盐生植物解磷菌的筛选及促生效应研究

为丰富耐盐碱的解磷菌资源,探究其对盐碱环境中非盐生植物的促生效果,利用选择性培养基,从新疆南部克孜勒苏柯尔克孜自治州荒漠盐碱地3种典型盐生植物中分离解磷菌,并基于16S rRNA基因的限制性酶切末端片段长度多态性（PCR-RFLP）和系统发育分析进行菌种鉴定,挑取解磷能力突出的优良菌株接种至拟南芥和小麦验证其促生效果。结果表明,共分离到141株解磷菌,解有机磷菌株的解磷率介于1.5%～7.6%之间,解无机磷菌株的解磷率介于1.1%～4.7%之间,其中解无机磷量与发酵液pH值呈显著负相关。所有菌株隶属于8个菌属,以肠杆菌属（Enterobacter）占绝对优势。接种解磷菌株显著增加了非盐碱胁迫下的拟南芥幼苗生物量,尤以解有机磷菌株MHSC29和解无机磷菌株MHCB24的作用最强。接种解磷菌对盐碱土中小麦的地上部分（株高、茎粗、地上干重、叶绿素含量）和地下部分（根干重）均有积极影响,以解有机磷菌株MHSC29、MHCC3和解无机磷菌株APCB2效果最突出。本研究所得菌株进一步充实了耐盐碱解磷菌种的资源库,具备开发为盐碱地微生物肥料的潜能。     

优良解磷菌株诱变选育与解磷培养基优化

对解磷菌枯草芽孢杆菌X1055进行紫外线诱变选育,筛选到优良解磷突变株1055Y1。该菌株摇瓶培养72h发酵液中有效磷含量最高达到5.22mg/L,解磷能力比出发菌株提高17.8%。在单因子试验筛选最适碳源、氮源基础上,通过Plackett-Burman设计,确定接种量、pH、KCl浓度等因素对突变株1055Y1解磷能力具有显著影响。应用爬坡试验和Box-Behnken设计的响应面法,对突变株1055Y1解磷培养基进一步优化。结果表明:在250ml发酵培养基中,接种量10.21ml、pH6.75、KCl浓度0.12g/L时,突变株1055Y1解磷达到最佳水平,发酵液有效磷含量达到7.03mg/L。     

产β-甘露聚糖酶内生菌的诱变育种及产酶条件优化

以刺槐豆内生菌Paenibacillus sp.CH-3为出发菌株,采用紫外-硫酸二乙酯-亚硝酸盐对其进行复合诱变,并对菌株的发酵条件进行了优化。结果表明：经过紫外线-硫酸二乙酯-亚硝酸盐复合诱变,获得一株高产β-甘露聚糖酶的突变菌株Paenibacillus sp.CH3-05,其酶活力为160.2U/mL,较出发菌株（42U/mL）提高了281.4%。其最佳发酵培养基为：酵母膏0.25%,魔芋粉3%,磷酸氢二铵0.25%,氯化钠0.1%,硫酸镁0.3%,磷酸氢二钾0.2%,CaCl22 mmol/L。最佳发酵条件为：初始pH 6.5,接种量2%,培养温度35℃,转速200 r/min,培养时间78 h,在该条件下测得酶活为233.5 U/mL,较出发菌株提高456%。     

一株高效解磷细菌的筛选、鉴定及其溶磷能力的研究

从武汉市黄陂区长期种植的蔬菜大棚作物根际分离筛选出多株解磷细菌,经过多次筛选纯化获得一株性状稳定的高效解磷细菌P1。根据生理生化特征和16S rDNA序列分析,鉴定菌株P1为根瘤菌属(Ensifer)。研究了不同发酵条件对P1菌株解磷能力的影响,确定了菌株P1的最佳培养条件为发酵时间7 d、初始pH值8、接种量2%,在该条件下菌株P1溶解磷酸三钙的量为443.11 mg/L。试验还发现菌株P1的溶磷量与培养液的pH值呈极显著负相关性。     

γ射线对斜卧青霉的诱变筛选及产酶条件优化

以斜卧青霉(Penicillium decumbens)A10为出发菌株,经450 Gy60Coγ射线诱变处理,选育出1株纤维素酶高产菌株A50,对其产纤维素酶的液态发酵条件进行研究优化,确定了所试因素的最佳组合,即主碳源浓度为5%,其中麸皮与玉米秸秆比例为1∶1,辅加碳源为0.1%的葡萄糖,辅加氮源为0.2%的磷酸氢二铵,Tween-80添加量为0.1%,培养基初始pH为5.0,300ml三角瓶的装液量为30ml、接种量10%、培养温度为32℃、摇床转速200r/min。发酵至60h时,纤维素酶活和滤纸酶活均达到最高,分别为27.28和1.98IU/ml,较出发菌株A10分别提高了33.2%和45.59%。     

一株耐盐解磷菌的解磷能力及对玉米敏感期生长的影响

从黄河三角洲盐碱化土壤中筛选了一株高效解磷真菌QL1501,经鉴定为草酸青霉菌,菌株QL1501对无机磷的解磷能力远大于对有机磷的解磷,解无机磷最大浓度达85.21 mg/L。菌株QL1501的最适生长pH值为8时菌体生长极好。当NaCl浓度为1%～5%时,菌株解磷能力变化不大,溶液中有效磷浓度为76.08～65.37 mg/L。当溶液中NaCl浓度高于7%时,菌体生长受到较大影响。接种解磷真菌QL1501处理的玉米株高、根干重和植株干重均显著高于未接种的对照处理,说明该解磷菌作为解磷生物肥料具有良好的效果。     

纤维素酶高产菌株桧状青霉9-3的诱变选育及产酶条件研究

本文以桧状青霉9-3为出发菌株,采用硫酸二乙酯（DES）诱变,通过筛选得到一株酶活力高且遗传稳定性良好的菌株H16,其滤纸酶活力、β-葡萄糖苷酶酶活力与蛋白产量均较出发菌株相比均提高了4倍左右。并通过对发酵培养基以及发酵条件的优化,确定了最佳的产酶条件为：微晶纤维素浓度为2%,玉米浆干粉浓度为1.5%,发酵温度为30℃,初始pH为5.5,装液量为30 mL/250 mL,发酵周期为5 d。在优化的条件下,该菌株的纤维素酶和蛋白产量均进一步提高25%左右。     

山西矿区复垦土壤中解磷细菌的筛选及鉴定

【目的】矿区复垦土壤贫瘠、 有效磷含量低。解磷细菌能够将有机磷和难溶性无机磷转化为可溶性磷,促进植物对磷素的利用。因此筛选和鉴定具有解磷能力的菌株,可为解决矿区生态恢复使用的微生物肥料提供菌种资源。【方法】采用平板分离法初筛菌株,得到D/d1.5的菌株,然后以磷酸钙为磷源,通过液体发酵试验复筛菌株,挑选出解磷率高于巨大芽孢杆菌(Bacillus megaterium)As1.223的菌株。以磷矿粉和卵磷脂为磷源,液体发酵试验测定菌株的解磷能力及磷酸酶活性。进行菌株的生长试验以测定菌株温度适宜性、 耐盐性及耐酸碱性。通过形态学、 基因序列分析及脂肪酸组成分析综合进行菌株鉴定。 菌落形态观察用营养琼脂平板培养基培养;菌体形态即细胞形态及其大小采用扫描电镜观察;基因序列分析采用16S rDNA序列测定,基因在线比对采用EzTaxon数据库;使用美国MIDI公司的Sherolock全自动细菌鉴定系统对菌株进行脂肪酸组成分析。【结果】利用无机磷和有机磷平板培养基,从山西省矿区复垦区土壤样品中筛选出19株解磷微生物,其中D/d1.5的有7株。在以磷酸钙为磷源的液体培养试验中,4株菌的解磷率高于巨大芽孢杆菌As1.223,解磷率为7.89%～12.61%,最高的为菌株Y14。4株菌对磷矿粉的解磷率为0.81%～1.21%,最高的为菌株Y14。在以卵磷脂为磷源的液体培养试验中,4株菌的解磷率与酸性磷酸酶活性分别为1.79%～3.07%和24.3～28.4U/L,均高于巨大芽孢杆菌As1.223; 碱性磷酸酶活性为11.9～50.2U/L;菌株Y14的解磷率与磷酸酶活性均最高。4株菌均有较强的环境适应能力,以Y14的适应性最强。H22、 Y11和Y34与假单胞菌属(Pseudomonas sp.)同源性在99%以上,Y14与泛菌属(Pantoea sp.)有99.79%的同源性; H22、 Y11和Y34的细胞脂肪酸组成特征峰与假单胞菌属(Pseudomonas sp.)相一致,Y14与泛菌属(Pantoea sp.)相一致;H22、 Y11和Y34被鉴定为假单胞菌(Pseudomonas sp.),Y14为泛菌属(Pantoea sp.)。【结论】分离、 筛选到4株高效解磷菌,对于磷酸钙和卵磷脂的解磷率均高于巨大芽孢杆菌As1.223。4株菌分别隶属于假单胞菌属(Pseudomonas sp.)和泛菌属(Pantoea sp.)。菌株Y14无机磷与有机磷平板的D/d值分别为3.28与1.59,降解磷酸钙、 磷矿粉、 卵磷脂的解磷率分别为12.61%、 1.21%、 3.07%,酸性与碱性磷酸酶活性分别为28.4 U/L和50.2 U/L,均为4株菌里最高的,且环境适应能力最强,生长温度为20～60℃,能耐受pH 4～11的酸碱梯度和2%～7%的盐分梯度,Y14被鉴定为泛菌属(Pantoea sp.)。4株菌均具有良好的解磷能力及较强的环境适应能力,可望进一步研发成为微生物肥料生产菌种。综合D/d值、 解磷率、 磷酸酶活性和生长试验,本试验最终确定适合山西矿区复垦农田推广的高效解磷菌菌株为Y14。     

作物根际解磷真菌YTY的离子束诱变及其解磷机理探讨

为筛选并构建高效的作物根际解磷真菌,探讨解磷真菌的解磷机理,本研究从小麦和棉花根际土壤中分离筛选了一株高解磷能力的真菌YTY,对其离子束诱变的最佳条件进行探讨,进一步构建YTY的高效解磷突变菌,并从有机酸角度研究YTY的解磷机理。结果表明,从作物根际土壤分离的解磷真菌YTY具有较高的解磷能力,形态学和ITS鉴定表明该菌为草酸青霉;YTY的最佳诱变条件为30 keV和1×10¹⁵ ions·cm^-2,利用该诱变条件获得了3株高效解磷突变株,即p-1-1、p-1-2、p-1-3,解磷能力分别较出发菌株YTY提高了56.88%、42.26%和32.15%;YTY培养液(5 d)的pH值为2.5,离子色谱法测得其中含有3种有机酸,即乳酸、乙酸和草酸,同时测得3株突变菌培养液的pH值为2.0,显著低于出发菌株YTY,且乳酸、乙酸、草酸和总酸含量均显著高于YTY,表明有机酸是YTY解磷的重要物质,且乳酸、乙酸、草酸是YTY解磷的主要有机酸。本研究结果为解磷真菌的离子束诱变选育提供了参考,并为真菌YTY解磷机理的探明及开发应用提供了理论依据和生物材料。     

产IAA菌株的UV和DES诱变筛选及培养条件优化

为了得到高产吲哚-3-乙酸(IAA)菌株,采用紫外(UV)诱变和硫酸二乙酯(DES)诱变的方法,对从烟草根际土壤中分离得到的一株产IAA并具有溶有机磷性状的促生菌进行诱变选育,并对获得的目标菌株的发酵培养条件进行正交优化。结果表明,菌株经UV诱变和DES诱变均能有效提高其IAA产量。诱变条件为 UV(15 W,30 cm)照射1 min或2 mg·mL^-1 DES处理30 min时,得到1株高产IAA的菌株UV19,其IAA产量为33.77 mg·L^-1,是出发菌株产量的299.48%。菌株UV19经10代继代,其产IAA能力和溶有机磷性状稳定遗传。菌株UV19产IAA培养发酵优化条件为10%装瓶量、初始pH值8、培养温度25℃、接种量3%、培养时间96 h、含500 mg·L^-1色氨酸的LB培养基,优化后IAA产量高达75.47 mg·L^-1,为优化前的2.23倍。本研究结果为菌肥及生物法生产IAA提供了基础材料及技术方案。     

低氮和干旱胁迫对富士和秦冠生长及氮素利用的影响

【目的】以富士（Fuji）、 秦冠（Qinguan）嫁接在平邑甜茶（Malus hupehensis Rehd.）上的当年生盆栽苗为试验材料,采用砂培方法,研究了缺氮胁迫和干旱对富士和秦冠生长情况、 光合参数、 植株各部位氮磷钾含量及氮素利用效率的影响,分析比较了低氮干旱条件下富士和秦冠生长及氮素利用的差异,以期为果树生产高效肥水利用提供理论指导。【方法】试验共设四个处理: 正常氮正常水（ZZ）、 低氮正常水（DZ）、 正常氮干旱（ZG）、 低氮干旱（DG）。氮素和水分均设置两个水平,分别为正常氮（6 mmol/L NO-3-N）、 低氮（0.3 mmol/LNO-3-N）、 正常供水（保持盆中砂子相对含水量为饱和含水量的80%~85%）、 干旱处理（保持盆中砂子相对含水量为饱和含水量的60%~65%）。【结果】富士和秦冠的生物量（茎和叶）、 株高茎粗等生长指标以及光合速率、 气孔导度、 蒸腾速率均为正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）,并且相对应处理下秦冠的以上指标均高于富士;正常供水下,缺氮处理使富士、 秦冠的根冠比比正常氮处理均有所增加,富士提高了2.05%,秦冠提高了22.40%。富士和秦冠的氮、 磷、 钾含量均表现出正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）; 氮、 钾元素含量在植株各部位的分布顺序依次是叶＞根＞茎,磷元素则是根＞叶＞茎;光合氮素利用效率（PNUE）和氮素利用效率表现为秦冠处理之间差异极显著,富士处理之间差异不显著;秦冠的PNUE和NUE明显高于富士,在低氮正常水（DZ）处理下,秦冠氮肥利用率比富士高42.07%,在低氮干旱（DG）处理下高64.14%;低氮胁迫下富士和秦冠的NUE显著提高,并且秦冠提高的幅度高于富士。【结论】施用氮肥能够显著提高富士与秦冠的干物质量,同等水肥条件下,秦冠生长优于富士;水分亏缺会减少叶片对氮的吸收,干旱条件下适度增施氮肥,可提高果树的抗旱能力;低氮干旱胁迫下秦冠的生长指标、 光合指标及氮素利用效率指标均优于富士,表现出较强的抗低氮干旱胁迫的能力。     

Pasture Vegetation Elemental Analysis by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a new technique for the analysis of plant material. This study investigates the application of LIBS to pasture-based plant samples. The LIBS measurements were obtained from pelletized pasture samples (100 samples) that had been also analyzed by inductively coupled plasma–optical emission spectroscopy (ICP-OES) following microwave digestion for calibration and comparison purposes. Comparisons for elements sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), boron (B), phosphorus (P), and sulfur (S) showed that LIBS could be used for almost all the standard profile total elements with concentrations down to low mg/kg levels (observed error of Na: 0.024 percent, K: 0.18 percent, Mg: 0.016 percent, Ca: 0.073 percent, P: 0.017 percent, Mn: 31 mg/kg, Fe: 150 mg/kg, Zn: 6.6 mg/kg, and B: 1.1 mg/kg). Elemental analysis at less than mg/kg levels was not possible using LIBS. The elements S and Cu were particularly difficult to analyze with reliability using LIBS at the concentration levels found in the plant samples. Replacing microwave digestion and subsequent ICP analysis with a direct analysis of dried plant samples using LIBS has the potential to improve the productivity and reduce the cost of testing.     

Faculty positions:Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,     

Biodiversity and ecogeography of wild Lactuca spp. in some European countries

Staff members of the Department of Botany of Palacký University in Olomouc and Gene Bank Department – Workplace Olomouc, Research Institute of Crop Production in Prague, Czech Republic, conducted an expedition in seven European countries (Austria, Czech Republic, France, Germany, Italy, the Netherlands, Switzerland) in August/September 1999 to collect wild Lactuca spp. germplasm and study its geographic distribution, ecology and biodiversity. During the mission, more than 600 locations were visited resulting in the collection of 602 seed samples (accessions) of wild Lactuca species and 13 seed samples of related genera (Chondrilla and Mycelis). Lactuca serriola f. serriola, L. serriola f. integrifolia, L. saligna and L. viminea subsp. chondrilliflora were prevalent in southern Europe (Italy, France), however, only L. serriola was common in central and western Europe (Austria, Czech Republic, Germany, Netherlands, Switzerland). The greatest diversity of Lactuca species was found in France, where also the most seed samples (165) were collected. The most characteristic habitats with a high density of Lactuca spp. populations were observed along roads and highways, grassy ditches, ruderal communities, and dust-heaps. Natural infections by powdery mildew (Erysiphe cichoracearum) and downy mildew (Bremia lactucae) on some wild Lactuca spp. were observed. Recent observations concerning the geographic distribution, population structure, habitats, and natural occurrence of diseases of Lactuca spp. are discussed. This assemblage of genetic resources of Lactuca spp. can serve as the basis of future studies of species diversification, spatial population structure, plant microevolution, domestication processes, and genetic variability of host-parasite interactions.     

Macroinvertebrates in North American tallgrass prairie soils: effects of fire, mowing, and fertilization on density and biomass

The responses of tallgrass prairie plant communities and ecosystem processes to fire and grazing are well characterized. However, responses of invertebrate consumer groups, and particularly soil-dwelling organisms, to these disturbances are not well known. At Konza Prairie Biological Station, we sampled soil macroinvertebrates in 1994 and 1999 as part of a long-term experiment designed to examine the effects and interactions of annual fire, mowing, and fertilization (N and P) on prairie soil communities and processes. For nearly all taxa, in both years, responses were characterized by significant treatment interactions, but some general patterns were evident. Introduced European earthworms (Aporrectodea spp. and Octolasion spp.) were most abundant in plots where fire was excluded, and the proportion of the total earthworm community consisting of introduced earthworms was greater in unburned, unmowed, and fertilized plots. Nymphs of two Cicada genera were collected (Cicadetta spp. and Tibicen spp.). Cicadetta nymphs were more abundant in burned plots, but mowing reduced their abundance. Tibicen nymphs were collected almost exclusively from unburned plots. Treatment effects on herbivorous beetle larvae (Scarabaeidae, Elateridae, and Curculionidae) were variable, but nutrient additions (N or P) usually resulted in greater densities, whereas mowing usually resulted in lower densities. Our results suggest that departures from historical disturbance regimes (i.e. frequent fire and grazing) may render soils more susceptible to increased numbers of European earthworms, and that interactions between fire, aboveground biomass removal, and vegetation responses affect the structure and composition of invertebrate communities in tallgrass prairie soils.     

Properties of anaerobically digested and composted municipal solid waste assessed by linking soil mesofauna dynamics and nitrogen modelling

We have studied the effect of anaerobically digested (ADMSW) and composted municipal solid waste (CMSW) on mineralization and foodweb dynamics to verify the hypothesis that ADMSW would immobilize N right after addition to soil in contrast to addition with CMSW. Another hypothesis was that the mesofauna (enchytraeids and microarthropods) would stimulate N release from the decomposer community. We measured excretion of -N and urea-N from the mesofauna and hypothesized that enchytraeids would release urea. ADMSW and CMSW were amended to pots with sandy loam and barley. The pots were divided into treatments with or without mesofauna. Mesofauna, plant N and biomass, soil N and ergosterol (fungal biomass) were measured over a 113-day period of four equidistant samplings. Soil respiration, N mineralization and N release by the mesofauna were modelled from concurrent studies. ADMSW- and CMSW-treated soils initially (<20 days) immobilized N. The amendments did not increase plant growth substantially, and this was probably due to N-limitation in the early stages of plant growth. Enchytraeid abundance was about three times higher in ADMSW- than CMSW-treated soils, indicating that ADMSW contained more labile compounds, bacteria, and microfauna. The mesofauna did not affect N-content, but the cumulated -N excreted by the mesofauna was estimated to be substantial and about one-fifth of total plant N in ADMSW. An explanation for this discrepancy might be that in the absence of the mesofauna, other members of the detrivore and microbivore community performed the mesofauna’s function. Neither enchytraeids nor microarthropods excreted urea.     

Faculty positions: Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,     

Faculty positions: Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,     

Variation in quality parameters between and within 14 Nordic tree fruit and berry species

Abstract

A 3-year study was carried out to investigate quality parameters in 14 tree fruit and berry species grown in southern Norway. The species were blueberry, apple, aronia, sour cherry, sweet cherry, red raspberry, strawberry, blackcurrant, gooseberry, red currant and elderberry, harvested along with wild bilberry, cloudberry and lingonberry. Significant differences between species were identified for all quality parameters. The coefficient of variation between species was lowest for pH (12.5%), dry matter (18.9%) and soluble solids (25.3%), followed by titratable acids (59.3%), total phenolics (83.8%), antioxidant capacity FRAP (85.7%) and antiradical power by the DPPH-assay (97.8%), total monomeric anthocyanins (132%) and ascorbic acid (137%). Average coefficient of variation within species were lower and ranged from 4 (pH) to 62% (ascorbic acid). Only the FRAP values were significantly affected by harvesting year with lower levels in 2004 than in 2005 and 2006. There were significant interactions between species and harvesting year for dry matter, soluble solids, pH, ascorbic acid and FRAP. The results indicate generic ranges in composition within species independent upon growing location and climate, and the composition of the tree fruits and berries is not likely to deviate from these ranges. It is concluded that desirable composition of tree fruits and berries and their products should primarily be achieved by selection among species rather than searching fors broadened variation within individual species.     

Potassium Fixation and Release Characteristics in Rhizosphere and Nonrhizosphere Soils for a Rapeseed–Rice Cropping Sequence

Potassium (K) fixation and release in soil are important factors in the long-term sustainability of a cropping system. Changes in K concentration and characteristics of K fixation and release in rhizosphere and nonrhizosphere soils in the rapeseed (Brassica napus L.)–rice (Oryza sativa L.) rotation were investigated using a rhizobox system. The concentrations of different forms of K in both rhizosphere and nonrhizosphere soils decreased with plants compared to without plants, regardless of K fertilizer application. Potassium uptake by crops mainly came from the rhizosphere soil. In the treatment without K fertilizer (–K), the main form of K supplied by the soil to the crops was 1.0 mol L^?1 nitric acid (HNO₃) nonextractable K, followed by nonexchangeable K, and then exchangeable K. In the treatment with K fertilizer (+K), the main K forms supplied by the soil to the crops were exchangeable K and nonexchangeable K. The amount and rate of K fixation after one cycle of the rapeseed–rice rotation was greater in rhizosphere soil than in nonrhizosphere soil. The amount and rate of K fixation of soil in the +K treatment were significantly less than in the –K treatment. The cumulative amounts of K released with 1.0 mol L^?1 ammonium acetate (NH₄OAc) and 1.0 mol L^?1 HNO₃ extraction increased with the increasing numbers of extractions, but the K-releasing power of soil by successive extraction decreased gradually and finally became almost constant. The release of K was less in rhizosphere soil than in nonrhizosphere soil. The release of K in the +K treatment was similar to that in the –K treatment in rhizosphere soil, but the K release in nonrhizosphere soil was greater with the +K than the –K treatment. Overall, the information obtained in this study will be helpful in formulating more precise K fertilizer recommendations for certain soils.