土地利用方式对酸性红壤丛枝菌根真菌群落的影响

为了研究土地利用方式对酸性红壤丛枝菌根真菌(arbuscular mycorrhizal fungi, AMF)群落的影响，调查了酸性红壤4种土地利用方式 (草地、玉米、花生和大豆) 下非根际和根际土壤AMF群落多样性和组成结构。结果表明：土地利用方式显著影响了AMF群落优势属球囊霉属(Glomus)和巨孢囊霉属(Paraglomus)的相对丰度，但是根际作用影响不明显。土地利用方式而非根际作用显著影响了AMF群落香农指数和物种丰富度，其中大豆地表现出最低的香农指数和物种丰富度。土地利用方式和根际作用都显著影响AMF群落组成结构，但是土地利用方式的作用强度明显高于根际作用。球囊霉属主要解释了不同土地利用方式之间的AMF群落组成差异。土壤pH是影响土壤AMF群落结构的最关键因子。因此，土地利用方式比根际作用表现出对酸性红壤AMF群落更大的影响，展现了土地利用变化在影响土壤AMF群落方面的重要作用。     

木薯根域AMF群落结构特征及多样性研究

土壤微生物是土壤—作物系统养分循环的重要驱动力,其中丛枝菌根真菌(Arbuscular mycorrhizal fungi,AMF)能够促进作物对养分的吸收。木薯是我国南方重要的经济作物,是多种行业的重要原材料。为揭示不同土壤质地木薯根域土壤AMF群落结构特征,解析土壤因子对AMF类群的影响。以木薯品种华南205 (SC205)为材料,通过田间根袋培养,利用高通量测序平台进行真菌扩增子测序,分析不同处理木薯根域AMF类群组成和多样性差异。结果表明,木薯根域土壤AMF主要为球囊霉属(Glomus)、无梗囊霉属(Acaulospora)、盾巨孢囊霉属(Scutellospora)、类球囊霉属(Paraglomus)和双型囊霉属(Ambispora)。优势属为球囊霉属和无梗囊霉属。两种土质各处理AMF属水平上无显著差异,种水平分布受土壤质地及根袋的影响,粘土AMF多样性(Simpson指数)高于砂质壤土。两种土质中都发现独有种,土壤质地对木薯根域AMF群落分布有一定的影响。RDA分析表明Glomus与速效磷、速效氮、铵态氮正相关;Acaulospora与速效磷,速效氮弱负相关;Scutellospora与所有速效养分负相关;Paraglomus与所有速效养分表现出正相关;Ambispora与大部分速效养分表现出负相关。木薯根域AMF资源丰富,不同土壤质地条件下的AMF群落组成和丰度存在差异,土壤速效养分与AMF群落结构差异密切相关。该研究为进一步探索AMF在木薯上的应用提供理论参考。     

喀斯特不同植被恢复阶段土壤AMF组成及多样性研究

选择贵州花江、织金、花溪3个典型喀斯特地段的不同恢复阶段(乔木、灌木和草本)土壤丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)为研究对象,基于AMF孢子的形态鉴定,计算AMF孢子密度、分离频度、物种丰度、重要值、物种均匀度指数及Shannon-Wiener多样性指数,研究喀斯特不同恢复阶段土壤AMF物种组成及多样性。结果表明:3个采样地段共分离AMF菌种4目8科10属68种,其中球囊霉属(Glomus)数量最大达35种,其次是无梗囊霉属(Acaulospora)为17种,巨孢囊霉属(Gigspora)、类球囊霉属(Paraglomus)及原囊霉属(Archaeospora)各1种;不同采样地段各植被恢复阶段的优势种不同,所有样地中层状球囊霉Glomus lamellosum具有最大的相对丰度、分离频度和重要值;AMF种分类水平上,花江样地不同恢复阶段AMF丰度表现为乔木灌木草本,织金样地为灌木草本乔木,花溪样地为灌木乔木草本;不同植被恢复阶段土壤AMF均匀度指数和香农多样性指数在花江和织金多表现为乔木灌木草本,花溪样地Shannon-Wineer指数则是灌木显著高于乔木和灌木阶段。研究表明,喀斯特土壤中因异质生境条件的差异AMF菌种组成和物种多样性具有较大的差异。     

不同土壤类型下AM 真菌分布多样性及与土壤因子的关系

以禾本科植物群落为研究对象, 研究了宁夏六盘山林地、银川农耕地、暖泉农耕地、固原农耕地、盐池沙地、灵武沙地6 个采样地点5 种土壤类型(黑垆土、灌淤土、黄绵土、灰钙土、风沙土)下AM 真菌物种多样性及其与土壤因子的关系。结果表明: 5 种土壤类型采样点的植被根际土壤中共鉴定出5 属48 种AM真菌, 其中, 无梗囊霉属(Acaulospora)1 种, 巨孢囊霉属(Gigaspora)3 种, 球囊霉属(Glomus)37 种, 类球囊霉属(Paraglomus)1 种, 盾巨孢囊霉属(Scutellospora)6 种, 各采样点土壤均以球囊霉属为优势属。地球囊霉(G.geosporum)和木薯球囊霉(G. manihotis)是6 个采样地点中的优势种。不同土壤类型各采样点AM 真菌各属的频度存在明显差异, 球囊霉属在各点均有出现, 频度值最高。具有较高植被多样性的暖泉样点, AM 真菌的种属数量较多。土壤环境因子对AM 真菌孢子密度的影响因所处土壤、植被类型不同而异。pH、全盐、速效钾、速效磷等土壤肥力因子, 在PCA 轴上能最大程度地解释AM 真菌孢子密度与土壤环境因子之间相互关系的大部分信息。宁夏不同土壤类型区域中AM 真菌种类及分布一定程度上与该采样点的植被类型、植物多样性和土壤肥力特征相对应。     

磷肥对酸性红壤上玉米不同部位丛枝菌根真菌群落的影响

为了研究不同磷肥水平下酸性红壤上玉米不同部位丛枝菌根真菌(Arbuscular mycorrhizal fungi, AMF)群落多样性和组成结构,明确玉米不同部位AMF群落的分布特征及对磷肥的响应差别,为提高酸性红壤磷素利用提供理论依据。本实验设置三个磷肥水平：不施磷、低磷(25 mg P /kg)和高磷(100 mg P /kg),玉米培养4周后,测定玉米生物量和土壤理化性质,利用高通量测序技术检测玉米根部、根际和非根际土壤AMF群落结构和多样性。结果显示,随着磷肥水平增加,玉米生物量显著提高,高磷处理下玉米地上部磷含量显著高于不施磷和低磷处理。取样部位(根部、根际和非根际)显著影响了AMF群落优势属球囊霉属(Glomus)、巨孢囊霉属(Paraglomus)和近明球囊霉属(Claroideoglomus)相对丰度,但是磷肥影响不显著。类似的,取样部位而不是磷肥显著影响了AMF群落香农指数和物种丰富度。非度量多维标度(NMDS)结果显示,根部样品与非根际和根际土壤样品群落距离更远,而相同取样部位中不同磷肥水平间群落组成更为相似；置换多元方差分析(PERMANOVA)进一步表明,取样部位而不是磷肥显著影响了AMF群落组成结构,主要表现在根部样品与根际和非根际土壤不同。因此,酸性红壤上玉米不同部位对AMF群落的影响明显高于磷肥作用,表明AMF应用于酸性红壤时应重点考虑作物部位的特性。     

西北地区赤霞珠葡萄根际土壤中AM真菌的多样性

对西北地区5个酿酒葡萄赤霞珠（Vitis vinifera L. cv. Cabernet Sauvignon）葡萄园根际土壤060 cm土层的AM真菌空间分布进行了研究。结果表明,葡萄根系可形成丛枝菌根,且侵染率较高,最高达79%; 在西北地区的5个样地中共分离出AM真菌4属22种,其中球囊霉属（Glomus）15种,无梗囊霉属（Acaulospora）4种,盾巨孢囊霉属（Scutellospora）2种,巨孢囊霉属（Gigaspora）1种。5个样地孢子密度大小顺序为: 陕西泾阳（JY）＞山西永济（YJ）＞陕西杨凌（YL）＞宁夏银川（YC）＞甘肃莫高（MG）。各样地葡萄根际土壤中AM真菌种的丰富度不同,陕西泾阳地区最高; 分布于葡萄根际的AM真菌按种类多少排序的属依次是: 球囊霉属无梗囊霉属盾巨孢囊霉属巨孢囊霉属,球囊霉属占据的比例保持着绝对优势; 根内球囊霉、摩西球囊霉、地表球囊霉在不同样地中均为优势菌株,副冠球囊霉,集球囊霉,细凹无梗囊霉是多数样地中的稀有种类。研究表明,葡萄与AM真菌具有良好的共生关系,二者协同进化产生了具有生态环境特异性的菌根真菌多样性; 葡萄根际存在较为丰富的丛枝菌根真菌资源,可供进一步开发利用。     

秸秆还田方式对丛枝菌根真菌群落和玉米磷素利用的影响

丛枝菌根真菌（arbuscular mycorrhizal fungi,AMF）与80%左右的植物可形成共生结构,在农田生态系统中对植物—土壤系统养分循环起重要作用。为改善我国南方典型瘠薄红壤加速酸化、磷有效性低和土壤生物功能退化等严重问题,采用高通量测序技术揭示秸秆还田方式对根际AMF群落、土壤磷酸酶活性和磷素利用率的作用机制。结果表明,不同秸秆还田方式显著影响土壤理化性质,其中秸秆猪粪配施处理显著提升有机碳（SOC）、全氮（TN）、全磷（TP）、有效磷（AP）以及酸性磷酸酶（acid phosphomonoesterase,ACP）和碱性磷酸酶（alkaline phosphomonoesterase,ALP）活性。秸秆还田显著影响AMF多样性和群落结构,球囊霉属（Glomus）和类球囊霉属（Paraglomus）是AMF群落的优势属,SOC是影响AMF多样性和群落结构的关键因子。秸秆猪粪配施处理对玉米磷素利用率的提升效果最佳,显著高于秸秆还田和秸秆生物质炭处理。AP、TP、ACP活性和AMF群落多样性显著影响了磷肥利用率。不同秸秆还田方式下根际AMF群落可能调控了土壤磷素活化过程...     

长期保护性耕作对丛枝菌根真菌多样性的影响

为了明确我国北方干旱地区长期保护性耕作以及深松对丛枝菌根真菌(AMF)多样性的影响,笔者于2014年在山西省临汾市连续22年实施保护性耕作的长期定位试验基地,针对免耕覆盖(NTS)、深松免耕覆盖(SNTS)及传统耕作(TT)3种处理方式,进行了不同耕作条件下土壤AMF物种丰度、孢子密度、Shannon多样性指数以及AMF侵染率等因素的比较研究。结果显示,长期保护性耕作(NTS和SNTS)共分离鉴定出AMF 7属9种,其中根孢囊霉属(Rhizophagus)和斗管囊霉属(Funneliformis)各2种,球囊霉属(Glomus)、近明球囊霉属(Claroideoglomus)、无梗囊霉属(Acaulospora)、硬囊霉属(Sclerocystis)和隔球囊霉属(Septoglomus)各1种;而传统耕作(TT)共分离鉴定出AMF 6属8种,没有检测到无梗囊霉属。NTS、SNTS和TT处理在不同土层的AMF优势种基本一致,0~40 cm土层为摩西斗管囊霉(Fu.mosseae)和变形球囊霉(G.versiforme),40~80 cm土层为摩西斗管囊霉、变形球囊霉和聚丛根孢囊霉(Rh.aggregatum),80~120 cm土层为聚丛根孢囊霉,120 cm土层以下只有NTS和SNTS处理中存在聚丛根孢囊霉,说明保护性耕作措施促进了AMF向土壤深层发展。NTS和SNTS处理在同一土层的AMF物种丰度、孢子密度和Shannon多样性指数均高于TT处理,SNTS处理高于NTS处理。同一耕作措施不同土层的AMF物种丰度、孢子密度和Shannon多样性指数均随土层加深而逐渐降低;NTS和SNTS处理在小麦各生育期的丛枝侵染率和孢子密度均高于TT处理;各处理在小麦拔节期的AMF侵染率最高,分别为14.9%、16.1%和10.6%,而在收获期的土壤孢子密度最高,分别为111.7个·(100g)~(-1)、125.0个·(100g)~(-1)和90.3个·(100g)~(-1)。研究认为,长期免耕覆盖、尤其深松免耕覆盖,提高了AMF多样性。该研究结果可为中国北方旱作农田生态系统中AMF自然潜力的充分发挥,以及保护性耕作技术的合理应用提供科学依据。     

科尔沁沙地结皮发育对土壤理化性质影响的研究

通过野外取样和室内分析,初步研究了科尔沁沙地植被恢复过程中结皮的理化性质及其结皮发育对下层土壤特性的影响。结果表明,半流动、半固定和固定沙丘分别发育了物理、地衣及苔藓结皮,结皮的厚度、紧实度、水分、粘粉粒含量及各种全效、速效养分随沙漠化逆转趋势依次增加。同时,结皮的存在增加了其下层土壤的容重值,提高了颗粒组成中的极细砂和粘粉粒含量,富集了结皮下土壤的有机质、全N、全P、速效N、速效P等养分,随着结皮的发育,结皮对下层土壤的上述影响作用从半流动沙丘到半固定、固定沙地呈逐渐增长的趋势。沙漠化逆转过程中,结皮对土壤养分的富集在0-5 cm范围内,由表及里呈递减趋势。同一沙丘结皮下0-2.5 cm层土壤的容重、粘粉粒含量、养分含量均高于2.5-5 cm层及对照无结皮层相对应的值。     

毛乌素沙地苔藓结皮对沙化土壤性质和细菌群落的影响

我国沙化土地占国土面积的17.93%,对北方地区经济和社会的发展、人们的生活以及生态平衡影响巨大。土壤生物结皮能有效防风固沙,微生物在其形成中起着重要作用。之前在对生物结皮微生物群落研究方面,缺乏对生物结皮层与同厚度裸沙表层之间以及它们各自下方土壤之间的比较与分析。采用高通量测序技术,对毛乌素沙地苔藓结皮层与裸沙表层,结皮下方土壤与裸沙下层土壤细菌群落结构进行了分析。结合土壤理化因子数据,分析了苔藓结皮对沙地细菌群落多样性的影响。结果表明：相比于裸沙表层苔藓结皮显著提高了土壤速效养分、全氮和有机质的水平,结皮下方土壤中速效养分、全磷和有机质含量均高于裸沙下层。结皮层及其下方土壤中粗粉砂和粉粒的含量显著高于裸沙表层和下层,表明苔藓结皮显著改善了沙地土壤的理化性质。速效磷、速效钾、速效氮、黏粒、粉粒、粗砂是影响沙地土壤细菌群落组成的重要环境因子。多样性分析显示,结皮下方土壤中细菌多样性最高。在苔藓结皮层中unclassifiled_f__Micromonosporaceae（小单孢菌科的未知属）,norank_c__Cyanobacteria（蓝藻纲的未知属）和Pseudonocardia（假诺卡氏菌属）的相对丰度都显著高于裸沙表层;在结皮下方土壤中norank_c__Acidobacteria（酸杆菌纲的未知属）和Rubrobacter（红色杆菌属）的相对丰度均显著高于裸沙下层,这些差异显著的物种对稳定沙地土壤结构具有重要作用。在研究生物结皮的过程中,对照沙地也要分层取样,微生物群落对比分析才更准确。因此,苔藓结皮的形成对沙地原有表层及下层土壤的细菌群落产生显著影响,利于生物固沙。研究结果为风沙治理和荒漠生态恢复提供了重要的微生物学理论依据。     

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。     

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.     

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.     

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,     

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,     

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.     

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.