【Objective】The aim of this research was to screen plant growth promoting rhizobacteria（PGPR） from the rhizosphere of the desert steppe shrub Cerasus humilis with excellent growth-promoting and disease-preventing properties. In this study, selective media were used to screen the bacteria on the root surface and in the rhizosphere soil of the Cerasus humilis. Acetylene reduction method,Salkowski method, molybdenum antimony colorimetric method and plate confrontation method were used to determine the nitrogenase activity,secretion of IAA, phosphorus and antagonism. Using Morphology, gram staining and molecular biology methods,10 strains with excellent rhizosphere growth-promoting were preliminarily identified. The results from 31 strains of bacteria which were screened showed that: the nitrogenase activity was 16. 22～328. 35 nmol C 2 H 4 /（h·mL）; the amount of IAA secreted was 3. 85～60. 19 μg/mL;the amount of dissolved organic phosphorus was 10. 66～118. 76 μg/mL;the amount of dissolved inorganic phosphorus was 1. 42～289. 93 μg/mL; strain WGB2 was effective against Fusarium solani,Bipolaris sorokiniana,Gibberella acuminata,Fusarium graminearum and Gibberella moniliformi,and the inhibition rates were 11. 85%,39. 91%,27. 64%,59. 84%,and 26. 22%,respectively. PGPR of Cerasus humilis showed that the number of bacteria on the root surface was significantly higher than that of the rhizosphere soil. Ten strains were preliminarily identified as belonging to Chryseomicrobium,Planomicrobium,Pseudomonas, Arthrobacter, Agrobacterium and Paenibacillus.

为了解灌丛凋落叶在灌草群落结构维持中可能存在的潜在化感作用,以东祁连山3种优势灌木和灌下优势草种垂穗披碱草(Elymus nutans)为供试材料,分析了不同浓度(0.01 g/L、0.025 g/L、0.05 g/L、0.075 g/L、0.1 g/L)的金露梅(Potentilla fruticosa)、川滇柳(Salix rehderiana)、头花杜鹃(Rhododendron capitatum)及灌间草本的凋落叶水浸提液,对垂穗披碱草种子萌发、幼苗形态和生理指标的影响.结果表明:(1)垂穗披碱草种子发芽率与发芽势在金露梅与川滇柳凋落叶浸提液处理下呈"低促高抑"的浓度效应,在灌间草本凋落叶浸提液处理时表现为先升后降,而头花杜鹃凋落叶浸提液处理时均下降,并在浓度超过0.075 g/L时种子不发芽.(2)灌丛凋落叶浸提液对垂穗披碱草幼苗根长与干重均表现出抑制作用,且随浓度增大而增强;金露梅、川滇柳与灌间草本凋落叶浸提液对垂穗披碱草幼苗苗高表现出"低促高抑"的浓度效应;而头花杜鹃凋落叶浸提液处理对垂穗披碱草幼苗鲜重与苗高均呈抑制作用.(3)垂穗披碱草幼苗CAT、SOD活性随着浸提液浓度升高均表现出先升后降的变化趋势;可溶性糖与可溶性蛋白在灌丛凋落叶浸提液浓度低于0.075 g/L时含量较高;MOD含量在金露梅凋落叶浸提液处理下随浓度升高而持续升高,而在川滇柳与灌间草本凋落叶浸提液处理下呈先升高后降低的趋势.综合来看,灌丛凋落叶浸提液对垂穗披碱草的化感作用由大到小依次为:头花杜鹃、川滇柳、灌间草本、金露梅,其中头花杜鹃对灌下草本植物影响较大,凋落叶化感作用是影响该地区灌草系统群落分布及灌草结构的重要因素.

为探明刈割与施肥影响河西地区豆禾混播草地稳定性的生态学机理,本研究以'清水'紫花苜蓿(Medicago sati-va)、无芒雀麦(Bromus inermis)和长穗偃麦草(Elytrigia elongata)建植的混播草地为对象,设置3个留茬高度(5 cm(A1),8 cm(A2)和 11 cm(A3))和6个施肥处理(CK(B1),150 kg P2O5·hm-2(B2),75 kg N·hm-2+225 kg P2O5·hm-2(B.),150 kg N·hm-2+150 kg P2O5·hm-2(B4),150 kg N·hm-2(B5),225 kg N·hm-2+75 kgP2O5·hm-2(B6)),并对各草种的生态位特征进行了分析.结果表明:相较于留茬高度,牧草重要值对施肥的响应更敏感,然而提高留茬可增加无芒雀麦重要值并控制过高的紫花苜蓿重要值,其中A2B3处理效果最好;A1可增大各牧草生态位宽度,且均在第3茬的A1B4处理最大;紫花苜蓿与无芒雀麦、紫花苜蓿与长穗偃麦草、无芒雀麦与长穗偃麦草间的生态位重叠分别在第2茬的A2B6,A2B1和A2Be处理最小.本研究认为:留茬8 cm,施150 kg N·hm-2+150 kg P2O5·hm-2氮磷肥对实现河西地区豆禾混播草地物种和谐共存及群落结构的长期稳定具有良好效果.

Scientific and rational modes of grazing utilization and fertilization management are important agronomic measures to maintain the production performance and community structure stability of legume-grass mixtures. The study aimed to explore the regulation and control mechanisms of grazing and fertilization on the production performance and community structure stability of perennial legume-grass mixtures, and to preliminarily determine the optimal mode of grazing utilization and fertilization management for legume-grass mixtures. In the Hexi Corridor area, a 4-year-old mixed grassland with Medicago sativa ‘Qingshui’, Bromus inermis, and Elytrigia elongata (at 1∶1∶1) were used as the study objects. The L16 (31×42) mixed level orthogonal experimental design was used with three heights prior to mowing: 20 cm (S1), 30 cm (S2), and 40 cm (S3); four mowing intensities: 2 cm (E1), 5 cm (E2), 8 cm (E3), and 11 cm (E4); four nitrogen application rates: 0 kg(N)∙hm−2 (N1), 75 kg(N)∙hm−2 (N2), 150 kg(N)∙hm−2 (N3), and 225 kg(N)∙hm−2 (N4); and the impacts of artificial mowing to simulate grazing utilization combined with nitrogen application on the community structure and production performance of mixed grassland were monitored and analyzed. The study showed that the height prior to mowing and the amount of nitrogen added had a greater impact on the production performance of mixed grasslands. The total biomass of grassland under the S3E2N4 treatment was the highest (17 707.80 kg∙hm−2), the crude protein content of mixed forage under the S1E1N4 treatment was the highest (15.46%), and the relative feeding value of mixed forage under the S3E1N3 treatment was the highest (184.93). Additionally, reducing the mowing intensity could increase utilization times and the proportion of gramineous forages in the community. Among them, the coverage ratios of leguminous forages and Gramineae grasses under the treatments S2E3N4, S1E3N3, S1E4N1, S2E4N3, and S1E1N1 were close to 1∶1 after simulated grazing utilization, and the treatments S2E3N4, S3E3N1 and S3E4N2 had the best effect on the number of forage branches. Furthermore, compared with the hay harvested by conventional mowing (cutting three times a year in the area), simulated grazing reduced the forage yield but greatly improved the nutritional value of the forage and could effectively inhibit the excessive growth of M. sativa ‘Qingshui’ in the community. At the same time, it maintained the stability of the legume-grass mixture community structure. In conclusion, when the management measures were as follows: the height prior to mowing was 30 cm, mowing intensity was 8 cm, and nitrogen application rate was 225 kg(N)∙hm−2 (S2E3N4), the stability of community structure and composition balance of mixed grassland were the best. In addition, mixed grassland also had good production performance (total biomass of grassland reached 15 173.41 kg∙hm−2; crude protein content of mixed forage reached 13.92%; relative feed value of mixed forage reached 156.93) under the S2E3N4 treatments. This management measure is a suitable reference for grazing utilization and fertilization management of mixed grasslands composed of M. sativa, B. inermis, and E. elongata, and may be popularized and applied in the Hexi Corridor and other similar regions. It can provide a scientific basis and technical support for optimizing the production and utilization of local legume-grass mixtures.

以酒泉盐碱地芨芨草(Achnatherum splendens)草丛为研究对象,选取冠幅相近、生长状况良好、大小适中的芨芨草草丛,对每株芨芨草草丛按4个垂直方位,每个方位按5个距离梯度(草丛中心、距草丛中心20、40、60、100 cm)设置样点,每个样点按5个土层深度(0～10,10～20,20～30,30～40,40～60 cm)进行土壤取样和分析.结果表明,芨芨草中土壤养分呈现如下的空间分布特征:(1)土壤有机质、全氮、全磷、碱解氮、速效磷、速效钾的含量随离草丛中心距离的减少而增加,随土层深度的增加而减少,土壤养分主要富集于草丛下,而且表层土壤更加明显.(2)与草丛外土壤相比,草丛内土壤含水量较高、pH值较低,对盐碱地恶劣的土壤环境治理恢复有重要作用.

为探究荒漠草原灌木欧李(Cerasus humilis)根系内生细菌固氮能力和其它特性.采用无氮培养基,从欧李根内分离获得20株内生固氮菌,并结合乙炔还原法测定固氮酶活性,钼锑抗比色法测定溶磷特性,Salkowski法测定分泌植物生长素(Indole acetic acid,IAA)能力,对筛选出固氮酶活性较高的菌株进行16S rDNA序列比对,确定其分类地位.结果表明,分离的内生固氮细菌均具溶磷和分泌IA A能力.所分离菌株固氮酶活性在31.45～424.81 nmol C2 H4·h-1·mL-1之间(NS 25最高),解有机磷量在26.62～99.18μg·mL-1之间(YNS 4最高),溶无机磷量在1.10～20.31μg·mL-1之间(WNS 21最高),分泌IAA量在3.86～47.00μg·mL-1之间(NS 22最高).10株固氮酶活性较高菌株经初步鉴定NS114-1和NS114-2为Bacillus pumilus,NS 25和NS 26为Bacillus parali-cheniformis,YNS 1为Brevibacterium frigoritolerans,菌株WNS 21和NNS 15为Bacillus velezensis,NS 8为Paenibacillus catalpae,YNS 6为Cytobacillus firmus,NNS 19为Bacillus sp..研究分离的内生固氮细菌具有溶磷和分泌IA A的能力,有望通过后续研制微生物菌剂为干旱地区植被恢复与生态重建发挥积极作用.

为探明多年生不同混播组合草地退化后的群落稳定性和可持续性,本研究以祁连山金强河地区22年前建植的6种混播草地为研究对象,对草地群落结构及地下芽库构成进行调查分析.结果表明:4组分混播草地能够较好的保留建植种的地下芽,且以建植种分蘖芽为主,而3组分混播草地地下芽主要由侵入种的分蘖芽、根茎芽、根颈芽和根蘖芽构成,建植种芽密度占比较低;分蘖芽密度与建植种植物盖度、密度和地上生物量正相关,根茎芽、根颈芽、根蘖芽密度与侵入种植物盖度、密度和地上生物量正相关.其中,混播组合"冷地早熟禾(Poacrymophila)+多叶老芒麦(Elymus sibiricus)+无芒雀麦(Bromus inermis)+扁穗冰草(Agropgyroncristatum)"草地地下芽结构最优,可适当延长混播草地使用年限,是适宜青藏高原高寒地区的混播草种组合.

刈割和施肥是豆禾混播草地生产过程中极为重要的田间管理措施,合理的留茬高度和氮磷配施模式可以有效提高混播草地的生产性能。为探究不同留茬高度和施肥模式对多年生豆禾混播草地产量与品质的影响,在河西走廊地区以紫花苜蓿、无芒雀麦和长穗偃麦草1∶1∶1建植的第3年豆禾混播草地为试验对象,利用裂区试验设计,以留茬高度为主区,设置5 cm（A 1 ）、8 cm（A 2 ）、11 cm（A 3 ）3个留茬高度,施肥模式为副区,设置不施肥CK（B 1 ）、单施磷肥:150 kg P 2 O 5 ·hm -2 （B 2 ）、低氮高磷:75 kg N·hm -2 +225 kg P 2 O 5 ·hm -2 （B 3 ）、氮磷平衡:150 kg N·hm -2 +150 kg P 2 O 5 ·hm -2 （B 4 ）、单施氮肥:150 kg N·hm -2 （B 5 ）、高氮低磷:225 kg N·hm -2 +75 kg P 2 O 5 ·hm -2 （B 6 ）6个施肥模式,在混播草地中豆科牧草初花期进行刈割,施肥方式为第1茬刈割后追施。结果表明:以A 3 B 3 (11 cm留茬高度和75 kg N·hm -2 +225 kg P 2 O 5 ·hm -2 的施肥模式)处理组合全年产量最高(19626 kg·hm -2 );A 2 B 2 (8 cm留茬高度和150 kg P 2 O 5 ·hm -2 的施肥模式)处理组合全年产量最低(14342 kg·hm -2 )。提高留茬高度会在一定程度上降低紫花苜蓿整体品质,提高禾本科牧草整体品质。增施氮肥的同时减施磷肥可有效提高牧草粗蛋白含量和相对饲用价值（RFV）,施用量过高会使牧草粗蛋白含量和相对饲用价值下降,最合理的氮磷配施模式为150 kg N·hm -2 +150 kg P 2 O 5 ·hm -2 。综合产量和品质的结果来看,适当的磷肥施用量可以显著提高牧草营养品质。利用TOPSIS综合评价模型对混播草地产量及各混播组分营养品质进行整体评价后得出:8 cm的留茬高度以及施150 kg N·hm -2 +150 kg P 2 O 5 ·hm -2 的氮磷为适宜在河西走廊地区紫花苜蓿+无芒雀麦+长穗偃麦草混播草地利用的留茬高度与施肥模式的组合。

在河西走廊绿洲边缘区,以紫花苜蓿(Medicago sativa)、红豆草(Onobrychis viciifolia)、无芒雀麦(Bromus inermis)、长穗偃麦草(Elytrigia elongata)组成的5种混播草地为对象,研究不同组合对多年生豆禾混播草地生产性能的影响.结果表明:1)豆禾混播不同程度提高了草地牧草产量,其中"紫花苜蓿+无芒雀麦+长穗偃麦草"混播组合的产量最高,与其他混播及单播相比,建植第1年产量提高了4.8％～92.5％,第2年提高了7.9％～134.9％,第3年提高了11.0％～313.6％.2)所有组合的混播草地土地当量比均大于1,其中"紫花苜蓿+无芒雀麦+长穗偃麦草"组合的土地当量比最高,且随建植年限的增加而提高,并趋于稳定.3)豆禾混播不同程度提高了牧草粗蛋白、粗脂肪、粗灰分和半纤维的含量与单位面积可消化营养物质产量,"紫花苜蓿+无芒雀麦+长穗偃麦草"组合的品质在所有混播组合中最优.4)通过TOPSIS模型对各处理的产量和品质的各项指标综合评价显示,"紫花苜蓿+无芒雀麦+长穗偃麦草"组合与理想混播组合的贴合度最高,是适合在河西走廊荒漠绿洲区推广种植的多年生豆禾混播草地组合.

As an endemic fruit tree in China, the Chinese dwarf cherry (Cerasus humilis (Bge.) Sok.) has substantial ecological and economic value. In 2018, characteristic symptoms of the crown gall of the Chinese dwarf cherry were observed in a nursery base located in Ningxia Hui Autonomous Region, China. The occurrence of the disease among seedlings was observed to be 9.48%. Diseased plants were collected and brought to the laboratory for the isolation of the pathogens. In this study, the isolates were identified by a combination of morphological, biochemical, pathogenicity-related, as well as molecular methods. The isolated strains were white, circular, domed, and glistening. Using 16S rRNA gene sequence analysis and biochemical tests, five strains were identified as Agrobacterium tumefaciens/ biovar 1. Polymerase chain reaction (PCR) was used to detect pathogenicity-associated genes in isolates through the amplification of the partial nucleotide sequences of tms2, virD2 and ipt genes, which proved that the isolates contained the Ti plasmid. In the pathogenicity assay, the crown gall symptom developed on the young stem of tomato and sunflower after inoculation. Based on its morphological, biochemical, pathogenicity and genetic characteristics, the pathogen of the Chinese dwarf cherry crown gall was identified to be A. tumefaciens/ biovar 1.