The effect of microorganisms and sorption on the protease activity of plant roots

The protease activity of sterile roots of wheat was zero or very low, so that the determined values did not exceed limits of the experimental error. Roots colonized by microorganisms had a significant protease activity. The activity of protease on seeds and roots of the plants growing in a medium inoculated with the soil microflora was higher than in cases when only the epiphytic microflora of seeds served as a source of microorganisms. Sterile roots inoculated with three different strains of bacteria isolated from the rhizosphere and producing protease exhibited a considerable protease activity. The protease activity of non-sterile roots of plants growing in the dark was higher than that of plants growing under normal illumination. Crystalline proteinase was adsorbed on sterile roots and the activity of the enzyme was decreased in this adsorbed state. The adsorption of the enzyme was only slightly higher in the presence of calcium ions. Treatment of roots with a sodum chloride solution, with dextran and ethanol increased the adsorption of the proteinase by roots.     

The relationship between rhizosphere nitrification and nitrogen-use efficiency in rice plants

Two different rice cultivars, Yangdao 6 [Indica rice cultivar with high nitrogen-use efficiency (NUE)] and Nongken 57 (Japonica rice cultivar with low NUE) were used to study the relationship between NUE and nitrification activity in the rice seedling rhizosphere soil using a rhizobox with three compartments, and a soil-slicing method. The roots of both rice cultivars developed aerenchyma tissue [expressed as percentage porosity of root (POR)], but Yangdao 6 showed better development than Nongken 57. This root morphology change results in more radial oxygen loss (ROL) into the rhizosphere. Leaf glutamine synthetase activity (GSA) and nitrate (NO3-) reductase activity (NRA) of Yangdao 6 were significantly higher than those of Nongken 57, while there was no significant difference in root NRA between the cultivars. The nitrification activities were maximal in rhizosphere soil, followed by those in the bulk soil and the root surface for both cultivars. The rhizosphere nitrification activity, NO3- concentration and abundance of ammonia-oxidizing bacteria (AOB) associated with Yangdao 6 were always higher than those of Nongken 57. Therefore, we conclude that the greater N uptake by Yangdao 6 when compared to Nongken 57 can be mainly attributed to the bigger capacity for nitrification in Yangdao 6.     

杨树人工林品种更替连作与非更替连作根际效应的比较

采用空间位移法对杨树人工林更替连作和非更替连作两种经营模式下土壤养分、土壤酶活性和土壤微生物的根际效应进行了比较研究,以期探明不同连作经营模式对杨树人工林土壤生态环境的影响,探讨品种更替对杨树人工林地力维持的生态效果。研究结果表明,更替连作和非更替连作均导致杨树人工林土壤发生不同程度的衰退,非更替连作导致的林地土壤衰退现象更为严重。杨树根际和非根际土壤养分在非更替连作中下降最为显著,土壤有机质的根际效应显著大于更替连作,而土壤速效N、P、K的根际效应在更替连作中显著增大。非更替连作导致根际和非根际土壤中过氧化氢酶、脲酶和碱性磷酸酶活性发生较大幅度的下降,而多酚氧化酶和过氧化物酶活性较大幅度的上升;更替连作也导致土壤酶活性有类似的变化趋势,但下降(上升)幅度远小于非更替连作,土壤酶活性的根际效应总体呈现非更替连作变化幅度强于品种更替连作的趋势。两种连作模式下土壤中可培养土壤微生物的数量变化大致呈现一致趋势,连作将导致根际和非根际土壤微生物数量整体下降,其中土壤细菌比例有所降低,真菌比例上升,土壤呈现从细菌型向真菌型转化的特点,非更替连作对土壤微生物的根际效应明显大于更替连作。更替连作和非更替连作根际效应的差异可能由不同杨树品种根系分泌物的差异所导致。     

Populations of Aerobic Bacteria Associated with the Roots of Apple and Cherry Plants

S ummary . The incidence of bacteria on the surface of apple and cherry roots was compared over a period of 20 months with those in rhizosphere and root-free soils. Seasonal variation in total and in Gram negative bacterial populations in soils and on roots was essentially similar. The highest numbers occurred between November and March and the lowest in September. Little general stimulation of bacteria near roots was detected and, on occasion, negative values were recorded for rhizosphere effect. The results indicated that edaphic factors rather than root activity had the major influence on population levels. Fluorescent pseudomonads were low in number and this suggests either that fruit tree roots were unable to support large numbers of these bacteria or that colonization from the soil populations was irregular. However, in contrast to other bacteria, there was a marked stimulatory effect on fluorescent pseudomonads, particularly in apple rhizo-spheres where a maximum rhizosphere/soil ratio of 131 was recorded.     

荒漠草原区土壤粒径组成对柠条根际土壤微生物数量及酶活性的影响

柠条(Caragana korshinskii)是荒漠草原区主要的造林绿化树种,研究其根际土壤微生物和酶活性与不同土壤类型土壤粒径组成的关系有重要意义,然而土壤粒径对荒漠草原柠条根际土壤微生物数量和酶活性的影响知之甚少,探讨土壤颗粒组分与微生物数量、土壤酶活性之间的关系,以及土壤颗粒组成对荒漠草原区固沙灌木植物柠条根际土壤微生物数量及酶活性的影响,可为揭示荒漠草原土壤退化及生态修复提供参考。以宁夏荒漠草原区土壤粒径组成差异显著的灰钙土、红黏土、风沙土环境下栽植的柠条为研究对象,研究不同土壤颗粒组成对根际土壤微生物数量及酶活性的相互关系与影响。结果表明:土壤微生物的数量表现为细菌放线菌真菌。根际土壤中的细菌、真菌数量显著高于非根际,且在3种不同类型的土壤中随着细砂粒的增多,真菌和放线菌数量逐渐降低,而细菌数量呈先增大后减小的趋势;根际与非根际土壤的蔗糖酶、碱性磷酸酶及过氧化氢酶活性均呈现出灰钙土红黏土风沙土的趋势,红黏土根际土壤中的脲酶活性显著高于灰钙土与风沙土;除过氧化氢酶外,土壤酶活性表现为根际高于非根际,在3种不同类型的土壤中随着细砂含量的增加,土壤酶活性均呈递减趋势。土壤颗粒组成与微生物数量之间没有明显的相关性,而与土壤酶活性之间显著相关,土壤酶活性与黏粒、粉粒呈正相关,与细砂、中砂呈负相关关系,根际土壤中酶活性更高,能够为植物及微生物提供更多的营养。     

麦棉套作棉花根际非根际土壤微生物和土壤养分

在麦棉套作栽培模式下,设置不隔根、纱网隔根和塑膜隔根3种麦棉套种方式,研究麦棉套作对棉花根际和非根际土壤微生物数量、活性和土壤养分（全氮、有效磷和速效钾）含量的影响,结果表明：麦棉套作有利于棉花根际与非根际土壤细菌的增殖,盛蕾期不隔根处理棉花根际土壤与非根际土壤细菌数量分别是塑膜隔根处理的2.57和2.81倍.但麦棉套作不利于土壤真菌和放线菌的增殖.细菌在土壤微生物区系中占99.9%.所以,麦棉套作显著提高了棉花土壤微生物数量,同时也增强了微生物活性.麦棉共处期纱网隔根处理棉花土壤全氮、有效磷、速效钾含量显著高于不隔根处理和塑膜隔根处理,证明麦棉套作系统中小麦根系分泌物与脱落物的存在对棉花土壤养分含量的增加有明显的促进作用,即存在种间营养补偿效应.而共处期不隔根处理套作棉土壤养分含量总体上显著低于隔根处理的现象则反映出小麦根系对棉花土壤养分的竞争作用大于其对棉花土壤养分的促进作用.小麦收获后,小麦根系对棉花养分的竞争作用解除,不隔根处理棉花土壤养分含量显著高于塑膜隔根和纱网隔根处理.     

Huge increase in bacterivores on freshly killed barley roots

Abstract Adding fresh roots to intact soil cores resulted in marked increases in microbial and microfaunal activity at the resource islands. Microbial activity increased in two phases following root addition. Respiratory activity and concentration of respiratory enzyme (dehydrogenase) in soil adhering to the roots was very high during the first three weeks resulting in anaerobic conditions in the soil. After a period of low respiratory activity and enzyme content, these quantities increased from 6 to 20 weeks, but not enough to maintain anaerobic conditions. Numbers of protozoa peaked earlier than the nematodes. Based on yield coefficients of microbes and bacterivores, the increase in bacterivores was in accordance with root-induced respiration activity. In soil adhering to roots, numbers of bacterial grazers (protozoa and nematodes) were up to 80 and 30 times higher, respectively, than in the surrounding soil. This effect is up to 20 times higher than observed around live root systems, which may suggest that the rhizosphere effect on microbivores could for the major part result from the decomposition of dead segments of the root system.     

Biochemical weathering of calcium-bearing minerals by rhizosphere micro-organisms,and its influence on calcium accumulation in trees

Summary The rhizosphere microflora of redcedar was found to have a higher percentage of calcium silicate-solubilizing rhizosphere bacteria than the rhizosphere microflora of white pine of similar age growing in the same locality under identical conditions. Though the species composition of the silicatesolubilizing microbial population varied considerably from winter to spring, the redcedar roots had more silicate-solubilizers than the white pine roots inboth seasons. Since redcedar is known to have a higher calcium content than white pine, these results indicate that calcium accumulation by redcedar and white pine is strongly influenced by the rate at which calcium is released from soil minerals by the weathering action of the trees' rhizosphere micro-organisms. A symbiotic relationship between the trees and the microflora is suggested.     

丛枝菌根化翅果油树幼苗根际土壤微环境

以我国二级濒危保护植物翅果油(Elaeagnus mollis)为供试植物, 通过温室盆栽试验, 研究接种丛枝菌根真菌对翅果油树幼苗根际土壤微生态环境的影响。试验设计分4个组: 摩西球囊霉(Glomus mosseae)单独接种组(GM)、脆无梗囊霉(Acaulospora delicata)单独接种组(AD)、混合接种组(GM + AD)、不接种的对照组(CK)。测定了菌根侵染率、生物量、根际微生物数量、土壤pH值、土壤酶活性及其对N、P营养的影响等指标。结果显示: 菌根真菌对3个接种组均有侵染, 其中, GM + AD的侵染率最大(90.5%), 生态学效应最好; 与对照组相比, 接种组的生物量均明显提高(p < 0.05), 其中GM + AD组生物量显著增加, 是CK组的2.2倍; AM菌根对根部微生物种群数量产生一定的影响, 主要是使根面上的细菌、放线菌、固氮菌的数量显著增加(p < 0.05); AM菌根使根际pH值降低, 与菌根侵染率呈显著负相关关系(p < 0.05); 接种组根际土壤磷酸酶、脲酶、蛋白酶的活性增加, 根际土壤的磷酸酶、蛋白酶的活性增加量与菌根侵染率呈极显著相关关系(p < 0.01); 接种组的根际土壤中, 可直接被植物吸收利用的N、P元素出现富集现象, 与菌根侵染率呈显著相关关系(p < 0.05)。研究表明: 丛枝菌根的形成改善了翅果油树幼苗的微生态环境, 提高了根际土壤肥力。     

BROWN ROOT ROT OF TOMATOES: II. THE FUNGAL FLORA OF THE RHIZOSPHERE

The fungal populations of soil and of the rhizosphere of tomatoes in steamed, fallowed and unsteamed plots were compared. Steaming greatly reduced the numbers of fungi in the soil, but fallowing had little effect. Soil bacteria were greatly reduced by steaming but increased to the level in the unsteamed plots after heavy watering. Outer rhizosphere fungal populations in unsteamed plots in July were larger than in the steamed plots, but by October this difference had disappeared, although roots in the unsteamed soil showed the greater development of disease.
Root surface counts indicated that the populations on actively growing roots in July in steamed and unsteamed plots reached similar levels, and there was a slight fall in numbers in both types of plot in October. Fungal infection of roots increased noticeably in unsteamed plots between July and October, although root surface numbers showed a decrease.
Of the fungal species isolated Colletotrichum atramentarium showed a distribution between soil and root surface which suggested that it was a root inhabiting fungus. Cephalosporium spp. were also found on the root surface and in roots, especially those from steamed soil.     

Numbers and locations of native bacteria on field-grown wheat roots quantified by fluorescence in situ hybridization (FISH)

Native bacteria, Pseudomonas and filamentous bacteria were quantified and localized on wheat roots grown in the field using fluorescence in situ hybridization (FISH). Seminal roots were sampled through the season from unploughed soil in a conservation farming system. Such soils are spatially heterogeneous, and many roots grow slowly through hard soil with cracks and pores containing dead roots remnant from previous crops. Root and rhizosphere morphology, and contact with soil particles were preserved, and autofluorescence was avoided by observing sections in the far-red with Cy5 and Cy5.5 fluorochromes. Spatial analyses showed that bacteria were embedded in a stable matrix (biofilm) within 11 microm of the root surface (range 2-30 microm) and were clustered on 40% of roots. Half the clusters co-located with axial grooves between epidermal cells, soil particles, cap cells or root hairs; the other half were not associated with visible features. Across all wheat roots, although variable, bacteria averaged 15.4 x 10(5) cells per mm(3) rhizosphere, and of these, Pseudomonas and filaments comprised 10% and 4%, respectively, with minor effects of sample time, and no effect of plant age. Root caps were most heavily colonized by bacteria along roots, and elongation zones least heavily colonized. Pseudomonas varied little with root development and were 17% of bacteria on the elongation zone. Filamentous bacteria were not found on the elongation zone. The most significant factor to rhizosphere populations along a wheat root, however, was contact with dead root remnants, where Pseudomonas were reduced but filaments increased to 57% of bacteria (P < 0.001). This corresponded with analyses of root remnants showing they were heavily colonized by bacteria, with 48% filaments (P < 0.001) and 1.4%Pseudomonas (P = 0.014). Efforts to manage rhizosphere bacteria for sustainable agricultural systems should continue to focus on root cap and mucilage chemistry, and remnant roots as sources of beneficial bacteria.     

The ability of plants to secrete proteases by roots.

The aim of our study was to find out if the culture medium of aseptically cultivated seedlings exhibits proteolytic activity and if this event is universal in angiospermous plants. Seedlings of 15 agricultural and wild-living plant species were cultivated for 14days without any addition of nutrients. Our studies showed that roots of higher plants could secrete proteases and that levels of proteolytic activity in the culture medium of individual species (and cultivars of the same species) could be significantly different. The differences between quantities of the secreted proteases were connected neither with the fresh weight of the growing seedlings nor with the surface of the root system. No proteins were required to induce secretion of proteases. The culture medium of a few studied species (Allium porrum, Zea mays, Helianthus annuus) showed the highest proteolytic activity at pH 7. Studies of the influence of standard protease inhibitors showed that examined proteases belong to the cysteine protease family. The results suggest that the apical parts of roots exuded proteases more intensively than mature parts. Our studies suggest that some plant species could develop a strategy to actively increase the level of free amino acids in the soil solution as a source of N. Our results may contribute to studying plant N nutrition in natural ecosystems and to increasing yield after organic fertilization of agricultural species.     

不同氮效率水稻生育后期根表和根际土壤硝化特征

通过田间试验研究了不同氮效率粳稻品种4007(氮高效)和Elio(氮低效)生育后期在N0(0 kgN hm-2)、N180(180 kgN hm-2)和N300(300 kgN hm-2)水平下根表、根际和土体土壤pH值、铵态氮(NH+4-N)和硝态氮(NO-3-N)含量、硝化强度和氨氧化细菌(AOB)数量.结果表明无论是齐穗期、灌浆期还是成熟期,根表土壤pH值均显著低于根际和土体土壤.土壤pH值范围在5.95至6.84之间变化.土壤NH+4-N含量随水稻生长显著下降,且随施氮量增加而显著增加.根表土壤NH+4-N有明显亏缺区,且随距水稻根表距离增加,NH+4-N含量逐渐升高.土壤NO-3-N含量随水稻生长显著增加,施氮处理均显著高于不施氮处理,但N180和N300处理差异不显著.NO-3-N含量表现为根际>土体>根表.水稻根表和根际土壤硝化强度随水稻生长显著下降,而土体土壤硝化强度随时间延长小幅增加.施氮显著提高4007水稻根表土壤在齐穗和收获期硝化强度以及Elio在齐穗期根际硝化强度,但在施氮处理N180和N300中无显著差异.在整个采样期间,土壤硝化强度均表现为根际>根表>土体.水稻根表和根际AOB数量随水稻生长而显著降低,而土体土壤AOB数量无显著变化.例如,根表土壤AOB数量在齐穗期、灌浆期和收获期分别为16.7×105、8.77×105个g-1 dry soil和8.01×105个g-1 dry soil.根表和根际土壤AOB数量无显著差异,但二者显著高于土体土壤AOB数量.就两个氮效率水稻品种而言,土壤pH值基本无差异.4007土壤NH+4-N含量均显著高于Elio.在齐穗期水稻根表、根际和土体土壤NO-3-N含量在N180水平下均表现为Elio显著高于4007.而在灌浆期和收获期,水稻根表、根际和土体土壤则表现为4007显著高于Elio.在所有采样期,两个水稻品种土体土壤硝化强度和AOB数量在3个施氮量下均无显著差异.Elio根表和根际土壤硝化强度和AOB数量在水稻灌浆期之前一直显著高于4007,而在灌浆期之后则显著低于4007,且最终产量和氮素利用率(NUE)显著低于4007,这可能是由于4007灌浆期后硝化作用强,根际产生的NO-3-N含量高,从而4007根吸收NO-3-N的量也高造成的.因此水稻灌浆期和收获期根表和根际硝化作用以及AOB与水稻高产及氮素高效利用密切相关.     

Metabolic Status of Bacteria and Fungi in the Rhizosphere of Ponderosa Pine Seedlings

We determined the quantity and metabolic status of bacteria and fungi in rhizosphere and nonrhizosphere soil from microcosms containing ponderosa pine seedlings. Rhizosphere soil was sampled adjacent to coarse, fine, or young roots. The biovolume and metabolic status of bacterial and fungal cells was determined microscopically and converted to total and active biomass values. Cells were considered active if they possessed the ability to reduce the artificial electron acceptor 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyltetrazolium chloride (INT) to visible intracellular deposits of INT formazan. A colorimetric assay of INT formazan production was also used to assess dehydrogenase activity. INT-active microorganisms made up 44 to 55% of the microbial biomass in the soils studied. The proportion of fungal biomass that exhibited INT-reducing activity (40 to 50%) was higher than previous estimates of the active proportion of soil fungi determined by using fluorescein diacetate. Comparison between soils from different root zones revealed that the highest total and INT-active fungal biomass was adjacent to fine mycorrhizal roots, whereas the highest total and active bacterial biomass was adjacent to the young growing root tips. These observations suggest that fungi are enhanced adjacent to the fine roots compared with the nonrhizosphere soil, whereas bacteria are more responsive than fungi to labile carbon inputs in the young root zone. Colorimetric dehydrogenase assays detected gross differences between bulk and rhizosphere soil activity but were unable to detect more subtle differences due to root types. Determination of total and INT-active biomass has increased our understanding of the role of spatial compartmentalization of bacteria and fungi in rhizosphere carbon flow.     

Control of Late Blight (Phytophthora capsici ) in Pepper Plant with a Compost Containing Multitude of Chitinase-producing Bacteria

Compost sustaining a multitude of chitinase-producing bacteria was evaluated in a greenhouse study as a soil amendment for the control of late blight (Phytophthora capsici L.) in pepper (Capsicum annuum L.). Microbial population and exogenous enzyme activity were measured in the rhizosphere and correlated to the growth and health of pepper plant. Rice straw was composted with and without a chitin source, after having been inoculated with an aliquot of coastal area soil containing a known titer of chitinase-producing bacteria. P. capsici inoculated plants cultivated in chitin compost-amended soil exhibited significantly higher root and shoot weights and lower root mortality than plants grown in pathogen-inoculated control compost. Chitinase and β-1,3-glucanase activities in rhizosphere of plants grown in chitin compost-amended soil were twice that seen in soil amended with control compost. Colony forming units of chitinase-producing bacteria isolated from rhizosphere of plants grown in chitin compost-amended soil were 10³ times as prevalent as bacteria in control compost. These results indicate that increasing the population of chitinase-producing bacteria and soil enzyme activities in rhizosphere by compost amendment could alleviate pathogenic effects of P. capsici.     

生姜根系不同生态位细菌群落多样性特征、组成及结构差异

生姜作为常见的调味品和传统中药材,是我国重要的经济作物之一。作为取食部分的生姜块茎与根系直接相连,其产量、品质与根相关细菌群落密切相关。然而,关于生姜根系微环境中细菌群落的特点仍鲜有报道,土壤环境能否衍生出宿主特异性内生菌群落尚不清楚。以生姜根系不同生态位细菌群落为研究对象,采用高通量测序技术,对非根际、根际及根内细菌进行16S rRNA基因测序。结果表明,不同生态位细菌群落多样性存在显著差异,其中非根际及根际细菌群落多样性(Shannon index, Observed species, Faith′s PD)显著高于内生菌群落。同时,各生态位共现网络稳定性和复杂度表现为非根际>根际>根内细菌群落。而在组成上,细菌群落在不同生态位差异显著(R²=0.57,P=0.001)。其中变形菌门(Proteobacteria)是根内的优势门,该门类下假单胞菌属(Pseudomonas)、短波单胞菌属(Brevundimonas)、寡养单胞菌属(Stenotrophomonas)及泛菌属(Pantoea)在根内显著富集。在根际细菌中,拟杆菌门(Bacteroid...     

Response characteristics of Scirpus trioueter and its rhizosphere to pyrene contaminated soils at different growth stages

Scirpus triqueter (Triangular club-rush), a typical wetland species, is used to study the response characteristics to pyrene. A pot experiment was conducted to investigate the growth parameters (height, diameter, shoot number, total volume, underground biomass, above-ground biomass and total biomass), and enzymes (catalase and superoxide dismutase) of S. triqueter. The characteristics of soil enzymes (catalase and polyphenol oxidase) and microorganisms (bacteria and fungi) were also assessed after pyrene treatment. Elevated pyrene concentration (80 mgkg(-1)) in the soil reduced the shoot number and biomass significantly, especially at the early growth stage. In root tissue, the enzyme catalase was activated at 80 mgkg(-1) of pyrene. Compared to roots, shoots had higher enzyme activities. Catalase activities in the rhizosphere increased throughout the growth period of S. triqueter. Polyphenol oxidase activities in the rhizosphere were higher than those in the bulk soil and unplanted soil. The populations of bacteria (total bacteria, pyrene-tolerant bacteria, and actinomyces) and fungi decreased under the stress of high pyrene concentration, while that of pyrene-tolerant bacteria increased with the increasing pyrene concentration. The presence of pyrene did not benefit the growth of S. triqueter. S. triqueter and soil enzymes varied within the growth stages. The presence of S. triqueter could improve the activity of soil enzymes and facilitate the propagation of microorganisms which could help eliminate pyrene contamination.     

西宁南山4种灌木根际和非根际土壤微生物、酶活性和养分特征

西宁南山区植被退化情况严重,人工造林植被恢复被看作是最有效的恢复手段,其中选择合适造林树种尤为关键。选择人工种植的唐古特白刺Nitraria tangutorum、柠条Caragana korshinskii、西北小蘗Berberis vernae和短叶锦鸡儿Caragana brevifolia共4种灌木树种造林试验区为研究对象,通过测定根际和非根际土壤微生物数量、酶活性及养分含量,综合比较种植4种灌木树种根际和非根际土壤肥力差异,科学评价其对土壤的改善效果。研究表明:(1)土壤微生物数量和酶活性总体呈现出根际高于非根际的规律,仅放线菌数量和脲酶活性出现了根际低于非根际现象。(2)土壤养分方面,4种灌木根际土壤和非根际土壤p H值、全N、全P、全K含量差异不显著,有机质、有效P、速效K含量均呈现出根际非根际,而碱解N则是根际非根际。(3)土壤酶活性与土壤微生物数量相关性不显著,土壤有机质含量与土壤细菌、真菌数量呈极显著正相关,有效P含量与土壤细菌、真菌和放线菌数量呈极显著正相关,速效K含量与过氧化氢酶、酸性磷酸酶活性呈显著正相关,全N、碱解N含量均与脲酶活性呈显著正相关。(4)从土壤肥力综合水平来看,根际非根际,其中根际土壤中西北小蘗柠条短叶锦鸡儿唐古特白刺,研究结果表明西北小蘗和柠条能大幅提高土壤肥力,改良土壤效果较好。     

Ryegrass enhancement of biodegradation in diesel-contaminated soil

A time-course pot experiment was conducted with ryegrass grown in soil experimentally contaminated with diesel oil. Relationships among plant growth variables, microbial activity and the dissipation rate of diesel oil over time were analyzed.Results indicate that ryegrass growth can lower the dissipation threshold. The residual rate of diesel oil in the rhizosphere was 55% lower than in the corresponding root-free soil, and the threshold reduction occurred after the development of plant roots. In the rhizosphere, the number of aerobic bacteria and the amount of soil dehydrogenase activity were higher than in the root-free soil and also showed a correlation with the growth of roots.The dissipation rate of diesel oil showed a correlation with soil dehydrogenase activity in both the rhizosphere and the root-free soil. A positive correlation was observed between the growth rate of roots and soil dehydrogenase activity in the rhizosphere. Moreover, the dissipation rate per dehydrogenase activity of the rhizosphere was higher than in the root-free soil. Ryegrass roots were determined, therefore, to be effective at enhancing the biodegradation of diesel-contaminated soil.     

青稞根腐病对根际土壤微生物及酶活性的影响

选取甘肃省卓尼县青稞种植区为研究地点,调查青稞根腐病的发病情况,并分别采集其健康植株和发病株根际的土壤,对比分析其土壤微生物生物量(碳、氮、磷)、微生物数量(细菌、真菌、放线菌)以及过氧化氢酶、蔗糖酶、脲酶、碱性磷酸酶、纤维素酶5种酶活性。结果发现,研究区10个采样点均有青稞根腐病的发生,发病率在5%—20%之间,不同地点发病率不同。根腐病的发生,会显著影响青稞根际微生物生物量,导致微生物生物量碳、氮、磷的含量发生变化,其中微生物生物量氮和磷含量整体降低,且不同采样点微生物量不同。土壤微生物数量总体呈现细菌放线菌真菌的趋势,但不同微生物对根腐病发病的响应不同,细菌和放线菌数量因根腐病的发生而减少,真菌的数量则增多;不同采样点土壤微生物数量不相同,细菌和真菌呈现区域性特征,放线菌的数量不呈现地域性。根腐病的发生还造成土壤酶活性的改变,其中蔗糖酶、脲酶、磷酸酶的含量因根腐病的发生而降低,而纤维素酶则升高,过氧化氢酶的变化没有规律。总而言之,根腐病的发生会使青稞根际土壤微生物组成发生改变,碳、氮、磷等物质代谢受到抑制,而能量代谢发生紊乱。因此,研究和防治青稞根腐病就必须重视土壤微生物及土壤酶的作用。