山东省禹城市夏玉米生长期水分利用特征分析

以山东省禹城地区夏玉米农田为例,利用氢氧稳定同位素技术测定2015年夏玉米生长期茎干水、大气降水以及不同深度土壤水的δD和δ18 O组成,利用直接对比法和多元线性混合模型法分析夏玉米对土壤水的利用情况,并分析农田降水—土壤水—作物水之间的转化规律。降水同位素测定结果显示禹城地区大气降水线方程为δD=6.55δ18 O-3.03(R2=0.88),斜率和截距均小于全球大气降水线,表明蒸发是导致同位素富集的主要过程。对夏玉米生长期水分来源特征分析表明,出苗期主要利用表层0—15cm土壤水,贡献率达73.9%;拔节期从土壤不同深处均吸收水分(0—55cm,81.8%),30—55cm处土壤水利用相对较多,也会利用同时期降雨;抽穗期较多利用深层土壤(30—55cm,71%),此时期浅层土壤蒸发强烈,土壤含水量快速减少,植物可利用水分较少。而30—100cm处土壤含水量受温度,土壤蒸发影响较小,为夏玉米生长持续提供稳定水分。灌浆期吸收各层土壤水分的量相近(15—100cm,72%),此时期无降水,温度下降,蒸发减弱,各层土壤含水量较稳定。成熟期主要吸收30—100cm处的土壤水分,贡献率达70%,表明降雨较少时,夏玉米吸收土壤水分依赖于较深层土壤。此外,夏玉米生长期水分来源受土壤体积含水量及土壤蒸发蒸腾的影响较大,同时降雨,大气温度及湿度会影响土壤含水量。通过水量平衡模型计算得出2015年夏玉米在出苗期、拔节期、抽穗期、灌浆期、成熟期的农田蒸散量分别为35.62,34.99,32.4,22.31,16.94mm。研究结果对于夏玉米不同生长期节水灌溉具有指导意义。     

基于同位素分析研究山东禹城夏玉米水分来源

以2016年山东省禹城市夏玉米为研究对象,通过测定分析不同生长期内降水、土壤水、植物水、地下水、地表水的稳定氢氧同位素值,并利用直接对比法和多元线性混合模型,分析不同水源对夏玉米不同生长期贡献率,进而研究其水分来源。结果表明:禹城市大气降水线方程为δD=7.80δ18 O+8.61,其斜率和截距均小于全球大气降水线方程,表明降水在降落过程存在蒸发富集过程。夏玉米不同生长期水分来源存在差异,出苗期由于土壤含水量较低,植物主要利用浅层地下水且利用率为89.6%;拔节期降雨量丰富,夏玉米主要利用0—10cm表层土壤水,利用率为85.8%;抽穗期夏玉米主要利用10—60cm土壤水,利用率达62.9%;生长到灌浆期,根系分布在较深土层且20—100cm土壤含水量稳定,夏玉米主要利用20—100cm土壤水,利用率为69.7%;成熟期植物主要利用大于60cm的深层土壤水,利用率达96.1%,此时期土壤含水量较低且根系分布可达深层土壤。     

华北山区油松侧柏降雨前后水分来源

北京山区处于季节性干旱的生态脆弱地带,研究其典型树种在降雨前后的水分来源对干旱区水分利用具有重要意义.本研究基于氢氧同位素技术,以北京山区典型乔木树种油松和侧柏为研究对象,测定分析树木枝条、土壤、地下水和降雨等氢氧同位素组成,探明2种乔木树种在降雨前后主要水分来源.结果表明:不同树种在同一时期的水分来源不同,同一树种在降雨前后水分来源不同.油松表层根系分布虽少,但在雨前仍能吸收利用含水量较高的表层土壤水,利用率为36.0％;为获得稳定水源,油松在降雨前后都利用发达的主根系吸收利用地下深层水分,利用率分别为38.0％和58.2％.侧柏在雨前干旱缺水时能利用深层水维持正常生理活动,利用率为71.2％,但分布在土壤表层0～ 20 cm的侧根系对降雨反应较为敏感,雨后的侧柏主要利用表层土壤水分,利用率为71.6％.试验结果将对于干旱半干旱地区人工造林、树种配置和缓解水资源短缺具有重要意义.     

旱季雨季对黄土丘陵退耕区植被根系分布及水分利用的影响

黄土丘陵区属于季节性干旱的区域,研究退耕生态系统植被根系分布及其水分利用特征对植被恢复具有重要意义。该研究利用稳定同位素技术,采集黄土区5种典型退耕植被群落的根系、土壤样品,分析根系形态结构和稳定同位素特征,探讨根系在不同季节的吸水策略。结果显示:旱季茵陈蒿、铁杆蒿、白羊草、达乌里胡枝子群落和油松的根长密度(16.3、21.7、17.3、17.3、6.0 mm/cm3)分别是雨季(1.7、2.1、3.2、5.9、4.2 mm/cm3)的9.4、10.2、5.3、2.9、1.4倍,茵陈蒿、铁杆蒿、白羊草根系对土壤水分季节变化的响应较为敏感。茵陈蒿群落仅可利用0~10 cm土壤水,旱季铁杆蒿、白羊草群落主要利用30~40 cm土壤深度的水分,雨季吸水深度上移至0~20 cm。旱季达乌里胡枝子和油松主要利用60 cm以下的土壤水分,雨季则吸收20~40 cm土壤水分。表明退耕植被群落根系在不同季节的吸水策略不同,旱季吸收较深的土壤水而雨季则吸收近地表的土壤水,吸水深度范围的季节变化与土壤水和根系分布变化相一致。该研究为黄土丘陵区退耕植被对流域生态水文过程影响的研究提供科学依据。     

黄土丘陵区植被群落水分利用策略对干旱胁迫的响应

为探讨气候变化下灌草群落中主要植物水分来源差异及动态变化。以黄土高原典型自然恢复植物(油蒿、苜蓿与藜)为研究对象,通过减少自然降水的15%(中度干旱)与30%(极端干旱)来控制干旱程度,研究植物水分利用来源与生长对干旱胁迫的响应特征。将植被群落潜在水源划分为浅层(0—20 cm)、中层(20—60 cm)与深层(60—120 cm)土壤水,采用稳定水同位素技术与MixSIAR模型定量分析不同干旱胁迫程度(减雨30%、减雨15%与对照)下植被根系水分吸收特征。结果表明：(1)土壤水与植物水中稳定氢氧同位素值(δD和δ¹⁸O)均位于当地大气降水线的右下方,说明土壤水同位素受蒸发影响发生富集;(2)3种典型植物在遭遇干旱胁迫时,其水分利用来源均可灵活转换于不同土层之间,呈浅层土壤水分利用比例减少,中层与深层土壤水分利用比例增加的规律,且随干旱胁迫程度增大愈加明显;(3)不同植被响应干旱胁迫的水分利用策略不同,平地,减雨30%、减雨15%及CK处理下油蒿均主要利用浅层土壤水(贡献率分别为48.2%,52.7%,57.6%),而藜分别主要利用来自中层(43.5%)、浅层(4...     

基于稳定氢氧同位素的黄土高原不同生长年限油用牡丹水分来源研究

[目的]探究油用牡丹的水分来源与用水策略,为合理种植、推广发展油用牡丹,提高牡丹成活率提供科学依据。[方法]以不同生长年份的2种油用牡丹为研究材料,利用稳定氢氧同位素探究其在春秋2个季节的水分来源。[结果]①由于根系更加发达,成年期油用牡丹的用水策略比幼年期有更强的自主选择性。春(旱)季,2种年龄油用牡丹都主要利用0—20 cm表层土壤水,但成年期(70.7%)比幼年期(61.8%)对水分的利用率更高。秋(雨)季,表层土壤含水量过高,成年期油用牡丹较幼年期则更趋向吸收深层土壤水分;②通过分析土壤含水率、油用牡丹吸收的不同来源水分的贡献率及它们之间的关系,可知贡献率越高的土层含水量越低。[结论]在黄土高原春秋2个季节,油用牡丹均倾向于吸收含水量较低土层水分,证明了其耐旱不耐涝的特性。     

基于稳定同位素技术的黄河支流河岸植被水分来源解析

[目的] 分析比较不同水分梯度下植物水的氢氧同位素特征,为黄河流域生态保护与防蚀控沙中适宜物种的筛选提供一定的理论基础。[方法] 采用氢氧稳定同位素技术,基于HYSPLI4气团轨迹模型和贝叶斯混合模型MixSIAR,分析黄河主要支流—西柳沟河流河岸不同水分梯度下优势植物对潜在水源利用率,进而提出不同植物的水分利用策略。[结果] 研究区在采样期间降水的水汽主要来源于西北季风输送和局地蒸发。在水分充足的河漫滩样地,植物以浅层土壤水（0—30 cm）为主要水源。距离河道较远的河谷阶地上,草本类植物主要利用浅层和中层土壤水（0—70 cm）,灌木类和高大草本类植物转而吸收更深层的土壤水（70—100 cm）,出现水文生态位分离的现象。[结论] 当水分缺乏时,灌木类植物会因为吸水模式的优势具有更强的生存竞争力。灌木类植物是黄河流域生态保护与防蚀控沙的适宜物种。     

露天煤矿排土场覆土厚度对土壤水分入渗及植物水分利用的影响

表土回覆是露天煤矿排土场生态修复的关键步骤，覆土厚度直接影响植物生长和复垦成本，为研究露天煤矿排土场不同覆土厚度对土壤水分入渗及植物水分利用的影响，采用室内土柱模拟试验，设置10,20,30,40,50 cm共5个覆土厚度，分别进行垂直入渗试验和室内盆栽试验(玉米),并结合氢氧同位素稳定示踪技术，研究不同覆土厚度土壤入渗和玉米水分利用特征，筛选研究区排土场最佳覆土厚度。结果表明：覆土厚度为10～30 cm(27.05～33.02 mm/min)的初始入渗速率显著高于40～50 cm(21.59～24.89 mm/min)的初始入渗速率(p<0.05),稳定入渗速率随覆土厚度的增加而增大，当覆土厚度高于40 cm后，随着覆土厚度的增加稳定入渗速率维持在3 mm/min左右。矸石层入渗过程受覆土层的影响较大，覆土厚度高于40 cm后，矸石层入渗速率基本稳定在土层连接面的入渗速率上。不同覆土厚度下玉米木质部水氢氧同位素值与土壤水氢氧同位素随土层变化曲线交点主要集中在覆土层，因此，玉米生长水分主要来源于覆土层。覆土厚度越大，2条线交点增多、交点分布范围增大，玉米对土壤水分的利用范围越大，...     

黄土高原不同林龄苹果树根系吸水策略对降水的响应

在黄土高原陕西省长武塬区选取品种和管理手段均相同的3种林龄果园(尚未结果的5年幼龄果园、已结果的8年初果园和13年壮果园)苹果树,采用空间换时间的试验设计,分别于2015年7月12日和8月19日对0—500cm深度土壤及对应取样处的苹果树枝条取样,测定土样和枝条样中水分的稳定氢氧同位素,并利用贝叶斯模型量化降水前后不同土层对苹果林耗水的贡献。结果表明:(1)不同林龄苹果树降雨前后的主要水分来源深度不同。干旱时,13年壮龄果树的主要吸水深度比5年和8年果树深;而生长旺季,雨季降水只能补充未挂果的5年幼龄果园土壤水分消耗,即使降水量很大,也无法满足已经开始挂果的8年和13年果园土壤水分消耗。(2)在干旱期,5年和8年果树50%以上的水分来自表层0—100cm土壤,而13年果树50%的水分来自100—300cm土层。而降水后,5年和8年果树的主要水分来源变为100—300cm土层,贡献值在40%左右;13年果园的主要水分贡献层为0—100cm土层,贡献了近50%的水分。(3)3种林龄果树根系对300—500cm土层土壤水分的吸收对降雨的响应非常弱,降雨前后贡献率始终保持在30%。     

基于氢氧同位素的油茶果实生长高峰期水分来源量化

量化丘陵区油茶果实生长高峰期水分来源,对油茶林的科学灌溉和生态管理至关重要。该研究以3～5年生的幼年油茶为对象,利用氢氧稳定同位素,分析果实生长高峰期油茶木质部水和根系活动层土壤水的同位素组成,应用线性混合模型和贝叶斯混合模型（MixSIAR）量化油茶根系吸水来源。结果表明：在果实生长高峰期,油茶主要利用0～30 cm土层土壤水,相比第一生长高峰期（4-6月）,第二果实生长高峰期（7-8月）的油茶吸水深度有所增加,其中,0～30、>30～60和>60～100 cm的贡献率分别为51.3%、28.2%和20.5%,3个土层（单位体积）对油茶根系吸水的贡献量分别为149.6、81.1和58.7 mm。线性混合模型和MixSIAR模拟的各土层土壤水对油茶的贡献比例略有差异,但结论基本一致。该研究可为制定南方丘陵区幼年油茶适宜灌溉制度及促进林地水肥一体化建设提供参考。     

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.