Specific features of bacterial communities in floodplain agrocenoses

The analysis of the taxonomic structure of the bacterial complexes in the alluvial soils of the Oka River valley allowed revealing the distinct differences in the spectrum of the bacterial dominants in the virgin and cultivated soils. Arthrobacter and pigment coryneform bacteria are shown to predominate in the virgin soil; bacilli and pseudomonades are common in the soil under vegetables. On cabbage leaves and carrot roots (both healthy and rotten), the spectrum of dominants is composed of two genera of enterobacteria: Pantoea and Erwinia. As a result of the plowing in of vegetables into the soil, enterobacteria accumulate; among them, phytopathogenic species are present. Within a year after this plowing in and the new yield, the enterobacteria practically disappeared, but myxobacteria and cytophages developed. Since these bacteria belong to the cellulose-destroying prokaryotes, the increase in their contents in the soil testified to their participation in the decomposition of the buried vegetable residues. Weeds are known to concentrate various bacterial forms in the phylloplane; they enter from different ecological niches: soil, water, meadow, and agricultural plants. Representatives of phytopathogenic bacteria as minor components were found on weeds.     

Specific features of soil temperature regimes in Georgia

Soil temperature regimes in Georgia are assessed on the basis of records of 60 meteorological stations within the period from 1947 to 1995. Heat exchange in the soil-air system, the effect of soil types and landforms on the temperature, and regularities of the temperature distribution pattern in the topsoil are discussed.     

The seasonal dynamics of yeast communities in the rhizosphere of soddy-podzolic soils

The annual dynamics of the number and taxonomic composition of yeast was studied in the rhizosphere of two plant species (Ajuga reptans L. and Taraxacum officinale Wigg.) in a forb-birch forest on soddy-podzolic soil. Eurybiont phyllobasidial cryptococci and red-pigmented phytobionts Rhodotorula glutinis were found to predominate in the phyllosphere of these plants, whereas the typical pedobionts Cryptococcus terricola and Cr. podzolicus occurred on the surface of roots and in the rhizosphere. The seasonal changes in the number and species composition of the yeast communities in the rhizosphere were more smooth as compared to those in the phyllosphere. In the period of active vegetation of the plants, the phytobiont yeasts develop over their whole surface, including the rhizoplane. Their number on the aboveground parts of the plants was significantly lower than that of the pedobiont forms. Thus, the above-and underground parts of the plants significantly differed in the composition of the dominant species of epiphytic yeasts.     

Specific features of soil formation in the taiga zone of Western Siberia

Specific features of soil formation in the taiga zone of Western Siberia are considered. The polygenetic nature of podzolic and gley-podzolic soils in the middle taiga zone, soddy-podzolic and soddy gley soils in the southern taiga zone, and meadow soils in the subtaiga zone is related to the pre-Holocene transformation of the lithogenic matrix upon activation of denudation and accumulation processes and the complicated Holocene evolution of these soils. A soil profile can be subdivided into separate layers according to the geomorphic features of the cryogenesis, the indices of interruption of soil formation, and the differences in the composition of the organic matter in the relict and modern humus horizons.     

Spatial heterogeneity in the metabolism and dynamics of isoproturon degrading microbial communities in soil

The characteristics of isoproturon [3-(4-isopropylphenyl)-1,1-dimethylurea] metabolism were investigated in soil taken from two transects within a single field. Along transect 1, complete degradation of the parent compound occurred within 18 days, and over 40% of ring C had been metabolised after 65 days. In these soils, both side chain and ring metabolism had a short lag phase, followed by a period of rapid degradation. Along transect 2, the rate of side chain metabolism was highly variable, and 20% of ring C had been metabolised after 65 days. The dynamics of isoproturon ring C metabolism were typical of cometabolic degradation, even at sites in which enhanced side chain metabolism occurred. Isoproturon degrading organisms were found in similar numbers in soil from the two transects prior to isoproturon application. In soils from transect 1, there was considerable proliferation of degrader organisms during the lag phase, in which 40% of the isoproturon was degraded. In most soils from transect 2, there had been no proliferation of isoproturon metabolising organisms at the point of 40% metabolism. Before enhanced degradation could develop, there was clearly a requirement for the isoproturon metabolising community to reach a threshold size. Immobilisation of isoproturon ring C into the microbial biomass and formation of bound residues was lower in soil from transect 2 relative to soil from transect 1. We conclude that the in-field spatial heterogeneity of isoproturon side chain and ring metabolism, the formation of bound residues and the immobilisation of pesticide residues in the biomass, results from variation in the development and significance of growth linked and cometabolic degradation.     

黄骅市土壤保持价值年内动态特征

掌握不同生态系统类型土壤侵蚀和土壤保持量的年内动态变化,对于区域水土保持重点及时序安排具有积极的指导作用。本研究在GIS支持下,运用通用土壤流失方程(USLE)对河北省黄骅市不同生态系统年内土壤侵蚀与保持量进行计算,并利用市场价值法、机会成本法对各生态系统类型年内各月的土壤保持价值进行测算,研究黄骅市土壤保持价值年内动态特征。研究表明,黄骅市全年各月土壤保持价值分配不均,年内动态特征与土壤保持量的季节动态变化规律一致,8月达到最大峰值,1—3月、10月、12月价值均为零,5—8月呈增加趋势,5—9月土壤保持价值占全年土壤保持价值的82.47%。从各生态系统类型来看,草地8月的单位面积土壤保持价值最大,为128.87元·hm?2;水域9月的单位价值最小,为11.23元·hm?2。从土壤保持价值构成来看,年内各土壤保持功能单位面积贡献价值大小排序为:减少土壤养肥流失价值减少淤泥淤积价值减少废弃土地价值。研究区各生态系统类型的土壤保持价值具有明显随季节变化的规律,在雨季受暴雨等短期大量降水的影响,土壤潜在的侵蚀量增大,而生态系统的土壤保持功能和价值在此过程得以发挥作用。     

地貌演替序列特征对土壤生物群动态的季节效应

Numerous studies have been devoted to the physical-chemical weathering processes leading to the creation of unique soil formations having their own history that induce soil-biotic diversity. However, the extent to which unique geomorphic formations influence soil biotic seasonal variation is not clear. Our aim was to define seasonal variations of soil biota in soils of different-aged terraces of the Makhtesh Ramon anticline erosional cirque in southern Israel. The strong effect of Makhtesh Ramon (Ramon Crater) erosional fluvial terrace age initiated by climatic changes during the Late Pleistocene–Early Holocene period on seasonal variations in both soil properties and the abundance and composition of soil biota were demonstrated. However, age dependence was not constant and values for observed soil properties and microbial activity were negligible between younger and older terraces for certain seasons, while free-living nematodes along with bacteria-feeding group were strongly dependent on the geomorphic features of the ages throughout the study period.     

Impact of organic amendments on the dynamics of soil microbial biomass and bacterial communities in cultivated land

In the course of a 1 year study on agricultural plots (mustard-beet) the impact of organic materials and soil management on soil microbial communities was assessed after amendment with three types of organic materials (sewage sludge, turkey manure and compost made of turkey manure and ligneous waste) and a mineral fertilizer. Transient impacts on potential metabolic activity, on genetic structure and on quantities of soil microorganisms, measured with three different methods (C_mic, total DNA content and CFU enumeration), were observed. The extent of these impacts depended on the composition of the amendment. The proportions of mineralisable carbon and lignin in organic materials seemed to influence the behaviour of the bacterial communities during the first 3 months after amendment. After a period of 6 months, no effect specific to the type of organic materials was detected. The dynamics of microbial biomass was assessed by both microbial carbon and by total DNA, but no correlation was found between the results; DNA seemed to be more sensitive to time-related variations in microbial biomass. Finally, although the bacterial functional and genetic structures were strongly modified between 3 and 6 months, this modification was not related to the type of amendment. This result suggests that organic amendments have less effect than seasonal variations or others anthropic factors such as the mechanical management of the soil.     

Temporal dynamics of soil nematode communities in a grassland plant diversity experiment

We report here on an 8-year study examining links between plant and nematode communities in a grassland plant diversity experiment, located in the north of Sweden on previous agricultural soil. The examined plots contained 1, 4 and 12 common grassland plant species from three functional groups; grasses, legumes and forbs. The same plant species composition was maintained in the plots through weeding and resowing during the experimental period. The hypotheses were (i) that the nematode community would shift towards a more diverse and mature fauna over time and (ii) that the effects of both plant species identity and plant species richness would increase over time. As hypothesized, the Bongers’ Maturity Index (a measure of nematode responses to disturbance) increased over time, but not nematode diversity. Instead, the nematode community development in the present grassland experiment seemed to be more characterized by shifts in dominance patterns than by colonization of new taxa. Clear temporal trends were found for plant-feeders and Adenophorea bacterial-feeders which increased in abundance over time in almost all plant treatments. Rhabditidae bacterial-feeders decreased in abundance over time, in particular in plots with legumes. Fungal-feeders, omnivores/predators and the two nematode indices PPI (Bongers’ Plant Parasitic Index) and NCR (Nematode Channel Ratio) had significant interactions between plant composition and time giving some support to our second hypothesis. Our results highlight the need for long-term experiments to examine plant species effects on soil fauna, especially on taxa belonging to higher trophic levels. The results also stress the importance of plant composition for belowground soil faunal communities.     

Structural and functional features of microbial communities in a soddy-podzolic soil under self-remediation conditions

The microbial component is one of the key factors responsible for soil fertility and soil quality. The sensitivities of some structural and functional parameters of soil microbial communities in soddy-podzolic soils under long-term self-remediation conditions were compared. The suitability of the parameters studied for quantifying the resilience of soil biota to agricultural intervention was studied.     

The effect of ditches, slope and peat thickness on the water regime of a forested gley soil

Abstract. The soil water regime was monitored at a forested experimental site in Cumbria, UK. Over an 83-week period following the clearfelling of 35-year-old Sitka spruce, soil water level measurements were related to total weekly rainfall in drainage treatment plots (10, 20 and 40 m ditch spacing) in three replicate blocks. Analysis showed a block × treatment interaction which might be related to soil differences between blocks. Significantly deeper soil water levels were measured in the most intensively drained plots of the two gently sloping blocks on a peaty gley soil. Drainage intensity had no effect on soil water level in the third block situated on a surface-water gley soil on a steep slope.     

Prey-predator dynamics in communities of culturable soil bacteria and protozoa: differential effects of mercury

We investigated whether the prey-predator dynamics of bacteria and protozoa were affected by inorganic mercury at concentrations of 0, 3.5 and 15 mg Hg(II) kg soil⁻¹. The amount of bioavailable Hg was estimated using a biosensor-assay based on the mer-lux gene fusion. The numbers of bacterial CFUs on the general medium 1/100 tryptic soy agar (TSA) were significantly decreased when the soil had been amended with Hg. In contrast, no effect was seen on the number of CFUs on the Pseudomonas-specific medium Gould's S1 agar. Protozoan numbers estimated by the most probable number (MPN) method with 1/100 TSB as growth medium were also negatively affected by Hg. The different fractions of protozoa were affected to different degrees suggesting that amoebae were less sensitive than slow-growing flagellates, which again were less sensitive than the fast-growing flagellates. In contrast, Hg did not induce any detectable changes in the diversity of flagellate morphotypes. In the treatment with 15 mg Hg kg⁻¹ a transiently increased number of bacteria was seen at day 6 probably concomitant with a decrease in the numbers of protozoa. This might indicate that Hg affected the prey-predator dynamics in communities of culturable bacteria and protozoa in soil. Furthermore, we showed that the number of Pseudomonas spp. was not affected by Hg whereas the number of bacteria growing on a general medium was.     

Common and distinguishing features of the bacterial and fungal communities in biological soil crusts and shrub root zone soils

Soil microbial communities in dryland ecosystems play important roles as root associates of the widely spaced plants and as the dominant members of biological soil crusts (biocrusts) colonizing the plant interspaces. We employed rRNA gene sequencing (bacterial 16S/fungal large subunit) and shotgun metagenomic sequencing to compare the microbial communities inhabiting the root zones of the dominant shrub, Larrea tridentata (creosote bush), and the interspace biocrusts in a Mojave desert shrubland within the Nevada Free Air CO₂ Enrichment (FACE) experiment. Most of the numerically abundant bacteria and fungi were present in both the biocrusts and root zones, although the proportional abundance of those members differed significantly between habitats. Biocrust bacteria were predominantly Cyanobacteria while root zones harbored significantly more Actinobacteria and Proteobacteria. Pezizomycetes fungi dominated the biocrusts while Dothideomycetes were highest in root zones. Functional gene abundances in metagenome sequence datasets reflected the taxonomic differences noted in the 16S rRNA datasets. For example, functional categories related to photosynthesis, circadian clock proteins, and heterocyst-associated genes were enriched in the biocrusts, where populations of Cyanobacteria were larger. Genes related to potassium metabolism were also more abundant in the biocrusts, suggesting differences in nutrient cycling between biocrusts and root zones. Finally, ten years of elevated atmospheric CO₂ did not result in large shifts in taxonomic composition of the bacterial or fungal communities or the functional gene inventories in the shotgun metagenomes.     

Influence of balsam poplar tannin fractions on carbon and nitrogen dynamics in Alaskan taiga floodplain soils

The feedbacks between plant and soil processes play an important role in driving forest succession. One poorly understood feedback mechanism is the interaction between plant secondary chemicals and soil microbes. In the Alaskan taiga, changes in nutrient cycling caused by balsam poplar (Populus balsamifera) secondary chemicals may affect the transition from alder (Alnus tenuifolia) to balsam poplar on river floodplains. We examined the effects of four poplar condensed tannin fractions on N cycling in alder and poplar soils. Tannins were added to forest floor samples from both poplar and alder sites. Samples were incubated for 1 month in the laboratory with soil respiration rates measured over the course of the incubation. At the end of the incubation we measured both net and gross nitrogen mineralization and nitrification, microbial biomass C and N, and the activity of various exoenzymes. In all soils, tannin additions reduced N availability, however, the mechanisms differed depending on the molecular weight of the tannin and the native soil microbial community. Low molecular weight tannin fractions served as a labile C source in poplar Oi, poplar Oe, and alder Oe horizons but were toxic to microbes in alder Oi. High molecular weight tannin fractions appeared to act primarily by binding extracellular substrates and thus limiting C and N mineralization, with the strongest effects observed in the alder soils.     

Structure and productivity of epiphytic algal communities onLobelia dortmanna L. in acidified and limed lakes

The epiphytic algal community growing onLobelia dortmanna L. was studied in two acidified lakes in southwestern Sweden from May through October 1980; Lake Gårdsjön (pH 4.3 to 4.7) and L. Högsjön (pH 6.3 to 6.7 after liming in 1978/79). In both lakes a layer of firmly attached diatoms,Eunotia veneris andE. rhomboidea, covered theLobelia leaves. Scanning electron microscope study revealed a mucoid matrix, and in L. Gårdsjön, heavy cover of detritus. The spring period in L. Gårdsjön was characterized by red algaBatrachospermum sp., which was followed by the appearance ofBinuclearia sp., andMougeotia spp. Blue-green algae appeared during the warmer period of the year. The spring period in L. Högsjön was characterized by the development of desmids. Diatoms dominated the community in the summer while green algae appeared in autumn. The biomass in L. Gårdsjön showed spring and late summer maxima, while in L. Högsjön it increased gradually reaching a maximum in autumn. Chlorophylla concentration was highest in L. Gårdsjön in late summer. Primary productivity rates calculated per unit substrate surface area at 1.0 m depth were highest in early summer and decreased in late summer. The results suggest that the liming of L. Högsjön caused significant structural changes in the epiphytic community, favoring diatoms and green algae, especially desmids. Blue-green algae were characteristic for L. Gårdsjön despite that lake's low pH. Productivity rates at 1.0 m depth show similar trends in both lakes.     

Specific features of the dynamics of salts in salt-affected soils subjected to long-term seasonal freezing in the south Transbaikal region

Observations over the dynamics of the freezing-thawing processes and the migration and accumulation of salts in the soils of the Ivolginsk Depression in Buryatia showed the existence of two stages in the annual cycle of salt migration: the short-term desalinization stage alternates with the long-term salinization stage. The latter stage actually combines two phases: the fall and winter phase of the migration of solutions towards the freezing front and the spring phase of the ascending migration of melt water towards the drying soil surface with further concentration of the solutions owing to evapotranspiration. The desalinization stage in the summer is only typical of the upper soil horizons because of the insufficient amount of summer precipitation; moreover, this stage is not observed every year. Thus, the salt regime of the soils of the depression is greatly affected by the seasonal soil freezing; the long-term salinization in the fall, winter, and spring seasons alternates with a short period of the leaching of salts at the end of summer.     

Effects of biochar on copper immobilization and soil microbial communities in a metal-contaminated soil

Purpose

Copper (Cu) contamination has been increasing in land ecosystems. Biochars (BCs) and arbuscular mycorrhizal fungi (AMF) are known to bind metals, and metallophyte can remove metals from soils. Will BC in combination with AMF contain the Cu uptake by a metallophyte growing in a metal-contaminated soil? The objective of this study was to investigate the effects of BCs on the Cu immobilization and over soil microbial communities in a metal-contaminated soil in the presence of AMF and metallophyte.

Materials and methods

Two BCs were produced from chicken manure (CMB) and oat hull (OHB). A Cu-contaminated sandy soil (338 mg kg^?1) was incubated with CMB and OHB (0, 1, and 5 % w/w) for 2 weeks. Metallophyte Oenothera picensis was grown in pots (500 mL) containing the incubated soils in a controlled greenhouse for 6 months. A number of analyses were conducted after the harvest. These include plant biomass weight, microbial basal respiration, and dehydrogenase activity (DHA), AMF root colonization, spore number, and glomalin production; changes in fungal and bacterial communities, Cu fractions in soil phases, and Cu uptake in plant tissues.

Results and discussion

The BCs increased the soil pH, decreased easily exchangeable fraction of Cu, and increased organic matter and residual fraction of Cu. The BCs provided favorable habitat for microorganisms, thereby increasing basal respiration. The CMB increased DHA by ～62 and ～574 %, respectively, for the low and high doses. Similarly, the OHB increased soil microbial activity by ～68 and ～72 %, respectively, for the low and high doses. AMF root colonization, spore number, and total glomalin-related soil protein (GRSP) production increased by ～3, ～2, and ～3 times, respectively, in soils treated with 1 % OHB. Despite being a metalophyte, O. picensis could not uptake Cu efficiently. Root and shoot Cu concentrations decreased or changed insignificantly in most BC treatments.

Conclusions

The results show that the BCs decreased bioavailable Cu, decreased Cu uptake by O. picensis, improved habitat for microorganisms, and enhanced plant growth in Cu-contaminated soil. This suggests that biochars may be utilized to remediate Cu-contaminated soils.

     

不同筛分方式对土壤团聚体及土壤微生物群落的影响

探究土壤团聚体组成、稳定性、有机碳含量及微生物数量在不同土壤筛分方式下的变化,对团聚体筛分方式进行优化。以黑土为研究对象,设置不同筛分方式处理,比较干土干筛、干土湿筛、润土干筛、润土湿筛4种筛分方式的优缺点。结果表明,润土干筛比干土湿筛处理≥2 mm粒径的土壤团聚体高出约85.97%,而在2～0.25、≤0.25 mm粒级中团聚体所占比例最高的干土湿筛比最低的润土干筛分别高出约80.90%、91.82%。>0.25 mm水稳性团聚体含量(R_0.25)在润土干筛下达到最高,为99.35%,该指标与土壤团聚体稳定性成正相关,其值越高则表示土壤抗蚀能力越强。干土湿筛处理下各粒级团聚体土壤有机碳分布平均。干土湿筛处理下,土壤细菌和放线菌的数量最高。而润土干筛处理下土壤真菌数量较高,与润土湿筛、干土干筛、干土湿筛3个处理方式相比有显著性差异。综上发现,干土湿筛处理下土壤团聚体稳定性更好,土壤微生物数量较高,在一定程度上对土壤结构、土壤质量起到优化的作用。     

长期施肥对黑土农田土壤微生物群落的影响

基于中国科学院海伦农业生态试验站长期定位试验区,应用实时荧光定量PCR(Real-time PCR)和变性梯度凝胶电泳(DGGE)技术研究了无施肥(NF)、单施N、P化肥(NP)以及化肥配施有机猪粪肥(NPM)等3种长期施肥措施对黑土区玉米田土壤微生物群落密度和结构的影响.Real-time PCR方法定量NF、NP及NPM措施土壤细菌群落基因组DNA质量分别为381、1 351和1 773 ng g-1干土,真菌群落基因组DNA质量分别113.3、127.3和20.6 ng g-1干土,真菌与细菌的比率分别为0.31、0.09和0.01,NPM措施显著低于另两种施肥方式(p＜0.05).DGGE方法研究表明,NP和NPM措施不能改善土壤细菌和真菌群落的多样性、均匀性及优势菌优势程度;但主成分分析结果显示NP和NPM措施均可改变土壤细菌和真菌群落的构成,且真菌群落的变化更为显著;聚类分析结果显示NP和NPM措施下细菌群落结构较相近,其相似系数为0.89,真菌群落中NP措施与NF措施相近,相似系数为0.63,高于NP与NPM措施的相似系数0.51.上述结果表明有机猪粪肥的长期施用可以显著降低黑土农田土壤真菌与细菌的比率,且明显地改变土壤细菌和真菌群落的结构.