Influence of soil on the interactions between endomycorrhizae and Azospirillum in sorghum

Sorghum (S. bicolor L. Moench cv. Bok 8) plants were grown in soil or sand-perlite low in plant-available N and P. Plants were inoculated with a vesicular-arbuscular mycorrhizal (VAM) fungus, or a strain of Azospirillum brasilense or both endophytes together. Plants received a nutrient solution which did not contain N or P. Increases in plant dry weight, shoot-to-root ratios, and the N content of dually-infected plants could be accounted for by summing the VAM and Azospirillum effects. For sorghum inoculated with both endophytes, the presence of A. brasilense in the rhizosphere increased VAM colonization and biomass, while the N input due to Azospirillum decreased, possibly due to competition for carbohydrates.Comparisons between sorghum grown with or without VAM-fungal infection in four growth media showed that edaphic factors other than P availability determined the host response to VAM infection. The P-fixing capacity of the soil, rather than the amount of available (NaHCO₃-extractable) P, influenced the balance between mutualistic and parasitic VAM-fungal growth.     

Pentachlorophenol interactions with soil

Pentachlorophenol (PCP) adsorption and desorption equilibrium was studied with two Menfro silt loam soils — upper horizon and lower horizon. For the adsorption studies the variables were: temperature (10 and 30 °C) and the amount of organic matter. The variables for the desorption studies were: temperature (10 and 30 °C), pH and the presence of an anionic and a cationic surfactant. The results from these studies confirmed the importance of soil organic matter for adsorption of PCP on the soils. The adsorption data at different temperatures indicated the physical nature of the adsorption process. The desorption data produced non-singularity and some PCP was irreversibly adsorbed onto the soil despite repeated washings. Increased pH increased the desorption of PCP from the soil. The anionic surfactant, sodium dodecylbenzene sulfonate (SDS) was able to desorb significant amounts of PCP from the soil at doses equal to critical micelle concentration (CMC). But, the nonionic surfactant, surfactant, Triton X-405 required a much higher dose (twice the CMC) to cause a significant desorption of PCP from the soil.     

有机物-金属相互作用对重金属负载土柱中粘土矿物吸附剂再生的影响

Natural clay minerals can play an important role in crude remediation of wastewater polluted with the heavy metals (HMs) Cu,Zn and Ni.The presence and timing of addition of natural dissolved organic matter (DOM) have a significant effect on the HM removal by clay mineral sorbents.However,the influence of the presence of DOM on the remediation of the used clay mineral sorbents once saturated with HMs is largely unknown.To resolve this,clay mineral-rich soil column of varying composition,loaded (i) with Cu,Zn and Ni only,(ii) first with DOM followed by Cu,Zn and Ni,or (iii) with DOM,Cu,Zn and Ni simultaneously,was used in a set of desorption experiments.The soil columns were leached with 0.001 mol L-1 CaCl2 dissolved in water as control eluent and 0.001 mol L-1 CaCl2 dissolved in DOM as treatment eluent.During the preceding loading phase of the sorbent,the timing of DOM addition (sequential or concurrent with HMs) was found to have a significant influence on the subsequent removal of the HMs.In particular when the column was loaded with DOM and HMs simultaneously,largely irreversible co-precipitation took place.Our results indicate that the regeneration potential of clay mineral sorbents in wastewater treatment will be significantly reduced when the treated water is rich in DOM.In contrast,in manured agricultural fields (where HMs enter together with DOM),HM mobility will be lower than expected from interaction dynamics of HMs and clay minerals.     

Effects of soil moisture and plant interactions on the soil microbial community structure

A greenhouse pot experiment was conducted to investigate the influence of soil moisture content and plant species on soil microbial community structure using cultivation-independent methods. White clover and ryegrass were grown individually or in a mixture. Plants were subjected to soil moisture content corresponding to 60% field capacity (FC) and 80% FC. Total plant biomass of white clover and ryegrass increased with increasing soil moisture contents. At a given soil moisture content, total biomass of white clover was lower in the ryegrass–clover (RC) mixture compared with those grown individually, while total biomass of ryegrass was higher. Microbial community structure assessed by phospholipid fatty acid analysis (PLFA) was more affected by plant species than soil moisture. Community level physiological profiles (CLPP), in terms of diversity of substrate utilization and average well colour development (AWCD) were affected by plant species and soil moisture. Soil moisture effects were more pronounced in clover than in ryegrass. AWCD and diversity of substrate utilization in the ryegrass–clover mix were similar to those of sole clover while they differed from that of ryegrass suggesting a dominant effect of clover in the mix.     

The effect of interactions between particles on soil infiltrability

Journal of Soils and Sediments - Soil infiltrability is an important topic in environmental and agricultural research and influences plant growth, soil erosion and water runoff. In this study, the...     

Influence of exchangeable potassium on soil erodibility

Abstract. Regular application of slurry manure in large quantities is thought to degrade soil structure and increase erodibility. One hypothesis links this to the large input of potassium which increases the exchangeable potassium percentage (EPP) and, thereby, dispersion. The effect of EPP on erodibility was quantified in three experiments. In the laboratory, eleven rainfall experiments were conducted using a silty topsoil from a typic Hapludalf which was fertilized to EPPs of 4 to 18%. Field rainfall experiments on 22 Inceptisols and Alfisols were used to examine whether the long-term application of monovalent cations (Na⁺, K⁺ and NH₄⁺) with slurry manure had changed soil properties, especially erodibility. In addition, erodibilities of 32 soils determined with natural and simulated rains were taken from literature. The experiments on these 65 soils together covered a wide range of soils, slopes and rainfalls. Dispersion by a large percentage of highly hydrated ions (K⁺, Na⁺) reduced the infiltration rate faster, caused runoff up to 5 min earlier, and increased sediment concentrations by 15g/l compared to low EPP soils. These changes increased soil erodibility of the Universal Soil Loss Equation (USLE) by 0.021 t × h/N × ha (where N = Newtons) for each 1% increase in EPP + ESP (exchangeable sodium percentage). The ESP contributed little to this increase as ESP was less than 1/10 of EPP in the experiments.
Fields with long-term manure application had similar chemical, physical and microbiological soil properties as fields without slurry manure except for slightly greater pH (+ 0.6) and P (+ 17 mg/kg) values. We conclude that, as long as the potassium input and output are balanced, the long-term use of slurry manure does not increase erodibility.     

Influence of microwave radiation on soil bacteria

Cultures of different soil bacteria were used in the experiment. Both the suppression and the stimulation of the growth were observed for different bacterial species under the impact of microwaves. Spore suspensions responded to microwave radiation upon a shorter time of exposure than suspensions of vegetative bacterial cells. The influence of microwave radiation on the biomass accumulation and the intensity of other physiological processes in different species of streptomycetes led to changes in the number and activity of these microorganisms in the soil microbial complex. Changes in the capacity of streptomycetes for assimilation of substrates under the impact of microwaves were identified by the method of multisubstrate testing.     

黑土区土壤侵蚀厚度对土地生产力的影响及其评价

为了研究黑土区土壤侵蚀厚度对土地生产力的影响,采用盆栽试验,人为剥离黑土表层0、5、10、15、20、25和30 cm土壤以模拟侵蚀厚度不同的耕层土壤,分析土壤侵蚀厚度对土壤理化性质、大豆生物性状和水分利用效率等指标的影响。并对TOPSIS(technique for order preference by similarity to ideal solution)模型进行改进,用于评价侵蚀厚度不同的土壤的土地生产力。结果表明:土壤全N、碱解N、全P、速效P、有机质含量和土壤田间持水率均随侵蚀厚度的增加而递减,土壤容重随侵蚀厚度的增加而递增。土壤侵蚀厚度对大豆生长有显著影响,随着侵蚀厚度的增加,大豆减产率呈"S型"曲线递增,产量、耗水量呈"Z型"曲线递减,水分利用效率呈指数曲线关系递减。改进的TOPSIS模型对不同侵蚀厚度下土地生产力的评价结果较为理想,计算的土地生产力指数随土壤侵蚀厚度的变化呈"Z型"曲线,与大豆产量的变化趋势相同,且二者呈指数函数关系,决定系数达0.996,均方根误差为0.65。研究结果可为黑土区土壤侵蚀防治提供理论依据。     

Influence of carbon amendments on soil denitrifier abundance in soil microcosms

It is known that carbon (C) amendments increase microbial activity in anoxic soil microcosm studies, however the effects on abundance of total and denitrifier bacterial communities is uncertain. Quantitative PCR was used to target the 16S rRNA gene for the total bacterial community, the nosZ functional gene to reflect a broad denitrifier community, and functional genes from narrow denitrifier communities represented by Pseudomonas mandelii and related species (cnorB_P) and Bosea/Bradyrhizobium/Ensifer spp. (cnorB_B). Repacked soil cores were amended with varying amounts of glucose and red clover plant tissue (0–1000 mg C kg^? 1 of soil) and incubated for 96 h. Carbon amendment significantly increased respiration as measured by cumulative CO₂ emissions. Inputs of red clover or glucose at 1000 mg C kg^? 1 of soil caused increased abundance in the total bacteria under the conditions used. There was about an approximate 2-fold increase in the abundance of bacteria bearing the nosZ gene, but only in treatments receiving 500 or 1000 mg C kg^? 1 of soil of glucose or red clover, respectively. Additions of ≥ 500 mg C kg^? 1 soil of red clover and ≥ 250 mg C kg^? 1 of glucose increased cnorB_P-gene bearing denitrifiers. Changes in abundance of the targeted communities were related to C availability in soil, as indicated by soil respiration, regardless of C source. Applications of C amendments at rates that would occur in agricultural soils not only increase microbial activity, but can also induce changes in abundance of total bacterial and denitrifier communities in studies of anoxic soil microcosms.     

Influence of cultivation on soil nitrogen pools

Abstract

Exchangeable NH₄, organic N, and fixed NH₄, were followed in three soil layers (0–25, 25–50, and 50–75 cm) of plots under conventional and minimum tillage in a 10—year field experiment. The main effect of both tillage treatments was a marked increase of fixed NH₄ during the first two years which was attributed to the heavy application of N fertilizers because soils were not fertilized prior to the experiment. Due to spatial variability of soil composition, a statistically significant increase over the 10—year was observed for total and fixed NH₄ only in the surface layer of conventionally tilled soils, probably due to thorough mixing caused by intense cultivation. In this layer the organic N pool did not appear to vary with the years, while the fixed NH₄ pool was influenced by N fertilization. A general trend was a uniform increase of the ratio between fixed NH₄ and total N. Under conventional tillage, the trend was similar for the three soil layers while the reduced amount of fixed NH₄ present in the upper soil layers (0—25 and 25–50 cm) was assumed to be caused by root absorption. Under minimum tillage, the increase of fixed NH₄ ratio was limited to the first 50 cm of soil, and was less pronounced in the top layer where maximum root accumulation is generally expected to be present. The data support the importance for crops of the fixed NH₄ pool.     

Influence of soil factors on the soil enzyme inhibition by Cd

A comparative study was conducted on the toxicity of Cd to alkaline phosphatase activity (ALP) and dehydrogenase activity (DHA) in 18 top soils with contrasting soil properties representative of 14 major soil types in China. Soil pH and carbonate content, soil organic matter, and cation exchange capacity (CEC) largely affected the Cd toxicity on two enzyme activities; with the soil pH having only minor effect on the median ecological dose values based on total Cd concentrations (ED_{50 T}). The values of ED_{50 T}/ED_{50 W} (based on water-soluble Cd content) of alkaline phosphatase and dehydrogenase were strongly influenced by pH and CEC contents, which explained up to 71% of the variation for alkaline phosphatase, 82% of the variation for dehydrogenase, and also were significantly correlated with the parameter K_F derived from Freundlich adsorption isotherms. This study suggests that the values of ED_{50 T}/ED_{50 W} could be useful to evaluate the buffer capacity of soils which protects soil enzymes from harmful effects of heavy metal.     

Influence of clay-solute interactions on aqueous copper ion levels

The extent to which Cu (II) species are removed from aqueous solution by kaolinite clay suspensions has been shown to vary with solution pH, the nature of any ligands present, and the order of contact of the :species. The ability of kaolin type clays to sorb both anions and cations introduces some unexpected effects, and raises some interesting queries in regard to the release of Cu from clay soils and stream sediments.     

Influence of a pyrethroid insecticide on soil fungi

The selective effect of the pyrethroid insecticide (Polytrin) on soil fungi was studied at three doses when incorporated in soil or in agar or liquid medium. Polytrin induced an inhibitory effect on soil fungi after 2, 5 and 40 days when applied at certain levels and a stimulatory effect after 20 days of treatment with the high dose. When incorporated in the agar medium, Polytrin decreased the total counts of fungi, particularly, Aspergillus and Penicillium at the high dose (10.0 ppm). In liquid medium, it showed no significant effect except in case of A. terreus which was significantly enhanced by the three doses.     

Influence of sea salts on the soil metabolism

Abstract

Microbial metabolism in reduction process of waterlogged paddy soils has been studied by Takai, Koyama, and Kamura (1, 2, 3, 4, 5, 6), Koyama (7, 8, 9, 10, 11, 12), and others. The results indicated that microbial metabolism in waterlogged soils takes place according to the following steps: (1) In the early stage of the incubation period, dissolved O₂, is consumed and the redox potential drops rapidly. (2) NO₂? and NO₂? are reduced to N₂. (3) Mn⁴⁺ is reduced to Mn²⁺. (4) Fe³⁺ is reduced to Fe²⁺. (5) SO₄ ²? is reduced to S^2?. (6) H₂ and CH₄ are produced. Takai and Chiang (13) reported that NH₄₊ and PO₄ ³⁺ in waterlogged paddy soils increase with the incubation period. Chiang and Takai (14) indicated that carbohydrates in the soil solutions almost remain constant throughout the incubation period, however, organic acids change similarly to those reported previously (5, 6).     

质地对土壤热性质的影响研究

土壤热性质是水热迁移研究中的重要参数之一。根据非稳态条件下热流方程的差分解和实测土壤温度资料计算了不同质地土壤的热扩散率，并得出了质地影响下的土壤导热率关系式。研究结果表明，对特定土壤而言，土壤导热率与含水率之间可建立幂函数关系；砂粒、粉粒和粘粒含量对土壤热性质有不同程度的影响；不同质地土壤的热性质与土壤水吸力之间存在良好的定量关系；此外，含盐土壤的导热率可表示为浓度的幂函数关系。     

Influence of variable inundation regimes on soil collembola

Soil collembola in floodplain habitats are known to react dynamically to inundation, showing direct negative effects of inundation as well as rapid regeneration after flooding. Unknown, however, are how these communities react to variable inundation and the role that spatial and temporal habitat heterogeneity plays. Therefore, the small-scale spatio-temporal dynamics of soil collembolan communities after varying inundation were studied in floodplain habitats in the Upper Rhine Valley in Germany. After frequent flooding, significant differences in density and species richness were found between different floodplain levels of the same location. Due to different species’ responses, major differences occurred in community structure. After infrequent inundation the densities and species richness of the same sites and especially hygrophilous components decreased dramatically. Between neighbouring sites, species exchange occurred and community structures became more similar. The results show that at the same locality soil collembola react dynamically as well as differentially to changes in the hydrological regime. Small-scale landscape heterogeneity allows a mixture of differentially reacting species to occur within the same regional metacommunity. Long-term stability of collembolan communities despite the high spatio-temporal heterogeneity of floodplains is thus maintained by metacommunity dynamics.     

Influence of PAH contamination on soil ecological status

Purpose

The purpose of this paper is to study the responses of soil biological parameters as indicator of ecological status on PAH-contaminated soil.

Materials and methods

Studies are conducted on the soils and natural grassy vegetation of monitoring plots subjected to Novocherkassk power station (NPS) emissions. Monitoring plots were established at different distances from the NPS (1.0–20.0 km).

Results and discussion

The level of polycyclic aromatic hydrocarbons (PAHs) around NPS is the highest at the monitoring plot located at distance 1.6 km to the northwest through the prevailing wind direction. Gradually, decrease of PAHs was observed while increasing the distance from the NPS through the prevailing wind direction. Calculation of correlations between PAH level and biological activity parameters of soils showed lack of dependence with total and every PAH content in all 12 studied monitoring plots. The most significant correlations were found between PAH content and enzyme activity in the monitoring plots situated through the prevailing wind direction from NPS.

Conclusions

The main pollution source in the studied area is NPS. It was found that contamination of soil by PAHs has a direct dependence on the activity of all biological communities in chernozems, as well as the activities of dehydrogenase and the phytotoxicity of soils. Inverse correlations have been revealed between the PAH contamination and abundance of soil bacteria.

     

Influence of irrigated agriculture on soil microbial diversity

Organic carbon (C), bacterial biomass and structural community diversity were measured in Southern Idaho soils with long term cropping histories. The soils tested were native sagebrush vegetation (NSB), irrigated moldboard plowed crops (IMP), irrigated conservation – chisel – tilled crops (ICT) and irrigated pasture systems (IP). Organic C concentration in soils decreased in the order NSB 0–5 cm > IP 0–30 cm = ICT 0–15 cm > IMP 0–30 cm > NSB 5–15 cm = NSB 15–30 cm. Active bacterial, fungal and microbial biomass correlated with soil C as measured by the Walkely Black method in positive curvilinear relationships (r² = 0.93, 0.80 and 0.76, respectively). Amplicon length heterogeneity (LH-PCR) DNA profiling was used to access the eubacterial diversity in all soils and at all depths. The Shannon–Weaver diversity index was used to measure the differences using the combined data from three hypervariable domains of the eubacterial 16S rRNA genes. Diversity was greatest in NSB 15–30 cm soil and lowest in the IMP soil. With the exception of IMP with the lowest diversity index, the samples highest in C (NSB 0–5 cm, IP 0–30 cm, ICT 0–15 cm) reflected lower diversity indices. However, these indices were not significantly different from each other. ICT and IP increase soil C and to some extent increase diversity relative to IMP. Since soil bacteria respond quickly to environmental changes, monitoring microbial communities may be one way to assess the impact of agricultural practices such as irrigation and tillage regimes.     

Influence of humate-solute interactions on aqueous heavy metal ion levels

The extent to which heavy metal ions (Cu, Pb, Zn, Cd) are removed from aqueous solution by humic acid suspensions has been found to vary with solution pH, concentration of competing cations, nature of the organic material, and the complexing power of any ligands present. The amount adsorbed in acid media increased with pH until the threshold value required for partial dissolution of the solid, and formation of soluble metal humates, was exceeded The adsorption maximum pH, and the apparent capacity at lower values, varied with the substrate used and cation being sorbed. The affinity order sequence, as derived from adsorption isotherm studies, was Pb > Cu > Cd > Zn ? Ca > Mg. The retention of metal ion by the solid was reduced in the presence of ligands, with zero uptake occurring when the soluble complexes formed had a greater effective stability than those resulting from humic acid-metal ion interactions. With environmental systems having a high organic content, the humic acid component can play a dominant role in determining the final distribution of metal ions, and for predictive purposes, investigation of the effect of pH on uptake is more informative than measurement of adsorption isotherm parameters, since the observed trends reflect differences in functional group properties, relative affinities and solubility effects. The curves have minima which fall within the pH spreads encountered in natural systems, and small pH changes can cause significant variations in solution levels.     

少免耕对晚稻土生物活性影响的研究

为探明少免耕对土壤生物学特征的影响,制定合理的耕作制度培肥土壤,进行了33％稻草总重量覆盖少免耕对晚稻土生物活性影响的定位试验研究。结果表明：晚稻分蘖盛期土壤纤维素酶活性表现为免耕〉翻耕〉少耕,木聚糖酶活性、过氧化氢酶活性为少耕〉免耕〉翻耕,脲酶活性、蛋白酶活性为翻耕〉少耕〉免耕,硝化作用强度为免耕〉少耕〉翻耕,微生物活度、氨化作用强度为少耕〉翻耕〉免耕。在晚稻收获期,土壤脲酶活性、过氧化氢酶活性、木聚糖酶活性表现为少耕〉免耕〉翻耕,微生物活度、蛋白酶活性、纤维素酶活性、氨化作用强度、硝化作用强度表现为翻耕〉少耕〉免耕。少免耕能够在一定程度上改善土壤生物性状,且覆盖少量稻草时少耕能够在一定程度上促进稻草分解,有利于水稻生长。