Biostimulant effects of rhizobacteria on wheat growth and nutrient uptake depend on nitrogen application and plant development

The capacity of plant growth-promoting rhizobacteria (PGPR) – Bacillus amyloliquefaciens GB03 (BamGB03), B. megaterium SNji (BmeSNji), and Azospirillum brasilense 65B (Abr65B) – to enhance growth and nutrient uptake in wheat was evaluated under different mineral N fertilizer rates, in sterile and non-sterile soils, and at different developmental stages. In gnotobiotic conditions, the three strains significantly increased plant biomass irrespective of the N rates. Under greenhouse conditions using non-sterile soil, growth promotion was generally highest at a moderate N rate, followed by a full N dose, while no significant effect was observed for the inoculants in the absence of N fertilizer. At 50N, plant biomass was most significantly increased in roots (up to +45% with Abr65B) at stem-elongation stage and in the ears (+19–23% according to the strains) at flowering stages. For some nutrients (N, P, Mn, and Cu), the biomass increases in roots and ears were paralleled with reduced nutrient concentrations in the same organs. Nevertheless, growth stimulation resulted in a higher total nutrient uptake and higher nutrient uptake efficiency. Furthermore, Abr65B and BmeSNji counteracted the reduction of root development caused by a high N supply. Therefore, combining PGPR with a proper cultivated system, N rate, and plant stage could enhance their biostimulant effects.     

盐蒿根际产ACC脱氨酶菌株的筛选及其促生效果研究

为了获取植物促生菌资源,提高植物耐盐胁迫能力,从盐蒿根际筛选产1-氨基环丙烷-1-羧酸(ACC)脱氨酶耐盐菌株,通过分子生物学手段进行鉴定并通过发芽试验和盆栽试验验证促生效果。从盐蒿根际筛选出两株产ACC脱氨酶耐盐菌株,其中菌株AhR1的ACC脱氨酶酶活为15.72 μmol/(mg·h),菌株AhR5的ACC脱氨酶酶活为48.38 μmol/(mg·h),除此之外两株菌还具有产生物被膜、产吲哚乙酸、解无机磷等功能。经鉴定,菌株AhR1 和AhR5均属于假单胞菌属(Pseudomonas)。油菜种子发芽试验表明,两株菌的低浓度菌液(OD600=0.1)均能够显著促进2‰～6‰盐含量下油菜根和芽的生长。油菜盆栽试验表明,菌株AhR1在4‰盐含量下对油菜干重的提升最大,达到22.07%;菌株AhR5在2‰盐含量下对油菜干重的提升最大,达到29.91%。菌株AhR1和AhR5均能够明显促进盐胁迫下油菜的生长,为盐碱地微生物肥料的开发和土壤改良提供了菌种资源和理论支持。     

Bacillus pumilus WP8 exhibits biocontrol efficacy against tomato bacterial wilt via attenuation of the virulence of the pathogenic bacterium

Bacillus pumilus WP8 is a plant growth-promoting rhizobacterium (PGPR) with good biocontrol efficacy against tomato bacterial wilt caused by Ralstonia solanacearum Rs1115. Biocontrol, however, is not due to antagonism of the pathogenic bacterium. Thus, we hypothesised that the biocontrol efficacy of WP8 was achieved by attenuation of Rs1115 virulence. Here, pot experiments for comparison of Rs1115 in different plant parts were conducted to investigate the ability of WP8 to prevent entry of Rs1115 into the regions of the plant above ground. Primary and secondary metabolite contents of WP8 and their inhibitory effects on twitching and swarming motilities of Rs1115 were determined by microscopic examination and crystal violet staining. The effects of WP8 metabolites on the expression of typical virulence genes in Rs1115 were established by quantitative PCR. Rs1115 abundance in the rhizosphere increased with time after inoculation. However, the shoots treated with WP8 were pathogen-free on days 3 and 6 after inoculation. In the WP8 + Rs1115 treatment group, the abundance of Rs1115 in shoots was 1.5?lg units higher on day 9 post-inoculation than that in the Rs1115 treatment group, while less Rs1115 was observed in the leaves. This indicated that WP8 prevented Rs1115 from spreading to the regions of the plant above ground. Furthermore, some heat-resistant secondary metabolites of WP8 (e.g. lipopeptides) inhibited the twitching and swarming motility of Rs1115. Moreover, the metabolites decreased the expression of typical virulence genes in Rs1115. Therefore, WP8 was shown to attenuate Rs1115 virulence, possibly through pumilacidin secretion.     

苜蓿根瘤菌及其菌剂研究与应用现状

根瘤菌与豆科植物共生是豆科植物固氮的重要方式,苜蓿作为一种优质豆科牧草,应用苜蓿根瘤菌剂可以提升豆科牧草的固氮功能,提高苜蓿产量,降低氮肥使用量,不仅可以改善土壤结构,还能够降低农业生产成本,进而促进农业可持续发展。本文介绍了根瘤菌研究和应用概况,从根瘤菌、苜蓿根瘤菌剂及促生菌与根瘤菌共接种等方面对苜蓿生长影响进行综述,并对根瘤菌及相关菌剂研究方向进行展望。     

植物根际促生菌促进小麦生长及提高其抗旱性的研究进展

干旱胁迫是影响小麦生长发育与产量形成最主要的非生物胁迫因子,近年来化肥的过量使用及全球气候变化产生的不利影响,导致小麦在生长过程中受到的干旱胁迫危害日趋严重。植物根际促生菌(PGPR)不仅可以协助小麦提高养分利用率,促进其生长发育,还能够通过自身作用或产生多种代谢产物协助小麦抵御干旱胁迫。本文归纳总结了PGPR促进小麦生长及提高其抗旱性的研究进展,为利用PGPR提高小麦促生抗旱的研究奠定了理论基础。     

接种植物根际促生菌对施用有机无机复混肥土壤N2O排放的影响

施用有机无机复混肥可提高土壤肥力、增加作物产量,但也增加温室气体氧化亚氮(N2O)的排放。采集江苏省句容市的复垦土壤样品设置室内土壤培养试验,研究接种植物根际促生菌(PGPR)对施用有机无机复混肥土壤N2O排放的影响。结果表明,接种PGPR菌株Azospirillum sp. TSA2S、Pseudomonas stutzeri NRCB010、Achromobacter denitrificans YSQ030和Bacillus subtilis NRCB002,相对于施肥不接种的对照显著减少了土壤N2O排放量;土壤N2O的累积排放量由高到低为NRCB002>TSA2S>NRCB010>YSQ030,其中N2O排放量分别减少了59%、62%、63%和72%。无论接种与否,施肥均显著提高了土壤中氨氧化古菌amoA、氨氧化细菌amoA以及全程硝化菌amoB、反硝化细菌nirS和nirK的基因拷贝数。接种携带nosZ基因的N2O还原细菌A. sp. TSA2S、P. stutzeri NRCB010、A. denitrificans YSQ030显著提高了施肥土壤中nosZⅠ和nosZⅡ的基因丰度。然而,接种不携带nosZ基因的B. subtilis NRCB002则没有明显改变施肥土壤中nosZⅠ和nosZⅡ的基因丰度。这些结果意味着接种4株具有N2O减排效应的PGPR菌株,分别从微生物介导的直接和间接机制减少了土壤N2O的排放。研究结果将为减少施用有机无机复混肥土壤N2O排放提供科学依据,也将为研发具有生态环境效应的新型生物肥料提供技术参考。