放牧强度对中国内蒙古草原土壤水分状况与通量的影响

In the past few decades,the increase in grazing intensity has led to soil degradation and desertification in Inner Mongolia grassland,China,due to population growth and shift in the socio-economic system.Two sites with different grazing intensities,continuous grazing site(CG) with 1.2 sheep ha 1 year 1 and heavy grazing site(HG) with 2.0 sheep ha 1 year 1,were investigated at the Inner Mongolia Grassland Ecosystem Research Station(43 37 50 N,116 42 18 E) situated in the northern China to i) characterize the temporal distribution of soil water content along soil profile;and ii) quantify the water fluxes as affected by grazing intensity.Soil water content was monitored by time domain reflectometry(TDR) probes.Soil water retention curves were determined by pressure membrane extractor,furthermore processed by RETC(RETention Curve) software.Soil matric potential,plant available water and water flux were calculated using these data.Both sites showed an identical seasonal soil water dynamics within four defined hydraulic periods:1) wetting transition coincided with a dramatic water increase due to snow and frozen soil thawing from March to April;2) wet summer,rainfall in accordance with plant growth from May to September;3) drying transition,a decrease of soil water from October to November due to rainfall limit;and 4) dry winter,freezing from December to next February.Heavy grazing largely reduced soil water content by 43%-48% and plant available water by 46%-61% as compared to the CG site.During growing season net water flux was nearly similar between HG(242 mm) and CG(223 mm) sites between 5 and 20 cm depths.However,between 20 and 40 cm depths,the upward flux was more pronounced at HG site than at CG site,indicating that water was depleted by root uptake at HG site but stored at CG site.In semi-arid grassland ecosystem,grazing intensity can affect soil water regime and flux,particularly in the growing season.     

二氧化碳升高与干旱对植物生理、土壤碳及土壤酶活的影响

Global climate models have indicated high probability of drought occurrences in the coming future decades due to the impacts of climate change caused by a mass release of CO2.Thus,climate change regarding elevated ambient CO2 and drought may consequently affect the growth of crops.In this study,plant physiology,soil carbon,and soil enzyme activities were measured to investigate the impacts of elevated CO2 and drought stress on a Stagnic Anthrosol planted with soybean (Glycine max).Treatments of two CO2 levels,three soil moisture levels,and two soil cover types were established.The results indicated that elevated CO2 and drought stress significantly affected plant physiology.The inhibition of plant physiology by drought stress was mediated via prompted photosynthesis and water use efficiency under elevated CO2 conditions.Elevated CO2 resulted in a longer retention time of dissolved organic carbon (DOC) in soil,probably by improving the soil water effectiveness for organic decomposition and mineralization.Drought stress significantly decreased C:N ratio and microbial biomass carbon (MBC),but the interactive effects of drought stress and CO2 on them were not significant.Elevated CO2 induced an increase in invertase and catalase activities through stimulated plant root exudation.These results suggested that drought stress had significant negative impacts on plant physiology,soil carbon,and soil enzyme activities,whereas elevated CO2 and plant physiological feedbacks indirectly ameliorated these impacts.     

蚯蚓与黑麦草相互作用对土壤中荧蒽去除的影响

Earthworms can promote the bioremediation of contaminated soils through enhancing plant growth and microorganism development. The individual and combined effects of earthworms and ryegrass (Lolium multiflorum Lam.) on the removal of fluoranthene from a sandy-loam alluvial soil were investigated in a 70-d microcosm experiment. The experiment was set up in a complete factorial design with treatments in four replicates: without earthworms or ryegrass (control, CK), with earthworms only (E), with ryegrass only (P), and with both earthworms and ryegrass (EP). The residual fluoranthene, microbial biomass C, and polyphenol oxidase activity in the soil changed significantly (P<0.01) with time. In general, the residual concentration of fluoranthene in the soil decreased sharply from 71.8-88.7 to 31.7-37.4 mg kg 1 in 14 d, and then decreased gradually to 19.7-30.5 mg kg 1 on the 70th d. The fluoranthene concentration left in the soil was the least with both earthworms and ryegrass, compared to the other treatments at the end of the experiment. Half-life times of fluoranthene in the E, P, and EP treatments were 17.8%-36.3% smaller than that of CK. More fluoranthene was absorbed by earthworms than ryegrass. However, the total amounts of fluoranthene accumulated in both the ryegrass and earthworms were small, only accounting for 0.01%-1.20% of the lost fluoranthene. Therefore, we assumed that microbial degradation would play a dominant functional role in fluoranthene removal from soil. We found that earthworms significantly increased microbial biomass C and polyphenol oxidase activity (P<0.01) in the presence of ryegrass at the end of the experiment. Furthermore, microbial biomass C and polyphenol oxidase activity were significantly (P<0.05) and negatively related to the residual fluoranthene concentration. This implied that earthworms might promote the removal of fluoranthene from soil via stimulating microbial biomass C and polyphenol oxidase activity.     

铬稳定同位素在丛枝菌根蒲公英中的分馏及根外菌丝对铬的吸收

As common soil fungi that form symbioses with most terrestrial plants,arbuscular mycorrhizal(AM) fungi play an important role in plant adaptation to chromium(Cr) contamination.However,little information is available on the underlying mechanisms of AM symbiosis on plant Cr resistance.In this study,dandelion(Taraxacum platypecidum Diels.) was grown with and without inoculation of the AM fungus Rhizophagus irregularis and Cr uptake by extraradical mycelium(ERM) was investigated by a compartmented cultivation system using a Cr stable isotope tracer.The results indicated that AM symbiosis increased plant dry weights and P concentrations but decreased shoot Cr concentrations.Using the Cr stable isotope tracer technology,the work provided possible evidences of Cr uptake and transport by ERM,and confirmed the enhancement of root Cr stabilization by AM symbiosis.This study also indicated an enrichment of lighter Cr isotopes in shoots during Cr translocation from roots to shoots in mycorrhizal plants.     

叶面施硅对西芹养分吸收、产量及品质的影响

采用田间小区试验,研究了叶面喷施不同形态硅对日光温室西芹生长发育、产量和品质的影响。结果表明:叶面施硅能显著促进西芹生长发育,调节不同生育时期西芹对氮、磷、钾养分的吸收。与对照相比, 采收期施硅植株株高、茎粗、叶绿素和叶片可溶性糖含量分别增加6.33%~9.22%,10.93%~14.50%,6.64%~9.26%和10.36%~13.12%; 叶片氮含量减少2.90%~6.35%;有机硅处理叶片磷含量增加41.39%;钾含量增加18.23%~77.65%;显著提高西芹单株重和产量,分别增加11.36%~17.64%和12.61%~17.52%;植株Vc含量增加24.82%~61.19%,硝酸盐含量降低3.60%~15.62%。结果说明硅肥施用一定程度上能够改善西芹的品质。     

外生根真菌对盐渍土中油松营养成分吸收和平衡的影响

Pinus tabulaeformis seedlings were grown under a factorial design to measure biomass accumulation and P, Na and K concentrations of plants, with 3 different ectomycorrhizal fungus (EMF) strains (Boletus edulis, Xerocomus chrysenteron and Gomphidius viscidus) and two P treatments (with or without extra P). Growth and mineral nutrition of pine seedlings were stimulated by three EMF under salinity stress. Na concentrations were changed and plant K and P concentrations were increased significantly by EMF. Adding extra P made no difference in accumulation of seedlings biomass, and did not assist element absorption of plants. Although three strains of EMF can all enhance the tolerance of pine seedlings to salinity stress, they may utilize different mechanisms because of different performance in absorption of elements. The increased P and K accumulation and the balance of ion concentrations might be due to the enhanced tolerance of EMF-inoculated plants to saline conditions.     

水淬渣与钢渣硅肥对玉米硅、磷养分吸收及产量的影响

硅作为有益元素对促进作物生长发育及增强抗逆性等方面有显著效果。本研究在2013—2014年进行了2年田间小区试验,对比研究了水淬渣硅肥和钢渣硅肥对玉米生长发育及产量的影响,分析了施硅对玉米硅、磷营养吸收及硅肥利用率的效应。结果表明:施硅可显著提高土壤有效硅含量(P0.05),如在抽雄、乳熟及成熟期水淬渣硅肥处理的土壤有效硅含量分别比不施硅肥处理(CK)处理提高36.9%、15.3%和9.7%;施硅处理均显著提高了玉米叶面积指数、干物质量和产量(P0.05),水淬渣和钢渣硅肥处理的玉米产量为17 979 kg/hm2和17 134 kg/hm2,分别比CK处理提高18.9%和13.3%。2年结果均显示硅肥处理显著提高了成熟期玉米植株的吸硅量与吸磷量(P0.05),水淬渣与钢渣硅肥处理的年均吸硅量分别比CK处理增加14.6%和10.4%,其年均吸磷量分别比CK处理增加11.5%和8.7%。玉米吸硅量与吸磷量呈极显著正相关(P0.01),硅肥处理可显著改善玉米生育期内磷素营养,提高磷肥偏生产力;水淬渣硅肥和钢渣硅肥年均硅肥利用率分别达38.9%和27.8%,且水淬渣硅肥利用率明显高于钢渣硅肥。     

铜盐毒害对紫鸭跖草养分吸收和生长的影响

通过含有不同浓度CuSO4的Hoagland营养液培养紫鸭跖草枝条,研究了紫鸭跖草对铜的耐性和超积累以及铜胁迫下紫鸭跖草生长和营养状况.结果表明:紫鸭跖草根部铜的积累量低浓度Cu2 供应时增加幅度不大,高浓度Cu2 供应时增加幅度较大;茎部的情况与根部相似;但叶部在低浓度Cu2 供应时铜的积累量几乎没有变化,高浓度Cu2 供应时铜的积累量增幅较大.在500 μmol · L-1和1 000 μmol · L-1铜处理下,紫鸭跖草整株铜积累量分别为866 mg · kg-1(DW)和1 130 mg · kg-1(DW).紫鸭跖草对铜的吸收和转运效率与铜的供给量呈正相关性.100～250 μmol · L-1铜的供应能明显促进紫鸭跖草生长.高浓度铜促进了钾、钙的吸收而阻碍了锌的吸收及镁向地上部分的运输,尽管如此,氮、磷、钾、镁、钙的浓度均在满足常规植物正常生长的浓度范围内.铜胁迫下对根部蛋白质表达活跃,氨基酸含量增加.研究结果表明紫鸭跖草对铜有很大耐性和富集能力.     

硅对大葱矿质元素吸收、 分配特性及产量和品质的影响

【目的】大葱因含有机硫化合物等功效成分而具有重要的保健和药用价值,为此,前人曾就氮、 磷、 钾、 硫等矿质元素与大葱产量、 品质及风味物质的关系进行了一些研究。硅作为一种公认的有益元素,在提高作物产量、 改善品质等方面具有重要作用,本试验研究了硅对大葱矿质元素吸收、 分配特性和产量及品质的影响,以期为大葱高效施肥提供科学依据。【方法】本研究以‘天光’和‘章丘’两个不同类型大葱品种为试材,供试硅源均为Na2SiO3·9H2O,通过盆栽Hoagland营养液培养和大田土壤栽培相结合的方法,分别研究了营养液不同硅水平(SiO2 0、 0.6、 1.2、 1.8 mmol/L)和土壤不同施硅量(SiO2 0、 150、 300、 450 kg/hm2)对大葱生长、 产量、 品质及硅、 氮、 磷、 钾含量、 吸收量的影响。【结果】营养液硅水平在1.8 mmol/L范围内,‘天光’和‘章丘’两品种大葱株高、 假茎长、 假茎粗、 植株干重以及单株产量均随硅浓度升高呈先上升后下降的趋势,且均以1.2 mmol/L的处理表现最好,其单株产量分别较不施硅提高了19.4%和30.9%; 适量施硅还显著提高了大葱游离氨基酸、 可溶性糖、 丙酮酸等含量,表明施硅有利于改善大葱品质。随营养液硅水平的升高,两大葱品种各器官硅含量均显著增加,在1.8 mmol/L处理时达最高,而钾含量则与之相反,氮、 磷含量则呈先上升后下降的趋势,均以1.2 mmol/L处理含量较高; 由于施硅促进了大葱生长,所以大葱对硅及氮、 磷、 钾的吸收量则均随硅水平的升高呈增加趋势。大田施硅试验表明,‘天光’和‘章丘’两品种大葱均以施硅量(SiO2)300 kg/hm2时产量较高,分别比对照增产15.4%和25.6%。【结论】大葱增施硅可显著增加大葱对硅及氮、 磷、 钾的吸收量,促进植株生长,提高产量和品质,但同一硅水平的增产率以‘章丘’品种显著高于‘天光’,且二者随硅水平变化的幅度也不相同,表明不同大葱品种对硅的反应敏感性存在显著差异。本试验条件下,以营养液硅水平1.2 mmol/L、 土壤施硅300 kg/hm2时较有利于大葱的生长及产量和品质的提高。     

磷硅肥配施对盐渍土壤水稻生长及养分吸收的影响

针对滨海盐渍化稻田土壤根系易受盐碱胁迫、磷素养分含量及有效性低的问题,采用田间微区试验研究磷肥与硅肥配施对滨海盐渍化稻田土壤水稻根系生长、土壤磷素含量、水稻磷营养、产量及经济效益的作用。试验采用双因素设计,磷肥设2个水平:P1,P_2O_5 64 kg/hm~2;P2,P_2O_5 128 kg/hm~2;硅肥分土施和喷施,土施设3个水平:Si1,SiO_2 0 kg/hm~2;Si2,SiO_2 60 kg/hm~2;Si3,SiO_2 120 kg/hm~2;Si4为叶面喷施SiO_215 kg/hm~2。结果表明,喷施硅肥与低量磷肥配施的P1Si4处理在各生育时期的水稻总根长、总表面积和总根体积均为最高,与P2Si4处理无显著性差异。同时,磷肥配施硅肥可有效提高滨海盐渍化水稻土壤磷素有效性,其中P2Si4处理速效磷含量显著高于P1Si3、P2Si1,分别高出35.16%,27.47%;高磷处理的土壤全磷含量高于低磷处理。且施用硅肥的P1Si3、P1Si4处理的水稻产量显著高于不施硅肥和少量施硅的P1Si1、P1Si2处理,其中P2Si3水稻产量达9 547.5 kg/hm~2;各处理的有效穗数无显著性差异,每穗实粒数P2Si3处理最高,达162.47个/穗。P2Si3处理水稻籽粒中磷积累量最高,且显著高于其他处理,比P1Si3、P2Si1处理分别高出8.46%,9.68%。在低磷或高磷施用条件下,叶面喷施硅肥(P1Si4、P2Si4)处理收入分别达到14 953.6,14 323.2元/hm~2。综上所述,与不施硅肥的处理相比,磷肥配施硅肥可显著促进滨海盐渍化土壤水稻根系生长,提高磷素有效性、水稻产量及经济效益,其中以P1Si4处理(叶面喷硅,P_2O_5 64 kg/hm~2)处理最佳。     

Root water uptake of pepper plants (Capsicum annuum L.) under deficit irrigation system

Root water uptake is a component of water balance that has not been clearly understood. This study was carried out in a completely randomized design with three replications under the greenhouse condition at Shahrekord University, Shahrekord, Iran. In this study, the root water uptake (RWU) by pepper plant under various irrigation water levels was investigated. Irrigation treatments included control (full irrigation level, FI) and three deficit irrigation levels, 80%, 60% and 40% of the plant's water requirement called DI₈₀, DI₆₀ and DI₄₀, respectively. A no-plant cover treatment with three replications was also used to measure evaporation from the soil surface. Daily measurements of volumetric soil moisture (VSM) were made at 10 cm intervals of the soil column. The differences between the measured VSM and the VSM in the next day, and evaporation rate at the soil surface at the same layer of the no-plant cover treatment were calculated and, eventually, the RWU in each layer per day was estimated. The results showed that the maximum and minimum RWUs were found in the FI and DI₄₀ treatments, respectively. The averages of root water uptakes in the DI₈₀, DI₆₀, and DI₄₀ treatments were reduced by 17.08%, 48.72% and 68.25%, respectively. Furthermore, in the DI₈₀ treatment, the reduced rate of water uptake was less than the reduced rate of water applied to the plants.     

烤烟根系分泌物对烤烟幼苗生长和养分吸收的影响

连作是烟草栽培中的普遍现象,已引起生长抑制、产量下降和品质恶化等问题。本试验采用溶液培养的方法,在培养液中分别加入未分组和分组后的烤烟根系分泌物,研究根系分泌物对烤烟幼苗生长和养分吸收的影响。结果表明,加入未分组的烤烟根系分泌物显著抑制幼苗的生长,降低根系活力,并随加入量的增加抑制作用增强;加入酸溶性、碱溶性、中性组分的根系分泌物,均降低幼苗根系活力,以中性组分的抑制作用较强。三种不同组分的根系分泌物均显著降低根系对NO3-、PO43-、K+离子的吸收,其中中性组分对NO3-吸收的影响最大,而酸溶性组分对K+的吸收抑制作用较强。推测在烤烟根系分泌物中,可能存在多种抑制烤烟生长和养分吸收的化学物质。     

Improving productivity and nutrients uptake of wheat plants using Moringa oleifera leaf extract in sandy soil

A field experiment was conducted on a sandy soil at Salhia El-Gdida, Al Sharqia government, Egypt, to study the effect of Moringa leaf extract on yield and nutrient uptake of wheat plants (Triticum aestivum cv.). Foliar spraying of Moringa leaf extract was done at 40, 70, and 90 days after planting at a rate of 0%, 1%, 2%, 3%, and 4%. Treatments of Moringa extract significantly increased straw and grain yield, biological yield, 1000 grain weight, yield efficiency, protein content, and nutrient uptake as compared to untreated plants in the both seasons. The highest values of straw and grain yield, quality yield, and nutrient uptake by plants were obtained with 4% of Moringa extract, while the lowest values were obtained with untreated plants. Also, the highest percentage increase in grain yield of 71% and 88% was recorded from the treatment 4% of Moringa extract in first and second seasons, respectively.     

Response of yield and nutrients uptake of pea plants to silicate under sandy soil conditions

Desertic soils in Egypt are mostly sandy soils and have issues, due to their sandy nature, related to physical properties and the low potential for productivity. The aim of this study was to investigate the effect of silicon as potassium silicate on yield and nutrient uptake of pea (Pisum sativum L.) plant in sandy soil during the growth seasons of 2014–2015. Spraying of different rates of silicon significantly increased yield, biomass, 100 seed weight and nutrients accumulation as compared to unsprayed plants. The greatest values of photosynthetic pigments, plant height, and nutrients accumulation of plants were observed with 500 mg L^?1 silicon. Also, the highest percentage increase in fresh pod yields and protein of 82.5% and 45%, respectively, was recorded from 500 mg L^?1 silicon.     

根系高效铵吸收系统是玉米获取氮素的重要补充机制

【目的】本研究旨在通过对植株根系铵吸收特征研究,揭示旱地玉米的氮素营养特征,研究结果为玉米补充氮素营养提供了一定的理论依据。 【方法】以玉米高产品种“郑单 958”为供试材料,采用水培试验模拟了玉米植株生长中的氮素营养环境,研究了玉米幼苗生长对不同氮素形态的反应;采用非损伤微测技术 (NMT),重点研究了不同供氮状况下玉米根系对 NH₄+ 的吸收特征,并与其吸收硝态氮的规律进行了比较;利用实时定量 PCR 技术,初步揭示了玉米根系中的铵吸收蛋白 (AMT) 基因对铵的响应特征。 【结果】单一供应铵态氮条件下,玉米地上部鲜重、全株干重及根系含氮量与纯硝态氮条件下相近,表明铵态氮也可作为玉米的有效氮源。非损伤微测研究结果表明,玉米幼苗根系铵吸收过程呈典型的高亲和吸收特征 (表观 Km 值约为 60 μmol/L),推测这一过程是由高亲和的转运体蛋白介导。氮饥饿预处理使根系的铵吸收速率 Vmax 和 Km 值分别降低了约 3 倍和 1 倍。这一现象与水稻等作物不同,暗示玉米的铵吸收过程可能不存在反馈抑制现象。另外,介质中硝态氮的存在对根系的铵吸收具有显著抑制作用 (抑制效果 > 20%);在供试微摩尔浓度范围内,根系对 NO₃– (100 μmol/L) 的吸收速率显著低于对相同浓度 NH₄+ 的吸收。进一步对主要在玉米根系中表达的铵吸收蛋白基因 ZmAMT1;1a 和 ZmAMT1;3 的定量 PCR 分析表明,上述基因在维持供铵状态下的表达量较缺氮处理均有显著提高,与铵吸收测定结果相符。 【结论】玉米根系中保留着高效铵吸收系统,在低硝态氮浓度下,该系统对铵态氮的高效吸收可作为其获取足够氮源的一个重要的机制。高硝态氮则抑制玉米根系对铵态氮的吸收,以避免氮素吸收利用系统在功能上的冗余。     

氮钾水互作对玉米苗期植株生长及钾素吸收的影响

采用盆栽试验方法探讨了氮钾水互作对玉米苗期植株生长及养分吸收的影响。结果表明,水分适宜能明显增加玉米植株株高和干物重,水分适宜条件下玉米株高和干物重较水分亏缺条件的分别增加7.8%和13.8%。增施氮肥能显著增加玉米植株株高和干物重,水分适宜条件下中氮水平的玉米株高和干物重分别较低氮水平的增加10.4%和8.7%,而水分亏缺条件下株高和干物重均随施氮水平的增加而明显增加;水分亏缺条件下,中高量施钾能显著增加玉米植株干物重。水分适宜条件下增施氮肥能明显促进玉米对钾素的吸收,在水分适宜和亏缺条件下,不同氮水平的玉米钾素吸收均随施钾水平的增加而显著增加。     

控释氮肥不同用量对移栽玉米幼苗生长及养分吸收的影响

通过盆栽试验,研究了控释氮肥不同用量对移栽玉米幼苗生长及养分吸收的影响。结果表明,玉米育苗期内适宜的控释氮素用量可形成健壮幼苗; 其最大安全控释氮素用量为N 200400 mg/plant,该用量下,移栽时单株可携带N 137290 mg。随控释氮肥用量的增加,植株地上部氮素浓度及氮素累积量增加; 磷素的浓度及累积量与控释氮肥的用量没有显著相关性; 控释氮肥的供应抑制了植株对钾的吸收。     

Silicon and salicylic acid promote different responses in legume plants

Abstract

The foliar application of silicon (Si) and salicylic acid (SA) can be beneficial to plants. However, there are doubts about the interaction of Si and SA in the physiology and yield of legume crop. The objective of this study was to evaluate the effects of foliar application of Si and SA on the photosynthetic variables and yield of soybean and bean grains. The experiments were composed by four treatments: potassium silicate and stabilized sodium at a concentration of 3.6?g?L^?1 Si in the absence and presence of SA (210?mg?L^?1), only SA, and without Si or SA. The interaction of Si with foliar SA enhanced photosynthesis only in soybean; it did not affect the physiological variables of bean and did not alter the yield of the two crops. The results indicated that foliar Si application at high concentrations, independently of SA application, increased the physiological variables of the soybean without affecting the yield; however, the combined application of Si and SA had an adverse effect on the physiology and yield of bean.     

Effect of concentration on uptake of some trace metals by plants

Abstract

The uptake by plants of somes trace metals at different concentrations was related closely to the decay constant, I. This means that for a 10‐fold increase in applied concentration, the increase in uptake was close to 4. 93 (10^0.693 = 4. 93). With some trace metals the value of Y (10^Y = ratio of uptake for 10‐fold increase in metal concentration was around 1. For generalized conditions the value of Y in the expression, (/ = uptake ratio, for different concentrations and varied around I. Some values of Y for whole plants were Ni, 0.699 with C.V. (coefficient of variation) 12.2%, Cu, 0.468 with C.V. 12.1%, Zn, 0.606 with C V. 31.5%, and Cd, 0.903 with C.V. 10.9%. From soil the values for shoots for Co were 0.855 (C.V. = 14.8%) without EDTA (ethylenediamine tetraacetic acid) and 0. 941 (C. V. = 20. 8%) with EDTA; for Cu with EDTA it was 0. 562 (C. V. = 25.8%). with EDTA; for Cu with EDTA it was 0.562 (C.V. =25.8%).     

Phosphorus application affects root length distribution and water uptake of upland rice in a column experiment

Abstract

Clay mineralogy of thirteen spodic horizon samples from seven Cryorthods developed on diverse materials (peridotite, andesite, lapilli, volcanic ash, slate, granite and granodiorite) in Chubu and Kanto, Japan was determined by successive chemical dissolutions with dithionitecitrate and 0.5 m NaOH-differential infrared spectroscopy in combination with chemical, X-ray diffraction, electron microscopic and thermogravimetric analyses. Thc major part of the soluble iron was found to be crystalline goethite. Presence of allophane (and imogolite) in the lower parts of the spodic horizons, but not in the upper parts, was interpreted as indicating a relatively limited supply of complexing fulvic acid from the overlying organic-rich horizons. The well-developed Al interlayers in the 2 : 1 type minerals associated with gibbsite suggest that the environment of the lower sub-horizons is rich in active aluminium,