Impact of cycloheximide addition on adenylates in soil

Cycloheximide inhibits specifically the ribosomal protein synthesis of eukaryotic cells, i.e. the metabolism of soil fungi. We measured cycloheximide effects on adenylates in 20 different soils (0-10 cm depth) from arable, grass and forest land with a large variety of soil properties. The aims were (1) to assess the interactions between cycloheximide effects and soil properties and (2) to prove the relationship between cycloheximide effects on ATP and the ergosterol-to-microbial biomass C ratio, which is an indicator for the fungal proportion of the total microbial biomass. The adenylates ATP, ADP and AMP were measured 6 h after adding either 10 mg cycloheximide per gram soil in combination with 24 mg talcum per gram soil or 24 mg talcum per gram soil solely. The medians of the relative increases in AMP and ADP were 45 and 25% and the medians of the relative decreases in ATP and adenylates were −36 and −12%. These changes in adenylate composition lead to a cycloheximide-induced relative decrease in the adenylate energy charge level of 15%. The relative decrease in ATP content after cycloheximide addition was significantly correlated with the ATP-to-microbial biomass C ratio, but not with the ergosterol-to-microbial biomass C ratio. The absolute increase in ADP and the absolute decrease in ATP were affected by the clay content according to principal component analysis. The reduction of the ATP-to-microbial biomass C ratio indicates that this ratio had the potential of being an important ecotoxicological indicator of direct toxic effects of organic pollutants on soil microorganisms.     

Application of the selective inhibition method to determine bacterial: fungal ratios in three beechwood soils rich in carbon — Optimization of inhibitor concentrations

Bacterial and fungal contributions to microbial respiration in three beechwood soils rich in C (two basalt soils and one limestone soil) were investigated by using streptomycin and cycloheximide to inhibit substrate-induced respiration after glucose (8000 g g^-1), N, and P addition to soil samples. The inhibitors were added as solutions (2000, 8000, and 16000 g g^-1) and the reduction in substrate-induced respiration after separate and combined inhibitor addition was measured in an automated electrolytic microrespirometer. Bacterial and fungal contributions to microbial respiration were calculated using the interval 6–10 h after inhibitor application. The microbial biomas was smaller in the two basalt soils (Oberhang and Mittelhang) than in the limestone soil (Unterhang). In the presence of both inhibitors, microbial respiration was inhibited by a maximum of 45, 45, and 25% in the two basalt soils and the limestone soil, respectively. Inhibition of microbial respiration was at a maximum at streptomycin and cycloheximide concentrations of 16000 g g^-1. The inhibitor additivity ratio approached 1.0 even at high inhibitor concentrations, indicating high inhibitor selectivity. Calculated prokaryote: eukaryote ratios indicated lower bacterial contributions to the microbial biomass in the Mettelhang (0.74) and Unterhang (0.73) than in the Oberhang (0.88) soil.     

Evaluation of the selective respiratory inhibition method for measuring the ratio of fungal:bacterial activity in acid agricultural soils

A procedure for the measurement of the fungal and bacterial contribution to substrate-induced respiration was tested in three arable soils. Glucose and different amounts of cycloheximide (eukaryote inhibitor) and streptomycin sulfate (prokaryote inhibitor) were added to soil suspensions, and respiration (CO₂ evolution) was measured. Streptomycin sulfate concentrations from 10 to 120 mg ml^–1 soil solution caused a stable inhibition of respiration. Amounts of cycloheximide ranging from 5 to 35 mg ml^–1 showed an increasing inhibition. In a test with separate and combined addition of the antibiotics at maximum inhibitory concentrations, inhibition by streptomycin was completely overlapped by cycloheximide. This indicated non-target inhibition which may lead to overestimation of fungal respiration. Experiments with sterilized soils inoculated with either fungi or bacteria confirmed that streptomycin selectively inhibited bacteria. Cycloheximide, however, did not only inhibit fungal respiration already at 2 mg ml^–1, but also increasingly inhibited bacterial respiration at increasing concentrations. Only at less than 5 mg cycloheximide ml^–1 was the condition of selective fungal inhibition fulfilled. When 2 mg cycloheximide and 10 mg streptomycin sulfate ml^–1 were applied, the sum of the separate inhibitions almost equalled the combined inhibition by the mix of both inhibitors in field samples. This method yielded fungal:bacterial respiration ratios of 0.50 to 0.60, and confirmed the dominance of bacteria in Dutch arable soils. The ratios obtained by the selective inhibitors were not correlated with, and were higher than, ratios of fungal:bacterial biovolume (0.19 to 0.46) as determined by microscopy and image analysis. Similar measurements in a forest soil (A-horizon) raised doubts on the reliability of the fungal inhibition by cycloheximide in this soil. It is concluded that the separate:combined inhibition ratio should always be checked, and comparison with other approaches is recommended. Received: 17 September 1996     

土壤中拟除虫菊酯微生物降解研究

微生物降解是拟除虫菊酯类农药从土壤中消去的主要途径。本文介绍了拟除虫菊酯降解菌的分离鉴定、降解基因的克隆以及微生物降解机理研究的近期成果,综合介绍了拟除虫菊酯异构体选择降解的特征、原因以及可能产生的环境效应,重点分析了农药疏水性、土壤吸附、重金属、土壤养分及长期施肥、共存农药对土壤中拟除虫菊酯微生物降解的影响,最后对土壤微生物修复前景进行了展望。     

手性异丙甲草胺在土壤中的选择性降解

Separation of chiral enantiomers and the dissipation of rac-metolachlor and S-metolachlor in soil were evaluated using achiral high-performance liquid chromatography （HPLC） and chiral gas chromatography （GC） methods. Under the experimental conditions the possible metabolite was considered to be N-（2-ethyl-6-methyl-phenyl）-2-hydroxy-acetamide. Because of the presence of two chiral elements （asymmetrically substituted carbon and chiral axis）, the baseline separation of metolachlor enantiomers was not achieved. S-metolachlor degraded faster in soil than rac-metolachlor. After a 42-day incubation, 73.4% of rac-metolachlor and 90.0% of S-metolachlor were degraded. However, due to the absence of biological processes the degradation process in sterilized soil showed no enantioselectivity. The results indicated that enantioselective degradations could greatly affect the environmental fate of metolachlor and should be considered when the environmental behavior of these compounds was assessed.     

西藏"一江两河"地区土壤退化特征

西藏"一江两河"地区日趋严重的土壤退化是由其生态环境的脆弱性、地貌结构的特殊性,特别是人类影响和干预的广泛性、非合理性决定的。在阐述土壤退化类型、特征的基础上,就土壤退化的发生机制进行了综合分析。     

我国设施农业土壤质量退化特征与调控研究进展

设施土壤质量退化已成为制约现代设施农业可持续发展的瓶颈。了解设施土壤退化成因与特征,并采取适宜的调控措施,对于促进设施农业持续健康发展具有重要意义。本文综述了国内目前设施农业土壤次生盐渍化、酸化、微生物区系破坏、养分失调、有害物质积累等5个方面的退化特征与成因。简述了生物、农业、工程3类调控措施在改良设施土壤方面的应用研究进展。并且针对我国设施土壤质量研究中存在的关于探索形成原因和控制机理方面的研究少,原创性设施土壤改良与调控技术仍然十分缺乏,大尺度、长时间设施土壤质量演变的长期定位研究和动态监测工作十分滞后,有关设施土壤退化因素叠加效应与交互作用机理研究尚未涉及等问题,提出应将构建设施土壤质量标准体系,开展设施土壤质量退化演变机理以及拓展调控与改良技术,系统研究不同退化形式之间的相互作用,以及拓展新技术在设施农业土壤研究中的应用等4方面作为今后研究的重点。     

二甲戊灵在两种土壤及马铃薯中的残留降解动态

在北京和安徽两地开展了田间试验,研究二甲戊灵在土壤与马铃薯植株中的残留降解动态与残留水平。试验样品中的二甲戊灵用乙腈提取,分散固相萃取净化,采用GCMS法,选择离子模式监测(SIM)定量测定。二甲戊灵在马铃薯块茎、植株和土壤的添加回收率分别为84.5%~89.8%、91.5%~101%和78.7%~88.1%,相对标准偏差分别为4.8%~8.5%、6.2%~8.2%和5.2%~7.8%。结果表明,二甲戊灵在马铃薯植株与土壤中的降解动态符合一级动力学模型,在安徽(潮土)和北京(褐土)两地土壤中的半衰期分别为21.0和30.1d,在马铃薯植株中的半衰期分别为9.5和10.6d。收获后,马铃薯块茎中二甲戊灵的残留量小于0.01mg·kg~(-1),低于欧盟规定的二甲戊灵在马铃薯中最大允许残留限量0.05mg·kg~(-1)。研究结果为了解二甲戊灵在环境中的残留水平及食物链迁移转化提供了参考。     

澳大利亚、中国和泰国的热带地区的土壤化学退化的量化及修复

Soil and land degradation in the tropics can be identified and described in terms of physical,chemical,and biological changes from its pristine state brought about by natural and anthropogenic influences.A characteristic of these ecosystems is their capacity to recycle nutrients through soil organic matter(SOM). Following disturbance through changed land management.SOM is rapidly mineralized and there is a cor responding decline in fertility and the variable charge component of the cation exchange capacity.As these ecosystems are strongly dependent on SOM for their functionality,changed land use can have irreversible impacts on the productivity of these systems.The paper focuses on quantifying chemical degradation throughbenchmaking using data from paried sites in tropical China and Thailand using surface charge finger printing.Using values taken from the fingerprint of an undistubed soil,an index of chemical degradation from ideality was calculated.Various management stratgeies that attempt to reverse degradative trends or improve poor quality soils in their natural condition are discussed.such as the ddition of natural clays and silicated materials.Results are present to whow the effect of each of the aforementional strategies on surface charge characteristics and associated increases in plant productivity.     

适宜水分和养分提高土壤中磺酸二甲嘧啶降解率

医疗和养殖过程中抗生素的广泛使用导致了土壤环境中抗生素的污染。为了解进入农田土壤中抗生素的降解规律,该文以养殖业广泛使用的磺胺二甲嘧啶和2种不同养分水平的土壤为试验材料,采用盆栽方法研究了肥料种类(有机肥、NPK肥、N肥、PK肥等)、耕作强度(翻耕、免耕)、水分条件(长期干燥、长期湿润、干湿交替、长期潮湿)及种植作物(种植蔬菜、不种蔬菜)对土壤中磺胺二甲嘧啶降解的影响。结果表明,与不施肥处理比较,施用有机肥、NPK肥、N肥可促进土壤中磺胺二甲嘧啶在土壤中的降解,并以施用有机肥的效果最为明显;但施用PK肥对土壤中磺胺二甲嘧啶的降解影响不明显。翻耕可促进土壤中磺胺二甲嘧啶的降解,干湿交替、长期湿润比长期干燥和长期潮湿土壤环境下更有利于磺胺二甲嘧啶的降解。种植蔬菜比不种蔬菜土壤的磺胺二甲嘧啶的降解率高,根际土壤中磺胺二甲嘧啶的降解高于总体土壤。高养分土壤中磺胺二甲嘧啶的降解一般高于低养分土壤。分析认为,施肥、土壤养分水平、种植蔬菜对土壤中磺胺二甲嘧啶的降解的影响可能主要与这些因素改变了土壤微生物活性有关;翻耕可促进土壤中抗生素的光降解强度。研究认为,施肥、耕作和水分管理可以在一定程度上加速土壤中磺胺二甲嘧啶的降解。     

Remote sensing of soil degradation: Progress and perspective

Soils constitute one of the most critical natural resources and maintaining their health is vital for agricultural development and ecological sustainability, providing many essential ecosystem services. Driven by climatic variations and anthropogenic activities, soil degradation has become a global issue that seriously threatens the ecological environment and food security. Remote sensing (RS) technologies have been widely used to investigate soil degradation as it is highly efficient, time-saving, and broad-scope. This review encompasses recent advances and the state-of-the-art of ground, proximal, and novel RS techniques in soil degradation-related studies. We reviewed the RS-related indicators that could be used for monitoring soil degradation-related properties. The direct indicators (mineral composition, organic matter, surface roughness, and moisture content of soil) and indirect proxies (vegetation condition and land use/land cover change) for evaluating soil degradation were comprehensively summarized. The results suggest that these above indicators are effective for monitoring soil degradation, however, no indicators system has been established for soil degradation monitoring to date. We also discussed the RS's mechanisms, data, and methods for identifying specific soil degradation-related phenomena (e.g., soil erosion, salinization, desertification, and contamination). We investigated the potential relations between soil degradation and Sustainable Development Goals (SDGs) and also discussed the challenges and prospective use of RS for assessing soil degradation. To further advance and optimize technology, analysis and retrieval methods, we identify critical future research needs and directions: (1) multi-scale analysis of soil degradation; (2) availability of RS data; (3) soil degradation process modelling and prediction; (4) shared soil degradation dataset; (5) decision support systems; and (6) rehabilitation of degraded soil resource and the contribution of RS technology. Because it is difficult to monitor or measure all soil properties in the large scale, remotely sensed characterization of soil properties related to soil degradation is particularly important. Although it is not a silver bullet, RS provides unique benefits for soil degradation-related studies from regional to global scales.     

土壤退化下草地演化的数值模拟及野外验证

Both theoretical and field observations were examined to study the close relationship between soil degeneration and the evolution of grassland vegetation. A general n-species model of equal competition under different degrees of soil degradation was applied to field data in order to probe the dynamic processes and mechanisms of vegetation evolution due to the effects of the soil‘s ecological deterioration on grassland vegetation. Comparisons were made between the theoretical results and the practical surveys with satisfactory results.     

Aspects of the adsorption and degradation of isoproturon in a heavy clay soil

Abstract. Degradation of isoproturon in a heavy clay soil followed first-order reaction kinetics with half-lives at 15 °C of 27 and 208 days in the topsoil and subsoil, respectively. Adsorption when shaken with 3 mm sieved samples of the soil fitted the empirical Freundlich relationship with k values of 3.25 in the topsoil and 1.06 in the subsoil. Adsorption in a static system with different sized aggregates of soil did not reach equilibrium, even after 24 hours contact, and the rate of adsorption was slower with larger aggregates. Following an adsorption period of 24 hours, desorption equilibrium was reached more rapidly with larger (6–10 mm) than with smaller (<3 mm) aggregates. Adsorption isotherms measured in a static system with a soil:water ratio typical of field conditions in winter also indicated less adsorption than that measured in shaken, laboratory systems with low soil:water ratios. The rate of change in water extractable residues of the herbicide was more rapid than that of total extract-able residues following application of isoproturon to the heavy clay soil in the field. The implications of the results for isoproturon leaching under field conditions are discussed.     

Estimated Holocene soil carbon-soil degradation in Nevada and Western Utah, USA

There is much interest in predicting future carbon-soil degradation and that occurring today. We have National Soil Survey Laboratory data to assess some of the soil carbon degradation in the Great Basin and western Utah. For this we included data on 32 Nevada and Utah soils on Pleistocene geomorphic surfaces at elevations of 973 to 3172 m. Their mean annual precipitation (MAP) ranges from 20 to 55 cm and mean annual soil temperatures (MAST) from 5 to 12 °C. The MAP and MAST closely correlate with elevation (E) (r = 0.96 and − 0.97 respectively). Mountain big sagebrush (Artemisia tridentata Nutt. ssp. vaseyana (Rydb.) Beetle) dominates vegetation at the higher, colder elevations. Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle and Young) and juniper (Juniperus L.) dominate at intermediate elevations. Little sagebrush (Artemisia arbuscula Nutt.) and related desert species dominate at the lower, warmer elevations. We used acid dichromate digestion and FeSO₄ titration to analyze for soil organic carbon (SOC) and bulk density and coarse fragments in the soils to put the data on a volume basis. The soils are well drained and uncultivated. Accumulation of organic carbon in each pedon (OCp) is correlated to MAP and MAST (r = 0.81, and − 0.78 respectively). We predicted OCp from the relationship,

(1)

r² = 0.64, S.E. = 1.30, n = 32. The soil OC degradation that may have occurred through the Holocene ranges from 35% at sites of the present Aridisols and Vertisols to 22% for the sites of the Mollisols and Alfisols. Eq. (1) shows that today, MAST rises of 1 to 3 °C would produce further OCp degradation from today's levels of 1% to 13% in Aridisols and Vertisols and 12% to 25% in the Mollisols and Alfisols respectively. It also shows that if the MAST drop of 6 °C predicted for the Pleistocene occurred, many of the Aridisols and Vertisols likely would have been Mollisols or Alfisols during the Pleistocene. A temperature rise of 1 °C in a century would likely move the Mollisol–Aridisol boundary from its present 2300 m elevation to an elevation of about 2900 m. A temperature rise of 3 °C in a century would likely move the Mollisol–Aridisol boundary from its present 2300 m elevation to elevations of the highest elevations in Nevada and to the middle of Idaho. Increasing the temperature by 3 °C will likely also increase the area affected by severe desertification in the southern Great Basin north by about 20%.     

土地退化/恢复中土壤可蚀性动态变化

利用EPIC公式计算了不同开垦和退耕年限的土壤可蚀性K值,对黄土高原典型自然恢复区子午岭林区土地退化/恢复过程中土壤可蚀性的动态变化进行了系统的研究。结果表明：土地开垦后,土壤颗粒向粗骨化方向发展,有机碳含量降低,土壤可蚀性逐渐增强;土地退耕过程中,土壤有机碳含量逐渐增加,肥力水平提高,可蚀性逐渐减小;土壤中有机碳含量、全氮含量、水稳性团聚体含量以及团聚度与土壤可蚀性K值相关最为密切;土壤可蚀性的强弱本质上取决于土壤有机碳含量,恢复植被以提高土壤有机质含量,促进土壤团聚体的形成,增强土壤团聚度,是降低土壤可蚀性能的重要途径。     

Suppression of chlorate degradation in longan plantation soil after multiple applications of chlorate and accelerated degradation by sugar amendment

Potassium chlorate is widely used as an active substance for flower induction in longan plantations for off-season production of fruits in northern Thailand. Contamination of groundwater with residual chlorate in soil is a cause for concern because of its toxicity to human health. Based on the assumption that potassium chlorate might adversely affect chlorate-reducing soil microorganisms due to its disinfecting nature, the effect of repeated applications of chlorate on chlorate decomposition in soil was examined in a laboratory study. In the longan plantation field soil which had received an annual application of potassium chlorate for three years, chlorate decomposition was slower than that in the soil without application. The suppression of chlorate decomposition was confirmed in the soil to which potassium chlorate was applied repeatedly in the laboratory. However, even in such soils that had received multiple applications of potassium chlorate, chlorate decomposition was remarkably enhanced by soil amendment with glucose or sucrose. Sugar amendment seemed to be an effective way of cleaning-up the residual chlorate in longan plantation field soils.     

设施条件下添加有机肥对土壤中土霉素消减作用

在设施条件下,通过在含有不同浓度(43.62、1638.78和10936.38μg/kg)土霉素的土壤中添加不同比例(5%、10%)有机肥,研究有机肥对土霉素消减的影响及其影响因素,并运用准一级动力学模型对土霉素消减动态的拟合。结果表明,在低污染处理组和高污染处理组28 d后土霉素消减进入平稳期,低污染处理组添加5%和10%有机肥后,消减率提高了17.71%和16.03%,半衰期缩短了9.02和9.50 d;高污染处理组添加5%和10%有机肥后,消减率提高了19.83%和17.93%,半衰期缩短了12.28和13.38 d。主成分分析对土壤理化性质与土霉素消减动态的分析结果表明土壤有机质、总氮及p H值与添加有机肥的比例呈较高的正相关性,土霉素的消减率与有机肥添加比例成一定的正相关性。与对照土壤比较,添加有机肥可促进土壤中土霉素的消减,并随土霉素初始浓度的增大作用更为明显,但有机肥添加比例对土霉素消减的促进作用没有显著差异。     

三峡库区秭归县土壤退化综合评价

建立了土壤退化评价指标及其评价标准,并对三峡库区秭归县的土壤退化强度、类型与空间变化 进行了评价与分析。结果表明,秭归县土壤退化中紫色土、石灰土、黄棕壤和黄壤的退化较为严重。林荒地比耕地土壤退化严重。耕地中旱地比水田退化严重。秭归县土壤退化类型以薄层化、粗骨化、旱化和养分贫瘠化为主,其中养分贫瘠化又以缺K和缺P趋势明显。土壤退化因人们对土壤利用方式和强度的差异而存在着空间变异,秭归县位于长江两岸河谷地带的一些乡镇土壤养分退化较为严重,而远离此的高山区地带的一些乡镇土壤退化较轻。     

尕海湿地植被退化过程中土壤碳矿化特征研究

以甘南尕海4种不同退化程度的湿地(未退化(UD)、轻度退化(LD)、中度退化(MD)及重度退化(HD))为研究对象,采用室内5 ℃、15 ℃、25 ℃、35 ℃ 培养法,测定不同土层 SOC 矿化速率和累积矿化量,运用一级动力学方程对土壤的半矿化分解时间(T_1/2)、有机碳矿化潜势(C₀)等参数进行拟合,分析温度、土壤深度和退化程度对土壤碳矿化过程的影响。结果表明：(1)在不同土层、不同温度下,各植被退化程度湿地土壤有机碳 CO₂ 释放量在整个培养期间大致可以分三个阶段,0-4 d快速生成 CO₂ 阶段,4-27 d缓慢生成 CO₂ 阶段,27-41 d平稳阶段;0-10 cm 土层各培养温度下,土壤有机碳矿化速率表现为UD＞LD＞MD＞HD。(2)培养期间,不同退化湿地土壤有机碳矿化速率均随土层加深而降低,表层 0-10 cm的矿化速率(1.14~16.23 mg/(g?d))均显著高于10-20 cm(1.05~2.85 mg/(g?d))和20-40 cm(0.94~1.26 mg/(g?d))土层。(3)整个培养期内,不同退化湿地土壤有机碳总累积矿化量排序为5 ℃(34.54 mg/g)、15 ℃(46.67 mg/g)、25 ℃(58.28 mg/g)和35 ℃(86.46 mg/g)。(4)双库一级动力学方程的C₀值随退化程度增加呈递减趋势,而C₀/SOC随着温度的升高而降低。