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1.
石灰性土壤普遍存在铁有效性低导致的植物缺铁黄化现象,严重影响农业可持续发展。筛选高效溶铁细菌并探讨其与菌根真菌（AMF）协同提高土壤有效铁含量、改善植物铁营养机制具有重要意义。以石灰性土壤和番茄（Lycopersicon esculentum）为试材进行盆栽试验,分别接种Advenella kashmirensis（B1）、Arthrobacter cupressi（B2）、Klebsiella variicola（B3）、Variovorax guangxiensis（B4）和Enterobacter ludwigii（B5）5株细菌,以不接菌处理为对照（CK）,筛选出高效溶铁菌株B1、B2和B3。将其与纯培养得到的AM真菌孢子（Rhizoshagu irregularis, Ri）组合,设置单独接种AM真菌（Ri）、单菌与Ri（B1+Ri、B2+Ri和B3+Ri）、菌群与Ri（B1+B2+B3+Ri）共接种处理,进一步探究单菌及菌群与AMF协同促进石灰性土壤难溶性铁的活化和促进植物铁吸收的机制。结果表明：（1）与对照相比,接种B1、B2和B3能够显著促进番茄生长,根系和地上部全铁积累量分别提高6.48倍和2.61倍（B1）、4.11倍和2.03倍（B2）、4.37倍和2.25倍（B3）;新叶活性铁含量分别提高74.21%、1.33倍和1.75倍。（2）与单接AMF相比,不同共接种组合显著增加番茄生物量,各部位平均全铁积累量显著提高58.32%~119.43%,其中B3+Ri处理、B1+B2+B3+Ri处理下番茄根系活性铁含量分别提高41.47%和44.30%、新叶活性铁含量分别提高12.61%和12.77%。不同共接种组合处理显著提高AM真菌的菌根侵染率,较单接AM真菌处理提高13.35%~30.99%;根系铁还原酶活性增加9.86%~22.07%,根系LeFIT1、LeFRO2和LeMYB72基因表达显著上调。与单接AM真菌相比,B3+Ri和B1+B2+B3+Ri处理下根际土壤pH分别降低0.21和0.09,土壤有效铁含量分别提高15.78%和55.23%。综上,AM真菌与3株高效溶铁细菌的协同作用可显著提高石灰性土壤铁有效性并改善植物铁营养,不同类型溶铁细菌与AMF的协同作用机制不同,为解决石灰性土壤铁有效性低的问题提供了微生物途径。 相似文献
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有机物料对平邑甜茶实生苗根系呼吸强度的影响 总被引：21，自引：6，他引：21
研究了几种有机物料对一年生平邑甜茶实生苗吸收根、生长根、褐色木质根呼吸强度的影响。结果表明,不同有机物料对三类根呼吸强度提高的程度不同,夏季为鸡粪>羊粪>花生秧处理;秋季羊粪>鸡粪>花生秧处理。整株根系呼吸强度,夏季鸡粪、羊粪和花生秧处理分别比对照提高56%、31%和25%;秋季羊粪比鸡粪处理高19%。吸收根、生长根和褐色木质根呼吸强度差异显著,夏季吸收根呼吸强度是褐色木质根的2～3倍、秋季为2～2.4倍;生长根呼吸强度是褐色木质根的1.5～1.9倍、秋季为1.3～1.7倍。白色根(吸收根与生长根之和)与褐色木质根各自的总呼吸量占整株根系呼吸量比例随季节变化而不同,夏季白色根所占比例超过50%,秋季褐色木质根呼吸量所占比例达68%～80%,在整株根系呼吸量中占主导地位。 相似文献
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青钱柳是我国重要的药用植物之一,研究生物菌肥对其生长、根系构型和根系性状的影响,可为立地困难的青钱柳人工林的高效栽培提供依据。 试验用生物菌肥包括2种解鳞菌即巨大芽孢杆菌M(Bacillus megaterium)和荧光假单胞菌F(Pseudomonas fluorescens)、2种固氮菌即褐球固氮菌C(Azotobacter chroococcum)和巴西固氮螺菌B(Azospirillum brasilence),菌肥处理材料包括青钱柳大田苗和盆栽苗处理。其中,大田苗设3个处理:2种解磷菌和2种固氮菌分别等量混和(MF、CB)和对照处理(CK);盆栽苗(大田土添加有机质)设6个处理,分别为2个单菌(M、C)、3个混和菌(各菌种等量混和MF、CB和MFCB)和对照处理(CK)。利用3D激光扫描技术构建青钱柳的根系形态,比较分析根系分布范围和根系性状。研究发现,1)施用生物菌肥的处理显著提高了青钱柳苗高、地径的相对生长率和土壤养分。大田试验中,MF处理促进苗高和地径的生长效果最好,MF是CK处理的2.37和1.69倍;盆栽试验中,MF处理促进苗高生长效果最好,是CK处理的1.18倍,CB处理促进地径生长效果最好,是CK处理的1.16倍。大田试验中,CB的土壤无机氮含量是CK处理的1.49倍,MF的土壤有效磷含量是CK处理的1.71倍;盆栽试验中,CB的土壤无机氮含量是CK处理的1.72倍,MFCB的土壤有效磷含量是CK处理的2.13倍。2)生物菌肥可显著提高大田植株根系水平分布与生物量。CB和MF处理的根系水平分布分别是CK的2.00和1.79倍;细根生物量CB是CK处理的1.73倍。3)生物菌肥显著影响了盆栽植株根系性状:CB处理的根系3D扫描点云数(73.2×103)显著大于CK(49.7×103);M、C和CB处理的细根表面积、体积显著高于CK,其中CB处理最大,分别是CK的1.56和2.06倍;菌肥处理(除M、MF和MFCB)的根系生物量均显著大于CK(P<0.05),其中CB处理最大。综合分析表明,无论是大田还是盆栽苗,生物菌肥可改善苗高、地径的相对生长率、土壤养分和根系性状,且固氮菌混和处理(CB)的改善效果最好。由此可见,合理施用生物菌肥可通过改善青钱柳根系性状来促进植株生长。 相似文献
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施用秸秆和接种蚯蚓对土壤温室气体排放的影响 总被引：1，自引：0，他引：1
通过施用秸秆并接种蚯蚓于微系统实验研究发现,在 21 天的培养期内,蚯蚓活动显著增加土壤C02和N20的排放速率,与对照处理相比,单接种蚯蚓处理与单施加秸秆的处理导致CO2排放量分别增加了60%和1.35倍,相应的N2O .排放量增加了1.06倍和3.94倍.另一方面,与单施加秸秆的处理相比,接种蚯蚓配合施加秸秆的处理导致C02和N20排放分别增加了41%和45%.施用秸秆显著提高了土壤微生物生物量C含量,而单接种蚯蚓处理的土壤相比对照处理反而降低.接种蚯蚓显著提高了土壤N03--N和NH4 -N含量,秸秆处理土壤并不显著增加土壤中的NH4 -N含量. 相似文献
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连作番茄根区病土对番茄生长及土壤线虫与微生物的影响 总被引：4，自引：0，他引：4
探索连作番茄根区病土对番茄根结线虫病的诱导效果及引起连作障碍的微生态机制,可为深入了解番茄连作障碍发生机理及探究番茄连作障碍防治方法提供科学依据。本研究利用盆栽试验,测定了番茄在健康土壤及接种病土土壤中生物学特性变化及根结线虫侵染状况,并分析鉴定了土壤中微生物及线虫的种类与数量。结果表明,接种连作番茄根结线虫病株根区病土会对番茄生长及根结线虫侵染产生影响:1)番茄苗期根系根结数达9个?株~(-1),健康土壤无根结;土壤线虫数量较健康土壤增加390.4%;收获期番茄根结线虫侵染率达62.7%,病情指数为80.0%。2)番茄生长受到抑制,叶片防御酶活性降低,收获期茎叶及根系鲜质量较健康土壤分别减少50.2%及33.1%,苗期番茄叶片PPO活性较健康土壤降低15.8%,POD活性较健康土壤增加24.0%,差异均达显著水平(P0.05)。3)番茄根系更易感染有害菌,根系内病原菌甘蓝假单胞菌数量较健康土壤增加463倍,根区土壤细菌、真菌及放线菌总数分别增加46.3%、94.5%及134.0%。4)食细菌线虫、食真菌线虫及植物寄生性线虫数量分别为健康根区土壤的3.3倍、1.6倍及7.3倍,其中的植物寄生线虫95.6%为根结线虫。综上所述,接入连作番茄根结线虫病株根区病土不仅导致番茄遭受根结线虫侵染,而且会导致土壤线虫总量及植物寄生线虫所占比例大幅增加,并使番茄根系内有害细菌数量显著增加,对番茄生长造成显著抑制作用,同时影响番茄的生理生化特性,受线虫侵染番茄防御性酶活性降低,使其更易被根结线虫及病原菌侵染,番茄根区土壤线虫、微生物及根系内优势细菌的种类与数量及其之间的作用发生改变。 相似文献
6.
不同铁营养状况下间作小麦对花生吸收Cd的影响 总被引：3，自引：0，他引：3
采用温室土壤盆栽实验,研究不同铁营养条件下间作小麦对2个品种花生吸收积累Cd的影响。结果表明,铁营养状况对白沙1016和花育20生物量的影响不显著。两品种花生根际土壤有效Cd含量在间作不缺铁时最高,分别为0.27,0.31mg/kg。单作时,白沙1016和花育20地上和根系Cd含量均高于间作处理,但差异不显著;而间作时,缺铁的白沙1016、花育20在根系Cd含量与不缺铁处理相比显著降低,分别减少了39.0%和34.3%。土壤铁营养对单作花生植株Cd迁移率影响较小;间作条件下,与不缺铁处理相比,土壤缺铁导致Cd的迁移率显著提高,白沙1016、花育20的Cd迁移率分别增加了1.1倍和0.6倍。间作时小麦根际Cd含量低于单作,并且在缺铁条件下,与花育20间作时小麦根系Cd含量最少为7.92mg/kg。单作时花生Cd的积累量均小于小麦;竞争吸收Cd的能力表现为白沙1016小麦花育20;缺铁间作模式下作物Cd的积累量最少。同时,小麦和花生间作模式可以减少2种作物对Cd的积累,从而可降低人类摄取重金属Cd的风险。 相似文献
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《土壤通报》2018,(6)
为探讨4种自生固氮菌,包括菌c:争论贪噬菌(Variovorax paradoxus),菌d:玉米固氮螺菌(Azospirillum zeae),菌f:苜蓿中华根瘤菌(Sinorhizobium meliloti)和菌j2:荧光假单胞菌(Pseudomonas fluorescens)对盐碱地玉米生长和土壤养分特性的影响,在田间微区试验条件下,研究了土施4种固氮菌对玉米大口期和成熟期不同器官氮素积累量及成熟期产量与产量构成因素的影响,并探讨了4种菌对土壤有效氮含量和土壤脲酶活性的影响。结果表明:菌剂处理可以增加大口期与成熟期玉米根、茎与叶的干物质质量,提高大口期玉米根冠比;增加玉米籽粒中氮素积累量,其中f与j2处理较CK差异显著;各菌剂处理玉米产量较CK分别增加了18.09%、77.91%、157.0%和108.1%,菌f和j2差异显著。不同菌剂处理均提高了土壤有效氮、速效磷和速效钾含量,在成熟期,d处理较CK土壤有效氮含量显著增加了24.32%。在大口期与成熟期,各菌剂处理均提高了土壤脲酶活性。综上,各菌剂处理能提高土壤有效氮含量,提高玉米产量。本研究可为研制滨海盐渍土专用微生物菌肥提供理论依据及技术支撑。 相似文献
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9.
玉米豆科覆盖作物间作对潮土酶活性和真菌群落特征的影响 总被引：2，自引：0，他引：2
黄淮海地区土地复种指数高，不具备休闲条件，致使土壤养分消耗严重，土壤微生物群落多样性下降。为改善土壤状况，本研究基于两年的玉米豆科覆盖作物（紫花苜蓿、大豆、花生）间作试验，探讨玉米豆科覆盖作物间作对土壤养分、酶活性以及真菌群落特征的影响，同时分析黄淮海平原潮土区玉米豆科覆盖作物间作的可行性。结果表明：间作条件下土壤碱解氮含量提高，土壤有机质含量无明显变化，玉米紫花苜蓿间作处理和玉米花生间作处理土壤有效磷含量表现上升趋势。所有间作处理土壤脲酶活性都高于单作玉米处理，间作花生处理和间作大豆处理的酸性磷酸酶活性较单作玉米处理分别增加了30.53%和18.70%；间作紫花苜蓿处理土壤碱性蛋白酶活性和蔗糖酶活性对比单作玉米处理有显著提高。间作紫花苜蓿处理和间作大豆处理对土壤优势菌门子囊菌门和被孢霉门的相对丰度有积极作用，其中间作紫花苜蓿处理子囊菌门的相对丰度提高了11.88%，间作大豆处理被孢霉门相对丰度增幅达45.39%，优势菌门丰度的提升有助于补充土壤氮源和碳源。玉米豆科覆盖作物间作可以补充土壤养分，改善土壤微生物群落结构，提高土壤酶活性，可能成为提高黄淮海平原潮土地区土壤质量、维持土壤稳定性的有效措施。 相似文献
10.
不同施肥处理对光合碳在花生-土壤系统中分配的影响 总被引：1，自引：1，他引：0
通过室内花生盆栽,设置NPK(常规氮磷钾施肥)、NPKS(常规氮磷钾加玉米秸秆)、NPKA(常规氮磷钾加腐殖酸)和CK(不施肥对照)4个不同的施肥处理,采用3次~(13)CO2脉冲标记的方法对不同施肥处理下光合碳在花生-土壤系统中的分配进行定量研究。结果表明:不同施肥处理对标记期内花生总生物量影响不显著,但是NPKA处理显著提升了花生根系生物量,较CK、NPK和NPKS分别高22.04%、19.47%和53.38%。NPKS处理地上部~(13)C丰度最高,但土壤中~(13)C丰度最低,NPKA处理土壤中~(13)C丰度最高。各处理地上部的~(13)C含量无显著差异,NPKA处理根系的~(13)C含量显著高于NPK且土壤~(13)C含量显著高于其他处理。NPKA处理地上部的~(13)C分配比例最低而土壤中分配比例最高,根系~(13)C分配比例与其他处理无显著差异,根系与土壤~(13)C分配比例之和显著高于其他处理。本研究表明腐殖酸能显著促进花生光合碳向地下部的转运。 相似文献
11.
低氮和干旱胁迫对富士和秦冠生长及氮素利用的影响 总被引：2，自引：2，他引：0
【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。 相似文献
12.
Aleš Lebeda Ivana Doležalová Eva Křístková Barbora Mieslerová 《Genetic Resources and Crop Evolution》2001,48(2):153-164
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. 相似文献
13.
Kyle Devey Michael Mucalo Gordon Rajendram Joseph Lane 《Communications in Soil Science and Plant Analysis》2015,46(4):72-80
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. 相似文献
14.
Thomas Larsen Jesper Luxhøi Jakob Magid Lars Stoumann Jensen Paul Henning Krogh 《Biology and Fertility of Soils》2007,44(1):59-68
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. 相似文献
15.
《中国生态农业学报》2014,(6)
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, 相似文献
16.
《中国生态农业学报》2014,(7)
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, 相似文献
17.
《中国生态农业学报》2014,(8)
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, 相似文献
18.
M.A. Callaham Jr. J.M. BlairT.C. Todd D.J. KitchenM.R. Whiles 《Soil biology & biochemistry》2003,35(8):1079-1093
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. 相似文献
19.
I.L. Boyd 《Biological conservation》2010,143(7):1664-1674
“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. 相似文献
20.
Soil-profile distribution of primary and secondary plant-available nutrients under conventional and no tillage 总被引：1，自引：0，他引：1
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. 相似文献