亚热带森林土壤微生物生物量及群落功能特征的城乡梯度变化

土壤微生物在土壤养分循环以及生物地球化学循环中起着重要作用,土壤微生物对环境变化响应灵敏.为研究城乡梯度环境变化对亚热带森林土壤微生物的影响,本研究选取合肥市大蜀山国家森林公园(城市林)、紫蓬山国家森林公园(远郊林)、六安市万佛山(乡村自然林)为样地,分析比较其微生物生物量碳(MBC)、微生物生物量氮(MBN)及微生物...     

Orchard floor management practices that maintain vegetative or biomass groundcover stimulate soil microbial activity and alter soil microbial community composition

Groundcover management systems (GMS) are important in managing fruit-tree orchards because of their effects on soil conditions, nutrient availability, tree growth and yields. We employed a polyphasic approach, incorporating measures of soil microbial abundance, activity and community composition, to study the long-term effects of different GMS on biotic and abiotic factors in an orchard soil. Four GMS treatments – Pre-emergence residual herbicides (Pre-H), post-emergence herbicide (Post-H), mowed-sod (Grass), and hardwood bark mulch (Mulch) – were established in 2-m-wide strips within tree rows in an apple orchard in 1992, and have been maintained and monitored annually until the present. We have measured soil water and nutrient availability, tree growth, and yields annually from 1993 to 2003. Soil nematode numbers and trophic groups were evaluated in July and Oct. 2001, and Sept. 2003. Numbers of culturable bacteria and fungi, soil respiratory activity, eubacterial and fungal community composition were determined in May and Sept. 2003. The Pre-H treatment soil had the fewest culturable bacteria, while the Grass treatment had the largest population of culturable fungi. Soil nematode population size and diversity were also affected by GMS treatments; the Pre-H treatment had the lowest ratio of (bacteriovores + fungivores) to plant parasitic nematodes. Soil respiration rates were higher in the Mulch than in other treatments during a 40-day incubation period. Hierarchical cluster dendrograms of denaturing gradient gel electrophoresis (DGGE) fingerprints for eubacterial community 16S rRNA genes indicated that Post-H and Grass treatments clustered together and separately from the Pre-H and Mulch treatments, which were also grouped together. The influence of GMSs on the fungal community, as assessed by PCR-DGGE of the internal transcribed spacer (ITS) region, was not as pronounced as that observed for bacteria. Soil fungal community composition under the Mulch differed from that under other treatments. The effects of GMS on soil microbial community abundance, activity, and composition were associated with observed differences in soil organic matter inputs and turnover, nutrient availability, and apple tree growth and yields under the different GMS treatments.     

施用控释氮肥对稻田土壤微生物生物量碳、氮的影响

借助农业部望城红壤水稻土生态环境野外观测试验站的控释氮肥试验,研究了施用控释氮肥对水稻不同生育期间稻田土壤微生物生物量碳、氮动态变化的影响。试验共设5个处理:①CK,(不施氮肥);②Urea(施用尿素);③CRNF(施用与处理②等氮量的控释氮肥);④70%CRNF(施用控释氮肥,用氮量为处理②的70%);⑤50%CRNF+M(施用控释氮肥和猪粪,总氮量为处理②的70%,其中控释氮肥用量为处理②的50%,猪粪含氮量为处理②的20%)。结果表明,施肥后10 d,施氮处理土壤微生物生物量碳和氮均达最高,随生育进程推进逐渐下降,成熟期有一定的回升;施肥初期,施用等氮量的控释氮肥处理(CRNF)土壤微生物量碳、氮含量较尿素处理(Urea)分别增加5.4%和22.5%,而水稻生育中后期,控释氮肥处理(CRNF)土壤微生物量碳、氮含量较尿素处理(Urea)下降幅度大,该处理向地上部提供氮素营养较尿素处理高;施氮量较高的CRNF处理,土壤微生物生物量碳低于控释氮肥节氮处理(70%CRNF),但在大多数取样时期,土壤微生物量氮高于控释氮肥节氮处理(70%CRNF);控释氮肥配施有机肥的节氮处理较其他单施化肥处理显著增加土壤微生物生物量碳、氮含量。控释氮肥与有机肥配施,不仅能节约氮肥用量,而且能明显地提高土壤微生物生物量碳、氮的含量。     

天台山七子花群落下土壤微生物生物量的季节动态

研究天台山七子花群落下土壤微生物生物量的季节变化规律及生态特性。根据实测数据分别对根际、根围微生物生物量碳、氮与土壤环境因子之间进行相关性分析,并建立了土壤微生物指标与环境因素之间的回归方程,以此为基础对天台山七子花群落下土壤微生物生物量的季节变化进行预测。回归分析表明：土壤温度、水分对微生物生物量的影响大于土壤pH值对微生物生物量的影响,而且土壤温度、水分对微生物生物量氮的影响大于对微生物生物量碳的影响。土壤温度对微生物生物量碳、氮的影响最大。     

Contrasting effects of extracts from invasive Reynoutria japonica on soil microbial biomass,activity, and community structure

Invasive plants may modify soil properties through the release of phenolic compounds. The effects of phenolics produced by a noxious invader, Reynoutria japonica, on soil microorganisms have rarely been studied in experimental conditions. We performed a laboratory experiment to assess the influence of extracts from R. japonica on soil microbial activity, biomass, and community structure. Two types of extracts (shoots and rhizomes) were added in four concentrations (control—no extract, low—extract diluted 100 times, medium—extract diluted ten times, and high—undiluted extract) to soil collected under native plant species. Concentrations of 12 phenolic compounds, namely catechin, chlorogenic acid, emodin, epicatechin, hyperoside, quercetin, physcion, piceatannol, polydatin, procyanidin B3, resveratrol, and resveratroloside were analyzed in the extract and soil. We measured the activity of five enzymes, namely acid and alkaline phosphatases, β-glucosidase, phenoloxidase, peroxidase, the activity of bacteria on Biolog Ecoplates, as well as the biomass of bacteria, saprotrophic fungi, arbuscular mycorrhizal fungi (AMF), and microbial community structure using phospholipid (PLFA) and neutral (NLFA) fatty acid analysis. Many microbial parameters, namely phosphatase activities, total microbial, AMF, and G?+?bacterial biomass, were reduced following the addition of extracts. This was likely related to phenolics as concentrations of these compounds in soil increased with the concentration of extract added. In contrast, saprotrophic fungi and G- bacteria were largely positively affected by extract addition. Shoot and rhizome extracts had relatively similar effects on the soil properties. The changes in soil biota caused by R. japonica invasion may have implications for restoration of invaded areas.

     

DNA extraction method affects microbial community profiles from soils and sediment

To evaluate whether different deoxyribonucleic acid (DNA) extraction procedures can affect estimates of bacterial community composition, based on the 16S ribosomal ribonucleic acid gene denaturing gradient gel electrophoresis (DGGE) profiles, we compared four in situ lysis procedures using three soils and one marine sediment. Analysis of DGGE profiles, generated by polymerase chain reaction of purified DNA extracts, demonstrated that the choice of DNA extraction method significantly influenced the bacterial community profiles generated. This was reflected both in the number of bands or ribotypes detected from each sample and in subsequent principle coordinate analysis and unweighted-pair group method using arithmetic average analyses. The methods also differed significantly in their robustness, i.e. reproducibility across multiple analyses. Two methods, both based on bead beating, were demonstrated to be suitable for comparative studies of a range of soil and sediment types. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Periodic carbon flushing to roots of Quercus rubra saplings affects soil respiration and rhizosphere microbial biomass

Patterns of root/shoot carbon allocation within plants have been studied at length. The extent, however, to which patterns of carbon allocation from shoots to roots affect the timing and quantity of organic carbon release from roots to soil is not known. We employed a novel approach to study how natural short-term variation in the allocation of carbon to roots may affect rhizosphere soil biology. Taking advantage of the semi-determinate phenology of young northern red oak (Quercus rubra L.), we examined how pulsed delivery of carbon from shoots to roots affected dynamics of soil respiration as well as microbial biomass and net nitrogen mineralization in the rhizosphere. Young Q. rubra exhibit (1) clear switches in the amount of carbon allocated below-ground that are non-destructively detected simply by observing pulsed shoot growth above-ground, and (2) multiple switches in internal carbon allocation during a single growing season, ensuring our ability to detect short-term effects of plant carbon allocation on rhizosphere biology separate from longer-term seasonal effects. In both potted oaks and oaks rooted in soil, soil respiration varied inversely with shoot flush stage through several oak shoot flushes. In addition, upon destructive harvest of potted oaks, microbial biomass in the rhizosphere of saplings with actively flushing shoots was lower than microbial biomass in the rhizosphere of saplings with shoots that were not flushing. Given that plants have evolved with their roots in contact with soil microbes, known species-specific carbon allocation patterns within plants may provide insight into interactions among roots, symbionts, and free-living microbes in the dynamic soil arena.     

Mineralization of C and N from microbial biomass in paddy soil

Summary Soil samples of paddy fields with different fertilizer managements in Yamaguchi Agricultural Experiment Station, Japan were used to investigate the contribution of microbial biomass to the pool of mobile plant nutrients in paddy soil. The quantities of nutrients mobilized in soils which had been fumigated or dried were closely related to the quantities available in freshly killed biomass. A K_N-factor (28 days) of 0.24 for the proportion of total N mineralized from dead biomass in paddy soils was obtained. It was observed that the C to N ratio mineralized from freshly killed biomass by chloroform fumigation of paddy soils was nearly 10 under aerobic conditions. For an approximate calculation of biomass C from the flush-N by chloroform fumigation of paddy soils, the equations of (B=33 Fn, 10 days) and (B=26 Fn, 28 days) were indicated. In oven-dried (70°C, 24 h) and rewetted soils, about 66% of N was mineralized from the freshly killed biomass during 28 days of incubation and the remaining 34% was derived from non-biomass organic matter of paddy soils.     

冻融循环对金川泥炭沼泽土壤微生物量及群落结构的影响

冻融作用显著改变土壤微生物活性及碳氮循环过程。以长白山金川泥炭沼泽0-15 cm和15-30 cm土壤为研究对象,进行室内冻融交替模拟实验。实验设置两个冻融幅度（-10-10℃和-5-5℃）。经过0/1/3/5/7/15次冻融循环后,分别采用氯仿熏蒸法和磷脂脂肪酸法测定泥炭沼泽土壤微生物量及磷脂脂肪酸含量,并与未进行冻融处理的FTC （0）对比。实验结果表明：冻融作用对土壤微生物量碳、氮及微生物磷脂脂肪酸含量有显著影响（P<0.001）。15次冻融交替作用后,土壤微生物碳（MBC）含量均显著增加,土壤微生物量氮（MBN）含量显著降低。两种冻融模式下,各类型微生物磷脂脂肪酸含量均显著降低。冻融作用显著改变了泥炭沼泽土壤微生物群落结构。冻融作用降低了土壤真菌/细菌比值（-5-5℃,0-15 cm土壤除外）,增加了革兰氏阳性菌/革兰氏阴性菌比值。-5-5℃冻融作用下,各土壤微生物磷脂脂肪酸含量变幅大于-10-10℃,土壤MBC的变化则与其相反,在-10-10℃变化幅度更大。两种冻融幅度下MBC与大部分微生物群落在15-30 cm土壤的变幅更大,这说明冻融作用对不同深度土壤微生物量和微生物群落结构的影响存在差异。冻融次数对土壤微生物量和各类型磷脂脂肪酸含量有显著影响（P<0.01）。相关性分析结果表明多种微生物磷脂脂肪酸含量与MBN含量呈正相关关系（P<0.01）,与DOC含量呈负相关关系（P<0.05）。综上,冻结作用促进了微生物的死亡,为融化期微生物生存提供更多碳源与营养物质,改变了土壤微生物群落结构。冻融期间各类型微生物磷脂脂肪酸含量降低,可能会降低泥炭沼泽土壤碳汇能力。     

Litter fingerprint on microbial biomass,activity, and community structure in the underlying soil

Aims

Little is known about how plant leaf litter decomposing on the soil surface is affecting microbial communities in the underlying soil. Here we examined the effects of decomposing leaf litter of different initial chemistry on biomass, stoichiometry, community structure and activity of microorganisms in the soil underneath the decaying litter layer.

Methods

Leaf litter from six different neotropical tree species with contrasted quality decomposed on top of a common tropical soil in a laboratory microcosm experiment over 98 days. At the end of the experiment we determined microbial biomass C, N, and P, microbial community structure (PLFA), and community level physiological profiles (CLPP) from the top soil.

Results

Despite growing in a common soil substrate, soil microorganisms were strongly affected by litter species, especially by the soluble litter fraction. While litters with low soluble C content did not affect the soil microbial community, litters with high soluble C content led to an increase of microbial biomass and to a structural shift to relatively more Gram-negative bacteria. Changing community structure resulted in changes of catabolic capacity of microorganisms to metabolize a range of different C substrates. The large differences in leachate N and P among litter species, in contrast, had no effect on soil microbial parameters.

Conclusions

Our data suggest that plant litter decomposing on the soil surface exhibit a strong and predictable leachate C-control over microbial community biomass, structure and function in the underlying soil.

     

Broad-scale analysis of soil microbial community DNA from Upland grasslands

We have applied a broad-scale approach to the analysis of DNA extracted from soils which support characteristic grasslands at an upland site in the UK. To test for the degree of coherence between microbial and vascular communities, grasslands were characterised as improved, semi-improved, or unimproved, according to the degree of management they had received and consequent botanical composition. Microbial DNA was extracted directly from the grassland soils and analysed by three techniques: (i) thermal denaturation, which profiles the guanine and cytosine (G÷C) base distribution within the community; (ii) cross hybridisation of the DNA which measures the degree of similarity between the samples; (iii) measurement of reassociation kinetics of denatured DNA, which provides a measure of the complexity of the DNA. Thermal denaturation revealed significant differences in the %G+C composition of the communities. DNA from the improved soil had the highest median %G+C value, whilst that from the unimproved soil had the lowest. The relative distribution of G+C bases also differed significantly between the samples from the three grasslands. Cross hybridisation of DNA from the different soils also indicated significant differences in the degree of similarity between the DNA from the grasslands, with unimproved showing 59% similarity to improved. Indices from the cross hybridisation assay suggested that, in terms of complexity, the samples ranked unimproved > semi-improved > improved. Reassociation kinetics supported this conclusion, but the rates of reassociation were such that less than 40% reassociation occurred over a 31-day period, thus preventing calculation of C _o t_1/2.     

Winter climate change affects growing‐season soil microbial biomass and activity in northern hardwood forests

Understanding the responses of terrestrial ecosystems to global change remains a major challenge of ecological research. We exploited a natural elevation gradient in a northern hardwood forest to determine how reductions in snow accumulation, expected with climate change, directly affect dynamics of soil winter frost, and indirectly soil microbial biomass and activity during the growing season. Soils from lower elevation plots, which accumulated less snow and experienced more soil temperature variability during the winter (and likely more freeze/thaw events), had less extractable inorganic nitrogen (N), lower rates of microbial N production via potential net N mineralization and nitrification, and higher potential microbial respiration during the growing season. Potential nitrate production rates during the growing season were particularly sensitive to changes in winter snow pack accumulation and winter soil temperature variability, especially in spring. Effects of elevation and winter conditions on N transformation rates differed from those on potential microbial respiration, suggesting that N‐related processes might respond differently to winter climate change in northern hardwood forests than C‐related processes.     

A note on the formation of microbial polysaccharide from wheat straw decomposed in the absence of soil

C hapman , S.J. & L ynch , J.M. 1984. A note on the formation of microbial polysaccharide from wheat straw decomposed in the absence of soil. Journal of Applied Bacteriology 56 , 337–342.
The proportions of neutral sugars in fresh and decomposed wheat straw polysaccharide were similar, irrespective of the oxygen concentration used during breakdown. Polysaccharide extracted by hot water from the decomposed straw was composed mainly of galactose, glucose and mannose with smaller quantities of arabinose, xylose, rhamnose, fucose and ribose. The presence of these sugars indicates a mainly microbial origin for the polysaccharide but with some soluble hemi-cellulose breakdown products. The polysaccharide precipitable with 70% (v/v) ethanol accounted for 0.5% (w/w) of the degraded straw. The extracted polysaccharide was shown to increase the aggregate stability of Mount St Helens volcanic ash.     

暖温带森林土壤微生物量、群落结构和活性对植物地下碳源的响应

该研究以典型的亚热带—温带过渡区森林为对象,采用野外过程监测和控制试验相结合的方法,利用磷脂脂肪酸和土壤胞外酶活性分别表征土壤微生物群落结构和活性,并结合微环境因子,重点探究土壤微生物生物量、群落结构和活性对植物地下碳输入的响应特征。结果表明：在观测周期内,处理均能显著降低三组年龄段林分的土壤微生物量碳,其变化幅度在－8.72％~－5.72％之间,其中在80年的林分中降幅最大,而在160年的林分中降幅最小;微生物量氮的变化规律与相应的微生物量碳的变化规律相似,但与对照相比其差异性均未达到显著性水平;另外,经壕沟处理2~4个月后,所有林分的土壤微生物量碳和氮与对照相比出现增加的现象。处理均能对三组年龄段林分的土壤微生物群落结构产生不同程度的影响,其中40年林分的土壤微生物群落对处理的响应程度要高于另外两个年龄段的林分;与对照相比,壕沟处理样方的腐生真菌的相对丰富度均下降明显,其中在40年和80年林分中的下降幅度达到显著水平,而细菌、放线菌和丛枝菌根真菌均无明显变化;壕沟处理样方的水解酶(β-葡萄糖苷酶和N-乙酰-葡萄糖苷酶)活性均显著下降,而氧化酶(酚氧化酶和过氧化物酶)活性的变化相对较小,除80年的林分外,其余林分均不显著。此外,处理均不能显著影响土壤的含水量和温度。该研究结果为初步阐明全球气候变化背景下森林土壤微生物结构及其功能的变化特征以及更加精确预测未来森林土壤碳的变化趋势提供了科学依据。     

有机无机缓释复合肥对土壤微生物量碳、氮和群落结构的影响

研究缓释复合肥不同用量对土壤微生物量碳、氮和群落结构多样性的影响,在农业生产上广泛应用缓释复合肥有着重要意义。试验采用室内长期恒温培养和磷脂脂肪酸法,以化肥和普通复合肥适量施用养分量为对比,研究缓释复合肥适量、高量和超高量施肥水平对土壤微生物PLFA含量的影响规律。结果表明,SRF1、SRF2、SRF3(缓释复合肥适量、高量和超高量)较CK(不施肥)和CF1(化肥适量)显著增加土壤微生物量碳,且较CK、CF1和CCF1(普通复合肥适量)显著增加土壤微生物量氮。土壤微生物量碳、氮随着缓释复合肥施肥水平的增加而增加,但没有随着施肥水平的倍量增加而倍量增加,且SRF2和SRF3无显著差异。缓释复合肥(SRF1、SRF2和SRF3)较CK、CF1和CCF1增加土壤PLFA的种类和含量,且总PLFA含量增加7.4%—26.7%、17.6%—38.7%和12.8%—33.0%,3个施肥水平以SRF2作用效果最好,总PLFA含量最高,分别较SRF1和较SRF3高16.4%和17.9%。土壤细菌、放线菌、革兰氏阳性菌和革兰氏阴性菌PLFA含量以SRF1和SRF2显著高于CF1和CCF1。主成分分析和聚类分析显示施肥处理分布较多PLFA的优势种群,SRF3与SRF1和SRF2的PLFA结构差别较大。综上认为,适量施肥水平以缓释复合肥较化肥和普通复合肥对土壤微生物的作用显著,其中缓释复合肥3个施肥水平以高量施肥水平作用最好。     

Tree species influences soil microbial community diversity but not biomass in a karst forest in southwestern China

中国西南喀斯特森林树种对土壤微生物群落多样性和生物量的影响陆地生态系统中植物种对土壤微生物群落结构的影响不一,而喀斯特生态系统中植物种对土壤微生物群落结构影响的研究尚未见报道。本研究利用磷酸脂肪酸(PLFA)法,分析了黔中高原型喀斯特常绿落叶阔叶混交林5个优势树种—窄叶石栎(Lithocarpus confinis Huang)、圆果化香(Platycarya longipes Wu)、滇鼠刺(Itea yunnanensis Franch.)、安顺润楠(Machilus cavaleriei H. Lév.)、云贵鹅耳枥(Carpinus pubescens Burkill)—与土壤理化性质对土壤微生物群落组成和生物量的影响。在测试的212个土壤样品 中共检测出132种PLFA,每个样品土壤微生物平均PLFA数量和生物量分别为65.97和11.22 µg g^–1。土壤表层(0–10 cm)的土壤微生物PLFA数量与下层(10–20 cm)土壤接近,但前者土壤微生物生物量显著高于后者(P < 0.05)。树种影响土壤微生物PLFA数量,但对土壤微生物生物量没有影响。云贵鹅耳枥附近的土壤微生物PLFA数量显著高于其他树种(P < 0.05),而其他树种土壤微生物PLFA数量接近。土壤微生物 生物量与表层土壤的理化性质无显著相关,但与下层土壤的有机碳、全氮和全磷含量呈显著正相关 (P < 0.05)。总之,黔中高原型喀斯特森林真菌/细菌生物量比率低,微生物总生物量低,但微生物群落多样性高。树种对土壤微生物群落多样性产生影响。