperal endometritis in dairy cows

Endometritis is an inflammation of the endometrial lining of the uterus without systemic signs, which is associated with chronic postpartum infection of the uterus with pathogenic bacteria. Nitric oxide (NO) is an inflammatory mediator that among other effects causes smooth muscle relaxation and mediated cytoimmunity and inflammation toxicity. To see if the nitric oxide concentration in plasma and uterine secrets is related with postpartum endometritis, NO concentrations in plasma and uterine secrets were measured in dairy cows with puerperal endometritis (clinical endometritis (n = 60) and subclinical endometritis (n = 58)). Cows with clinical or subclinical endometritis showed higher concentrations of NO in both plasma and uterine secrets when compared with normal cows and the highest concentrations of NO in plasma and uterine secrets were found in dairy cows with clinical endometritis. Expression level of NOS2 mRNA in endometrial biopsies from cows with puerperal endometritis was also higher and the highest expression of NOS2 mRNA was found in cows with clinical endometritis. The results showed that concentrations of NO in plasma and uterine fluid are related with the degree of endometritis which may be useful to diagnose the endometritis in dairy cows.     

Effects of nitric oxide on bovine polymorphonuclear functions.

The effects of nitric oxide (NO) on the functionality of polymorphonuclear neutrophils (PMNs) in bovine milk or blood were investigated. In 2 experiments, mastitis was induced by infusing both hind quarters with saline containing Escherichia coli endotoxins. In addition, the left hind quarter was infused with aminoguanidine, an inhibitor of the inducible form of NO synthase (iNOS). At various times after infusion, somatic cells were isolated from milk samples, and superoxide (O2-) production induced by phorbol myristate acetate was evaluated. In both experiments, the addition of aminoguanidine had no inhibitory effect on the number of milk somatic cells or on their O2- production. The effect of NO and iNOS inhibitors on the functionality of bovine PMNs isolated from blood was investigated in vitro. The neutrophils did not produce NO. A neutrophil:monocyte co-culture system was used to study the effect of NO derived from monocytes on O2- production by bovine neutrophils. Neither NO derived from activated monocytes nor the iNOS inhibitors aminoguanidine and L-N6-(1-iminoethyl)lysine had an effect on the ability of bovine neutrophils to release O2-. Moreover, aminoguanidine did not affect the ability of bovine neutrophils to phagocytose bacteria. These results suggest that inhibition of NO release during inflammation does not interfere with the migration of immune cells to the site of infection or the ability of these cells to destroy pathogens. Thus, NO does not appear to play a major role in the control of the functions of bovine neutrophils.