生物固氮是生态系统氮素的主要来源,而土壤根瘤菌的多样性及其在大豆上的应用效果还需深入研究.本研究采集了东北黑土大豆种植区8个样点的大豆土壤根瘤样本,共分离出94株菌,经16S rRNA及共生基因(nodC、nifH)分析鉴定,其中70株为根瘤菌,且均属于慢生根瘤菌属.为进一步验证根瘤菌的应用效果,根据系统发育分析结果挑选了 7株代表性土著根瘤菌,基于实验室条件开展了菌株与大豆结瘤及促生能力测定试验.结果表明:与不接种根瘤菌的对照相比,7株土著根瘤菌都具有较好的促生及结瘤能力,其中,菌株H7-L22和H34-L6的表现尤为突出,前者处理的大豆株高显著提高了 25.7％,后者处理的大豆根瘤干重比其他土著根瘤菌处理高20.9％～67.1％.选取这两株高效根瘤菌进一步开展大豆根瘤菌接种田间试验,发现接种混合根瘤菌剂的促生效果显著优于单一接种处理,与不接种对照相比,H7-L22处理的大豆增产8.4％,而混合菌剂处理的大豆产量增加了 17.9％,同时大豆的四粒荚数也显著提升.综上,根瘤菌菌剂的应用能够显著提升大豆产量,从而减少大豆生产过程中对氮肥的依赖,有助于提升土壤健康水平,促进东北黑土地区农业的绿色发展.

Suppression of roots and/or their symbiotic microorganisms,such as mycorrhizal fungi and rhizobia,is an effective way for alien plants to outcompete native plants.However,little is known about how invasive and native plants interact with the quantity and activity of nutrient-acquisition agents.Here a pot experiment was conducted with monoculture and mixed plantings of an invasive plant,Xanthium strumarium,and a common native legume,Glycine max.We measured traits related to root and nodule quantity and activity and mycorrhizal colonization.Compared to the monoculture,fine root quantity(biomass,surface area)and activity(root nitrogen(N)concentration,acid phosphatase activity)of G.max decreased in mixed plantings;nodule quantity(biomass)decreased by 45％,while nodule activity in N-fixing via rhizobium increased by 106％;mycorrhizal colonization was unaffected.Contribution of N fixation to leaf N content in G.max increased in the mixed plantings,and this increase was attributed to a decrease in the rhizosphere soil N of G.max in the mixed plantings.Increased root quantity and activity,along with a higher mycorrhizal association was observed in X strumarium in the mixed compared to monoculture.Together,the invasive plant did not directly scavenge N from nodule-fixed N,but rather depleted the rhizosphere soil N of the legume,thereby stimulating the activity of N-fixation and increasing the dependence of the native legume on this N source.The quantity-activity framework holds promise for future studies on how native legumes respond to alien plant invasions.

Plants harbor diverse microbes(including bacteria,fungi,archaea,protists,and viruses)both inside and outside their tissues,so called the plant-associated microbiome.Decades of research have demonstrated the importance of plant microbiome in pro-moting the productivity and health of the plant in natural environ-ment because of their essential functions in improving plant nutrition and plant resistance to biotic and abiotic stresses(Trivedi,Leach,Tringe,Sa,& Singh,2020).Thus,a plant can be regarded as a holobiont comprising the host plant and the associ-ated microbiota(Hassani,Durán,& Hacquard,2018).Within the plant microbiota,mutualistic fungal and bacterial symbionts(e.g.mycorrhizal fungi and Rhizobia)are striking examples of microor-ganisms playing crucial roles in nutrient acquisition(Martin &van der Heijden,2024)and non-symbitic plant growth-promoting rhizobacteria or fungi(PGPR or PGPF)also have drawn interest due to their ability to improve soil properties and confer stress toler-ance in plants(Upadhyay et al.,2023).

Most leguminous plants establish symbiotic relationships with rhizobia to form root organs called nodules(Ferguson et al.,2010).Nodules are specialized organs containing bacterial symbionts,which can provide enormous amounts of fixed nitrogen to their plant hosts(Peoples et al.,2009).Soybean(Glycine max),an economically important grain and oil crop,forms symbiotic nitrogen-fixing nodules,which reduces the demand for chemical nitrogen fertilizers and pro-motes yield(Saito et al.,2014).Nodule development is spatiotempo-rally regulated by the action of a number of transcription factors(TFs),such as NODULATION SIGNALING PATHWAY 1(NSP1),NSP2,DELLA,NODULE INCEPTION(NIN),NUCLEAR FACTOR-Ys(NF-Ys),and ETHYLENE RESPONSE FACTOR Required for Nodulations(ERNs),which trigger transcriptional responses(Oldroyd and Long,2003;Jin et al.,2016;Liu et al.,2019;He et al.,2021).Mutations in genes encoding any of these TFs abolish early symbiotic gene expression in the host,indicating that they function early in the Nod factor signaling pathway(Borisov et al.,2003;Jin et al.,2016;He et al.,2021).TFs also play key roles in regulating the division of cortical cells in legumes.The SHORT ROOT(SHR)-SCARECROW(SCR)module and LATERAL ORGAN BOUNDARIES DOMAIN PRO-TEIN 16(LBD16)accumulate and are active in cortical cells,enabling them to dedifferentiate and undergo divisions in nodule primordia(Soyano et al.,2019;Dong et al.,2021).

为揭示丛枝菌根真菌(AMF)和根瘤菌在白三叶氮(N)同化中的作用,该研究对白三叶进行单一或联合接种隐类球囊霉(Paraglomus occultum)和三叶草根瘤菌(Rhizobium trifolii),分析其对白三叶的生长、光合作用、叶片N和氨基酸含量以及N同化相关酶活性的影响.结果表明:(1)单一接种AMF或根瘤菌以及联合接种AMF和根瘤菌均显著增加了白三叶的株高、匍匐茎长度、叶片数、地上部生物量、总生物量、叶绿素b和总叶绿素含量、稳态光量子效率和叶片N含量,这种增强效应是联合接种>单一AMF>单一根瘤菌>未接种处理.(2)联合接种AMF和根瘤菌显著增加了白三叶叶片中丙氨酸、精氨酸、天冬酰胺、天冬氨酸、谷氨酰胺、谷氨酸和组氨酸的含量,显著提升了叶片N同化相关酶如硝酸还原酶、亚硝酸还原酶、谷氨酰胺合成酶、谷氨酸合成酶、谷氨酸脱氢酶、天冬酰胺合成酶和天冬氨酸转氨酶的活性,显著促进AMF对白三叶根系的侵染.综上认为,联合接种AMF和根瘤菌通过激活N同化相关酶活性有效促进N同化,产生更多氨基酸,进一步促进白三叶植株生长;联合接种AMF和根瘤菌具有协同作用,有效促进了白三叶的N同化.

根瘤菌是一类革兰氏阴性菌,能与特定的宿主植物共生形成根瘤,将空气中的分子态氮转变为植物可以利用的氨态氮.研究根瘤菌的生物地理分布格局及形成机制,不仅具有理论上的意义,还对根瘤菌接种剂的选择具有指导意义.目前,随着分子生物学技术的发展,以及根瘤菌多样性研究数据的积累,根瘤菌生物地理学取得了较大的进展.本文综述了根瘤菌生物地理学的研究方法及现状,并对今后的重点研究方向作了展望.

根瘤菌剂在大豆上能否充分发挥共生固氮效应涉及到根瘤菌的结瘤固氮能力、与大豆品种的匹配性、土壤特性等多种因素.黑龙江省是我国大豆的主产区之一,为筛选得到适于在黑龙江推广应用的根瘤菌资源,从黑龙江、河北和湖南等地区采集土壤样品,采用大豆结瘤法,从10个土样中分离获得59株大豆根瘤菌株,再依据BTB显色反应和16S rDNA分析,鉴定出36个慢生型大豆根瘤菌.沙培结果表明,有34株根瘤菌能够在大豆品种黑农61上有效结瘤;再从中选出4株共生效应较好的菌株做进一步实验.匹配实验表明,这4株菌SN2-5、NW5-3、SN7-2和SN10-3同样能与黑龙江另外16个主栽大豆品种结瘤;与不接根瘤菌的对照组相比,SN2-5、NW5-3、SN7-2和SN10-3处理的大豆的根瘤固氮酶活和生物量显著提高,且整体表型优于HN01和USDA110.土壤盆栽实验结果表明,NW5-3、SN10-3、SN7-2在黑土中具有显著的接种效果,且在10 mmol/L NH4NO3高氮处理下,4个优良供试菌均能够与黑农61结瘤.与不加氮素的处理相比,其中NW5-3和SN10-3形成根瘤具有近50％的固氮酶活性.本研究筛选的4个慢生型大豆根瘤菌SN2-5、NW5-3、SN7-2、SN10-3与黑龙江的主栽大豆品种具有良好匹配性能,可进一步用于黑龙江大豆产区的田间实验.

Leguminous plants can establish symbiotic associations with diazotropic rhizobia to form nitrogen-fixating nodules, which are classified as determinate or indeterminate based on the persistence of nodule meristem. The formation of nitrogen-fixing nodules requires coordinating rhizobial infection and root nodule organogenesis. The formation of an infection thread and the extent of nodule formation are largely under plant control, but vary with environmental conditions and the physiological state of the host plants. Many achievements in these two areas have been made in recent decades. Phytohormone signaling pathways have gradually emerged as important regulators of root nodule symbio-sis. Cytokinin, strigolactones (SLs) and local accumulation of auxin can promote nodule development. Ethylene, jasmonic acid (JA), abscisic acid (ABA) and gibberellic acid (GA) all negatively regulate infection thread formation and nodule development. However, salicylic acid (SA) and brassinosteroids (BRs) have different effects on the formation of these two nodule types. Some peptide hormones are also involved in nodulation. This review summarizes recent findings on the roles of these plant hormones in legume-rhizobial symbiosis, and we propose that DELLA proteins may function as a node to integrate plant hormones to regulate nodulation.

During the establishment of rhizobia-legume symbiosis,the cytokinin receptor LHK1 (Lotus Histidine Kinase 1) is essential for nodule formation.However,the mechanism by which cytokinin signaling regulates symbiosis remains largely unknown.In this study,an LHK1-interacting protein,LjCZF1,was identified and further characterized.LjCZF1 is a C3HC4-type RING finger protein that is highly conserved in plants.LjCZF1 specifically interacted with LHK1 in yeast two-hybrid,in vitro pull-down and co-immunoprecipitation assays conducted in tobacco.Phosphomimetic mutation of the potential threonine (T167D) phosphorylation site enhanced the interaction between LjCZF1 and LHK1,whereas phosphorylation mutation (T167A) eliminated this interaction.Transcript abundance of LjCZF1 was upregulated significantly after inoculation with rhizobia.The LORE1 insertion mutant and clustered regularly interspaced short palindromic repeats (CRISPR)/CRlSPR-associated protein 9-mediated knockout mutant Lotus japonicus plants demonstrated significantly reduced number of infection threads and nodules.In contrast,plants over-expressing LjCZF1 exhibited increased numbers of infection threads and nodules.Collectively,these data support the notion that LjCZF1 is a positive regulator of symbiotic nodulation,possibly through interaction with LHK1.

ROS include superoxide anion radical (O2-),hydrogen peroxide (H2O2),singlet oxygen (O.O),hydroxyl radical (OH.),and hydroxyl anion (OH-).O2-,the radical with the highest oxidation compacity to produce H2O2,OH.and OH-,is a byproduct of aerobic respiration in organisms.Rhizobia and their legume hosts are aerobic organisms,and nitrogen-fixing nodules formed on legume roots are developed from their symbiotic interactions.Therefore,ROS are generated in legume nodules through aerobic respiration by both symbiotic partners.