miR-let-7a在大白猪甲状腺中的表达及其对甲状腺细胞凋亡的影响

microRNA(miRNA)是一类内源性的非编码RNA,广泛参与细胞的生长发育、分化、增殖和凋亡等生物学过程.为了研究miR-let-7a对猪(Susscrofa)甲状腺的生长发育及甲状腺细胞凋亡的调控作用,本研究利用免疫荧光技术鉴定了大白猪的甲状腺组织及体外培养的甲状腺细胞,利用实时荧光定量PCR(qRT-PCR)检测了miR-let-7a在不同生长阶段大白猪甲状腺组织中的表达量变化,通过转染miR-let-7a mimics并利用流式细胞术检测了转染组与未转染组的甲状腺细胞凋亡率的差异性,同时预测了miR-let-7a与细胞凋亡相关基因的靶向关系.结果发现,甲状腺组织和细胞中的甲状腺球蛋白(thyroglobulin,TG)发出绿色荧光,表明体外培养的甲状腺细胞功能正常.qRT-PCR结果显示,胚胎期随着胚龄的增加,miR-let-7a表达量逐渐增加.出生后miR-let-7a表达量下降,于60日龄达生长期最小值,之后有所上升,至90日龄后其表达量再次下降,120日龄后随日龄的增加let-7a表达量呈现逐渐增加的趋势.凋亡结果发现,和对照组相比,转染组细胞凋亡率明显升高(P＜0.05).根据研究结果推测,miR-let-7a的表达直接或间接影响了甲状腺细胞凋亡的调控过程.研究结果为深入研究猪甲状腺miR-let-7a的功能机制提供了有益的线索.     

Let-7基因家族序列分析及其在鹅生殖周期内的表达变化

近年来有研究表明Let-7家族成员(Let-7s)在动物生长发育过程中起着重要的调节作用,其不仅与肿瘤发生发育有关,还参与了雌性动物的生殖。为揭示let-7家族在鹅(Anser cygnoides)生殖周期内的表达变化规律,通过查阅现有文献与mi RBase检索let-7家族各成员序列,利用NCBI与Ensembl数据库,确定let-7s在各物种基因组中的位置。同时利用q RT-PCR检测鹅生殖周期内卵巢组织let-7s表达量。结果共搜索到300多条脊椎动物let-7s序列,包含11个成员(let-7a、let-7b、let-7c、let-7d、let-7e、let-7f-5p、let-7g、let-7h、let-7i、let-7j、let-7k),let-7s在真核动物中分布广泛,且保守性高;大部分成员均位于基因间隔区(intergenic region,IGR),仅let-7e、let-7f-5p和let-7g三者在哺乳动物中定位在基因区。q RT-PCR检测结果显示,let-7g与let-7h在就巢期的表达量显著高于开产前期、产蛋期和产蛋后期(P0.01),而let-7a、let-7b、let-7c和let-7f-5p在产蛋期和就巢期表达量差异不显著(P0.05)。因此,Let-7s家族在进化中保持着高度保守性,且let-7g和let-7h在鹅生殖周期内有着一定的调节作用。本研究为深入探究let-7家族在鹅生殖期间的调控作用提供参考。     

阉割对金华猪甲状腺球蛋白(TG)和甲状腺过氧化酶(TPO)基因表达的影响

采用荧光定量PCR技术分析阉割与非阉割金华猪甲状腺组织中甲状腺球蛋白(TG)和甲状腺过氧化酶(TPO)基因在60、90和120日龄时表达水平.结果表明:(1)组内日龄间比较,阉割组猪TG和TPO基因在90日龄时的表达量均显著高于60和120日龄(P＜0.05);非阉割组猪TG基因在120日龄时的表达量显著低于60和90日龄(P＜0.05),TPO基因在不同日龄间的表达量差异不显著(P＞0.05).(2)组间同日龄比较,发现阉割后TG和TPO基因在60,90和120日龄的表达量都显著高于或低于非阉割组(P＜0.05).研究结果提示,阉割后,TG和TPO基因表达量的升高可能会加快猪的生长发育和提高猪肉的肌内脂肪含量.     

广西新黄鸡腔上囊和胸腺的发育及其T淋巴细胞的分布

10日龄鸡胚腔上囊开始形成囊腔和皱褶,并偶尔见到T淋巴样细胞;12日龄鸡胚出现淋巴滤泡;17日龄鸡胚滤泡髓质基本形成;3日龄雏鸡滤泡皮质出现。18日龄鸡胚开始形成DIA,随日龄的增长,DIA由腔上囊背侧近导管开口处逐渐扩展到导管背侧;7周龄前后到达与泄殖腔相连处。随着滤泡及DIA的形成,T淋巴样细胞分别出现于其中。滤泡中T淋巴样细胞的百分率,胚胎期大于孵出后。出生后T淋巴样细胞主要聚集于DIA内。9～11周龄腔上囊生长达到最大值,21.5～52周龄腔上囊消失。 14日龄鸡胚胸腺开始出现髓质,并可在其中检出ANAE细小颗粒型细胞,其百分率出生后大于胚胎期。但10～12日龄鸡胚胸腺中有大量的未成熟的胸腺细胞呈ANAE斑点型反应     

鸡下丘脑高丰度差异性表达let-7a的组织表达谱及其功能分析

前期对固始鸡1日龄和36周龄下丘脑miRNA的Solexa测序分析表明,let-7a为鸡(Gallus domesticus)下丘脑发育过程高丰度差异性表达miRNA.为全面了解鸡let-7a的功能,采用实时定量PCR检测了1日龄和36周龄固始鸡两个发育阶段13种组织中let-7a的表达情况.结果表明:let-7a在所检测的组织中呈广泛性表达,其在下丘脑中的表达趋势与高通量测序结果一致;1日龄时,let-7a在下丘脑和肾脏中高丰度表达,在肺中低丰度表达,其他组织中适度表达;36周龄时,let-7a在各组织中的表达量都较低,除了在肺中的表达量较1日龄上升外,其余各组织的表达量都下降.同时,采用两种算法预测了let-7a的靶基因,并对107个共有靶基因进行了基因本体功能(Go)富集分析和京都基因与基因组百科全书(KEGG)通路分析,结果显示:靶基因主要在生物学过程调节相关的生物学过程中富集,尤其是与矿物质和磷代谢相关的调节过程;且在粘着斑、细胞外基质受体互作、丝裂原活化蛋白激酶(MAPK)信号通路等3个通路中显著富集(P＜0.01).这些结果为进一步研究let-7a功能提供了有益线索.     

钙调磷酸酶催化亚基A基因(PPP3CA)在不同品种鸭发育早期肌肉中的表达及其与肌纤维特性的相关性

钙调磷酸酶催化亚基A(protein phosphatase 3 catalytic A,PPP3CA)是PPP3C在骨骼肌中的主要亚型,在肌纤维分化中起重要作用.为研究PPP3CA基因在不同品种鸭(Anas platyrhynchos domestica)发育早期肌肉中的表达规律及其与肌纤维特性的相关性,本研究选用生长速度差异较大的金定鸭和高邮鸭,采用实时荧光定量PCR检测鸭13、17、21、25和27胚龄及7日龄胸肌和腿肌中PPP3CA mRNA的表达水平.结果表明,两鸭种同一肌肉组织中PPP3CA mRNA的表达表现出显著的时间特异性,而品种和性别效应并不显著.两鸭品种胸肌和腿肌中PPP3CA mRNA的表达模式虽不同,但均是在13胚龄(13embryonic day,E13 d)时最高,且在出雏后7日龄时极显著高于27胚龄(出雏前)(P＜0.01).胸肌中PPP3CA mRNA在21胚龄时显著低于其他各胚龄或日龄(P＜0.01);腿肌中PPP3CA mRNA在21胚龄时表达量较高,27胚龄时降到最低,且极显著低于其他各胚龄或日龄(P＜0.01).相关性分析结果显示,两鸭品种腿肌PPP3CA mRNA表达量与本研究前期检测的肌纤维类型、直径、面积和密度等肌纤维特性呈现不同程度的线性相关;两鸭品种胸肌和腿肌PPP3CA mRNA表达量与均与本研究前期检测的类胰岛素生长因子(insulin-like grow factor-Ⅰ,IGF-Ⅰ)mRNA表达量呈显著的正相关(P＜0.05或P＜0.01).初步推测鸭发育早期骨骼肌中PPP3与肌纤维类型和肌纤维生长发育密切相关,与IGF-Ⅰ可能共同参与了对骨骼肌生长发育的调节.本研究结果将有助于了解PPP3在鸭肌肉早期发育中的作用,并为改良鸭肉品质提供理论依据.     

应用两种方法克隆猪miRNA let-7b及let-7c

microRNA(miRNA)为一类大小约22个核苷酸的非编码小分子RNA,它们能通过与靶mRNA的3'UTR(非编码区)完全互补导致mRNA降解,或不完全互补结合阻断mRNA翻译.研究分别利用构建小RNA的cDNA文库和RNA加尾及引物延伸RT-PCR克隆法从猪骨骼肌中鉴定了miRNA let-7b和let-7c,结果显示这两种直接克隆法特异性高,对包含这2个miRNA的前体序列折叠后显示具有茎-环结构特征.其中猪的let-7b还未见报道,而let-7c克隆结果与预测的完全一致,通过克隆的方法证实了猪中的let-7b和let-7c,比较后认为这两种方法各有优缺点,为推动猪miRNA的克隆鉴定提供了新的策略.     

猪背膘组织二脂酰甘油酰基转移酶基因(DGAT1和DGAT2)的发育性表达分析

酰基辅酶A:二脂酰甘油酰基转移酶(acyl-coA:diacylglycerol acyltransferase,DGAT)是催化甘油三酯合成最后一步反应的关键酶,包括DGAT1和DGAT2两种;阐明其在发育过程中的表达规律对于找到控制中外猪种脂肪沉积能力差异的基因十分必要.本研究分别用RT-PCR和实时荧光定量RT-PCR的方法分别对莱芜猪和杜洛克3日龄仔猪和成年猪背膘组织中DGAT1和DGAT2 mRNA表达量进行了分析.结果表明,莱芜猪和杜洛克成年猪DGAT1 mRNA的表达量均高于3日龄仔猪,分别为5.0倍和2.7倍;成年猪DGAT2 mRNA表达量高于3日龄仔猪,分别为27.6倍(P＜0.01)和4.8倍(P＜0.05).两品种成年猪和3日龄仔猪DGAT2基因表达量的变化均高于DGAT1.品种间同一发育时期比较,杜洛克3日龄仔猪背膘组织中DGAT2基因的表达量高于莱芜猪,但成年莱芜猪背膘组织中DGAT2基因的表达量高于杜洛克,差异均不显著(P＞0.05).提示DGAT2基因可能与中外猪品种脂肪沉积能力的差异有关.     

五指山猪不同组织中肌细胞生成素基因Myf4及生肌调节因子Myf6的表达

本文通过运用Real-time PCR技术,检测肌细胞生成素基因Myf4和生肌调节因子Myf6在出生后的第30天、第210天、第360天（出生到体成熟）的五指山猪肌肉组织中的表达变化,以及Myf4、Myf6在体成熟五指山猪肌肉、心、肝、脾、肺、肾、胃、小肠组织中mRNA相对表达情况。结果表明：Myf4及Myf6基因在五指山猪出生后在肌肉组织中的mRNA表达水平随着五指山猪的生长年龄生长而显著增长（p〈0.05）;Myf4及Myf6基因在成年五指山猪以上8种组织中均有表达,其中在肌肉组织中相对表达量最高。本研究结果将为五指山猪肌肉生长发育及矮小性状形成机理提供参考。     

猪MiR-148a对肝脏发育调控的初步研究

mi R-148a是mi R-148/152家族中的一员,对细胞增殖、细胞分化、癌症发生等生物过程有重要的调控作用。本研究采用Real-time quantitative PCR(q RT-PCR)方法,定量检测mi R-148a在金华猪(Sus scrofa)不同发育时期肝脏中的表达变化,结果显示,mi R-148a在胚胎期的肝脏中表达量最高;出生后,随着日龄的增加表达量逐渐降低;为了了解mi R-148a的生物学功能和过程,对其进行GO(gene ontology)功能注释和KEGG(kyoto encyclopedia of genes and genomes)通路分析。结果显示,mi R-148a参与肝脏的生长发育调控过程。为了验证mi R-148a的靶基因,利用胎鼠(Mus musculus)肝细胞构建mi R-148a过表达和抑制表达的细胞模型,以此来探究mi R-148a的表达变化对靶基因在m RNA水平的影响。结果发现,在小鼠胎肝细胞中过表达mi R-148a可以显著降低CCAAT增强子结合蛋白α基因(CCAAT-enhancer binding protein-alpha,Cebpa)的表达量(P<0.05)。进一步检测发现,在金华猪肝脏生长过程中Cebpa与mi R-148a的表达呈负相关。根据这些结果推测,mi R-148a可能在肝脏发育过程中通过降低Cebpa的表达来调控细胞增殖和分化效应之间的平衡。     

半滑舌鳎甲状腺激素受体β基因(TRβ)的克隆与表达分析

甲状腺激素在鲽形目仔鱼的变态过程中起着重要的作用,而甲状腺激素的生物效应是由甲状腺激素受体(thyroid hormone receptors,TRs)介导的。本研究利用RACE技术克隆了半滑舌鳎(Cynoglossus semilaevis)TRβ基因的全长,并对其功能进行了生物信息学分析。结果显示,TRβ基因(GenBank登录号:No.KJ499433)cDNA全长为2 345 bp,开放读框(open reading frame,ORF)长1 188 bp,编码396个氨基酸,5'-UTR和3'-UTR分别长454和703 bp。通过氨基酸序列比对发现,TRβ氨基酸序列铰链区有一段由9个氨基酸残基组成的插入序列,推测这段序列可能为硬骨鱼类TRβ基因所特有的。实时荧光定量PCR技术分析结果显示,TRβ基因在各组织中均有表达,且在肝组织中的表达量显著高于其他组织(P0.05);因此推测TRβ基因在半滑舌鳎成鱼各组织中具有多样性的功能,而且其在肝脏的新陈代谢中起到重要的调节作用。在半滑舌鳎仔鱼变态时,TRβ基因的表达量随变态开始而迅速增加,在变态高峰期到达最高。药物处理实验结果显示,正常变态和提前变态的仔鱼TRβ基因的表达水平均随变态开始而迅速上调,而变态被抑制的仔鱼中TRβ基因的表达量则未出现显著变化,表明TRβ是调控半滑舌鳎仔鱼变态过程的重要基因,在半滑舌鳎生长发育早期阶段起较关键作用。本研究为深入解析半滑舌鳎变态的分子机制提供了理论依据和参考。     

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,     

Assessing the effectiveness of conservation measures: Resolving the “wicked” problem of the Steller sea lion

“Wicked” problems are those that are complex and that change when solutions are applied. Many conflicts in conservation fall into this category. The study approached the problem of how to constrain the apparent wickedness of a problem in the conservation management of a species by using simple empirical indicators to carry out iterative assessment of the risk to a population and to document how this risk evolves in relation to the addition of new data and the implementation of management actions. Effects of high levels of uncertainty within data and also concerning population structure were examined through stochastic simulation and by exploration of scenarios. Historical trends in the example used, the Steller sea lion, showed rapid declines in abundance in some regions during the 1980s. The current total population is 130,000-150,000 Steller sea lions through Alaska and British Columbia and this number has been stable since about 1990 in spite of regional differences in population dynamics. Regional differences in the sequence of changes in the number of pups and non-pups, suggested that an internal re-distribution of juveniles could have happened between 1980 and 1990. Current productivity also appears close to the long-term mean. Stochastic population projection using various scenarios showed that, based upon this history, the risk of extinction for the population has declined and is below reasonable thresholds for considering the population to be endangered. The trends in risk suggest that management actions taken since 1990 have probably been effective. Consequently, the conservation management objectives for the Steller sea lion are probably being met. The approach provides a mechanism, based upon experience and scenario analysis, for exploring future policy options and may help to constrain the debate amongst stakeholders about the cost-benefit trade-offs associated with different options.     

Soil-profile distribution of primary and secondary plant-available nutrients under conventional and no tillage

Nutrient distributions under no tillage (NT) compared with conventional disk-and-bed tillage (CT) management in the warm, humid region of the southeastern USA need to be assessed so that future placement, quantity, and type of fertilizers can be altered, if necessary, to efficiently match crop demands. We determined soil-profile distributions of pH, N, P, S, K, Ca, Mg, Na, Zn, Fe, Mn, and Cu to a depth of 0.9 m at the end of 8.5 years of continuous CT and NT management on a Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in southcentral Texas. Most dramatic changes occurred within the 0–0.05 m depth, where soil under NT had lower pH, Fe, and Cu than under CT, but greater P, K, Zn, and Mn. Greater P and K under NT than under CT also occurred below the till-zone (0.15–0.3 m). At a depth of 0–0.3 m, soil under NT contained greater amounts of extractable P, K, Zn, Fe, Mn, and Cu than under CT. Nitrogen fertilization had little effect on nutrient distributions, except resulting in greater extractable K at 0–0.05 m and greater nitrate at 0–0.15 m. Few changes in soil-profile distributions were observed for extractable S, Ca, Mg, and Na. Long-term continuous use of NT on this fine-textured, high-fertility (except for N) soil had no apparent adverse effects on nutrient distributions relative to CT, but enhanced conservation and availability of P, K, Zn, Fe, Mn, and Cu near the soil surface where crop roots proliferate.     

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.     

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.