Alternate partial root-zone irrigation induced dry/wet cycles of soils stimulate N mineralization and improve N nutrition in tomatoes

Given the same amount of irrigation volume, applying alternate partial root-zone irrigation (PRI) has improved crop N nutrition as compared to deficit irrigation (DI), yet the mechanisms underlying this effect remain unknown. Therefore, the objective of this study was to investigate whether PRI induced soil dry/wet cycles facilitate soil organic N mineralization hereby contributing to the improvement of N nutrition in tomatoes. The plants were grown in split-root pots in a climate-controlled glasshouse and were subjected to PRI and DI treatments during early fruiting stage. ¹⁵N-labeled maize residues were incorporated into the soils. Results showed that PRI resulted in 25% higher net ¹⁵N mineralization than did DI, indicating that the enhanced mineralization of soil organic N alone could account for the 16% increase of N accumulation in the PRI than in the DI plants. The higher net N mineralization under PRI was coincided with an intensified soil microbial activity. In addition, even though soil chloroform fumigation labile carbon (CFL-C, as an index of microbial biomass) was similar for the two irrigation treatments, a significant increase of chloroform fumigation labile nitrogen (CFL-N) was found in the PRI wetting soil. Consequently, the C:N ratio of the chloroform fumigation labile pool was remarkably modified by the PRI treatment, which might indicate physiological changes of soil microbes or changes in labiality of soil organic C and N due to the dry/wet cycles of soils, altering conditions for net N mineralization. Moreover, in both soil compartments PRI caused significantly less extractable organic carbon (EOC) as compared with DI; whilst in the PRI wetting soil significantly higher extractable organic nitrogen (EON) was observed. A low EOC:EON ratio in the PRI wetting soil may indicate an increasing net mineralization of the organic N as a result of microbial metabolism. Conclusively, PRI induced greater microbial activity and higher microbial substrates availability are seemingly responsible for the enhanced net N mineralization and improved N nutrition in tomato plants.     

Application of the chloroform fumigation-incubation method to the estimation of soil microbial biomass in burned and unburned Japanese red pine forests

Abstract Estimation of soil microbial biomass in burned and unburned Japanese red pine forests was attempted using the chloroform fumigation-incubation method. As the amount of CO₂-C evolved from the fumigated soil for 10–20 days after fumigation (designated as F') was always lower than that from the unfumigated soil during the same period (UF'), the formula, microbial biomass-C(M) = the amount of CO₂-C evolved from the fumigated soil for 0–10 days after fumigation, F) − F'/ k _c, was proposed instead of Jenkinson's conventional formula, M = (F − UF')/ k _c. The k _c value was also determined as 0.30 using 3 fungal and 3 bacterial cultured species as internal standards. Microbial biomass-C calculated by (F − F')/0.30 decreased with soil depth at both the burned (Nenoura, 3.5 years after fire) and unburned (Ato) sites, showing the significant correlation with the decrease of soil respiration and organic C content along soil depth. Microbial biomass-C in the 0–2 cm soil layer at the burned site at Nenoura was 130 mg/100 g dry soil and those in the HF horizon and 0–2 cm soil layer at the unburned site at Ato were 686 and 146 mg/100 g dry soil, respectively.     

高寒草甸不同植被土壤微生物数量及微生物生物量的特征

用稀释平板法和氯仿熏蒸法研究了藏嵩草草甸、小嵩草草甸、矮嵩草草甸、禾草草甸、杂类草草甸及金露梅灌丛土壤的微生物数量、生物量及有机质的变化特征.结果表明:0～40 cm土层细菌和放线菌数量、微生物生物量碳和土壤有机质含量均以藏嵩草草甸最高,其微生物生物量及土壤有机质显著高于其它5种植被;真菌数量以金露梅灌丛最高;由表层到深层,随着土壤深度的增加以上各项指标均呈下降趋势.通径分析表明:土壤各生物环境因子之间存在着不同程度的相关性;土壤微生物数量、生物量及土壤有机质含量均与土壤水分含量存在显著的相关关系,说明土壤水分是调节高寒草甸生态系统土壤微生物代谢及物质转化的关键因子.     

Status of copper in some calcareous and non-calcareous soils of Egypt

Summary To assess the status of copper in Egyptian soils, surface and subsurface soil samples were collected from various geographical regions of Egypt and of various genesis. The samples were analyzed for the total Cu, water-soluble plus exchangeable as well as the acid-extractable and EDTA-extractable Cu. The total Cu varied between 3.5 and 72.3 ppm. Less than 2% of this copper was in the soluble plus exchangeable form. The highest values of total and soluble plus exchangeable copper were found in the alluvial soils while the sandy soils had the least amounts. This was attributed to the high clay and organic matter content of the alluvial soils in addition to the dominance of montmorillonitic clay minerals in their fine fraction. The calcareous soils showed intermediate values of total and soluble plus exchangeable Cu due to their lower organic matter and clay mineral content. The clay mineralogy of these soils revealed the dominance of illitic and kaolinitic minerals which are relatively poor in Cu and other trace elements.Because of their relatively higher organic matter content, the alluvial soils had a large percentage (up to 43%) of their total Cu in the EDTA extractable form. The calcareous soils, on the other hand, had a large percentage (up to 52%) of their Cu in the acid-extractable form. The EDTA extractable Cu was correlated with the organic matter content of the soils. Since the pH of the EDTA extract was found to be dependent on the CaCO₃ content of the soils, it was suggested that the method be modified so that the final pH of the extract is constant for all soils.     

Phytotoxicity and distribution of copper in tropical soil amended with sewage sludge and copper sulfate

Abstract

A greenhouse experiment was conducted to evaluate phytotoxicity and distribution of Cu in a tropical soil amended with sewage sludge (Sw) and copper sulfate (CuSO₄.5H₂O). Samples of a clay soil from the State of Paraná, Brazil were collected at depth of 0–20; 20–40 and 40–60 cm, and brought to the laboratory to be properly accommodated in experimental units (PVC tubes). The Cu treatments were performed by the application of Sw (10 t ha-¹) amended with Cu (SB-T), and by CuSO₄. H₂O (WB-T). Lettuce plants were cultivated in the amended soil in order to predict the toxicity of the Cu. The experiment was conducted for 70 days, and then the lettuce plants and soil samples were collected for analysis. A sequential method was used to separate soil Cu into following fractions: exchangeable, amorphous iron oxide bound, crystalline iron oxide bound, organic matter bound and residual bound. The experimental results showed that Fe, Zn, K, P, Cu and organic matter amounts of the soil increased with the treatment SB-T. The toxic phyto-available Cu content in the soil for the lettuce plants was 80.00 mg kg^-1. A percolation study showed that the Cu contents were larger for the first 20 cm of depth, indicating that the metal was not transported down the soil profile. The Cu content of different fractions declined in an order residual > amorphous iron oxide > crystalline iron oxide > organic matter > exchangeable, regardless of treatment performed. Additionally, the Cu contents added from treatments were determined mainly in amorphous iron oxide fraction.     

Microbial activity and soil respiration under nitrogen addition in Alaskan boreal forest

Climate warming could increase rates of soil organic matter turnover and nutrient mineralization, particularly in northern high‐latitude ecosystems. However, the effects of increasing nutrient availability on microbial processes in these ecosystems are poorly understood. To determine how soil microbes respond to nutrient enrichment, we measured microbial biomass, extracellular enzyme activities, soil respiration, and the community composition of active fungi in nitrogen (N) fertilized soils of a boreal forest in central Alaska. We predicted that N addition would suppress fungal activity relative to bacteria, but stimulate carbon (C)‐degrading enzyme activities and soil respiration. Instead, we found no evidence for a suppression of fungal activity, although fungal sporocarp production declined significantly, and the relative abundance of two fungal taxa changed dramatically with N fertilization. Microbial biomass as measured by chloroform fumigation did not respond to fertilization, nor did the ratio of fungi : bacteria as measured by quantitative polymerase chain reaction. However, microbial biomass C : N ratios narrowed significantly from 16.0 ± 1.4 to 5.2 ± 0.3 with fertilization. N fertilization significantly increased the activity of a cellulose‐degrading enzyme and suppressed the activities of protein‐ and chitin‐degrading enzymes but had no effect on soil respiration rates or ¹⁴C signatures. These results indicate that N fertilization alters microbial community composition and allocation to extracellular enzyme production without affecting soil respiration. Thus, our results do not provide evidence for strong microbial feedbacks to the boreal C cycle under climate warming or N addition. However, organic N cycling may decline due to a reduction in the activity of enzymes that target nitrogenous compounds.     

贵州万山汞矿区污染土壤中汞的形态分布特征

利用优化Tessier连续化学浸提法对贵州万山汞矿区污染土壤中汞的形态分布进行研究.结果表明,稻田土壤中汞主要以残渣态形式存在(79.65%),其次为有机结合态(19.97%)、氧化态(0.31%)、特殊吸附态(0.04%)和溶解态与可交换态(0.03%);除特殊吸附态外,其他各形态汞含量均随距污染源距离增加而降低,特殊吸附态汞在分析土壤中含量变化不明显;生物可利用性(溶解态与可交换态和特殊吸附态)汞占总汞比例较低,但在污染土壤中其含量明显高于未受污染地区.     

Mineralization of C and N from microbial biomass in paddy soil

Summary Soil samples of paddy fields with different fertilizer managements in Yamaguchi Agricultural Experiment Station, Japan were used to investigate the contribution of microbial biomass to the pool of mobile plant nutrients in paddy soil. The quantities of nutrients mobilized in soils which had been fumigated or dried were closely related to the quantities available in freshly killed biomass. A K_N-factor (28 days) of 0.24 for the proportion of total N mineralized from dead biomass in paddy soils was obtained. It was observed that the C to N ratio mineralized from freshly killed biomass by chloroform fumigation of paddy soils was nearly 10 under aerobic conditions. For an approximate calculation of biomass C from the flush-N by chloroform fumigation of paddy soils, the equations of (B=33 Fn, 10 days) and (B=26 Fn, 28 days) were indicated. In oven-dried (70°C, 24 h) and rewetted soils, about 66% of N was mineralized from the freshly killed biomass during 28 days of incubation and the remaining 34% was derived from non-biomass organic matter of paddy soils.     

南亚热带3种人工林土壤微生物生物量和微生物群落结构特征

以我国南亚热带格木、红椎和马尾松人工林为对象,采用氯仿熏蒸浸提法和磷脂脂肪酸法(PLFA)分析了林地土壤微生物生物量和微生物群落结构组成.结果表明: 林分和季节因素均显著影响土壤微生物生物量、总PLFAs量、细菌PLFAs量和真菌PLFAs量,且干季林分下的土壤微生物生物量、总PLFAs量、单个PLFA量均大于雨季.红椎人工林土壤微生物生物量碳(MBC)和总PLFAs量最高,而格木人工林土壤微生物生物量氮(MBN)最高.土壤pH值对土壤丛枝菌根真菌(16:1ω5c)的影响达到极显著正相关水平.土壤总PLFAs量、革兰氏阳性菌(G⁺)以及腐生真菌(18:2ω6,9c)、革兰氏阳性菌/革兰氏阴性菌(G⁺/G^-)与土壤有机碳、全氮和全磷显著相关,表明土壤有机碳、全氮、全磷含量是影响该地区土壤微生物数量和种类的重要因素.外生菌根真菌(18:1ω9c)和丛枝菌根真菌与土壤碳氮比值呈极显著相关.     

外源水溶性有机物及温度对红壤铜形态的影响

利用模拟培养试验研究了外源水溶性有机物（DOM）添加量和培养温度对红壤中Cu形态的影响. 结果表明: 与不添加DOM比较, 添加不同量的DOM均可提高土壤中交换态Cu的含量、降低铁锰结合态Cu含量; 随着培养时间的延长,不同DOM添加量下土壤交换态Cu含量呈逐渐下降趋势;至试验结束时,DOM添加量为250 mg·L^-1时土壤交换态和碳酸盐结合态Cu含量最高, 添加量为500 mg·L^-1时铁锰结合态Cu含量最高;不同DOM添加量下, 土壤中有机结合态Cu含量较CK增加10.67%～23.66%. 在25 ℃和45 ℃温度条件下, 添加DOM后土壤交换态和铁锰结合态Cu含量均随培养时间的延长呈下降趋势, 但在5 ℃下变化趋势相反; 3种温度下添加DOM后土壤碳酸盐结合态Cu含量有随培养时间延长而增加的趋势. 随着培养温度的升高,土壤有机结合态Cu含量增加, 但在温度较低(5 ℃)时土壤残渣态Cu含量下降.     

Fate and Mobility of Copper in Soil of Cocoa Plantations in Two Southwestern States of Nigeria Treated with Copper-Based Fungicides

Soils from cocoa plantations treated with Boudreaux mixture in two southwestern states of Nigeria were collected at different depths, 0–15 cm and 15–30 cm, and subjected to five-stage sequential extraction to obtain the speciation forms of copper: exchangeable, carbonate, manganese and iron oxides, organic and residual fractions. The Cu content in the extracts from the sequential extraction was read with an Atomic Absorption Spectrophotometer (AAS). The total Cu content of the soil and the physicochemical parameters of the soils were also determined. The results from the study showed that the soils had high organic matter and copper is mostly bounded to the more mobile exogenic phase much more than the stable lithogenic phase, indicating higher mobility. Within the exogenic species, carbonate fraction was the highest followed by the organic bound and the exchangeable fraction in decreasing order. Cu was not detected in the Fe/Mn bound fraction. The implication is that the fate of the administered Cu-based pesticide is more in the relatively stable carbonate bound species than the other, more mobile phase. The results showed variation in the distribution of the copper species from one depth to another. The most transported metal from the surface to the lower layer is the exchangeable fraction. The carbonate bound species is less mobile and is not readily transported into the bottom soil layer. The organic bound Cu has nearly equal distribution between the top and bottom soils and there was little or no transport of the residual metal specie from the top to the bottom. The existence of copper in the soil largely in the anthropogenic (exogenous) phase is not the most desirable for the ecosystem. This may increase the availability of Cu in the cocoa plant and bean and may lead to potential exposure risk.     

A comparison of phospholipid and chloroform fumigation analyses for biomass in soil: potentials and limitations

Abstract A sensitive method for estimating living biomass, based on a direct extraction of phospholipids, was applied to soil. The variation between replicate soil samples was generally below 10%. Recovery from soil was qualitative. Estimates of biomass from the phospholipid assay were not correlated with estimates from the chloroform fumigation-incubation method (CFIM). In non-fumigated soil a significant reduction (25–57%) of biomass, as determined from phospholipid analysis, was observed during the 10-day incubation. The concentration of phospholipids was reduced by 21–54% during the 24-h chloroform fumigation, decreasing further during the 10-day incubation. Phospholipid, carbon dioxide evolution and inorganic nitrogen were followed in a growth experiment with additions of glucose and glucose + ammonium. The conversion of phospholipids into biomass-C units is discussed in relation to the observed ratios of phospholipid to CFIM biomass-C, as well as to the ratios estimated from the growth experiment.     

Cellulose and lignin degradation in forest soils: Response to moisture,temperature, and acidity

The concentration of lignin in plant tissue is a major factor controlling organic matter degradation rates in forest ecosystems. Microbial biomass and lignin and cellulose decomposition were measured for six weeks in forest soil microcosms in order to determine the influence of pH, moisture, and temperature on organic matter decomposition. Microbial biomass was determined by chloroform fumigation; lignin and cellulose decomposition were measured radiometrically. The experiment was designed as a Latin square with soils of pH of 4.5, 5.5, and 6.5 adjusted to 20, 40, or 60% moisture content, and incubated at temperatures of 4, 12, or 24°C. Microbial biomass and lignin and cellulose decomposition were not significantly affected by soil acidity. Microbial biomass was greater at higher soil moisture contents. Lignin and cellulose decomposition significantly increased at higher soil temperatures and moisture contents. Soil moisture was more important in affecting microbial biomass than either soil temperature or soil pH.     

Reduction of nitrate in clayey subsoils controlled by geochemical and microbial barriers

Vertical distribution of redox zones, concentrations of redox‐sensitive constituents, numbers of aerobic heterotrophic bacteria, and potential denitrification activity were studied in 1‐m cores taken at the transition between the oxidized and reduced layers in two Danish clayey subsoils. Based on the matrix soil colors, a redox sequence of oxidized, suboxic, and reduced zones was identified at both sites. The geochemical composition of the oxidized brown colored zone (to depths of 2.6 and 3.2 m) was characterized by high concentrations of NO₃ ^? and low amounts of total organic carbon, exchangeable forms of NH₄ ⁺, Fe²⁺, and Mn²⁺, and structural Fe(II) in the clay minerals. In the underlying 20‐ to 30‐cm‐deep suboxic zone, decreasing NO₃ ^? concentrations were observed together with increasing amount of exchangeable forms of Fe²⁺ and Mn²⁺, and structural Fe(II). Finally, in the reduced grey zone, NO₃ ^? was no longer present and maximum concentrations of other redox sensitive constituents occurred. Throughout the subsoils, the distribution of exchangeable Fe²⁺ corresponded most closely to changes in the colors of redox zones. The low‐organic Havrebjerg site displayed geochemical profiles indicating that NO₃ ^? was chemically reduced by structural Fe(II) in the clay minerals of the suboxic zone, and that the Fe(II) formed a geochemical barrier for the downward progression of NO₃ ^?. Aerobic heterotrophic bacteria occurred only in low numbers at this site and potential denitrification activity was very low. In contrast, the Sparresholm site had a significant population of bacteria in the suboxic zone, which also contained a heterogeneous distribution of potential denitrification activity. Specific microsites with facilitated transport of soluble organic substrates are proposed to support the denitrification activity in a heterogeneous distribution, constituting a microbial barrier for downward progression of NO₃ ^? in this subsoil.     

长期不同施肥制度对潮棕壤微生物生物量碳、氮及细菌群落结构的影响

以沈阳生态站长期定位试验为研究平台,采用传统氯仿熏蒸方法和现代PCR-DGGE技术探讨了长期不同施肥制度对土壤微生物生物量碳和氮及细菌群落结构的影响.结果表明:在整个试验期,土壤微生物生物量碳和氮的动态变化趋势基本相同;长期施用有机肥可显著提高土壤有机碳和土壤微生物生物量碳和氮含量,而长期施用化肥明显降低土壤pH,土壤微生物生物量碳和氮含量也显著降低.DGGE图谱表明:不同施肥处理的细菌16S rDNA多数条带分布相同,28条带中有18条为共有条带,说明潮棕壤中细菌类群较稳定,但其数量受到施肥的影响;长期施用有机肥促进潮棕壤细菌群落结构的多样性,而施用化肥处理则降低了其多样性.     

Uptake and transfer factors of137Cs by mushrooms

Summary The¹³⁷Cs content of 118 species (668 samples) of higher fungi collected in the period from August 1984 to October 1989 at three different locations in Styria, Austria, was determined by gamma-spectrometry. The Cs-content of most mushrooms has been increasing since September 1986. In order to find out which factors determine the¹³⁷Cs-contamination of mushrooms and the transfer-value soil to mushroom, the concentration of total and plant-available radiocesium in soils as well as the pH-value, the content of humus, clay, silt, sand, exchangeable cations, the composition of the clay minerals, and the particle size distribution of the soils of two different locations were examined. The higher the¹³⁷Cs contamination of the soil, the thicker the layer of humus and the higher the content of humus, the lower the pH-value, and the lower the amount of essential cations, especially of K⁺, the higher the amount of¹³⁷Cs plant-available will be. Therefore, the contamination of the mushrooms in the coniferous forest of Koralpenblick (1000 m) is higher than in the mixed forest at the Rosenberg around Graz at approx. 500 m height. Of 26 different species of mushrooms measured at both sites, only 61% show the highest TF-values soil to mushrooms also at the Koralpenblick. In the spruce forest at Koralpenblick there are many species of mushrooms with high¹³⁷Cs-contamination which were not found at the Rosenberg. However, the properties of the species to which a mushroom belongs are more important than environmental conditions and soil properties. The transfer values of⁴⁰K stay within narrow bounds, whereas those of¹³⁷Cs differ widely.Dedicated to Prof. Dr. Otto Härtel on the occasion of his 80th birthday     

选择性抑菌剂对添加稻草红壤旱土团聚体磷素微生物转化的影响

为了进一步探明红壤旱土磷素微生物固持的机理,采用室内模拟培养试验研究了微生物类群对红壤旱土团聚体(0.2～2mm)磷素转化的作用.结果表明:在培养90d期间,添加稻草处理能显著提高红壤旱土团聚体的微生物生物量碳、生物量磷、提取磷(Olsen法)和有机磷的含量.在培养前期(5～30d),与添加稻草处理比较,稻草+真菌抑制剂(放线菌酮)、稻草+细菌抑制剂(四环素+链霉素硫酸盐)处理团聚体微生物生物量碳含量分别降低10.5%～31.8%和6.8%～11.6%,前者的降低幅度显著大于后者(P0.01),此后加入抑菌剂处理团聚体微生物生物量碳基本保持稳定.添加细菌抑制剂处理团聚体微生物生物量磷含量在培养5～20d期间比加真菌抑制剂处理高10.0%～28.8%,差异显著(P0.01).表明真菌和细菌均参与红壤旱土团聚体磷素的固持,但真菌的作用明显大于细菌.     

Radiocaesium in an organic soil and the effect of treatment with the fungicide ‘Captan’

Soil fungi accumulate radiocaesium from contaminated soil and it has been hypothesised that this may alter the plant availability and movement of the radionuclide in soil. The effect of twice-monthly addition of an aqueous suspension of the fungicide ‘Captan’ on the changes in a peaty podzol soil at 2 sites, contaminated 2 or 3 years earlier by the injection of ¹³⁴Cs, has been quantified. The sites had different soil acidity and vegetation cover. The less acid soil (pH_water 5.0) had been improved by the addition of lime and fertilizer and was reseeded with grass and clover. The more acid soil (pH_water 3.8) was under hill grasses, herbs and heather. On both sites the addition of fungicide did not alter the amount or concentration of radiocaesium in plant material sampled monthly or the depth distribution of radiocaesium in the soil profile. The concentration of the fungal constituent, ergosterol, in the soil, measured monthly, was unaffected by the fungicide treatment but evidence was obtained from a pot experiment to show that ergosterol decomposes slowly in cold, wet soils. On the more acid soil, two weeks after the last application of fungicide, there was a decline in active fungi as measured by fluorescein diacetate staining. Chloroform fumigation of the more acid soil resulted in a small increase in the amount of ¹³⁴Cs exchangeable with 1 M ammonium acetate. Radiocaesium in seven different fungi grown in pure culture was found to be almost entirely extractable (> 95%) with 1 M ammonium acetate. Another, Amanita rubescens, showed some retention and 88% was extractable. These findings do not preclude the fungal biomass as an important soil component controlling plant availability of radiocaesium from acid, organic soils by maintaining radiocaesium in a biological cycle, but make it unlikely that any fixation by fungi in a chemical sense is involved.     

根瘤菌对土壤铜、锌和镉形态分配的影响

以湖南郴州红壤和河北巩义褐土为供试土壤。制备Cu、Zn、Cd污染土壤。接种大豆根瘤菌(Rhi-zobium fredii)HN01,用连续提取法浸提土壤中不同形态的重金属．结果表明。褐土接种根瘤菌后固相结合态Zn总量降低10％。专性吸附态、氧化锰结合态和有机结合态Zn减少达9％～26％．红壤中结合态Zn的总量变化不显著,但专性吸附态和氧化锰结合态Zn含量显著减少。交换态Zn含量显著增加．褐土中接种根瘤菌抑制了Cu向土壤溶液的释放,固相结合态Cu总量增加18％,可交换态、专性吸附态、氧化锰结合态和有机结合态的Cu增加20％～54％．接种根瘤菌对土壤中Cd的溶解没有明显的抑制或促进作用,但改变了红壤中各形态Cd的含量高低顺序．Cd污染红壤中可交换态和有机结合态Cd含量分别增加22％和11％,专性吸附态和氧化锰结合态Cd分别减少14％和29％．根瘤菌对不同类型重金属及不同土壤中重金属形态影响的差异主要与土壤pH降低有关．     

原生动物与解磷微生物协同解磷作用

磷是农业生产重要的限制因素之一,土壤生物包括原生动物和微生物在土壤磷素转化过程中起着重要的作用。通过纯培养和土壤培养试验发现,供试的原生动物能够提高磷矿粉的有效磷,土壤有效磷含量也显著增加。所溶解出来的磷很大一部分以无机磷酸盐的形式贮藏在细胞内,熏蒸时才释放出来,少部分磷转化为生物量磷。原生动物与解磷菌之间没有显著的相互促进作用。