Methyl-mercury affects microbial activity and biomass,bacterial community structure but rarely the fungal community structure

Monomethyl-mercury is one of the most toxic compounds. Methylation of Hg usually appears under anoxic conditions. In Swiss forest soils, methyl-Hg concentrations of up to 3 μg kg⁻¹ soil dw have been observed, but the impact of methyl-Hg on soil microorganisms have rarely been examined so far. In this study, we investigated the effect of increasing concentrations of methyl-Hg (0, 5, 20, 90 μg kg⁻¹ soil dw) on the microbial communities in various forest soils differing in their physico-chemical properties. Experiments were conducted in microcosms under controlled conditions and the basal respiration (BR), the microbial biomass carbon (MBC) and the bacterial and fungal community structures using T-RFLP-profiling were investigated. BR was significantly affected by methyl-Hg. In general, the BR increased with increasing methyl-Hg concentrations, whereas the MBC was significantly reduced. Bacterial communities were more sensitive to methyl-Hg than fungal communities. In five out of seven soils, the bacterial community structures differed significantly between the treatments whereas the fungal communities did not. The impact of methyl-Hg on the soil bacterial communities was site specific. In one soil, a methyl-Hg concentration of already 5 μg kg⁻¹ soil dw significantly affected the relative abundance of 13% bacterial operational taxonomic units (OTU), whereas in other soils concentrations of even 90 μg kg⁻¹ soil dw rarely affected the abundance of OTUs. In this study, for the first time, the impact of methyl-Hg on soil bacterial and fungal communities in forest soils was assessed. We showed that its impact strongly depends on the physico-chemical conditions of the soil and that bacterial communities were more sensitive to methyl-Hg than fungi.     

施用沼肥对茄子田节肢动物群落结构与茄子产量的影响

在等氮、等磷、等钾施肥条件下, 对茄子田分别施用化肥、沼肥加化肥减半、沼肥加饼肥, 研究施用沼肥对茄田节肢动物群落结构及茄子产量的影响。结果表明: 在节肢动物种类与数量上, 沼肥加饼肥处理茄子田的害虫种类为3.67±0.88 种·4m^-2, 显著低于化肥处理和沼肥加化肥减半处理, 且沼肥加化肥减半处理显著低于化肥处理; 害虫个体数量为64.67±4.06 头·4m^-2, 目标害虫桃蚜的数量为31.67±0.56 头·4m^-2、二十八星瓢虫个体数量为8.00±0.15 头·4m^-2, 显著低于化肥处理, 且与沼肥加化肥减半处理差异不显著; 蜘蛛类的个体数量为12.67±1.76 头·4m^-2, 优势种天敌大腹园蛛的个体数量为7.67±0.67 头·4m^-2, 显著高于化肥处理, 且与沼肥加化肥减半处理差异不显著。在节肢动物群落多样性上, 沼肥加饼肥处理茄子田的节肢动物群落多样性指数为1.68±0.04, 均匀度指数为0.53±0.003, 显著高于化肥处理和沼肥加化肥减半处理; 优势集中性指数为0.33±0.02, 显著低于化肥处理, 且与沼肥加化肥减半处理差异不显著。在节肢动物群落稳定性上, 沼肥加饼肥处理Ss/Si 指数为0.112 5±0.001 1, 显著高于化肥处理, 且与沼肥加化肥减半处理差异不显著; Sn/Sp 指数为1.650 0±0.005 5, 显著高于化肥处理和沼肥加化肥减半处理。沼肥加化肥减半、沼肥加饼肥处理的茄子产量与化肥处理相比无显著差异。     

Effect of varying solution calcium or magnesium concentrations in the presence or absence of aluminum on yield and plant calcium or magnesium concentrations in wheat

The effect of varying solution calcium (Ca) and magnesium (Mg) concentrations in the absence or presence of 10 μM aluminum (Al) was investigated in several experiments using a low ionic strength (2.7 × 10^‐3 M) solution culture technique. Aluminium‐tolerant and Al‐sensitive lines of wheat (Triticum aestivum L.) were grown. In the absence of Al, top yields decreased when solution Ca concentrations were <50 μM or plant Ca concentrations were <2.0 mg/g. Top and root yields decreased when solution Mg concentrations were <50 μM or plant Mg concentrations were <1.5 mg/g. There were no differences between the lines in solution or plant concentrations at which yield declined. Increasing solution Ca concentrations decreased plant Mg concentrations in the tops (competitive ion effect) but increased plant Mg concentrations in the roots of wheat. This suggests that Ca is competing with Mg when Mg is transported from the roots. Increasing solution Mg concentrations decreased plant Ca concentrations in the tops and the roots (competitive ion effect). In the roots, increasing solution Mg concentrations decreased plant Ca concentrations at a lower solution Ca concentration in the Al‐sensitive line than the Al‐tolerant line. In the presence of Al, increasing solution Ca and Mg concentrations increased yield (Ca and Mg ameliorating Al toxicity). Yield increased until the sum of the solution concentrations of the divalent cations (Ca+Mg) was 2,000 μM for the Al‐tolerant line or 4,000 μM for the Al‐sensitive line. The exception was that yield decreased when solution Mg concentrations were > 1,500 μM and the solution Ca concentration was 100 μM (Mg exacerbating Al toxicity). The ameliorative effects of solution Ca or Mg on Al tolerance were not related to plant Ca or Mg concentrations per se.     

钙对茄子嫁接苗生长和抗冷性的影响

研究了营养液缺Ca处理对茄子嫁接苗抗冷效应的影响。结果表明,缺Ca严重影响了植株的生长发育。在低温胁迫下,与供Ca处理相比,缺Ca处理显著降低了茄子嫁接苗和自根苗叶片总可溶性蛋白、热稳定蛋白和可溶性糖含量,细胞内可溶性Ca和结合Ca含量也显著降低。在相同的低温胁迫时间内,嫁接苗的总可溶性蛋白、热稳定蛋白、可溶性糖含量、细胞内可溶性Ca和结合Ca含量显著高于自根苗。低温胁迫下茄子嫁接苗总可溶性蛋白、热稳定蛋白、可溶性糖含量的提高是由于嫁接苗细胞内可溶性Ca和结合Ca含量的变化引起的。表明Ca含量的变化是其抗冷性强的内在原因,对增强茄子嫁接苗碳水化合物含量和提高植株抗冷性方面起着重要的作用。     

Increasing species and trophic diversity of mesofauna affects fungal biomass,mesofauna community structure and organic matter decomposition processes

A laboratory mesocosm experiment was set up to study the effects of five mesofauna model communities on litter fungal biomass (ergosterol content) and litter decomposition parameters (litter mass remaining, N concentration) for 4 months. The five treatments were: (1) no soil mesofauna, (2) the collembolan Folsomia fimetaria, (3) an assemblage of the collembolan species Isotomurus prasinus, Hypogastrura assimilis, F. fimetaria, Mesaphorura macrochaeta and Protaphorura armata, (4) the same collembolan assemblage plus the enchytraeid Enchytraeus crypticus, and (5) the six species plus the predaceous mite Hypoaspis aculeifer. After 30, 60, 90 and 120 days of incubation, six mesocosms of each treatment were sacrificed and biomass, species richness and dominance were measured. Changes occurred during the study with an increase in total detritivore biomass and a decrease in species richness with strong dominance by a few species in multispecies mesocosms. A vertical stratification of species was also observed in the mesocosms. Litter mass loss and N mineralisation were reduced with the introduction of fauna and showed the largest effects in the multispecies detritivore treatments. Ergosterol production was only temporary reduced in the multispecies treatments reflecting an effect of mesofauna on fungal biomass related to diversity rather than the biomass of mesofauna. An inhibitory predator effect was observed on functional decomposition parameters and indicated top-down control of decomposition via detritivorous mesofauna.     

Soil structure and soil-borne diseases: using epidemiological concepts to scale from fungal spread to plant epidemics

Many epidemics of root diseases involving soil fungi depend on the interplay between fungal growth and the spatial and temporal heterogeneity of the soil environment. Colonization or infection of a root occurs at fine scales with growth and movement of fungal mycelia through soil. However, epidemics are observed at coarser scales, and depend on a cascading spread through populations of roots. We briefly review conventional analyses of soil‐borne epidemics and argue that these treat soil physical conditions at scales too coarse to be meaningful for interactions between soil, plants and fungi, and fail to consider the effect of soil physical conditions on the underlying epidemiological processes. Instead, we propose a conceptual epidemiological framework that integrates spatial scales and use this to review the effect of soil structure on the dynamics of soil‐borne pathogenic fungi. Using the soil‐borne fungal plant pathogen Rhizoctonia solani as an example, we demonstrate that invasion of fungi into host populations is critically affected by environmental conditions operating at each of two scales: (i) at the microscopic scale (μm ? cm) the fungus preferentially explores certain pathways in soil, and small changes in soil physical conditions make the fungus switch from small, dense colonies to large, sparse and rapidly expanding ones; (ii) at the larger scale (cm ? dm) a critical density of susceptible hosts is required, in excess of which fungi switch from non‐invasive to invasive spread. Finally, we suggest that the approach will increase the applicability of research dealing with microscopic soil–plant–microbe interactions towards the solution of large‐scale epidemiological problems.     

Evaluation of the potential of fungal and plant laccases for active-packaging applications

Laccases from Trametes versicolor (TvL), Myceliophthora thermophila (MtL), and Rhus vernicifera (RvL) were investigated with regard to their potential utilization as oxygen scavengers in active packages containing food susceptible to oxidation reactions. The substrate selectivity of the laccases was investigated with a set of 17 reducing substrates, mainly phenolic compounds. The temperature dependence of reactions performed at low temperatures (4-31 °C) was studied. Furthermore, the laccases were subjected to immobilization in a latex/clay matrix and drying procedures performed at temperatures up to 105 °C. The results show that it is possible to immobilize the laccases with retained activity after dispersion coating, drying at 75-105 °C, and subsequent storage of the enzyme-containing films at 4 °C. TvL and, to some extent, MtL were promiscuous with regard to their reducing substrate, in the sense that the difference in activity with the 17 substrates tested was relatively small. RvL, on the other hand, showed high selectivity, primarily toward substrates resembling its natural substrate urushiol. When tested at 7 °C, all three laccases retained >20% of the activity they had at 25 °C, which suggests that it would be possible to utilize the laccases also in refrigerated food packages. Coating and drying resulted in a remaining enzymatic activity ranging from 18 to 53%, depending on the drying conditions used. The results indicate that laccases are useful for active-packaging applications and that the selectivity for reducing substrates is an important characteristic of laccases from different sources.     

沙质草地生境中植物群落对土壤质地演进的响应

利用空间代替时间,选取6个沙地生境类型(硬质灰钙土H_1,沙质灰钙土H_2,固定沙地H_3,半固定沙地H_4,半流动沙地H_5和流动沙地H_6),通过对其土壤颗粒组成、草地植物群落结构及数量特征的分析,研究沙质草地植物群落演替对土壤沙化过程的响应。结果表明:(1)从硬质灰钙土到流动沙地,物种丰富度分别为9,12,9,9,9,5种;演替初期(H_1-H_2)多年生草本植物种占绝对优势,演替中期(H_3-H_4)一年生植物优势度明显,演替后期(H_5-H_6)则以半灌木占主导地位;各演替阶段禾本科植物均有很高的优势度,在半流动沙地阶段成为最大优势物种,在沙质灰钙土后藜科植物优势度保持相对稳定,菊科和豆科植物分别在固定沙地和半固定沙地阶段逐渐消失。(2)物种多样性在沙质灰钙土最高,到固定沙地持续递减,而到流动沙地时又增大,生态优势度与物种多样性变化趋势正好相反,均匀度表现出先减小后增大的趋势,相邻的两个群落间具有较高的相似度。(3)从硬质灰钙土到流动沙地,0—10cm土层土壤黏粉粒含量极显著减少(p0.01),而粗砂粒极显著增加(p0.01),土壤颗粒分形维数由2.52下降到1.73。(4)一年生草本植物优势度与土壤黏粉粒含量、土壤颗粒分形维数呈显著负相关(p0.05);豆科植物优势度与土壤粉粒组分、土壤颗粒分形维数间呈显著正相关(p0.05);物种多样性与粉粒组分含量呈极显著正相关(p0.01),与细砂粒组分含量、土壤颗粒分形维数间呈显著正相关(p0.05)。     

Non-streptomycete actinomycetes as biocontrol agents of soil-borne fungal plant pathogens and as plant growth promoters

Among soil microorganisms, bacteria and fungi and to a lesser extent actinomycetes, have received considerable attention as biocontrol agents of soil-borne fungal plant pathogens and as plant growth promoters. Within actinomycetes, Streptomyces spp. have been investigated predominantly, mainly because of their dominance on, and the ease of isolation from, dilution plates and because of the commercial interest shown on the antibiotics produced by certain Streptomyces spp. Many of non-streptomycete actinomycetes (NSA) taxa are therefore rarely reported in literature dealing with routine isolations of biocontrol agents and/or plant growth promoters from plant and soil. It is clear that special isolation methods need to be employed in routine isolations to selectively isolate NSA. Some interesting information exists, albeit in relatively few reports compared to that on other microorganisms, on the biological activities of NSA, especially in relation to their mechanisms of action in the biological control of soil-borne fungal plant pathogens and plant growth promotion. This review presents an overview of this information and seeks to encourage further investigations into what may be considered a relatively unexplored area of research. Certain soil environmental factors, especially in horticultural systems, could be manipulated to render the soil conducive for the biological activities of NSA. A variety of NSA isolated by selective methods have not only shown to be rhizosphere competent but also adapted for an endophytic life in root cortices. Some of the NSA, including endophytic strains that have shown potential to suppress soil-borne fungal plant pathogens, are able to employ one or more mechanisms of antagonism including antibiosis, hyperparasitism and the production of cell-wall degrading enzymes. Strains of NSA promote plant growth by producing plant growth regulators. Enhancement of plant growth by the antagonists are considered to help the host by producing compensatory roots that mask the impact of root diseases.     

Comparative efficiency of acid phosphatase originated from plant and fungal sources

A study was conducted to demonstrate the comparative efficiency of acid phosphatase generated by plants or fungi towards the hydrolysis of different organic P compounds present in soil. The results revealed that acid phosphatases were most efficient in the hydrolysis of glycerophosphate followed by lecithin and phytin. The P release increased with increase in enzyme concentration. Acid phosphatase generated from fungal sources showed three times greater efficiency in the hydrolysis of phytin, two times greater efficiency in hydrolysis of lecithin than plant phosphatase. Both sources were at par in hydrolyzing glycerophosphate. The results suggest that acid phosphatase generated from plant and fungal sources is different and microbial acid phosphatase to be more efficient than that from plant sources.     

Trichoderma harzianum T-E5 significantly affects cucumber root exudates and fungal community in the cucumber rhizosphere

The Fusarium wilt in cucumbers, caused by the pathogenic fungus Fusarium oxysporum f. sp. cucumerinum, is a serious and destructive disease worldwide. An effort was made to explore the role of Trichoderma harzianum T-E5 in reducing the incidence of Fusarium wilt. Three treatments (Control, T1, and T2) were established in the greenhouse experiment. The effects of T-E5 on the composition of root exudates and fungal community in the cucumber rhizosphere were measured. Compared with the control, the application of a bio-organic fertilizer (BIO) enriched with T-E5 was found to decrease the incidence of Fusarium wilt notably and promote the growth of cucumber plants. Based on real-time PCR, the population of F. oxysporum in the control without T-E5 increased from 10³ to 10⁴ ITS copies g⁻¹ soil, whereas the population decreased from 10³ to 10² ITS copies g⁻¹ soil in the T1 and T2 treatment groups when T-E5 was included. Significant difference in fungal community was also found among the treatment groups. HPLC analysis showed that the detected levels of phenolic compounds in control were significantly higher than the levels in the samples subjected to T1 and T2 treatments. The root exudates from the control group significantly increased the numbers of germinating spores of the pathogen compared with those from the samples treated with T1 and T2. In conclusion, the modification of root exudates and the fungal community by the application of BIO might account for the effective suppression of Fusarium wilt disease in cucumbers.     

Loblolly pine plant community structure and soil solution aluminum,organic acids,calcium, magnesium,and pH

Abstract

Vegetative cover may influence soil chemical properties by producing organic acids that can modify the toxicity are responsible for high levels of nontoxic soil solution aluminum (Al). This study was conducted to determine the effect of loblolly pine (Pinus taeda L.) plant community structure, i.e., differing vegetative covers, on exchangeable cation distribution, and soil solution concentration of aluminum (Al) and organic acids. Soil was sampled were taken from 8‐year‐old forest plots with differing plant community structure (herbaceous‐hardwood‐pine, herbaceous‐pine, hardwood‐pine, and pine only), and measured for exchangeable cations. Soil solution extracts were analyzed for Al, organic acids, and the major cations and anions. There were significant differences in exchangeable Al, and calcium (Ca) among communities. Soil pH was highest in the herbaceous‐pine community, while other communities did not differ in soil pH. Oxalic, citric, malic, and succinic acids were detected in soil solution for all communities, but did not differ significantly among communities. Calculated Al activity was less than those determined by the 8‐hydroxy quinoline (15 sec) method. For these conditions, calculated Al activities did not change by accounting for the Ca‐ and magnesium (Mg)‐organic acid complex. The Al activities found were similar to previous reported levels that were considered nontoxic.     

Effect of salt stress on tomato plant and the role of calcium

Abstract

Salinity is one of the serious abiotic stresses that has adverse effects on plant growth. The aim of this study was to investigate the effect of sodium chloride (NaCl) on germination and growth parameters of tomato plant as well as the role of Ca²⁺as an ameliorating agent. 100?mM NaCl and two concentrations of calcium (5 and 10?mM) were applied to tomato seeds and seedlings. This study was carried out in a Completely Randomized Design (CRD) with a total of six treatments each comprising of three replicates. The application of 100?mM of NaCl delayed the germination time by 27.6%, reduced the seedling length and seedling vigor by 24.33% and germination stress tolerance by 27.6% as compared to control. Salinity also reduced the plant growth (root and shoot length, root fresh and dry weight, shoot fresh and dry weight, membrane stability, relative water content and leaf area), whereas the application of calcium mitigated the negative effects of salinity on germination and growth to a greater extent. With increased calcium concentration, growth and germination increased significantly both alone and in the salt-affected plant. 10?mM calcium showed best results and enhanced the promptness index by 20.7%, seedling length and vigor by 15.1% and GSI by 20.7%. It also improved root fresh and dry weight, shoot fresh and dry weight, relative water content and leaf area. Similarly, 5?mM calcium also increased plant height and membrane stability index. The present study suggests that application of Ca²⁺ enhanced the growth of tomato plant under saline conditions.     

Litter type, but not plant cover, regulates initial litter decomposition and fungal community structure in a recolonising cutover peatland

Cutover peatlands are often rapidly colonised by pioneer plant species, which have the potential to affect key ecosystem processes such as carbon (C) turnover. The aim of this study was to investigate how plant cover and litter type affect fungal community structure and litter decomposition in a cutover peatland. Intact cores containing Eriophorum vaginatum, Eriophorum angustifolium, Calluna vulgaris and bare soil were removed and a mesh bag with litter from only one of each of these species or fragments of the moss Sphagnum auriculatum was added to each core in a factorial design. The presence or absence of live plants, regardless of the species, had no effect on mass loss, C, nitrogen (N) or phosphorus (P) concentrations of the litter following 12 months of incubation. However, there was a very strong effect of litter type on mass loss and concentrations of C, N and P between most combinations of litter. Similarly, plant species did not affect fungal community structure but litter type had a strong effect, with significant differences between most pairs of litter types. The data suggest that labile C inputs via rhizodeposition from a range of plant functional types that have colonised cutover bogs for 10-15 years have little direct effect on nutrient turnover from plant litter and in shaping litter fungal community structure. In contrast, the chemistry of the litter they produce has much stronger and varied effects on decomposition and fungal community composition. Thus it appears that there is distinct niche differentiation between the fungal communities involved in turnover of litter versus rhizodeposits in the early phases of plant succession on regenerating cutover peatlands.     

Activated carbon addition affects substrate pH and germination of six plant species

Activated carbon (AC) is widely used in ecological studies for neutralizing allelopathic compounds. However, it has been suggested that AC has direct effects on plants because it alters substrate parameters such as nutrient availability and pH. These side-effects of AC addition may interfere with allelopathic effects. In this study we analyzed three widely used commercial AC brands and analyzed their effect on pH, their ability to retain glucosinolates, and their effect on the germination of six plant species. AC brands differed significantly in their effect on pH values when added to different substrates. Glucosinolates were completely adsorbed by all brands, indicating that AC is suitable as adsorbent for this compound class. Finally, AC addition to substrates had differential effects on seed germination of Arabidopsis thaliana, Plantago lanceolata, Solidago canadensis, and Lotus corniculatus, whereas no effect was found on the germination of Lactuca sativa and Brassica oleracea. We suggest that scientists using AC should always include an experimental control to test for direct effects of AC addition on both substrate parameters and plant performance.     

Low and variable critical concentrations of calcium in plant tissues

Abstract

Calcium seems to be required by higher plants (and in parts of higher plants) in variable concentrations and much confusion exists about plant requirements of it. When most heavy metal concentrations are low, the calcium requirement in plants can also be low. Levels of calcium of 800 or less and up to 2000 ppm of dry weight are adequate under some conditions. Even though the requirement may be low, these levels are not much above critical concentrations and deficiency problems are easily encountered. Some calcium deficiency problems seem to be related to this phenomenon.     

Soil texture affects the conversion factor of electrical conductivity from 1:5 soil-water to saturated paste extracts

Electrical conductivity(EC) of soil-water extracts is commonly used to assess soil salinity. However, its conversion to the EC of saturated soil paste extracts(ECe), the standard measure of soil salinity, is currently required for practical applications. Although many regression models can be used to obtain ECe from the EC of soil-water extracts, the application of a site-specific model to different sites is not straightforward due to confounding soil factors such as soil texture. This study was...     

Cross-modality of texture and aroma perception is independent of orthonasal or retronasal stimulation

To assess the influence of orthonasal and retronasal stimulation on cross-modal interactions between texture and flavor perception of food, a series of experiments have been conducted. Healthy human subjects were exposed to strawberry aroma pulses delivered by a computer-controlled stimulator based on air dilution olfactometry. Just prior to exposure to the aroma, the human subjects consumed water, custard, or protein gels with different textures without any added aroma. The aroma was delivered as a sequence of aroma pulses, in either an orthonasal or a retronasal fashion. The retronasal presentation of aroma with concomitant presentation of texture is thought to more closely mimick the in vivo flavor release of semisolid food products as compared to orthonasal stimulation. The time between oral consumption of the food, including swallowing, and the exposure to the aroma varied between 0.5 and 6.5 s. The subjects rated the intensity of the strawberry aroma. It was observed that the intensity of aroma decreased with increasing firmness of the food that was consumed. Aroma pulses delivered 6.5 s after swallowing were perceived as being more intense as compared to aroma pulses delivered immediately after swallowing. In conjunction with late delivery, the effect cross-modal interactions apparently decreased. Significantly higher odor intensities were reported for the aroma stimuli supplied orthonasally in comparison to retronasal administration. The observed cross-modal effect of texture on aroma intensity was not significantly altered by the mode of aroma delivery, i.e., orthonasal or retronasal stimulus administration.     

The influence of tillage on the structure of rhizosphere and root-associated arbuscular mycorrhizal fungal communities

Soil environmental factors affect the structure of arbuscular mycorrhizal (AM) fungal communities present in soil. However, it is not understood to which degree management practices such as tillage lead to dissimilarities between intra- and extraradical AM fungal communities. This study aims to assess the influence of two different soil management practices (conventional tillage and no-till) on the diversity of AMF communities, both in rhizosphere soil and inside corn roots. We hypothesized that under no-till, roots are colonized as they grow through the undisturbed fungal mycelia left from the previous crop whereas under conventional tillage they are colonized by those propagules that survived disturbance and can re-establish in their new relocated and mixed environment. We predicted that the degree of similarity of AM fungal communities inside versus outside the roots would be greater under no-till than under tillage. Using terminal restriction fragment length polymorphism (T-RFLP) and denaturing gradient gel electrophoresis we observed a different AM fungal community present in roots under no-till than under conventional tillage. Moreover, the communities present in the rhizosphere soil were different than in the roots of the corn plants. These results suggest that soil management does alter the diversity of AM fungal communities associated with corn roots and that plants influence the structure of the AMF community colonizing their roots. Sequencing results indicated that the majority of AMF species found in this agricultural soil was Glomus spp. However, further work is required to determine the extent to which AM fungal genotypic alterations by soil management influences competitive relationships.