科尔沁沙地生物结皮的土壤种子库特征

通过野外取样和室内分析,初步研究了科尔沁沙地两种生物结皮在干、湿两种处理下土壤种子库种类组成、密度以及物种多样性等特征。结果表明：①科尔沁沙地藻结皮和苔藓结皮土壤种子库的总密度为干旱藻结皮〈湿润藻结皮〈干旱苔藓结皮〈湿润苔藓结皮。两种结皮上种子库的数量存在显著差异,对于干、湿处理的两种结皮,苔藓结皮上种子库的总密度均大于藻结皮上种子库的总密度;②两种生物结皮在干旱、湿润两种处理中共出现了6科、15种植物,种子库的组成以一年生草本植物、中生植物为主,二者百分比均超过76%;③在干旱藻结皮、湿润藻结皮、干旱苔藓结皮和湿润苔藓结皮上,种子库物种多样性表现出湿润处理下的结皮高于干旱处理的结皮。由此表明,在半干旱的科尔沁沙地,水分是限制结皮土壤种子库中种子萌发的主要因子,而生物结皮则通过对水分入渗与再分配的调控作用影响结皮种子库中种子的萌发。     

黄土高原典型生物结皮对坡面产流产沙过程的影响

[目的] 明确不同类型生物结皮坡面产流产沙过程及其影响因素，为评价生物结皮的水土保持功能提供理论依据。[方法] 选取黄土高原常见藻结皮和苔藓结皮为研究对象，系统研究降雨条件下结皮类型及破坏前后对坡面产流产沙的影响。[结果] ①生物结皮可显著增强土壤黏结力，藻结皮和苔藓结皮土壤黏结力是裸地（4.53 kPa）的1.52倍和1.25倍，结皮破坏后其土壤黏结力仍高于裸地，分别是裸地的1.22，1.10倍；②生物结皮可以增加坡面产流，抑制坡面产沙。藻结皮和苔藓结皮产流量分别增加了21.64%和55.75%，产沙量分别减少了94.06%和89.24%。结皮破坏后，产流量分别增加了58.76%和59.66%，产沙量分别减少了16.18%和29.45%，仍可促进产流，抑制产沙；③随累积径流量的增加，累积产沙量增长速度由大到小依次为：裸地 > 藻结皮去除 > 苔藓结皮去除 > 苔藓结皮覆盖 > 藻结皮覆盖。黏结力是表征生物结皮抑制土壤侵蚀的有效指标。随黏结力的增大，产沙量呈线性降低（R²=0.66）。[结论] 增加生物结皮覆盖并有效防止生物结皮被破坏，可最大程度发挥其水土保持功能。     

黄土高原不同降雨强度下生物土壤结皮对坡面流水动力参数的影响

[目的]明确不同降雨强度下生物土壤结皮对坡面流水动力参数的影响,进一步评估生物结皮的水土保持功能。[方法]以黄土高原典型藻结皮和苔藓结皮为研究对象,系统研究了60,90,120,150,200 mm/h雨强下生物土壤结皮对坡面流水动力参数的影响。[结果](1)所有雨强下藻结皮和苔藓结皮坡面流流型均为层流,除200 mm/h雨强下苔藓结皮坡面流为急流外,所有雨强下藻结皮和苔藓结皮流态均为急流;(2)藻结皮在90,120,150,200 mm/h雨强下流速、径流量和径流系数分别是60 mm/h雨强的1.76～3.9,4.89～9.26,3.91～4.13倍,苔藓结皮则为1.34～2.56,5.86～13.81,2.46～4.26倍,流速和径流量均随雨强呈线性函数增加(R²≥0.85,p<0.01),径流系数呈幂函数增加(R²≥0.49,p<0.05);(3) 60,90,120,150,200 mm/h雨强下藻结皮阻力系数和曼宁糙率系数变化范围分别为0.15～0.74,0.01～0.03,苔藓结皮则为0.82～3.02,0.03～0....     

不同程度干扰下人工固沙植被区生物结皮对草本植物生长的影响

通过对沙坡头人工固沙植被区不同类型的生物结皮进行不同程度的人工干扰,对生长在结皮上的两种草本植物雾冰藜和小画眉草的繁衍和生长进行了研究。结果表明：与未受干扰的对照相比,轻度干扰下3种类型生物结皮上雾冰藜的密度、冠幅、高度、根系长度和生物量都有显著增加,重度干扰下3种类型结皮上的雾冰藜生长有所增加,密度则显著下降;轻度干扰下苔藓和藻类苔藓混生结皮上的小画眉草生长有所增加,密度基本未变,藻类结皮上小画眉草密度和生长都无显著变化。重度干扰下苔藓和藻类苔藓混生结皮上的小画眉草生长有所增加,密度和生长量下降。同时分析讨论了两种维管束植物在生物结皮受到干扰时不同表现的机理。     

冻融交替对不同生物结皮土壤饱和导水率的影响

  目的  生物土壤结皮在干旱、半干旱地区分布广泛,能显著影响土壤饱和导水率的大小,为探明冻融交替对不同类型生物结皮土壤饱和导水率的变化。  方法  以神木六道沟流域混合结皮（藻结皮 + 苔藓结皮）和苔藓结皮土壤为研究对象,采用室内模拟冻融实验的方法,测定不同冻融交替次数和初始含水率共同作用下生物结皮土壤饱和导水率（Ks）的变化。  结果  （1）冻融条件下,苔藓结皮和混合结皮的存在相比裸土均降低了土壤Ks。（2）同一冻融次数下,苔藓结皮和混合结皮土壤Ks随初始含水率增加总体呈现先增大后减小的趋势;同一初始含水率下,两种结皮土壤Ks随冻融次数增加呈现逐渐增大的趋势。（3）冻融后苔藓结皮土壤Ks显著大于混合结皮土壤,在同一冻融条件下,初始含水率为8%时,冻融3次和7次后两种结皮土壤Ks相差最大,表现为苔藓结皮土壤Ks分别是混合结皮土壤的2.1和2.3倍。（4）冻融通过影响结皮层容重和结皮厚度及结皮下层土壤有机质和 > 0.25 mm团聚体含量进而影响Ks,冻融次数对结皮厚度及有机质含量有极显著影响（P < 0.01）,对结皮容重有显著影响（P < 0.05）,初始含水率对 > 0.25 mm团聚体含量有极显著影响（P < 0.01）。（5）冻融环境下苔藓结皮和混合结皮土壤的Ks均与冻融次数呈极显著正相关（P < 0.01）,与结皮容重呈极显著负相关（P < 0.01）。并对两种结皮Ks与其他因子进行偏最小二乘回归分析,结果表明苔藓结皮土壤Ks的主要影响因子依次为结皮容重 > 冻融次数 > 结皮厚度,而混合结皮土壤Ks的主要影响因子为冻融次数 > 结皮容重。  结论  冻融交替对生物结皮土壤饱和导水率有较显著影响,且冻融作用主要是通过影响结皮厚度、结皮容重及结皮下层土壤大团聚体颗粒及有机质含量来影响生物结皮土壤饱和导水率。     

汶川地震生态治理区土壤种子库及其与地上植被的关系

为了比较地震灾区不同气候类型植被恢复区土壤种子库时空分布特征,采用野外调查取样和室内试验相结合的方法,研究了四川省汶川县威州镇和绵竹市汉旺镇4类生态治理区[干旱干暖河谷受损治理区(DHD)、干旱干暖河谷未受损区(DHU)、亚热带湿润季风气候受损治理区(HMD)、亚热带湿润季风气候未受损区(HMU)]土壤种子库的萌发动态、数量特征、物种组成、多样性特征及其与地上植被之间的关系。结果表明:未受损区具有2个萌发高峰期,受损治理区只有1个萌发高峰期,不同气候类型治理区土壤种子库在不同土壤深度表现出不同的萌发潜力;4类治理区土壤种子库平均密度为192~1 544粒·m?2,表层密度和平均密度均为未受损区受损治理区,干旱干暖河谷气候区亚热带湿润季风气候区;4类治理区共有50种植物萌发,草本植物占显著优势;HMU、HMD、DHU、DHD地上植被与土壤种子库物种组成的S?rensen相似性系数分别为26.23%、44.9%、30.77%、16.00%,Jaccard相似性系数分别为15.09%、28.95%、18.18%、9.09%;不同类型样地土壤种子库特有种和共有物种均表现出不同的生活型格局。基于以上分析结果,在灾区进行植被恢复时,应该考虑治理区的气候环境,因地制宜的进行人工引种和制定恢复措施。     

生物结皮发育对风沙土盐基离子释放和矿物风化的影响

为探明生物结皮发育对风沙土盐基离子释放和矿物风化的影响,以进一步明确生物结皮的风化成土作用。以典型风沙土上发育的生物结皮为对象,通过模拟淋溶试验比较不同类型生物结皮(藻结皮、藻—藓混生结皮和藓结皮)覆盖土壤的盐基离子释放规律,探究盐基离子释放量随淋溶液pH的变化趋势,以及量化生物结皮覆盖土壤的矿物风化速率。结果表明:矿物风化反应阶段不同种类盐基离子的淋出量均较为平缓,生物结皮覆盖土壤的各盐基离子总淋出量表现为Ca²⁺＞K⁺＞Mg²⁺＞Na⁺,其中藻结皮覆盖土壤的盐基离子总淋出量最高,比无结皮、混生结皮和藓结皮分别增加了112.0%,31.2%,27.1%。淋溶液pH显著影响盐基离子的淋溶释放,且其作用程度因离子种类和结皮类型而异。生物结皮覆盖提升了土壤的易风化矿物含量、风化程度和速率,藻结皮、混生结皮和藓结皮覆盖土壤的风化速率相比无结皮分别提升了61.2%,27.1%,152.6%,并且风化速率随淋溶液pH降低而提升。综上,生物结皮能显著促进风沙土矿物风化,其对风沙土改良和修复具有积极意义。     

毛乌素沙地植被类型对生物结皮及其下伏土壤养分的影响

为了解旱区荒漠生物结皮的养分效应及其同植被灌丛间的关系,研究以毛乌素沙地广泛分布的苔藓、藻结皮为对象,选取4类典型植被样地,深入探讨了植被对生物结皮及其下伏土壤的养分分布的影响。结果表明:(1)沙蒿植被冠层下的藻结皮及其下伏土壤的全氮、全磷、有机质含量显著高于植被冠层间,沙柳、柠条群落则为植被冠层下的相应值显著低于植被冠层间(p0.05)。(2)沙蒿、沙柳、柠条3种群落的生物结皮及下伏土壤养分含量均随土层加深逐渐降低,而草地则表现为5—10 cm土层的土壤养分显著高于上层土壤;苔藓结皮的全氮、有机质表现为:柠条草地沙柳沙蒿,苔藓结皮的全磷以及藻结皮的养分含量均表现为:草地柠条沙蒿沙柳。(3)总体上,各类型植被下的苔藓及藻结皮均能够显著增加表层0—10 cm土壤的养分含量,且苔藓结皮的养分富集作用优于藻结皮。     

藻类与微生物添加对高陡边坡生物结皮人工恢复的影响

[目的]研究微生物与藻类对生物结皮野外恢复的影响,优化黄土高陡边坡生物结皮防护技术,为区域生态修复提供新的思路和方法。[方法]利用完全试验,研究藻类(小球藻+硅藻复合藻液)、功能性微生物(胶质芽孢杆菌、巨大芽孢杆菌)两因素对人工恢复生物结皮发育状况的影响。[结果]①不同处理间发育差异明显,藻+巨大芽孢杆菌处理的生物结皮盖度中位数最大,均值为61.41%;,仅胶质芽孢杆菌处理的生物结皮厚度中位数最大,均值为2.58 mm;仅添加3 g藻处理的苔藓株高度中位数最大,均值为2.67 mm;②藻处理能够在不同添加水平下(1和3 g/m~2)显著解释(p0.05)样方间生物结皮的盖度、厚度与株密度发育差异,其添加量以2～3 g/m~2为宜;③功能性微生物对生物结皮盖度、厚度及苔藓株高度影响不明显(p=0.91/0.93/0.49),且与藻类无明显交互作用。[结论] 45°黄土边坡人工恢复生物结皮是可行的。在环境适宜的坡面喷洒藻液、接种苔藓茎段碎片,开展生物结皮恢复,能够有效构建具有一定覆盖度与厚度、发育良好的生物结皮防护层。     

沙漠人工植被区生物结皮类土壤的蒸发特性——以沙坡头沙漠研究试验站为例

沙漠人工植被区的建立有助于生物结皮的形成和发育，它将显著改变植被区土壤的持水性能和蒸发过程。利用室内蒸发法研究了流沙和沙漠植被区生物结皮类土壤的蒸发特性。结果表明，随固沙年限的延长生物结皮层及其下的亚土层逐年增厚、容重下降、土壤持水能力增加，且苔藓结皮优于藻类结皮。当土壤样品完全饱和后，生物结皮土壤的蒸发量明显高于流沙，苔藓结皮高于藻类结皮，并随固沙年限的延长而增加；但是蒸发过程表现出明显的阶段性（P〈0．05）。在蒸发的第一阶段（速率稳定阶段），与流沙相比生物结皮的存在有利于蒸发；但在蒸发的第二阶段（速率下降阶段）生物结皮却抑制蒸发。分析后认为，正是生物结皮具有较高的持水能力，在蒸发的第一阶段增加了水分被蒸发的可能性；当土壤干旱时，结皮可以将水分束缚在土壤中从而抑制了蒸发。     

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.     

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.     

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.     

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.     

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.     

Karyotypic and genome size variation in Cajanus cajan (L.) Millsp. (pigeonpea) and some wild relatives

Detailed karyotypes and 4C DNA amounts have been studied in five cultivars of Cajanus cajan and 20 species belonging to Cajanus, Rhynchosia, Dunbaria, Flemingia and Paracalyx. C. cajan shows intraspecific variability and its karyotype is most similar to that of C. cajanifolius (sect. Cajanus) in the morphology and number of satellite chromosomes and the lack of any correlation between chromosome size within the complement and asymmetry. Karyotypes of C. lineatus and C. sericeus belonging to sect. Atylia are similar with respect to maximum r-index and the ratio of longest and shortest chromosomes in their respective complements. C. acutifolius (sect. Frutocosa) is distinct in having a very low ratio (1.44) between the longest and the shortest chromosomes, while in C. albicans, C. goensis, C. scarabaeoides (sect. Cantharospermum) there is no chromosome pair with r-index >2.0. C. mollis and C. volubilis (sect. Volubilis) show similarity with regard to ratio between the longest and the shortest chromosomes and a distinct chromosome pair with an arm ratio of 2.7 and C. platycarpus is distinct (sect. Rhynchosoides) in having the smallest ratio (1.36) between the longest and the shortest chromosomes. 4C DNA amounts in Cajanus and Rhynchosia vary between 3.28 pg to 11.69 pg and 4.92 pg to 11.13 pg respectively, while in Dunbaria, Flemingia and Paracalyx these vary between 4.70 and 7:06 pg. In the genus Cajanus karyotypic features and 4C DNA amounts agree with the sectional classification and bring out a close relationship between C. cajan and C. cajanifolius. This is supported by studies based on seed protein patterns, isozyme analysis, trypsin and chymotrypsin inhibitor patterns, RFLP and RAPD data and crossability relationships. A clear relation between DNA amount and abnormalities effecting the extent of pairing and recombination in interspecific hybrids shows the importance of this study in developing future breeding programme involving C. cajan and its wild relatives that are of potential value.     

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.