祁连山哈溪林区典型植被土壤阳离子交换量和交换性盐基离子的变化特征

选择祁连山东段哈溪林区的高山灌丛林、祁连圆柏林和青海云杉林3种典型植被土壤为研究对象,研究了其0～100 cm土层土壤阳离子交换量(CEC)和交换性盐基离子(K~+、Na~+、Ca~(2+)、Mg~(2+))的垂直分布规律。结果表明,随土层深度增加,高山灌丛林、祁连圆柏林和青海云杉林的土壤CEC值均不断减小,不同植被按其土壤CEC值大小排序为祁连圆柏林>青海云杉林>高山灌丛林;土壤交换性K~+、Na~+、Ca~(2+)、Mg~(2+)含量随土层深度变化规律各不相同,交换性K~+含量不断减小,交换性Na~+、Ca~(2+)、Mg~(2+)含量没有明显的变化规律;不同森林土壤交换性盐基总量(TEB)变化规律各不相同,按其值大小排序为青海云杉林>祁连圆柏林>高山灌丛林;土壤中交换性K~+、Na~+、Ca~(2+)和Mg~(2+)含量占TEB比例大小为Ca~(2+)>Mg~(2+)>Na~+>K~+;不同森林土壤盐基饱和度(BSP)变化规律亦不相同,按其大小排序为青海云杉林>祁连圆柏林>高山灌丛林。     

磁化微咸水灌溉对土壤交换性盐基离子组成的影响

在淡水资源贫乏的土壤盐渍化地区,通过对磁化微咸水灌溉后土壤交换性盐基离子组成和水溶性盐分的测定分析,探讨地下微咸水灌溉对土壤交换性盐基离子组成的影响。结果表明:(1)微咸水灌溉中土壤交换性Mg~(2+)、K~+、Na~+降低0.7%~25%,其交换性盐基饱和度(BSP)降低7.9%~32.4%;交换性Ca~(2+)和交换性盐基总量(TEB)提高6.7%~7.9%,BSP Ca~(2+)(Ca~(2+)在交换性盐基中所占百分比)提高1.5%~3.0%;(Ca~(2+)+Mg~(2+))/TEB、Ca~(2+)/K~+、Ca~(2+)/Mg~(2+)和Mg~(2+)/K~+均增加0.6%~51%,K~+/TEB则降低13.2%~31.3%;(2)磁化微咸水灌溉后,土壤交换性K~+、Ca~(2+)、TEB和BSP K~+、BSP Ca~(2+)含量提高13.2%~31.3%;交换性Na~+、Mg~(2+)和BSP Na~+、BSP Mg~(2+)均降低为9.3%~56.5%,呈显著差异水平(P0.05),且各交换性盐基离子平均含量大小依次为Ca~(2+)Mg~(2+)Na~+K~+;Ca~(2+)/K~+、Ca~(2+)/Mg~(2+)、(Ca~(2+)+Mg~(2+))/TEB、K~+/TEB均提高3.7%~47.8%,Mg~(2+)/K~+则降低47.8%~55.4%;(3)土壤交换性盐基离子与水溶性盐基离子K~+、Na~+、Ca~(2+)、Mg~(2+)之间总体呈极显著相关(P0.01),与(Ca~(2+)+Mg~(2+))/TEB均表现为极显著相关(P0.01)。综上所述,磁化微咸水灌溉改变了土壤盐基离子的交换特性和离子组成,对降低土壤盐渍化地区长期应用微咸水灌溉产生的土壤盐分积聚有良好的作用。     

不同灌溉方式对设施土壤交换性盐基组成及比例的影响

为全面评价不同灌溉方式下设施土壤养分供应状况,以设施土壤为研究对象,采用田间试验与室内分析相结合的方法,对连年采用沟灌、滴灌和渗灌灌溉下的设施土壤有机质含量、阳离子交换量、盐基离子组成及其比列进行了研究。结果表明:3种灌溉方式土壤有机质、阳离子交换量及盐基离子含量表层较高,不同灌溉方式间表层土壤有机质含量及阳离子交换量表现为渗灌高于沟灌,沟灌高于滴灌,土壤交换性盐基离子含量总体以渗灌处理最高。各灌溉方式0—60cm土层土壤盐基离子饱和度大小顺序均为Ca~(2+)Mg~(2+)K~+Na~+,Ca~(2+)、Mg~(2+)饱和度随土层深度的增加而增大,K~+、Na~+饱和度总体呈随土层加深先降低后上升的变化趋势。Ca~(2+)、Mg~(2+)饱和度在0—30cm土层滴灌最高,30—60cm土层渗灌最高。K~+饱和度总体以渗灌为高,沟灌居中,滴灌最低。土壤Ca/K、Mg/K值总体以滴灌最高,沟灌次之、渗灌较小。从不同灌溉方式对设施土壤交换性盐基组成及比例的影响来看,采用滴灌方法不仅能省水,有效供应养分,更有利于保持养分之间的平衡,是一种较为合适的灌溉方法。     

不同植被覆盖对养分在土壤水稳性团聚体中分布特征的影响

研究了重庆缙云山不同植被覆盖下土壤结构的稳定性,以及土壤有机碳和养分在水稳性团聚体中的分布特征.结果表明:不同植被覆盖对土壤水稳性团聚体的分布和土壤结构稳定性有显著影响.竹林土壤>0.25 mm水稳性团聚体含量以及土壤结构的稳定性显著低于马尾松林和草地土壤.植被覆盖对养分在土壤水稳性团聚体中的分布模式没有显著影响,在>2mm水稳性团聚体和<0.053 mm粒级的粉砂与粘粒组分中,有机碳、全氮、全磷以及交换性K~+、Na~+、Ca~(2+)、Mg~(2+)的浓度最高;地表植被覆盖的变化对有机碳、全氮、全磷和交换性盐基离子在各粒级水稳性团聚体中的含量产生显著影响,草地和竹林土壤有机碳和全氮显著高于马尾松林土壤,主要表现在0.25-0.053 mm粒级水稳性团聚体中有机碳和全氮含量,草地和竹林土壤显著高于马尾松林土壤;而草地土壤>2 mm水稳性团聚体和<0.053 mm粒级的粉砂与粘粒组分中的磷显著高于马尾松林和草地土壤.不同植被覆盖下土壤水稳性团聚体中交换性盐基离子均以Ca~(2+)、Mg~(2+)为主,占交换性盐基总量(Total exchangeable bases TEB)的91.8%～92.9%.草地土壤各个粒级的TEB都要大于其他两种植被覆盖下的土壤.     

免耕与常规耕作潮棕壤交换性阳离子的剖面分布特征

通过田间定位试验.研究了不同耕作方式对潮棕壤0-100 cm深度6个土层土壤交换性阳离子的影响.结果表明,与常规耕作相比,免耕使土壤表层pH显著增,.而电导率下降;同时,免耕增加了表层土壤可交换性K~+含量,降低了可交换性Na~+含量,但对可交换性Ca~(2+),Mg~(2+)和阳离子交换量没有产生显著影响.相关分析结果表明,可交换性K~+与土壤养分含量没有显著相关性,而可交换性Na~+,Ca~(2+),Mg~(2+)和阳离子交换量与有机质和全氮含量均呈负相关关系.     

砒砂岩区不同退耕还林措施土壤颗粒及交换性能分布特征

为研究砒砂岩区退耕还林还草措施下林地和草地的土壤结构及土壤交换性能对其措施的响应,选取柠条林、油松林、小叶杨林和本氏针茅草地为研究对象,并以荞麦坡耕地为对照,通过野外取样与室内试验相结合的方式,采用分形理论探究土壤粒径分布(PSD)、阳离子交换量(CEC)和交换性盐基总量(ECEC)及其组成(Na~+、K~+、Ca~(2+)、Mg~(2+))的分布特征,并分析其相关性关系。结果表明:(1)实施退耕还林措施后,草地和林地的PSD分布范围、非均一性、离散程度均高于坡耕地,且柠条林的土壤粉粒含量、PSD分布范围的增幅效果最显著(P0.05);土壤剖面垂直层次上,草地有利于增加表层土壤的细粒组分和粒径的分布范围,而林地更有利于对深层土壤粒径的改良与细化;(2)研究区交换性盐基组成主要以碱土金属为主(Ca~(2+)、Mg~(2+)),不同措施的土壤ECEC和CEC值由大到小依次为柠条林油松林小叶杨林草地坡耕地。草地表层土壤交换性能优于底层土壤,而林地与之相反;(3)黏、粉粒和细砂是决定研究区土壤交换性能的细粒土壤和粗粒土壤,粉粒是CEC、ECEC的主要贡献因子,多重分形维数可较好地描述土壤交换性能与土壤颗粒间的关系。不同措施以柠条林对土壤颗粒组成和土壤交换性能的改良效果最优。     

模拟酸雨淋溶下强风化土壤矿物风化计量关系研究

矿物风化计量关系对于定量土壤酸化速率至关重要。我国亚热带地区矿物风化强烈,土壤的酸敏感性高。为获取强风化土壤在矿物风化过程中元素释放特征及其化学计量关系,选取花岗岩发育的富铁土,先用EDTA-乙酸铵溶液洗脱土壤胶体上吸附的盐基离子,然后采用改进的Batch法,将洗脱盐基土壤与未洗脱盐基土壤同时进行模拟酸雨淋溶。结果表明:(1)洗脱盐基土壤与未洗脱盐基土壤的盐基离子(K~+、Na~+、Ca~(2+)和Mg~(2+))释放情况存在显著差异,洗脱盐基后土壤在淋溶中释放的盐基来源为矿物风化,释放缓慢而平稳;(2)未洗脱盐基土壤在淋溶初期,盐基的释放量较大,随着淋溶的进行,释放量迅速下降,淋溶后期的释放速率与洗脱盐基土壤接近,这说明未洗脱盐基土壤在淋溶初期释放的盐基主要来源于阳离子交换过程,后期则主要来源于风化过程;(3)洗脱盐基土壤和未洗脱盐基土壤经酸雨淋溶释放的各盐基化学计量关系(K~+∶Na~+∶Ca~(2+)∶Mg~(2+))以及盐基离子与硅的化学计量关系(BC∶Si)差异较大,由于未洗脱盐基土壤受到阳离子交换的影响,因此只有洗脱盐基土壤的矿物风化计量关系可以作为定量估算土壤酸化速率的依据。     

喀斯特山区不同生态恢复下石灰土钙形态特征

以喀斯特高原峡谷区典型石灰土草地、退耕还草、林草间作等不同生态恢复模式为研究对象,分层采集整个剖面土壤,采用改进的BCR提取方法,通过冗余分析(RDA)等方法分析不同生态恢复模式下土壤钙的形态特征及其影响因素。研究表明:在不同生态恢复状态下,林草间作地土壤全钙、水溶态钙和酸溶态钙质量分数最高,草地土壤交换态钙质量分数最高;有机态钙含量在不同生态恢复模式土壤中没有显著差异;钙形态占全钙比均存在交换态酸溶态有机态水溶态含量的顺序。在垂直方向,耕地和退耕还草地土壤全钙及有效钙、酸溶态钙含量表现为表层底层,而林草间作地和草地则为表层底层;有机态钙含量在剖面上变化波动不大,平均值为0.33 g/kg;有效态钙及酸溶态钙在不同生态恢复下均具有空间差异性和表聚性,且与土壤pH、有机质、CEC、全氮、速效氮等土壤基本理化性质呈极显著正相关关系,通过冗余分析得出,土壤CEC、氮素和pH为影响钙素形态分布的主要因素。研究结果有助于深刻认识喀斯特山区土壤钙迁移转化规律,为喀斯特生态脆弱区生态环境恢复重建和水土保持等方面提供科学依据和理论指导。     

土壤盐分离子对乌鲁木齐小白菜Pb含量的影响研究

为研究土壤中盐分离子对小白菜Pb含量的影响,采取正交试验L_(16)4~5和盆栽试验方法,分析了5种阳离子(Ca~(2+)、Mg~(2+)、K~+、Na~+、Pb~(2+))和3种阴离子(SO_4~(2-)、Cl~-、NO_3~-)对小白菜地上部和根系中Pb含量的影响。结果表明,试验条件下小白菜地上部Pb含量为0.215~0.930 mg·kg~(-1),根系中Pb含量为1.648~24.33 mg·kg~(-1),可食用部分超标率达81.3%。土壤盐分离子对小白菜地上部Pb含量影响顺序为:Ca~(2+)Mg~(2+)Na~+Pb~(2+)K~+。根据相关性分析,土壤中Ca~(2+)与小白菜地上部Pb含量呈显著负相关(r=-0.540 3,P0.05),Na~+和Pb~(2+)呈正相关但不显著。Mg~(2+)和K~+呈负相关,也不显著。Cl~-和NO_3~-与小白菜地上部Pb含量呈显著负相关(r=-0.540,P0.05),SO_4~(2-)呈正相关,但不显著。对小白菜根系Pb含量影响顺序为:Pb~(2+)K~+Na~+Ca~(2+)Mg~(2+),土壤中Pb~(2+)对小白菜根系Pb的含量呈显著正相关(r=0.483,P0.05),Ca~(2+)、Mg~(2+)、K~+、Na~+、SO_4~(2-)、Cl~-和NO_3~-相关性不显著。乌鲁木齐土壤中固有的盐分离子对小白菜可食用部分Pb的吸收没有抑制作用。     

张掖盆地北部地下水溢出带土壤盐分特征分析

探明张掖盆地北部地下水溢出带土壤含盐量、盐分组成及盐分离子的空间分布特征,为当地土壤盐渍化防治和土地资源管理及其可持续利用提供理论依据。土壤盐分数据分析使用了描述性统计、Kriging插值、相关性分析及主成分分析方法。结果表明:研究区土壤以强碱性为主,其阴离子以SO_4~(2-)为主,阳离子以K~++Na~+为主,全盐含量和盐分离子含量具有较强的空间变异性;研究区北部土壤大多数属于非盐渍化等级,而中部及西南部土壤以硫酸盐型轻盐渍化等级为主;SO_4~(2-)、Cl~-、Mg~(2+)、K~++Na~+、Ca~(2+)是引起全盐含量变化的主导因素,盐分离子间具有相关性,且以SO_4~(2-)与Mg~(2+)相关性最高,而Cl~-与K~++Na~+相关性最高;全盐含量、SO_4~(2-)、Cl~-、Mg~(2+)、K~++Na~+、Ca~(2+)是表征研究区土壤盐渍化现象的特征因子;土壤盐渍化的盐分主要是以镁盐为主的硫酸盐和以钠盐、钾盐为主的氯化物。     

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.