基于RUSLE模型的2000-2010年长江三峡库区土壤侵蚀评价

[目的]探究三峡库区土壤侵蚀程度,为区域土壤侵蚀合理化治理提供依据。[方法]采用RUSLE模型,结合多源数据（MODIS-NDVI,DEM,土地利用等）,定量评价长江三峡库区2000-2010年的土壤侵蚀时空分布。[结果]①三峡库区除西部地区外,其它地区土壤侵蚀情况严重;2000-2010年,长江沿岸以剧烈侵蚀和极强度侵蚀为主;②三峡库区土壤侵蚀状况在2000-2010年间得到一定程度的改善,强度以上土壤侵蚀面积由2000年的1.71×10⁶ hm²下降为2010年的6.82×10⁵ hm²;库区内平均侵蚀模数由2000年的36.75 t/（hm²·a）下降为2010年的22.79 t/（hm²·a）;③三峡库区经过多年侵蚀治理,强度、极强度、剧烈侵蚀面积逐渐减少的同时,轻度、中度土壤侵蚀面积在逐渐增加。[结论]研究区需要进一步加强对轻度、中度土壤侵蚀的治理。     

紫色丘陵区小流域土壤侵蚀产沙空间分布的 137Cs法初步研究

该文通过紫色丘陵区响水滩小流域不同土地利用类型、不同坡度和坡长、不同地貌部位土壤剖面中 ¹³⁷Cs含量的测定与分析，对其侵蚀空间分布进行了估算。研究结果表明：该流域 ¹³⁷Cs含量的背景值为1870 Bq/m²；流域内坡耕地、林地的年平均侵蚀强度分别为4468、1759 t/(km²·a)；土壤侵蚀量与坡长、坡度均指数相关；丘顶、丘坡和鞍部的年平均侵蚀强度分别为2125、4676、3625 t/(km²·a)。结果表明土地利用类型、坡长和坡度、地貌部位对土壤侵蚀量影响很大，坡耕地是该流域泥沙的主要来源。     

赣南地区土壤保持功能的时空变化特征

[目的] 分析赣南地区土壤保持功能时空特征,为提升该区土壤保持能力和维护南方丘陵生态安全屏障提供科学依据。[方法] 利用InVEST模型,计算2000,2010,2018年赣南地区不同土地利用类型、不同高程、不同坡度、不同县域的土壤保持强度,分析土壤保持强度与NDVI空间相关性和赣南地区土壤保持功能时空特征。[结果] ①2000—2018年,研究区耕地、灌林地、水域和未利用土地面积都处于减少趋势,城镇用地和农村居民地面积都有较大的增长。②土壤保持强度由189.93 t/（hm²·a）上升为190.50 t/（hm²·a）,其中有林地土壤保持强度最高,并由259.85 t/（hm²·a）上升为262.03 t/（hm²·a）。③赣南地区土壤保持强度呈现四周高、中部低的分布格局,随海拔升高先升高再降低,随坡度升高而升高。④土壤保持强度与NDVI在双变量局部空间自相关分析中呈现显著正相关（p<0.01）,高高集聚区在赣南地区北部、西部及南部;高低集聚区为中部地区（于都县）;低低集聚区为高经济发展地区（章贡区、赣县区、南康区）。[结论] 赣南地区土壤保持强度与土地利用类型、高程、坡度、NDVI、经济发展水平有着密切关系。为保证土壤保持强度与土壤保持量的稳步提升,应增加低海拔低坡度地区土壤保护措施,并提高中低山区土地利用类型的空间变异性,缓解赣南地区水土流失状况。     

中国东北漫川漫岗典型黑土区沟道侵蚀特征

[目的] 通过对450 km²黑土区进行实测调查，旨在评估研究区沟道侵蚀现状。[方法] 选取沟道侵蚀严重的450 km²的漫川漫岗黑土区为调查区域，首先在谷歌卫星影像上进行侵蚀沟识别和定位，再对侵蚀沟立体形态进行实地测量。[结果] ①研究区土地利用以耕地为主，耕地、建设用地、林地、草地分别占研究区总面积的85%，8%，6%，1%。②研究区坡耕地占86%，坡度0.25°~3.0°占64%，大于5°的占12%。③共有侵蚀沟1 049条，其中耕地中侵蚀沟577条，占总侵蚀沟条数的55%；沟壑密度1.2 km/km²，按沟壑密度衡量沟蚀强度为中度；沟壑面积比例为2.89%，以此界定沟蚀强度为剧烈。④研究区侵蚀沟平均长度、宽度、深度和面积分别为996，13.1，2.7 m和2.4 hm²。[结论] 漫川漫岗黑土区沟道侵蚀严重，主要危害坡耕地，但侵蚀沟相对较小，易于治理。     

晋西黄土区极端降雨后浅层滑坡调查及影响因素分析

极端降雨引发的浅层滑坡,造成了严重的环境破坏与社会经济损失。为探究极端降雨条件下土地利用、植被类型和地形因素对浅层滑坡的影响,通过对山西省吉县蔡家川流域2021年10月3—6日极端降雨引发的浅层滑坡进行实地调查,分析了极端降雨的特征与过程,不同土地利用和植被状况条件下、不同地形条件下浅层滑坡的数量与破损面积。结果表明:(1)极端降雨降雨量为年平均降雨量的31.2%,达到了161.3 mm,降雨历时84 h,峰值降雨强度7 mm/h,平均降雨强度2.1 mm/h,发生该种程度降雨的频率为0.16%,为625年一遇的极端降雨。(2)蔡家川流域内的农地小流域、人工林小流域和次生林小流域共计发生浅层滑坡479处,破损面积达183 881 m²,90%的浅层滑坡面积小于885 m²。(3)单位面积上浅层滑坡的数量与破损面积均表现为农地小流域(214个/km²,109 241 m²/km²)>人工林小流域(163个/km²,48 779 m²/km²)>次生林小流域(42个/km²,17 176 m²/km²),在小流域尺度上森林植被对浅层滑坡的防治作用显著高于农地,且次生林地预防浅层滑坡的作用优于人工林地。(4)浅层滑坡发生的坡面坡度为10°~80°,浅层滑坡数量与破损面积均随着坡度的增大而增大,在40°~50°达到峰值,坡度>50°后,浅层滑坡数量与破损面积随坡度增大而减少,坡度是影响浅层滑坡的主导因素。(5)浅层滑坡发生在坡向为22.5°~337.5°的坡面上,浅层滑坡数量和破损面积随坡向变化并未表现出明显的规律性,坡向对浅层滑坡的影响不大。     

土地利用变化对泥沙连通性及泥沙输移的影响——以重庆市涪陵页岩气开采区为例

[目的] 探究人类活动强烈干扰区景观格局变化对泥沙传输过程的影响,为控制土壤流失为目标的土地利用优化提供科学参考。[方法] 运用土壤侵蚀方程、泥沙连通指数等方法分析了页岩气开采区重庆市涪陵区城东片区页岩气开采前后（2010—2019年）土地利用格局的变化,及其泥沙连通性和泥沙输移的响应。[结果] ①研究区2010—2019年,耕地减少,建设用地及林草用地增加。②因土地利用格局变化导致的土壤侵蚀变化微弱,整个研究区土壤侵蚀量减小,从2010年的3.12减小到2019年2.78 t/（hm²·a）,整个区域的侵蚀策源地是旱耕地。③2010—2019年,整个研究区的连通性指数（IC）呈现减小趋势,从-0.46减小到-0.65,整个区域泥沙输移比减小,泥沙流失量由0.83 t/（hm²·a）减少到0.62 t/（hm²·a）。[结论] 土地利用变化除影响土壤侵蚀量外,还影响了泥沙连通性进而减小了土壤流失量。重庆市页岩气开采未造成区域土壤流失发生明显增大,阻断旱耕地的泥沙连通性仍是控制区域土壤流失的有效途径。     

基于USLE的广东省山区土壤侵蚀量估算及特征分析

基于通用土壤流失方程(universal soil loss equation,USLE)、遥感和ArcGIS空间分析技术,通过合理选择USLE模型中各土壤侵蚀因子的计算方法,对广东省山区土壤侵蚀量进行了估算,并对山区土壤侵蚀随土地利用类型、土壤类型、坡度及海拔高度的分布特征进行了分析。结果表明,广东省山区2000年土壤侵蚀总量为1.23×10⁸ t,年均侵蚀模数为1 080t/(km²·a),侵蚀强度为轻度。不同土地利用类型中,旱地的侵蚀强度最高,达2 055t/(km²·a),林地和草地的侵蚀模数较小,分别为908和932t/(km²·a)。不同坡度等级的土壤侵蚀特征表现为坡度越陡,侵蚀强度越大。不同海拔高度的侵蚀特征表现为在0~1 600m高度,侵蚀强度随海拔高度的升高而增大;海拔高于1 600m时,侵蚀强度随海拔高度的升高而下降。     

东南丘陵地区土壤侵蚀时空变化及其驱动因素——以湖南省张家界市为例

[目的] 探究东南丘陵地区土壤侵蚀状况和其空间分布,为当地的水土流失和水土保持提供理论依据。[方法] 基于修正版通用流失方程(RUSLE)和地理探测器,选取中国东南丘陵地区的湖南省张家界市为研究区域,探究其土壤侵蚀的时空特征变化,并对土壤侵蚀的驱动力因子进行分析。[结果] ①张家界市2000,2010,2020年平均土壤侵蚀量为1.03×10⁷,2.05×10⁷,6.74×10⁶ t/a,20 a平均土壤侵蚀量呈先增加后减少趋势。②土壤侵蚀以林地侵蚀为主,其他地物类型呈不同程度的侵蚀,其中侵蚀主要集中于8°~35°坡度区域,侵蚀强度随坡度增加而增加。③研究区内土壤侵蚀由植被覆盖度、坡度、土壤属性和高程等共同作用,特别是植被覆盖度的驱动作用最明显,各因子产生交互关系时,以坡度和植被覆盖度交互时影响力最强。[结论] 张家界土壤侵蚀分布具有明显的时空差异,后续需要在保障生态安全的前提下,合理开展水土保持工作。     

蔗区小流域泥沙有机碳入河负荷的时空变化特征及其影响因素

[目的] 针对广西红壤区典型小流域坡耕地甘蔗土壤有机碳流失问题,探究其流失时空特征和影响因素,解析流域泥沙有机碳在甘蔗不同生长时期入河负荷时空变化,为揭示自然降雨侵蚀下土壤有机碳流失的影响机制提供科学依据。[方法] 试验区位于广西壮族自治区崇左市扶绥县客兰水库水源区那辣小流域,流域分为下游子流域(S₁)和上游子流域(S₂,S₃)。利用无人机技术和径流泥沙自动监测—采样系统对甘蔗4个生长时期(苗期、分蘖期、伸长期和成熟期)入河泥沙有机碳及植被覆盖度等进行监测,并利用皮尔逊相关分析,确定入河泥沙有机碳与降雨径流、植被覆盖度和施肥等影响因素的关系。[结果] ①甘蔗苗期的流域泥沙有机碳入河负荷占整个生长期总流失量的61.1%,显著高于其他生长期,其特征为苗期(5.1 kg/hm²)＞成熟期(1.6 kg/hm²)＞伸长期(1.4 kg/hm²)＞分蘖期(0.3 kg/hm²)。②流域降雨径流和植被覆盖度与泥沙有机碳入河负荷呈极显著相关,分别解释了泥沙有机碳入河负荷生长期变化的45%和54%;而流域施肥和土壤容重与泥沙有机碳入河负荷呈显著相关,分别解释了泥沙有机碳入河负荷生长期变化的79%和36%。[结论] 流域入河泥沙有机碳流失变化主要是由降雨径流、植被覆盖度、施肥和土壤容重所引起。在蔗区小流域,通过增加植被覆盖以减少地表径流的冲刷及调控施肥时间,对降低土壤有机碳流失具有重要作用。     

基于GIS的黄土高原小流域土壤侵蚀定量评价

以小流域为单元进行土壤侵蚀量的定量评价研究,是探索土壤流失规律和评价流域治理效益的一个重要途径和内容。根据修正通用土壤流失方程（RUSLE）,在ArcGIS软件平台下,以QuickBird遥感影像作为主要数据源,计算了黄土高原南小河沟小流域土壤侵蚀量并定量分析了土壤侵蚀量与坡度和土地利用的关系。结果表明:南小河沟小流域年土壤侵蚀量88 504.2 t/a,平均土壤侵蚀模数为2 438.98 t/（km²·a）,属于轻度接近于中度侵蚀强度,土壤侵蚀得到有效控制。随着坡度的增大土壤侵蚀量明显增加,>25°区域产生全流域80%以上的土壤侵蚀量。不同植被类型的土壤侵蚀模数依次为:天然草地>未成林地>疏林地>灌木林地>人工草地>乔木林地。改善疏林地、未成林地和天然草地的结构,加强难利用地和荒坡地的治理,提高植被覆盖度,是降低土壤侵蚀量的主要途径。     

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.