内蒙古温带草原土壤微生物生物量碳的空间分布及驱动因素

【目的】探索内蒙古温带草原土壤微生物生物量碳的空间分布特征以及驱动因素。【方法】在内蒙古自治区境内沿着年均温、年降水梯度选择17个草原样点,在土壤剖面上分0-10 cm、10-20 cm、20-40 cm、40-60 cm、60-100 cm五层,分别采集土壤样品,测定土壤微生物生物量碳以及主要的环境和生物影响因子,分析不同草地类型以及不同土壤深度土壤微生物生物量碳的差异,探索非生物因子和生物因子对土壤微生物量碳的影响。【结果】草甸草原土壤微生物量碳最高,典型草原次之,荒漠草原最低。在0-10 cm土壤中,草地类型间的微生物量碳变异系数高于草甸草原和典型草原,低于荒漠草原;在0-100 cm土壤中,草甸草原样点间的微生物量碳的变异系数低于典型草原和荒漠草原。土壤微生物量碳与年降水、土壤含水量、粘粒含量、土壤养分元素、地上生物量、地下生物量呈显著正相关,与年均温和土壤p H值呈显著负相关关系。随着土壤深度的增加,土壤微生物量碳显著减少,非生物因子与微生物量碳的相关性减弱,草地类型间以及同一草地类型不同样点间的变异系数增加。0-10 cm土壤微生物量碳与10-40 cm土壤微生物量碳的相关指数高于0.5,与40-100 cm的土壤微生物量碳的相关指数小于0.3。【结论】内蒙古温带草原土壤微生物量碳的垂直分布呈现一定的规律性,且非生物因子对微生物量碳的影响也呈现垂直减弱的规律。     

Soil microbial community structure across a thermal gradient following a geothermal heating event

In this study microbial species diversity was assessed across a landscape in Yellowstone National Park, where an abrupt increase in soil temperature had occurred due to recent geothermal activity. Soil temperatures were measured, and samples were taken across a temperature gradient (35 to 65 degrees C at a 15-cm depth) that spanned geothermally disturbed and unimpacted soils; thermally perturbed soils were visually apparent by the occurrence of dead or dying lodgepole pine trees. Changes in soil microbial diversity across the temperature gradient were qualitatively assessed based on 16S rRNA sequence variation as detected by denaturing gradient gel electrophoresis (DGGE) using both ribosomal DNA (rDNA) and rRNA as PCR templates and primers specific for the Bacteria or Archaea domain. The impact of the major heating disturbance was apparent in that DGGE profiles from heated soils appeared less complex than those from the unaffected soils. Phylogenetic analysis of a bacterial 16S rDNA PCR clone library from a recently heated soil showed that a majority of the clones belonged to the Acidobacterium (51%) and Planctomyces (18%) divisions. Agar plate counts of soil suspensions cultured on dilute yeast extract and R2A agar media incubated at 25 or 50 degrees C revealed that thermophile populations were two to three orders of magnitude greater in the recently heated soil. A soil microcosm laboratory experiment simulated the geothermal heating event. As determined by both RNA- and DNA-based PCR coupled with DGGE, changes in community structure (marked change in the DGGE profile) of soils incubated at 50 degrees C occurred within 1 week and appeared to stabilize after 3 weeks. The results of our molecular and culture data suggest that thermophiles or thermotolerant species are randomly distributed in this area within Yellowstone National Park and that localized thermal activity selects for them.     

Interactive influences of climate and parent material on soil microbial community structure in Bornean tropical forest ecosystems

Climate and parent material strongly control vegetation structure and function, yet their control over the belowground microbial community is poorly understood. We assessed variation in microbial lipid profiles in undisturbed forest soils (organic and surface mineral horizons) along an altitudinal gradient (700, 1,700, and 2,700 m a.s.l. mean annual temperature of 12–24°C) on two contrasting parent materials (acidic metasedimentary vs. ultrabasic igneous rock) in Mt. Kinabalu, Borneo. Soil organic carbon and nitrogen concentrations were generally higher at higher altitudes and, within a site, at upper soil horizons. Soil pH ranged from 3.9 to 5.3, with higher values for the ultrabasic soils especially at higher altitudes. The major shifts in microbial community structure observed were the decline in the ratio of fungal to bacterial lipid markers both with increasing soil depth and decreasing altitude. The positive correlation between this ratio with soil C and N concentrations suggested a strong substrate control in accord with the literature from mid to high-latitude ecosystems. Principal component analysis using seven groups of signature lipids suggested a significant altitude by parent material interaction—the significant difference in microbial community structure between the two rock types found at 2,700-m sites developed on weakly weathered soils diminished with decreasing altitude towards 700-m sites where soils were strongly weathered. These results are consistent with the hypothesis that parent material effect on soil microbial community (either directly via soil geochemistry or indirectly via floristic composition) is stronger at an earlier stage of ecosystem development.     

Soil microbial diversity and community structure across a climatic gradient in western Canada

Soil microbial functional diversity was assessed along a climatic gradient in Western Canada. Mineral soil samples were collected from jack pine (Pinus banksiana Lamb.) stands along an 800km transect between Prince Albert, Saskatchewan and Gillam, Manitoba. Microbial communities were isolated from the soil samples, washed and inoculated into wells of Gram-negative Biolog microplates. Optical density values were used to calculate Shannon diversity indices and to perform principal component analysis. Colour development rank plots (CDR) were created by expressing optical density values as a percentage of total colour development and plotting the wells in descending order. Soil microbial functional diversity decreased with increasing latitude and correlated positively with measures of atmospheric temperature and pH. Soil microbial diversity may be lower in northern sites due to decreased productivity, nutrient limitation and higher acidity. CDR plots are consistent with a trend of increasing environmental harshness moving north along the transect.     

Soil influence on Cu and Co uptake and plant size in the cuprophytes Crepidorhopalon perennis and C. tenuis (Scrophulariaceae) in SC Africa

Cuprophytes are plants that mostly occur on Cu-rich soil in SC Africa. Crepidorhopalon perennis is endemic of a single site. C. tenuis has a broader niche, from normal to Cu-rich soil. Both have been considered as Cu-Co accumulators. We examined soil factors controlling heavy metal accumulation and plant fitness in natural populations. Plant mass and element concentrations in plants and soil were determined in 153 samples from five populations of C. tenuis on copper soil (CTC), two on normal soil (CTN) and the single population of C. perennis (CP). Soil in Cu-sites had higher concentrations of Ca, Mg, P, Mn, Zn, Cu, Co. Plants from Cu-sites were larger and had higher Cu and Co content, and lower Mg, Mn and Ca. Cu in shoots was influenced positively by Cu and Mn and negatively by Ca in the soil. Co in shoots was influenced positively by Co and negatively by Mn and Fe in the soil. Shoot mass was influenced positively by Cu and Mn (CT) or by Cu and Co (both species pooled) in the soil. The results suggest that C. tenuis and C. perennis are genuinely cuprophilous species. Large variation in metal accumulation in shoots can be accounted for by synergistic and antagonistic interactions among several heavy metals, yielding specific accumulation patterns in different populations.     

高山森林土壤微生物群落结构和功能对模拟增温的响应

将高山森林土壤装入PVC管中(土壤有机层在上、矿质土壤层在下)培养10周,以高山森林土壤年均温为对照,采用室内人工气候箱分别模拟增温2和4 ℃,研究土壤微生物群落和土壤酶活性对温度升高的响应.结果表明: 温度升高显著降低了土壤有机层中细菌、矿质土壤层中革兰氏阴性菌(G^-)PLFAs含量,但对土壤真菌无显著影响.温度升高引起革兰氏阳性菌和阴性菌比值(G⁺/G^-)升高,改变了微生物群落结构.增温对漆酶、β-葡萄糖酶、酸性磷酸酶和N-乙酰葡糖胺糖苷酶活性没有显著影响.土壤微生物群落之间呈现出协同增长的趋势,真菌、细菌、G⁺、G^-等微生物群落之间均呈显著正相关.土壤有机层中β-葡萄糖苷酶与土壤微生物群落对碳源利用的竞争,导致β-葡萄糖苷酶活性与土壤有机层细菌、真菌、G⁺呈显著负相关.高山森林不同土壤微生物类群对增温的响应不同,细菌比真菌对温度的响应更敏感,真菌对增温有一定的耐受能力.     

Effects of livestock grazing intensity on soil biota in a semiarid steppe of Inner Mongolia

Intensive livestock is known to significantly affect soil physical and chemical parameters in steppe ecosystems. However, the effects on soil biological parameters still remain unknown. We hypothesized that intensive grazing would significantly decrease the size and diversity of soil biota due to deterioration of the soil environment and reduction in vegetation cover, while the adapted grazing intensity would improve the biological parameters. Soil samples were collected from five sites with different grazing intensities and history in a semiarid steppe of Inner Mongolia in August 2005. Two sites were long-term ungrazed since 1979 (UG79) and 1999 (UG99), one had been moderately grazed in winter (WG), one continuously grazed moderately (CG) and one long-term site was heavily grazed (HG). Soil microbial biomass carbon (C), basal respiration (BR), catabolic diversity of soil microbial communities, protozoa and nematodes abundance were measured. Soil physicochemical variables were also measured to establish the relationships between soil biological parameters and key soil physical and chemical properties. Soil microbial biomass C, BR, biomass specific respiration (qCO₂) and soil protozoa abundance were significantly lower at the HG site compared to the UG79 site, but no clear differences were found in the other sites. However, soil nematodes abundance increased with increasing grazing intensity, and the abundance of soil amoeba were greater in CG than in the other sites. Principal component analysis (PCA) of Biolog data revealed large differences in catabolic capacity of soil microbial communities between UG79, HG and UG99, WG, CG. However, Shannon??s diversity index did not indicate marked effects of grazing intensity on substrate catabolic community structure. In conclusion, heavy grazing negatively affected soil microbial biomass, activity and protozoan abundance, but positively influenced soil nematodes abundance and did not affect soil microbial catabolic diversity. Based on these results, CG may provide an appropriate grazing intensity to be used in the long term in the semiarid steppe of Inner Mongolia.     

Response of the microbial community to copper oxychloride in acidic sandy loam soil

AIMS: Determining the response of different microbial parameters to copper oxychloride in acidic sandy loam soil samples using cultivation-dependent and direct microscopic techniques. METHODS AND RESULTS: Culturable microbial populations were monitored for 245 days in a series of soil microcosms spiked with different copper oxychloride concentrations. Microbial populations responded differently to additional Cu. Protistan numbers and soil metabolic potential decreased. Experiments with more soil samples revealed that metabolic potential was not significantly affected by < or =100 mg kg(-1) additional Cu. However, a negative impact on protista was noted in soil containing only 15 mg kg(-1) EDTA-extractable Cu. The negative impact on protistan numbers was less severe in soils with a higher phosphorous and zinc content. CONCLUSIONS: Bacterial populations responded differently, and protista were most sensitive to elevated Cu levels. Protistan numbers in soil from uncultivated land were higher and seemed to be more sensitive to additional Cu than the numbers of these organisms in soil originating from cultivated land. SIGNIFICANCE AND IMPACT OF THE STUDY: Protistan sensitivity to small increases in Cu levels demonstrates the vulnerability of the soil ecosystem to Cu perturbations, especially when the importance of protista as link in the flow of energy between trophic levels is considered.     

Variations in Soil Microbial Communities and Residues Along an Altitude Gradient on the Northern Slope of Changbai Mountain,China

Altitudinally-defined climate conditions provide specific vegetation types and soil environments that could influence soil microbial communities, which in turn may affect microbial residues. However, the knowledge is limited in terms of the degree to which microbial communities and residues present and differ along altitude. In this study, we examined the soil microbial communities and residues along the northern slope of Changbai Mountain, China using phospholipid fatty acid (PLFA) and amino sugar analysis, respectively. Soil samples were taken from five different vegetation belts defined by climates. Principal component analysis (PCA) revealed substantial differences in soil microbial community composition among study sites, appeared to be driven primarily by soil pH and C/N ratio on the first principal component (PC1) which accounted for 50.7% of the total sample variance. The alpine tundra was separated from forest sites on the second principal component (PC2) by a signifiscantly higher amount of fungal PLFA (18:2ω6,9). Soil pH and C/N ratio were also correlated with the ratios of Gram-positive to Gram-negative bacteria (Gm⁺/Gm⁻), glucosamine to galactosamine (GluN/GalN), and glucosamine to muramic acid (GluN/MurA). Both total PLFAs and amino sugars were positively correlated with soil organic carbon, inorganic nitrogen, available phosphorus and potassium. We concluded that soil pH and C/N ratio were the most important drivers for microbial community structure and amino sugar pattern, while substrate availability was of great importance in determining the concentrations of microbial communities and residues. These findings could be used to facilitate interpretation of soil microbial community and amino sugar data derived from measurements in latitude or managed forests.     

全球森林土壤微生物生物量碳氮磷化学计量的季节动态

土壤微生物生物量在森林生态系统中充当具有生物活性的养分积累和储存库。土壤微生物转化有机质为植物提供可利用养分, 与植物的相互作用维系着陆地生态系统的生态功能。同时, 土壤微生物也与植物争夺营养元素, 在季节交替过程和植物的生长周期中呈现出复杂的互利-竞争关系。综合全球数据对温带、亚热带和热带森林土壤微生物生物量碳(C)、氮(N)、磷(P)含量及其化学计量比值的季节动态进行分析, 发现温带和亚热带森林的土壤微生物生物量C、N、P含量均呈现夏季低、冬季高的格局。热带森林四季的土壤微生物生物量C、N、P含量都低于温带和亚热带森林, 且热带森林土壤微生物生物量C含量、N含量在秋季相对最低, 土壤微生物生物量P含量四季都相对恒定。温带森林的土壤微生物生物量C:N在春季显著高于其他两个森林类型; 热带森林的土壤微生物生物量C:N在秋季显著高于其他2个森林类型。温带森林土壤微生物生物量N:P和C:P在四季都保持相对恒定, 而热带森林土壤微生物生物量N:P和C:P在夏季高于其他3个季节。阔叶树的土壤微生物生物量C含量、N含量、N:P、C:P在四季都显著高于针叶树; 而针叶树的土壤微生物生物量P含量在四季都显著高于阔叶树。在春季和冬季时, 土壤微生物生物量C:N在阔叶树和针叶树之间都没有显著差异; 但是在夏季和秋季, 针叶树的土壤微生物生物量C:N显著高于阔叶树。对于土壤微生物生物量的变化来说, 森林类型是主要的显著影响因子, 季节不是显著影响因子, 暗示土壤微生物生物量的季节波动是随着植物其内在固有的周期变化而变化。植物和土壤微生物密切作用表现出来的对养分的不同步吸收是保留养分和维持生态功能的一种权衡机制。     

Molecular analysis of prokaryotic diversity in the deep subsurface of the former Homestake gold mine,South Dakota,USA

A culture-independent molecular phylogenetic analysis was carried out to study the prokaryotic diversity in two soil samples collected from the subsurface (1.34 km depth) of the former Homestake gold mine, Lead, South Dakota, USA at two sites, the Ross shaft and number 6 Winze. Microbial community analyses were performed by cloning and sequencing of 16S rRNA genes retrieved directly from soil samples. Geochemical characterization of soils revealed high amount of toxic metals such as As, Cd, Co, Cr, Cu, Ni, Pb, Zn, and U at both the sites. Phylogenetic analyses showed that soil samples were predominantly composed of phylotypes related to phylum Proteobacteria. Other phyla detected in libraries were Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexi, Chlorobi, Firmicutes, Gemmatimonadetes, Nitrospirae, Planctomycetes, Verrucomicrobia, and candidate divisions OP10 and TM7. The majority (>95%) of the phylotypes retrieved in the libraries were most closely related to environmental sequences from yet-uncultured bacteria representing a hitherto unidentified diversity. The archaeal communities at both the sites exhibited lower diversity and were most closely affiliated to uncultivated species within the Crenarchaeota. Results showed the existence of diverse microbial populations in deep subsurface environment of the Homestake gold mine. Statistical analyses demonstrated that each site harbored phylogenetically distinct microbial populations that were more diverse at Ross site compare to winze site.     

Comparison of soil microbial communities from two distinct karst areas in Hungary

Karst areas belong to the most exposed terrestrial ecosystems, therefore their study have a priority task in Hungary, as well. The aim of this study was to compare the structure, activity and diversity of soil microbial communities from two distinct Hungarian karst areas (Aggtelek NP and Tapolca-basin). Soil samples were taken three times from 6 distinct sites, from different depths. Soil microbial biomass C (MBC), microbial biomass N (MBN), basal respiration (BRESP) and substrate induced respiration (SIR) were measured. The phylogenetic diversity of bacterial communities was compared by Denaturing Gradient Gel Electrophoresis (DGGE). The highest MBC, MBN, BRESP and SIR values were measured in the rendzina soil from Aggtelek. On the basis of biomass and respiration measurements, microbial communities differentiated mainly according to soil depths whereas DGGE profiles of bacterial communities resulted in groups mainly according to sampling sites.     

Microbial carbon use efficiency in different ecosystems: A meta-analysis based on a biogeochemical equilibrium model

Soil microbial carbon use efficiency (CUE) is a crucial parameter that can be used to evaluate the partitioning of soil carbon (C) between microbial growth and respiration. However, general patterns of microbial CUE among terrestrial ecosystems (e.g., farmland, grassland, and forest) remain controversial. To address this knowledge gap, data from 41 study sites (n = 197 soil samples) including 58 farmlands, 95 forests, and 44 grasslands were collected and analyzed to estimate microbial CUEs using a biogeochemical equilibrium model. We also evaluated the metabolic limitations of microbial growth using an enzyme vector model and the drivers of CUE across different ecosystems. The CUEs obtained from soils of farmland, forest, and grassland ecosystems were significantly different with means of 0.39, 0.33, and 0.42, respectively, illustrating that grassland soils exhibited higher microbial C sequestration potentials (p < .05). Microbial metabolic limitations were also distinct in these ecosystems, and carbon limitation was dominant exhibiting strong negative effects on CUE. Exoenzyme stoichiometry played a greater role in impacting CUE values than soil elemental stoichiometry within each ecosystem. Specifically, soil exoenzymatic ratios of C:phosphorus (P) acquisition activities (EEA_C:P) and the exoenzymatic ratio of C:nitrogen (N) acquisition activities (EEA_C:N) imparted strong negative effects on soil microbial CUE in grassland and forest ecosystems, respectively. But in farmland soils, EEA_C:P exhibited greater positive effects, showing that resource constraints could regulate microbial resource allocation with discriminating patterns across terrestrial ecosystems. Furthermore, mean annual temperature (MAT) rather than mean annual precipitation (MAP) was a critical climate factor affecting CUE, and soil pH as a major factor remained positive to drive the changes in microbial CUE within ecosystems. This research illustrates a conceptual framework of microbial CUEs in terrestrial ecosystems and provides the theoretical evidence to improve soil microbial C sequestration capacity in response to global change.     

Microbial characteristics of soils on a latitudinal transect in Siberia

Soil microbial properties were studied from localities on a transect along the Yenisei River, Central Siberia. The 1000 km‐long transect, from 56°N to 68°N, passed through tundra, taiga and pine forest characteristic of Northern Russia. Soil microbial properties were characterized by dehydrogenase activity, microbial biomass, composition of microbial community (PLFAs), respiration rates, denitrification and N mineralization rates. Relationships between vegetation, latitude, soil quality (pH, texture), soil organic carbon (SOC) and the microbial properties were examined using multivariate analysis. In addition, the temperature responses of microbial growth (net growth rate) and activity (soil respiration rate) were tested by laboratory experiments. The major conclusions of the study are as follows: 1. Multivariate analysis of the data revealed significant differences in microbial activity. SOC clay content was positively related to clay content. Soil texture and SOC exhibited the dominant effect on soil microbial parameters, while the vegetation and climatic effects (expressed as a function of latitude) were weaker but still significant. The effect of vegetation cover is linked to SOC quality, which can control soil microbial activity. 2. When compared to fine‐textured soils, coarse‐textured soils have (i) proportionally more SOC bound in microbial biomass, which might result in higher susceptibility of SOC transformation to fluctuation of environmental factors, and (ii) low mineralization potential, but with a substantial part of the consumed C being transformed to microbial products. 3. The soil microbial community from the northernmost study region located within the permafrost zone appears to be adapted to cold conditions. As a result, microbial net growth rate became negative when temperature rose above 5 °C and C mineralization then exceeded C accumulation.     

喀斯特地区土壤表层CO2释放通量的影响因素Ⅰ:规律

测定了贵州喀斯特地区土壤表层CO2释放通量,同时还测定了土壤微生物生物量碳以及土壤可溶性有机质含量和土壤湿度。研究表明,贵州喀斯特地区全年土壤表层CO2释放通量与温度变化呈正相关关系,与土壤微生物生物量碳呈负相关关系;当温度＞20℃时,土壤表层CO2释放通量与土壤湿度呈正相关,与土壤可溶性有机碳含量呈负相关。     

Biokinetic analyses of adaptation and succession: microbial activity in composting municipal sewage sludge

The interactions between temperature and the microbial communities in composting municipal sewage sludge were studied to determine the optimal temperature range for efficient decomposition (stabilization) of the sludge. Information concerning thermophilic successions in such communities was also obtained. Samples were taken from several different temperature areas in a production-scale composting pile throughout the 19-day processing run. Optimum temperatures for microbial activity, determined as the rate of [14C]acetate incorporation into microbial lipids, were determined for each sample. Biomass was determined from the lipid phosphate content of the sample. Maximal activities were generally found in samples coming from lower-temperature areas (25 to 45 degrees C), whereas samples from high temperatures (55 to 74 degrees C) usually had relatively little activity. The temperature giving the optimum activity in samples incubated at a variety of temperatures during the assay tended to increase as the composting time progressed, but never exceeded about 50 degrees C. Many of these temperature response curves were similar in nature to curves reported for purified enzyme systems and pure cultures of bacteria. Comparisons of the apparent energies of activation calculated for different temperature ranges over time also indicated that the overall community was better adapted to higher temperatures during the latter part of the composting run. It was also found that the relationship between the apparent energies of activation and the apparent energies of inactivation (apparent heats of denaturation) consistently changed with sample temperature throughout the composting run, suggesting that the microbial communities from hotter samples were better adapted to high temperatures than those from cooler samples, and vice versa.(ABSTRACT TRUNCATED AT 250 WORDS)     

Biokinetic analyses of adaptation and succession: microbial activity in composting municipal sewage sludge.

The interactions between temperature and the microbial communities in composting municipal sewage sludge were studied to determine the optimal temperature range for efficient decomposition (stabilization) of the sludge. Information concerning thermophilic successions in such communities was also obtained. Samples were taken from several different temperature areas in a production-scale composting pile throughout the 19-day processing run. Optimum temperatures for microbial activity, determined as the rate of [14C]acetate incorporation into microbial lipids, were determined for each sample. Biomass was determined from the lipid phosphate content of the sample. Maximal activities were generally found in samples coming from lower-temperature areas (25 to 45 degrees C), whereas samples from high temperatures (55 to 74 degrees C) usually had relatively little activity. The temperature giving the optimum activity in samples incubated at a variety of temperatures during the assay tended to increase as the composting time progressed, but never exceeded about 50 degrees C. Many of these temperature response curves were similar in nature to curves reported for purified enzyme systems and pure cultures of bacteria. Comparisons of the apparent energies of activation calculated for different temperature ranges over time also indicated that the overall community was better adapted to higher temperatures during the latter part of the composting run. It was also found that the relationship between the apparent energies of activation and the apparent energies of inactivation (apparent heats of denaturation) consistently changed with sample temperature throughout the composting run, suggesting that the microbial communities from hotter samples were better adapted to high temperatures than those from cooler samples, and vice versa.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of soil macroaggregates crushing on C mineralization in a tropical deciduous forest ecosystem

Soil aggregates strongly influence C dynamics by affecting microbial activity. Our study tested the effect of soil crushing on C mineralization by laboratory incubation experiments of soil samples from a tropical deciduous forest ecosystem in Western Mexico. Soil samples were taken in January (dry season) and in October (rainy season). For each sampling date, the incubation experiment had a two factorial design with litter and macroaggregates (>250 μm) crushing as the main factors, both with two levels (with and without). At both sampling dates, the soil samples with intact macroaggregates had significantly higher C mineralization than the soil samples in which macroaggregates were crushed. The pH of leached solution was higher in the crushed soil samples than in uncrushed soil samples. The reduction of C mineralization caused by the disruption of soil aggregates is explained by the disturbance of environmental conditions within macroaggregates. The effect of macroaggregates crushing also reduced the differences of C mineralization between both seasons. We concluded that macroaggregates promote microbial activity by reducing the impact of variations in soil chemical and physical environmental conditions.     

Initial Copper Stress Strengthens the Resistance of Soil Microorganisms to a Subsequent Copper Stress

To improve the prediction of essential ecosystem functioning under future environmental disturbances, it is of significance to identify responses of soil microorganisms to environmental stresses. In this study, we collected polluted soil samples from field plots with eight copper levels ranging from 0 to 3,200 mg Cu kg^?1 soil. Then, the soils with 0 and 3,200 mg Cu kg^?1 were selected to construct a microcosm experiment. Four treatments were set up including Cu0-C and Cu3200-C without further Cu addition, and Cu0-A and Cu3200-A with addition of 57.5 mg Cu kg^?1 soil. We measured substrate-induced respiration (SIR) and potential nitrification rate (PNR). Furthermore, the abundance of bacterial, archaeal 16S rRNA genes, ammonia-oxidizing bacteria and archaea amoA genes were determined through quantitative PCR. The soil microbial communities were investigated by terminal restriction fragment length polymorphism (T-RFLP). For the field samples, the SIR and PNR as well as the abundance of soil microorganisms varied significantly between eight copper levels. Soil microbial communities highly differed between the low and high copper stress. In the microcosm experiment, the PNR and SIR both recovered while the abundance of soil microorganisms varied irregularly during the 90-day incubation. The differences of microbial communities measured by pairwise Bray–Curtis dissimilarities between Cu0-A and Cu0-C on day 0 were significantly higher after subsequent stress than before. However, the differences of microbial communities between Cu3200-A and Cu3200-C on day 0 changed little between after subsequent stress and before. Therefore, initial copper stress could increase the resistance of soil microorganisms to subsequent copper stress.     

Risk assessment of heavy metal toxicity through contaminated vegetable from sewage water: Implications for populace health

The present investigation was carried out to evaluate the levels of metals and metalloids in okra (Abelmoschus esculentus) irrigated with city wastewater. Soil and vegetable samples from two different sites irrigated with wastewater were wet-digested and analyzed. Arsenic (As) was found higher at both sites and Cr was many-fold lower at both sampling sites. Among all heavy metals, Mn and Zn were abundant. Highest value of coefficient factor was found for Cr and the lowest for Cd. The high transfer value was recorded for Cu at site-I and for Ni at site-II. Copper and Se showed negative and significant correlations between soil and vegetable, whereas Mn, Zn, As, Cd, Cr, and Ni showed positive but non-significant correlations. Pollution load index in this vegetable was found to be higher for Cd and lower for Cu. Health risk index at site-I was in the order of As > Mn > Mo > Pb > Cd > Ni > Zn > Se > Fe > Co > Cr > Cu, whereas the same order was observed at site-II of the sampling locations. Thus, the health risks of metals through ingestion of vegetables were of great concern in the study area.