La/P/Ni改性分子筛催化裂解生物油模型化合物

为研究不同分子筛催化剂对生物油催化裂解特性的影响,该文采用稀土元素La、非金属元素P以及活泼金属元素Ni对ZSM-5分子筛催化剂进行改性,在连续式固定床反应器中对乙酸乙酯、二丙酮醇、糠醛和愈创木酚等生物油模型化合物进行催化裂解试验,进而对比HY、HZSM-5、ZSM-5催化剂以及改性后ZSM-5催化剂对模型化合物的催化裂解反应特性以及脱氧效果。试验结果表明:在反应温度为400℃、反应质量空速为4/h条件下,经La/P/Ni改性ZSM-5分子筛催化剂,模型化合物有机相收率提高,结焦率下降;HY分子筛所得有机相收率最低,结焦率最高。模型化合物各组分裂解难易程度由易到难为二丙酮醇乙酸乙酯糠醛愈创木酚;改性后ZSM-5分子筛使组分单一转化率和总转化率均出现下降;HZSM-5分子筛作用下,反应转化率达到最高。模型化合物催化裂解脱氧产物以芳香烃为主,经La改性ZSM-5分子筛作用后,其芳香烃选择性较ZSM-5略微上升;P和Ni改性后,芳烃选择性下降;HZSM-5对于芳香烃选择性最高,达7.36%;HY对于芳香烃选择性最低,仅为3.15%。通过液体产物组分分析进一步探讨模型化合物反应路径,从而为生物油的催化裂解提供一定的理论基础和科学依据。     

针叶木木质素单体模型化合物热解研究进展

木质素目前是唯一可持续生产芳香基化合物的可再生资源。然而，当前绝大多数的木质素未能得到有效利用。热解可以将木质素快速转化为生物炭、生物油和生物气等产物并实现其资源化和高值化利用的有效途径。愈创木基单元是针叶木木质素的主要组成单元，且其结构中的甲氧基和酚羟基等官能团在木质素中广泛存在，因此作为模型化合物被广泛应用。愈创木酚类化合物直接热解产物以苯酚类和邻苯二酚类化合物为主，且热解温度对其热解过程具有一定影响，提高热解温度提高转化率且产生少量芳烃和更多的烯烃，且愈创木基结构单元的C4取代基官能团对愈创木酚直接热解的影响较小。分子筛由于具有独特结构和酸性位点，是催化裂解愈创木酚脱氧制备芳烃和单酚的有效催化剂。催化热解反应条件（如热解温度、重时空速和原料分压等）对催化热解产物具有重要影响；且在热解过程中添加氢供体可以显著提高愈创木酚脱氧率并降低催化剂的积碳。热解机理方面，愈创木酚基化合物直接热解反应主要反应途经是自由基反应，且结构单元中的甲氧基与焦炭形成具有直接关系。初步热解产物邻苯二酚及其衍生的邻羟基苯醌是形成气体产物的重要中间体。与直接热解不同的是，愈创木酚催化热解的主要反应机理是"烃池机理"。该研究通过对愈创木酚类化合物直接热解研究、催化热解研究和反应机理等方面进行总结和综述，期望加深对木质素热解过程的理解，为木质素热解产物的调控提供理论指导。     

ZSM-5催化生物质三组分和松木热解生物油组分分析

为了更清晰地研究三大组分(纤维素、木聚糖、木质素)在介孔ZSM-5参与下的催化热解过程,该研究首先对生物质的三大基本组分和云南松木粉进行热解,然后在介孔ZSM-5催化剂存在的条件下对微晶纤维素、木聚糖、碱性木质素三大组分和云南松进行催化热解。采用气质联用仪对生物油的化学组分进行分析。通过对比ZSM-5参与前后的生物油的主要化学组分的变化,对催化剂的催化机理进行探究。研究结果表明,催化热解过程中,介孔ZSM-5将纤维素直接热解得到的β-D阿洛糖、糠醛、3-丙基戊二酸和2,4-戊二烯酸转化为1-甲基萘、2,6-二甲基萘,纤维素催化热解得到的生物油中的芳烃含量为63.89%。半纤维素催化热解过程中,催化剂将生物油中的糠醛从67.78%降低为2.66%,有效提高芳烃化合物,包括萘、2-甲基萘的含量,催化热解后得到的生物油中总芳烃含量达到36.81%。木质素催化热解过程中,介孔ZSM-5有效降低生物油中2,6-二叔丁基对甲酚的量(从82.33%降至77.97%),并大幅地提高1,8-二甲基萘和1,7-二甲基萘的量,生物油中总芳烃相对含量达到14.14%。云南松催化热解过程中,催化剂有效降低云南松直接热解得到生物油中2-甲氧基-4-甲基苯酚和(Z)-异丁子香酚的含量,并将芳烃化合物总量提高到53.99%(主要是1-甲基萘、1-亚甲基-1氢-茚和2,6-二甲基萘)。随着催化剂使用次数的增加,生物油中含氧化合物相对含量增加,烃类化合物的相对含量明显降低,从53.99%降至43.32%,元素分析结果表明生物油中的碳含量逐渐减少,氧含量逐渐增加。但是,催化剂经过焙烧再生后,催化活性基本完全恢复。     

不同Si/Al的氢型分子筛催化热解对生物油特性的影响

为考察对于氢型分子筛(HZSM-5)的Si/Al变化和添加量对生物质热解液化的影响,该文通过离子交换法制备HZSM-5催化剂,采用激光粒度分析仪、比表面积及孔径分析仪和X射线衍射仪对催化剂的粒度、孔隙及晶体结构等性质进行表征,并在最佳油产率温度下进行木屑的催化热解。对无催化剂和不同催化条件下得到的生物油进行气相色谱质谱联用分析,结果表明,分子筛作用下,生物油产率明显降低(最大降幅8%),含水率增加。同时,液体产物中醛类、酯类、酮类、呋喃等含氧化合物及酸含量均有所降低,提高了烃类和酚类的含量,峰面积百分比最高达到12.57%和39.36%,对催化剂催化调控改善生物油品质提供了一定的科学依据。     

生物基呋喃与甲醇耦合催化热解制备芳烃化合物

为了提高芳烃的选择性产率和减少催化剂的积碳,以生物基呋喃为原料,以甲醇为耦合试剂进行催化共热解,探讨工艺条件对芳烃的选择性产率的影响,同时对其转化路径以及催化剂的积碳进行分析。结果表明:呋喃与甲醇耦合协同催化共热解可以有效的提高芳烃的选择性产率,二者具有明显的协同效应,甲醇的添加促进了甲醇制烯烃(methanol to olefin,MTO)反应、Diels-Alder环加成反应以及苯烷基化反应的发生,高温促使多烷基化合物以及萘及其同系物选择性产率的增加;强酸性促进了甲醇的脱水以及Diels-Alder环加成反应;同时,羰基抑制了呋喃环和烯烃的Diels-Alder反应,而羟基的存在有效的促进了甲苯以及二甲苯的生成,因此,当采用HZSM-5(SiO2/Al2O3=25)为催化剂,当热解温度为500℃,催化温度为550℃,MF∶甲醇=1∶5,物质的进样量为0.2 mL/min时,其芳烃的选择性产率达到99.73%,积碳量达到11.06%,苯、甲苯、二甲苯以及乙苯的总含量达到40.49%,萘及其同系物的含量仅为10.15%,有效的提高了烷基苯的选择性产率。     

活性炭催化生物质与低密度聚乙烯共热解

为探究生物质主要组分与聚烯烃塑料在活性炭共催化热解过程的相互作用机理,该研究采用磷酸活化法制备了活性炭催化剂,利用固定床反应器对纤维素、木聚糖、木质素、花旗松单独催化热解及其与低密度聚乙烯共催化热解产物的产率及组成进行了分析。结果表明,活性炭催化纤维素和木聚糖单独热解的主要产物为呋喃类物质,其质量分数分别为78.6%和83.2%;而活性炭催化木质素热解的主要产物为简单酚类物质（86.6%）。与理论计算值相比,四种混合物共催化热解所得液体产率降低了8.7%～11.4%,气体产率提高了22.6%～64.0%;液体产物中芳烃和轻质脂肪烃（C9～C16）的质量分数增加而氧化物的质量分数降低;气体产物中H2的体积分数有所增加而CO和CO2的体积分数明显降低。活性炭催化剂作用下,生物质三组分与低密度聚乙烯之间相互作用的影响程度有所不同。     

Raney-Ni催化生物油轻质组分加氢制备含氧燃料

鉴于生物油的高含氧量,将其轻质组分在温和条件下转化为以饱和醇为主要成分的含氧燃料可能成为生物油利用的新思路。该文以自制Raney-Ni为催化剂,研究在高压反应釜中反应温度（100～180℃）、氢气冷压（4～8 MPa）、催化剂用量（0.5～2 g）对生物油轻质组分催化加氢改质的影响;对Raney-Ni催化剂进行N2吸附脱附、X射线衍射（X-ray diffraction）、扫描电镜（scanning electron microscope）表征,分析催化剂失活机理,研究催化剂的重复使用性能。试验结果表明：反应温度和反应初压对生物油加氢产物分布的影响较大,在反应温度为140℃、氢气初压为6.0 MPa 时,产物中饱和醇的相对含量（以GC峰面积百分比计算）最高可达53.51%;当催化剂用量从0.5 g增加到1 g时,产物中饱和醇的含量显著提升,由25.42%提高到51.89%,进一步提高催化剂用量对饱和醇含量的提高影响不大;一次与二次催化剂催化生物油加氢反应产物中饱和醇含量由53.51%降为29.20%,活性显著降低可能与催化剂孔道内部及表面的活性中心被覆盖进而降低反应效率有关。加氢过程中,除有酮醛酚类化合物的加氢反应和酸与醇的酯化反应外,存在醇脱水成醚的反应发生。与烃类液体燃料相比,含氧燃料以其优异的燃烧性能逐渐被人们所青睐。将生物油的轻质组分加氢制备含氧燃料有望成为生物油的应用提供新思路。     

盐酸洗涤与烘焙预处理对甜高粱秸秆热解生物油组分的影响

针对生物质热解生物油氧含量高、腐蚀性强、化合物种类繁多等问题,该研究提出以盐酸洗涤和烘焙预处理相结合的方式来提高生物油品质。甜高粱秸秆预处理前后的物化特性表明单纯酸洗有利于挥发分的生成,单独烘焙预处理降低了H/C以及O/C,使能量产率达95.13%,并促进了炭的生成;酸洗-烘焙联合预处理对生物炭和不可冷凝气体都有一定的促进作用。采用管式炉热解装置制备生物油,利用气相色谱质谱联用仪(GC-MS)分析甜高粱秸秆样品热解生物油成分,结果表明:酸洗、烘焙和联合预处理使甜高粱秸秆热解生物油中化合物的种类分别在111种基础上减少了62、58和68种,酮类、酸类和呋喃类的含量均降低;酸洗对酮类中丙酮的降低作用明显,而烘焙预处理促进了酚类的生成,酸洗-烘焙显著减少乙酸的产量并促进糖类化合物的生成,尤其对珍贵稀有的D-阿洛糖促进作用显著;同时,酸洗、酸洗-烘焙预处理还分别促进了新物质壬酸和戊酸的生成;单纯烘焙有利于提高生物质中富含-OH官能团的纤维素相对含量,从而使生物油中酚类含量明显升高,生物油中虽没有形成新物质,但对pH值改善较为明显。该研究可为生物质热解生物油品质的提高及高值化产物的定向热解提供参考。     

烘焙与HZSM-5催化剂联用改善柏木热解产物品质

为研究烘焙与催化剂对生物质热解产物特性的耦合影响机制,该文选用HZSM-5催化剂,对不同温度（200、230、260、290℃）烘焙后的柏木进行热解试验。结果发现,将烘焙与HZSM-5催化剂联用后,随着烘焙温度的升高,催化热解后积碳量呈下降趋势,最高降低了62.6%;气体产物中CO的体积分数从53.69%降低至40.84%,H2和CO2的体积分数分别增大了43.1%和35.04%,CH4的体积分数整体变化不明显;液体产物中,酸类物质大幅减少,芳香烃类产物显著增多,酚类产物发生富集;结果表明,烘焙与HZSM-5催化剂的联用有效地改善了快速热解产物尤其是生物油的品质。但是也要指出,烘焙温度过高时,积碳量增多、芳香烃类产物减少,因此柏木适宜的烘焙温度应该选择在230～260℃之间。     

温度对竹材烘焙过程中气固液三相产物组成及特性的影响

烘焙预处理可有效降低生物质原料的含水率和O/C比、提高能量密度、可磨性和疏水性,进而减少热解油中水分和含氧化合物的含量,改善生物油的稳定性和品质。该文采用程序控温管式炉、热重-红外联用仪(TGA-FTIR)和快速热解-气质联用仪(PY-GC/MS)等开展生物质烘焙试验研究,研究烘焙温度(210、240、270和300℃)对毛竹烘焙过程中气、固、液三相产物的特性影响。试验结果表明:(1)烘焙固体产物:随烘焙温度升高,固体产物中固定碳和C元素含量显著增加,使得原料的热值从18.85 MJ/kg增加至23.12 MJ/kg,能量密度增加;O元素含量显著减少,使得O/C比值从0.74降低至0.42。(2)烘焙气体产物:烘焙气体成分主要为H_2O、CO_2、CO和CH_4组成,其中CO_2含量最高,其次为H_2O、CH_4和CO,所有气体产物含量随烘焙温度的升高而逐渐增加。(3)烘焙液体产物:烘焙液体产物主要由酸类、酮类、呋喃类、酚类以及醛类等有机物构成,其中酸类、酚类和呋喃类相对含量较高,最高可达20.34%、22.05%和31.42%,酮类、醛类含量相对较少,分别占10.43%与8.26%,随烘焙温度升高,酸类含量先增加后减少,呋喃类、酚类、酮类含量逐渐增加,醛类含量变化规律不显著。(4)基于对烘焙气、固、液体产物分析可知,竹材中的氧元素主要以H_2O、CO_2、CO和有机酸等形式脱除,烘焙预处理能有效提高竹材能量密度,去除水分与含氧化合物,提高烘焙固体产物的利用价值。研究结果可为竹材能源化利用提供参考。     

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.     

Electron donor and pH relationships for biologically enhanced dissolution of chlorinated solvent DNAPL in groundwater

Biologically enhanced dissolution offers a method to speed removal of chlorinated solvent dense non-aqueous-phase liquid (DNAPL) sources such as tetrachloroethene (PCE) and trichoroethene (TCE) from aquifers. Bioremediation is accomplished by adding an electron donor to the source zone where fermentation to intermediates leading to acetic acid and hydrogen results. The hydrogen and possibly acetic acid are used by dehalogenating bacteria to convert PCE and TCE to ethene and hydrochloric acid. Reductive dehalogenation is thus an acid forming process, and sufficient alkalinity must be present to maintain a near neutral pH. The bicarbonate alkalinity required to maintain pH above 6.5 is a function of the electron donor: 800 mg/L of bicarbonate alkalinity is sufficient to achieve about 1.2 mM TCE dechlorination with glucose, 1.7 mM with lactate, and a much higher 3.3 mM with formate. Laboratory studies indicate that in mixed culture, formate can be used as an electron donor for complete conversion to ethene, contrary to pure cultures studies indicating it cannot. Various strategies can be used to add electron donor to an aquifer for DNAPL dehalogenation while minimizing pH problems and excessive electron donor usage, including use of injection-extraction wells, dual recirculation wells, and nested injection-extraction wells.     

Enhanced establishment and growth of giant cardon cactus in an eroded field in the Sonoran Desert using native legume trees as nurse plants aided by plant growth-promoting microorganisms and compost

To evaluate the feasibility of long-term desert reforestation technology of mixed vegetation, cardon cactus (Pachycereus pringlei) seedlings from indoor and outdoor nurseries were planted in the field adjacent to one seedling of potential legume nurse trees: mesquite amargo (Prosopis articulata), yellow palo verde (Parkinsonia microphylla), and blue palo verde (Parkinsonia florida). Some of the planting holes were also supplemented with common dairy compost. Additionally, the combinations of legume tree–cactus were inoculated with either a consortium of desert arbuscular mycorrhizal (AM) fungi, plant growth promoting bacteria (PGPB; the diazotroph Azospirillum brasilense Cd, and the phosphate solubilizer Paenibacillus sp.), or a mixture of all. The field experiments were evaluated periodically during 30 months for survival and growth. Cardons reared in an outdoor screen house survived better in the field than those reared in a controlled growth chamber and hardened later outdoors. Association with any legume nurse tree increased survival and enhanced growth of untreated cardons. For cardons growing alone, application of either compost, AM fungi, and all the treatments combined increased survival. For these plants, no treatment affected plant growth during the first 3 months after transplanting. Later, all treatments, except for AM fungi, enhanced plant growth. However, only 2 years after transplanting the enhanced growth effect of AM fungi was also significant. In the presence of the legume nurse trees, transient positive effects on cardon growth were recorded. General evaluation after 30 months of cultivation showed that the treatments positively affected cardon growth when growing alone or in combination only with mesquite amargo but not with the other two legume trees. This study proposes that young legume trees have the capacity to enhance survival and growth of cardon cactus, depending on the legume cactus combination. Additional treatments such as compost or PGPB can either amplify the effect or else attenuate it.