The effects of pesticides on the diversity of culturable soil bacteria

The numbers of culturable soil bacteria in plots that had received either no pesticides or the full combination (aldicarb, chlorfenvinphos, benomyl, glyphosate, plus chlorotoluron or triadimefon) over a 20 year period were compared. Differences were very small although there were consistently higher numbers on the treated plot, possibly reflecting the greater crop yields which had been reported previously. There was no significant difference in numbers of bacterial colonies with homology to a nif gene probe in soils from the two plots. Genetic fingerprinting of Pseudomonas fluorescens isolates from the plots, using ERIC-PCR, showed that the dominant strains in the two populations were not the same although there was no obvious difference in the degree of diversity. Substrate utilization by microbial populations from the two plots was compared using Biolog plates. The population from the pesticide-treated plot showed a higher rate of substrate utilization which could reflect a slightly higher inoculum of heterotrophic bacteria, but could also indicate greater metabolic diversity in the population.     

三峡库区岸坡消落带草地、弃耕地和耕地土壤微生物及酶活性特征

为研究不同用地方式对三峡库区消落带土壤性质的影响,选取三峡库区重庆忠县汝溪河流域典型消落带为研究区域,研究不同用地类型(草地、弃耕地、耕地)、不同土层间(0—10 cm、10—20 cm)土壤微生物、土壤酶活性和土壤化学性质的各自特征及其相互关系,旨在为该地区消落带生态恢复实践提供理论依据。研究发现:除蛋白酶活性、全磷含量、碱解氮含量外,不同用地类型对土壤各生化特性均产生了显著影响;与之不同,土层仅对细菌数量、放线菌数量、真菌数量、蔗糖酶活性、脲酶活性以及土壤有机质含量产生显著影响,但对其他生化性质影响不显著;用地类型与土层两者的交互作用仅对蔗糖酶活性影响显著。同时,弃耕地土壤的细菌数量在3种用地类型中最高;真菌、放线菌数量在草地中最高,耕地次之,弃耕地最低。弃耕地中的过氧化氢酶、蔗糖酶、蛋白酶和脲酶活性与其他两种用地类型相比较高,而耕地中磷酸酶活性则显著高于弃耕地和草地土壤。草地土壤全氮、有效磷以及速效钾含量均显著低于耕地,而草地0—20 cm土层的有机质含量却显著高于弃耕地和耕地;3种用地类型的全磷、全钾、碱解氮含量差异均不显著,弃耕地的pH值显著高于另外两种用地类型。另一方面,三峡库区消落带土壤的各生化指标间存在一定的相关性。pH值和微生物数量及酶活性间的关系最为密切,土壤真菌和放线菌数量与土壤有机质含量呈极显著正相关。研究结果表明,与弃耕地和耕地相比,草地在稳定消落带土壤环境、固持土壤营养元素、提高土壤肥力方面作用更为显著;相对而言,耕地的土壤微生态环境较差,故在消落带实施退耕还草、恢复草本植被等具有重要意义。     

氮沉降对杉木人工林土壤有机碳矿化和土壤酶活性的影响

为探讨氮沉降对亚热带森林土壤有机碳矿化及土壤酶活性的影响规律,在杉木人工林中开展了野外模拟N沉降试验。试验设计为4种处理,分别为N0（对照）、N1（60 kg N?hm-2?a-1）、N2（120 kg N?hm-2?a-1）和N3（240 kg N?hm-2?a-1）,每处理重复3次。通过28 d的培养后发现,各土层有机碳日均矿化量随培养时间的延长呈下降趋势,而有机碳累计矿化量则逐步增加。不同氮沉降处理下各土层有机碳累计矿化量总体趋势表现为：随着氮沉降量的增加而降低,日均矿化量降低幅度以N1最大,其次是N0和N2,N3降幅最小。相同N沉降处理下,参与土壤碳循环的6种主要酶（蔗糖酶、纤维素酶、淀粉酶、β-葡糖苷酶、多酚氧化酶、过氧化物酶）活性、土壤有机碳日均矿化量和有机碳累计矿化量均随土层加深而降低。氮沉降对6种土壤酶活性的影响存在差异,对纤维素酶和多酚氧化酶具有促进作用,而对淀粉酶和过氧化物酶表现出一定的抑制作用;中-低氮沉降（N1、N2）对蔗糖酶无影响,而对β-葡糖苷酶具有促进作用,高氮沉降（N3）促进了蔗糖酶活性,但抑制了β-葡糖苷酶活性。表层土壤中,土壤有机碳累积矿化量与土壤纤维素酶、β-葡糖苷酶、过氧化物酶活性呈显著正相关。因此,氮沉降促进了表层土壤纤维素酶、多酚氧化酶和蔗糖酶的活性,但在一定程度上抑制了淀粉酶和过氧化物酶,对土壤有机碳矿化也表现出明显的抑制作用。     

生物覆盖对杨树人工林根际土壤微生物、酶活性及林木生长的影响

研究了不同覆盖材料和不同覆盖量对杨树人工林根际微生物和酶活性动态变化及杨树生长的影响.结果表明：采用4种材料对杨树林地表进行覆盖后,其根际细菌和真菌数量均高于对照,其中白茅和白栎的效果最佳,分别为对照的3.56和2.43倍.随覆盖量的增加,细菌、真菌数量增多,7.5 kg·m^-2处理的细菌平均数量分别比对照高49.58％,真菌数量是对照的6.14倍.生物覆盖后,细菌和真菌数量的年变化趋势相似,均与土壤温度的变化同步,且7月最大,12月最小.脲酶和磷酸酶的活性也随着覆盖量的增加而增强.不同覆盖材料间,脲酶、磷酸酶活性变化均为马桑＞蕨类＞白茅＞白栎＞CK.根际土壤脲酶和磷酸酶活性的年动态变化与细菌与真菌的年变化相似,且7月最高,12月最低.生物覆盖对杨树的树高、胸径和生物量具有显著的促进作用.     

Meloidogyne incognita Infested Soil Amended With Chicken Litter

The effects of chicken litter on Meloidogyne incognita in cotton, Gossypium hirsutum cv. DPL50 were determined in field microplots. Litters (manure and pine-shaving bedding) from a research facility and a commercial broiler house were used. Treatments consisted of 0.25%, 0.5%, and 1% litter by dry weight of soil for each kind of litter. Three control treatments consisted of soil not amended with litter, with and without nematodes, and one treatment to which mineral fertilizer was added at a nitrogen rate equivalent to that of the 0.5% litter rate, with nematodes. Microplots were inoculated at planting with 900 eggs/100 cm³ soil in 1993 and 1,000 eggs/100 cm³ soil in 1994. At 92 and 184 days after planting, nematode population densities decreased linearly with increasing rates of litter. Nematode numbers at midseason were larger in plots treated with mineral fertilizer than in plots treated with a rate of litter equivalent to the 0.5% rate. Fungal and bacterial population densities fluctuated throughout the growing season. Bacterial numbers had a positive linear relationship, with increasing rates of litter only in October 1993; however, significant positive relationships were observed throughout the 1994 growing season. In 1994, nematode population density at 92 days after planting decreased linearly with increasing bacterial numbers 30 days after planting. No other significant relationships between nematode densities and microbial densities were observed. Fungi and bacteria isolated from the litter and litter-amended soil were identified. Fungal genera isolated included Acremonium, Aspergillus, Eurotium, Paecilomyces, Petriella, and Scopulariopsis, whereas bacteria genera included Arthrobacter, Bacillus, and Pseudomonus.     

Effects of moisture on soil microorganisms and nematodes: A field experiment

The effects of soil moisture changes on bacteria, fungi, protozoa, and nematodes and changes in oxygen consumption were studied in a field experiment. In one plot the soil was drip-irrigated daily for 10 days, while an adjacent plot experienced one rainfall and was then allowed to dry out. Oxygen consumption was the parameter measured which responded most rapidly to changes in soil moisture content. Lengths of fluorescein diacetate-active hyphae paralleled oxygen consumption in both plots. Total hyphal length was not affected by one rainfall but increased from 700 mg^–1 dry weight soil to more than 1,600 m in less than 10 days in the irrigated plot. In the rain plot, bacterial numbers doubled within 3 days and declined during the following period of drought. In the irrigated plot, numbers increased by 50% and then remained constant over the duration of the study. Only small changes in protozoan numbers were observed, with the exception of the last sampling date in the irrigated plot when large numbers of naked amoebae were recorded 2 days after a large natural rainfall. Nematode numbers, especially obligate root feeders, increased in both treatments. The increases were caused by decoiling rather than growth. The results indicate that fungal respiration was dominating, while bacteria, lacking a suitable source of energy, were less active, except for the first days.     

大气CO2浓度增高对麦田土壤硝化和反硝化细菌的影响

硝化和反硝化细菌是土壤中与氮转化有关的微生物菌群 ,大气CO2 浓度升高可能对它们的数量产生影响。位于中国无锡的稻 麦轮作农田生态系统FACE平台 2 0 0 1年 6月开始运行。本试验在 2 0 0 3年小麦生长季研究了土壤 (0～ 5cm和 5～ 10cm土层 )中硝化和反硝化细菌在大气CO2 浓度升高条件下的变化。试验采用最大可能法 (MPN)计这两种微生物菌群的数量。结果表明 ,0～ 5cm土层硝化菌数拔节期和成熟期FACE低于对照 ,而孕穗期FACE高于对照 ,5～ 10cm土层硝化菌数越冬期与成熟期FACE低于对照 ,大气CO2 浓度升高使得麦田土壤硝化细菌数目减少。 0～ 5cm土层各个生长期反硝化菌数FACE与对照均没有明显差异 ,5～ 10cm土层反硝化菌数拔节期FACE低于对照 ,大气CO2 浓度升高对麦田土壤反硝化菌的影响不大。     

Fungal and bacterial growth in soil with plant materials of different C/N ratios

Fungal (acetate-in-ergosterol incorporation) and bacterial (leucine/thymidine incorporation) growth resulting from alfalfa (C/N=15) and barley straw (C/N=75) addition was studied in soil microcosms for 64 days. Nitrogen amendments were used to compensate for the C/N difference between the substrates. Fungal growth increased to a maximum after 3–7 days, at five to eight times the controls, following the addition of straw, and three to four times the controls following the addition of alfalfa. After 20–30 days, the fungal growth rate converged with the controls, resulting in a cumulative fungal growth two to three times the controls following straw addition and about 20% higher than the controls following alfalfa addition. The bacterial growth rate reached rates five times the controls following alfalfa addition and twice that of the controls following straw addition after 3–7 days. It remained elevated after 64 days. The cumulative bacterial growth was two and four times the controls following straw and alfalfa addition, respectively. A negative correlation was found between N addition and bacterial growth, while N stimulated fungal growth. Thus, the C/N ratio of the additions (substrate and extra N) could not entirely explain the different results regarding fungal and bacterial growths. Respiration was not always related to the combined growth of the microorganisms, emphasizing the requirement for a better understanding of growth efficiencies of fungi and bacteria.     

Long-term effect of mineral fertilizers and amendments on microbial dynamics in an alfisol of Western Himalayas

The microbial dynamics expressed in terms of culturable microbial populations i.e. bacteria, fungi, actinomycetes and Azotobacter were measured after 33 years of continuous application of mineral fertilizers and amendments to an acid alfisol. The bacterial, fungal and Azotobacter populations were maximum in plots treated with mineral fertilizers and FYM (100%NPK+FYM) while actinomycetes population was maximum in mineral fertilizes and lime treated plots (100%NPK+Lime). The bacterial population decreased and fungal population increased with increasing levels of NPK i.e. from 50% to 150%NPK. Bacillus species of bacteria and Gliocladium, Aspergillus and Rhizopus species of fungi were the main dominating culturable microorganisms in all the treatments. The FYM and lime amended plots sustained crop productivity and microbial populations at higher levels than rest of the mineral fertilizer treatments. The nitrogenous fertilizers alone had the most deleterious effect on crop productivity and the biological soil environment.     

转Bt基因抗虫棉根际微生物区系和细菌生理群多样性的变化

在大田栽培条件下 ,以转 Bt基因抗虫棉 GK-12和常规棉花泗棉 3号作为材料 ,在棉花不同发育时期 ,于 2 0 0 1和 2 0 0 2连续两年测定棉花根际土壤细菌、放线菌和真菌数量的变化 ,并在 2 0 0 2年棉花的花铃期和吐絮期对根际细菌生理群的数量和多样性进行了分析 ,结果表明 :虽然不同年份和生育期棉花根际微生物数量存在差异 ,但是 ,年度间和相同的发育时期棉花根际微生物的数量变化趋势一致。在棉花的苗期和吐絮期 ,转 Bt基因抗虫棉根际微生物的数量与对照差异不显著 ;在棉花的花铃期 ,转 Bt基因抗虫棉根际细菌的数量比对照增加 ,放线菌的数量差异不显著 ,而真菌的数量变化没有规律。在棉花发育的花铃期和吐絮期 ,Bt棉根际细菌生理群的总数量比常规棉增加 ,但是根际细菌生理群的 Simpson指数、Shannon-Wiener指数和细菌生理群分布的均匀度下降     

Initial decay of woody fragments in soil is influenced by size, vertical position, nitrogen availability and soil origin

Fast-growing bacteria and fungi are expected to cause the initial stage of decomposition of woody fragments in and on soils, i.e. the respiration of sugars, organic acids, pectin and easily accessible cellulose and hemi-cellulose. However, little is known about the factors regulating initial wood decomposition. We examined the effect of wood fragment size, vertical position, nitrogen addition and soil origin on initial wood decay and on the relative importance of fungi and bacteria therein. Two fractions of birch wood were used in microcosm experiments, namely wood blocks (dimensions: 3 × 0.5 × 0.5 cm) and sawdust (dimensions: 0.5–2 mm). The woody fragments were enclosed in nylon bags and placed on top of- or buried in an abandoned arable soil and in a heathland soil. After 15, 25 and 40 weeks of incubation, fungal biomass was quantified (as ergosterol and chitin content) and bacterial numbers were determined. The results indicated that initial wood decay was mostly caused by fungi; bacteria were only contributing in sawdust in/on abandoned arable soil. Larger fragment size, burial of fragments and nitrogen addition positively influenced fungal biomass and activity. Fungal biomass and decay activities were much lower in woody fragments incubated in/on heathland soil than in those incubated in/on abandoned arable soil, indicating that soil origin is also an important factor determining initial wood decay.     

The influence of sampling strategies and spatial variation on the detected soil bacterial communities under three different land-use types

To determine the influence of pooling strategies on detected soil bacterial communities, we sampled 45 soil cores each from a eucalypt woodland, a sown pasture and a revegetated site in an Australian landscape. We assessed the spatial variation within each land-use plot, including the influence of sampling distance, soil chemical characteristics and, where appropriate, proximity to trees on the soil bacterial community, by generating terminal restriction fragment length polymorphism profiles of the bacterial 16S rRNA genes. The soil bacterial community under the revegetated site was more similar to the original woodland than the pasture, and this result was found regardless of the soil- or the DNA-pooling strategy used. Analyzing as few as eight cores per plot was sufficient to detect significant differences between the bacterial communities under the different plots to be distinguished. Soil pH was found to be most strongly associated with soil bacterial community composition within the plots and there was no association found with proximity to trees. This study has investigated sampling strategies for further research into the transitions of soil microbial communities with land-use change across broader temporal and spatial scales.     

机场草坪植被调控对土壤细菌群落结构与功能的影响

为了探究植被调控对土壤细菌群落结构和功能的影响,对天津滨海国际机场草地植被进行单一草坪植物建植和高强度刈割,在调控后第3年的春、夏、秋季节取调控区土壤样本,利用16S rRNA基因高通量测序和PICRUSt软件,分析了不同植被调控方式下土壤细菌组成、多样性及季节性变化,预测细菌功能特征。结果表明,各样地共有的优势菌门（相对丰度>5%）有变形菌门（Proteobacteria）、放线菌门（Actinobacteria）、酸杆菌门（Acidobacteria）、芽单胞菌门（Gemmatimonadetes）和绿弯菌门（Chloroflexi）。与对照区相比,刈割调控区土壤放线菌门相对丰度显著增加;单一草坪建植调控区,夏季土壤芽单胞菌门相对丰度显著增加（P<0.05）。刈割调控、高羊茅及黑麦草调控区,土壤细菌门之间相关性较对照分别减弱21.4%、46.4%和67.9%,使细菌网络结构更为简单。夏季和秋季3个调控区土壤细菌群落的Shannon指数和Chao1指数显著高于对照区,而秋季Simpson指数显著低于对照区（P<0.05）。KEGG代谢途径差异分析可知,刈割调控、高羊茅和黑麦草调控区,土壤细菌分别有25、24和23个代谢通路的功能基因丰度显著低于对照区,主要体现在聚糖的生物合成与代谢、细胞运动、细胞生长与死亡、核苷酸代谢等通路上。可见,机场植被调控改变了土壤细菌群落的组成,简化了细菌网络结构,代谢功能也明显下降。     

不同填闲模式对黄瓜根际土壤酶活性及细菌群落的影响

以温室连作3年黄瓜土壤为研究对象,以黄瓜为主栽作物,以青葱、小麦、油菜为不同季节填闲作物设置盆栽试验,采用常规化学方法、PCR-DGGE及qPCR技术,研究不同填闲模式对黄瓜土壤酶活性及细菌群落的影响.结果表明: 随着种植茬次的增加,填闲小麦处理的土壤脲酶、中性磷酸酶及转化酶活性均显著高于填闲青葱和油菜处理,同时油菜处理显著高于青葱处理;不同填闲模式间黄瓜根际土壤细菌群落结构不同,冬季填闲青葱和夏季填闲小麦处理维持了相对较高的多样性指数.qPCR检测结果表明: 随着种植茬次的增加,小麦处理的土壤细菌数量显著高于青葱和油菜处理.综上,不同填闲模式对土壤酶活性和细菌群落均产生一定影响,改变了土壤环境,其中夏季填闲小麦能保持相对较高的土壤酶活性、土壤细菌群落结构多样性及细菌数量.
     

不同种植年限香榧根际土壤微生物多样性

为探明不同种植年限对香榧根际土壤微生物群落特征的影响,采用高通量测序技术,分析种植5 a、10 a和15 a香榧根际土壤细菌、真菌的群落结构和多样性特征.结果表明: 在种植15 a的香榧土壤中细菌Chao1指数、ACE指数和Shannon指数显著降低,Simpson指数无显著变化.NMDS分析显示,种植年限对细菌群落结构变化有显著影响,而种植5 a和10 a香榧林地土壤具有相似的细菌群落.细菌相对丰度、多样性以及群落结构(基本上由变形菌、放线菌、酸杆菌和绿弯菌组成)的变化与有机质、C/N、全氮呈极显著相关.香榧根际土壤真菌Chao1指数和ACE指数随种植年限的增加显著降低,Shannon指数和Simpson指数在种植10 a香榧林地中较高.真菌NMDS分析显示,相同种植年限土壤真菌群落聚在一起,不同种植年限之间能明显分开.真菌优势菌群主要包括子囊菌门、担子菌门、接合菌门.有机质是影响真菌丰富度、多样性和群落结构变化的主要因子.综上,香榧根际土壤微生物群落随种植年限不同而发生明显变化,种植年限、C/N、土壤全氮和有机质含量是影响香榧根际土壤微生物群落结构的主要因子.     

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.     

超高产夏玉米田土壤微生物与土壤酶的动态变化

为揭示超高产夏玉米田（产量>15 000 kg·hm^-2）土壤微生物与土壤酶活性动态变化特性,在国家玉米工程技术研究中心（山东）试验场进行夏玉米生长季农田土壤微生物与土壤酶活性研究. 在连续3年产量15 000 kg·hm^-2以上的超高产夏玉米田中选择一块超高产田（HF, 产量为20 322 kg·hm^-2）与常规生产田（CF, 产量为8920.1 kg·hm^-2）进行对比分析,主要测定0～20 cm土层土壤细菌、真菌与放线菌数量及脲酶和转化酶活性. 结果表明：播种后超高产田与常规生产田土壤微生物（细菌、真菌与放线菌）数量均表现出先升高后下降的趋势,超高产田在玉米生长后期土壤微生物数量低于常规生产田,细菌与放线菌表现尤其明显,收获期超高产田B/F值（细菌与真菌数量比）比播种期高2.03倍,比常规生产田高3.02倍,常规生产田收获期与播种期的B/F值变化不显著;超高产田土壤脲酶活性在播种31 d（拔节期）后低于常规生产田,转化酶活性播种58 d（开花期）后快速下降,低于常规生产田.     

Estimation of abundance dynamics of gram-negative bacteria in soil

Bacterial succession in soil was studied for two variants of initiation (moistening and moistening with addition of glucose). To determine the numbers of viable gram-negative bacteria, the modified nalidixic acid method was applied. The numbers of gram-negative bacteria revealed by this method were 2 to 3.5 times higher than those determined by the traditional method. In a developing community, the highest total bacterial numbers were observed on day 7; afterwards their numbers decreased and stabilized at a level exceeding four-to fivefold the initial one. In both experimental variants, the highest numbers of viable gram-negative bacteria were revealed on day 15 (75–85% of the total bacterial numbers). Morphology of these bacteria suggests their classification as cytophagas (chitinophagas) utilizing chitin from the dead fungal mycelium.     

Comparison of temperature effects on soil respiration and bacterial and fungal growth rates

Temperature is an important factor regulating microbial activity and shaping the soil microbial community. Little is known, however, on how temperature affects the most important groups of the soil microorganisms, the bacteria and the fungi, in situ. We have therefore measured the instantaneous total activity (respiration rate), bacterial activity (growth rate as thymidine incorporation rate) and fungal activity (growth rate as acetate-in-ergosterol incorporation rate) in soil at different temperatures (0-45 degrees C). Two soils were compared: one was an agricultural soil low in organic matter and with high pH, and the other was a forest humus soil with high organic matter content and low pH. Fungal and bacterial growth rates had optimum temperatures around 25-30 degrees C, while at higher temperatures lower values were found. This decrease was more drastic for fungi than for bacteria, resulting in an increase in the ratio of bacterial to fungal growth rate at higher temperatures. A tendency towards the opposite effect was observed at low temperatures, indicating that fungi were more adapted to low-temperature conditions than bacteria. The temperature dependence of all three activities was well modelled by the square root (Ratkowsky) model below the optimum temperature for fungal and bacterial growth. The respiration rate increased over almost the whole temperature range, showing the highest value at around 45 degrees C. Thus, at temperatures above 30 degrees C there was an uncoupling between the instantaneous respiration rate and bacterial and fungal activity. At these high temperatures, the respiration rate closely followed the Arrhenius temperature relationship.