水分胁迫对茶树叶片叶绿素荧光特性的影响

以"铁观音"和"福鼎大白茶"两个茶树品种为试验材料,研究水分胁迫对茶树叶片叶绿素荧光特性的影响.结果表明:水分胁迫下,茶树叶片的基础荧光(Fo)显著升高,最大荧光(Fm)、可变荧光(Fv)、PSⅡ原初光能转化效率(Fv/Fm)、PSⅡ的潜在活性(Fv/Fo)显著下降,表明水分胁迫使茶树叶片PSⅡ反应中心受到伤害;水分胁迫还可降低茶树的光化学反应速率(Prate),缩短荧光上升时间(T1/2),抑制PSⅡ反应中心电子的传递(ETR降低),导致天线色素热耗散速率(Drate)、非光化学猝灭(qN)和光合功能相对限制值(LPFD)升高,光化学猝灭(qP)和PSⅡ实际光化学效率(Yield)显著下降.比较水分胁迫下"铁观音"和"福鼎大白茶"叶片叶绿素荧光变化发现,"铁观音"PSⅡ反应中心的胁迫耐性较强,叶片光化学效率较高.     

覆膜对不同施肥条件下玉米拔节期光合参数与荧光参数的影响

为探明覆膜对早春东北黑土玉米叶片光合生理特征的影响,在大田条件下,研究了覆膜对不同施肥条件下玉米拔节期叶片光合参数与叶绿素荧光参数的影响.结果表明:覆膜能够显著增加不同施肥条件下玉米拔节期叶片光合速率、蒸腾速率、气孔导度和水分利用率,而对其他光合参数如细胞间隙CO2浓度和气孔限制值影响不显著.就施肥条件而言,覆膜对N、P处理玉米拔节期叶片光合参数的影响明显强于其他施肥处理.覆膜能够增加施P和PK处理玉米拔节期叶片Fm、Fv/Fm和Fv/Fo值,而显著降低了施NPK处理玉米拔节期叶片相应的荧光参数,覆膜对其他施肥处理玉米拔节期叶片叶绿素荧光参数的影响不显著.     

Cs对菠菜叶片光合作用影响的研究

为了揭示Cs对植物光合作用的影响机理,本文采用不同浓度的CsCl(0、1、5、10、20 mmol·L-1)和石英砂培处理菠菜幼苗15 d,分析测定了Cs在菠菜中的积累分布以及Cs对菠菜叶片叶绿素含量、光合气体交换参数、叶绿素荧光参数、类囊体膜电子传递速率、类囊体膜吸收光谱和77k低温荧光光谱的影响.结果表明:Cs处理显著降低菠菜叶片的叶绿素含量;随着Cs处理浓度的增加,尤其在处理浓度大于10 mmol·L-1时,叶片净光合速率(Pn)、气孔导度(Gs)、胞间CO2浓度(Ci)以及蒸腾速率(Tr)显著下降;叶片叶绿素荧光参数分析表明,Cs处理浓度大于10 mmol· L-1时,光系统Ⅱ(PSⅡ)反应中心遭到破坏;类囊体膜电子传递活性分析表明高浓度Cs处理抑制PSⅡ放氧侧的电子传递活性;类囊体膜室温吸收光谱和77K低温荧光光谱分析表明高浓度Cs会破坏类囊体膜的结构,导致叶绿素的结合状态受损,从而使类囊体膜光能的吸收、传递和分配受到抑制,并且会导致类囊体膜上PSⅡ和PSⅠ的色素蛋白发生不同程度的降解.本研究可为Cs污染的植物修复提供一定理论依据.     

侧柏叶温及叶绿素荧光特性对土壤水分胁迫的响应简

为了研究土壤水分与植物生长间的关系,以侧柏为材料进行盆栽试验,人工控制土壤水分,设置4个水分梯度（正常供水、轻度水分胁迫、中度水分胁迫、重度水分胁迫）,测定其叶温和叶绿素荧光参数.结果表明：随着干旱胁迫的加剧,叶温和非光化学淬灭升高;初始荧光F0总体上表现为逐渐上升的趋势;而最大荧光Fm、可变荧光Fv、PSⅡ最大原初光化学量子效率Fv/Fm、PSⅡ的潜在活性Fv/F0、PSⅡ实际光化学量子效率和表观光合电子传递速率均表现为下降.参数的日变化呈现单峰型曲线：PSⅡ实际光化学量子效率和非光化学淬灭的日变化曲线为凹形,而表观光合电子传递速率日变化曲线为凸形.可知干旱胁迫导致PSⅡ的电子传递效率降低,降低了光能利用率,影响其光合作用.     

低氮胁迫对耐低氮玉米品种苗期光合及叶绿素荧光特性的影响

【目的】叶绿素荧光参数经常用来评价光合器官的功能和环境压力的影响,不同玉米基因型耐低氮胁迫能力差异较大,与光合及叶绿素荧光特性对低氮胁迫的响应机制有关。本文以耐低氮能力差异较大的4个玉米杂交种为试验材料,研究了低氮胁迫对不同耐低氮性玉米品种苗期光合及叶绿素荧光特性的影响,以期明确耐低氮胁迫玉米品种的光合机制。【方法】采用二因素完全随机设计盆栽试验,因素A为不同耐低氮性玉米品种:‘正红311’、‘成单30’和不耐低氮品种‘先玉508’、‘三北2号’;因素B为不同氮素水平:正常氮CK(霍格兰完全营养液,N 15 mmol/L)、低氮胁迫LN1(N 0.5 mmol/L)、极低氮胁迫LN2(N 0.05 mmol/L)。测定了苗期单株干物质积累量,单株氮素积累量,叶片叶绿素含量与荧光特性,以及光合效率指标。【结果】低氮胁迫下玉米苗期单株干物质积累量、单株氮素积累量、叶片叶绿素含量等生理指标显著下降,但耐低氮品种的下降幅度显著低于不耐低氮品种;低氮胁迫下玉米苗净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)显著降低,胞间CO2浓度(Ci)显著升高,净光合速率(Pn)、气孔导度(Gs)和蒸腾速率(Tr)的降幅及胞间CO2浓度(Ci)的增幅耐低氮品种均显著低于不耐低氮品种;低氮胁迫下可变荧光(Fv)、最大荧光(Fm)、PSⅡ潜在活性(Fv/F0)、PSⅡ最大光化学效率(Fv/Fm)、PSⅡ有效光量子产量(Fv'/Fm')和光化学猝灭系数(q P)等叶绿素荧光特性也均显著降低,耐低氮品种下降幅度显著低于不耐低氮品种;低氮胁迫下耐低氮品种PSⅡ实际光量子产量(ΦPSⅡ)降低,不耐低氮品种有所增加;而耐低氮品种非光化学猝灭系数(NPQ)升高,不耐低氮品种有所降低。【结论】耐低氮玉米品种能够减缓低氮胁迫对植株光合系统的影响,进而保证植株较高的氮素积累,提高叶片叶绿素含量,维持较高的PSⅡ有效光量子产量(Fv'/Fm')和光化学猝灭系数(q P),为光合作用提供充足的光能;从而保持了较高的净光合速率(Pn),保证了耐低氮品种在低氮条件下保持较高的干物质生产。     

不同灌水模式对南方辣椒叶绿素荧光参数的影响

为了实现辣椒节水、优质、高效生产,在避雨栽培条件下,利用OS5-FL调制荧光仪研究了不同灌水模式对辣椒叶绿素荧光参数的影响。结果表明,在4个生育阶段,辣椒的可变荧光、最大荧光、可变荧光与最大荧光比、可变荧光与初始荧光比、光化学淬灭系数与非光化学淬灭系数均随着灌水量的减少而降低,而初始荧光则随着灌水量的减少而升高。说明辣椒叶片PSⅡ反应中心因水分胁迫而受到了破坏,使PSⅡ原初光能转换效率和PSⅡ潜在活性降低,使光合电子传递、光合原初反应过程及热耗散能力受到抑制。DI50、2PRD和1PRD 3种处理下的辣椒各叶绿素荧光参数虽然在4次观测中均未表现出显著差异,但1PRD处理与对照相比变化最小。该研究可为南方避雨栽培下辣椒灌水模式的选择和节水、优质、高产辣椒栽培提供参考。     

不同施肥方式对超高产夏玉米叶绿素荧光特性及产量性状的影响

通过田间试验,研究了不同施肥方式下超高产夏玉米叶片叶绿素荧光参数、SOD活性、细胞膜稳定性及产量性状。结果表明,“种沟施肥+拔节期追氮+大喇叭口期追氮”有利于提高玉米叶片的PSⅡ原初光化学效率（Fv/Fm） 、PSⅡ量子效率（ΦPSII）和光化学猝灭系数（qP）, 降低非光化学猝灭系数（NPQ）。“种沟施肥+拔节期追氮+大喇叭口期追氮”和控释肥这两种施肥方式对提高叶片叶绿素含量和SOD活性,降低MDA含量和相对电导率的效果较好。控释肥对提高玉米子粒千粒重的效应较大,“种沟施肥+拔节期追氮+大喇叭口期追氮”显著提高玉米子粒产量。为了获得高产,应采用种沟施肥+拔节期追氮+大喇叭口期追氮的施肥方式,而控释肥则有利于简化施肥作业,提高劳动效率。     

外源硫化氢对盐胁迫下加工番茄幼苗光合参数及叶绿素荧光特性的影响

为探究外源硫化氢(H_2S)对盐胁迫下加工番茄幼苗光合作用和光合荧光参数的影响,以耐盐性不同的2个加工番茄KT-7(耐盐性强)和KT-32(耐盐性弱)为材料,采用分光光度法、CIRAS-3型光合仪和Imaging-PAM调制荧光成像系统分别测定光合色素含量、光合参数和叶绿素荧光参数。结果表明,外源H_2S提高了盐胁迫下加工番茄幼苗的生长及叶绿素a、叶绿素b、胡萝卜素含量、净光合速率(P_n)、气孔导度(G_s)、叶片蒸腾速率(Tr)、PSⅡ最大光化学效率(F_v/F_m)和PSⅡ实际光化学效率(ΦPSⅡ);降低了胞间CO_2浓度(Ci)、PSⅡ调节性能量耗散的量子产额[Y(NPQ)]和非光化学猝灭系数(NPQ);而PSⅡ非调节性能量耗散的量子产额[Y(NO)]稳定在较低水平。此外,外源H_2S对KT-32的缓解效应强于KT-7。综上所述,外源H_2S通过提高加工番茄幼苗叶片的光合色素量和光合电子传递效率,有效地缓解盐胁迫对加工番茄叶片PSⅡ的伤害。本研究结果为探究外源H_2S增强加工番茄耐盐性研究提供了科学依据。     

被动荧光探测水分胁迫对玉米叶片影响的初步研究

利用叶绿素荧光被动探测方法初步探讨了水分胁迫对玉米叶片生理机能的影响。水分胁迫梯度通过将离体叶片放在干燥器时间不同而获得。室内采用积分球耦合ASD光谱仪，结合加/不加滤光片照明的方法得到反射率差值光谱，即代表叶绿素荧光光谱。结果表明随着叶片含水率的降低，叶绿素荧光发射峰的位置几乎没有变化，峰高在686 nm处有先上升后逐渐降低的趋势，在740 nm处则缓慢下降。双峰比值Dif₆₈₆/Dif₇₄₀与叶片含水率呈负相关关系(R²=0.3850，n=21)，不同水分胁迫程度下利用调制式荧光仪测定的荧光参数Fv/Fm与740 nm荧光光谱峰值线性正相关，与双峰比值有负相关趋势。表明该被动方法可以探测水分胁迫引起的叶片光系统受胁状况，为田间被动遥感探测植物叶绿素荧光和生理状态提供参考。     

叶绿素荧光成像技术下的柑橘黄龙病快速诊断

柑橘黄龙病被称为柑橘的"癌症",具有极强的传染性,造成柑橘产业巨大的经济损失。为探究病原菌对宿主光合作用进程中对光能吸收、分配和利用的影响,并实现柑橘黄龙病的快速诊断,该研究利用叶绿素荧光成像技术对感染黄龙病不同程度柑橘叶片的叶绿素荧光特性和相应淀粉、蔗糖、葡萄糖和果糖含量进行研究,分析了叶片的叶绿素荧光图像与淀粉、蔗糖、葡萄糖和果糖含量之间的关系,并构建了柑橘黄龙病快速诊断模型。结果表明,染病叶片中的淀粉、蔗糖、葡萄糖和果糖出现异常累积,糖代谢异常与病原菌的侵染有关;宿主的叶绿体光系统Ⅱ(Photosystem Ⅱ, PSⅡ)反应中心遭受破坏,导致最小荧光产量上升,PSⅡ的最大光量子效率下降及PSⅡ中有活性的光反应中心数量减少,染病叶片的光化学反应的能力降低,激发能被转换成不可调制荧光淬灭的比例上升;叶绿素荧光参数能够精确地反演出叶片的淀粉、蔗糖、葡萄糖和果糖含量,两者具有很强的相关性。利用叶绿素荧光参数构建的随机森林模型对柑橘黄龙病诊断的总体识别正确率为97.50%。采用叶绿素荧光成像技术能够实现柑橘黄龙病快速无损检测,可为柑橘黄龙病的早期预警提供新方法。     

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.     

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.