广州市土地利用多情景模拟及其生态风险时空响应

[目的]探讨景观生态风险对土地利用格局变化的响应规律,为促进土地资源可持续利用和维护区域生态安全提供科学支持。[方法]基于2001—2017年广州市土地利用演变情况,利用未来土地利用模拟(FLUS)模型模拟2025年自然发展情景与"三线"(生态保护红线、永久基本农田保护红线、城镇开发边界线)约束情景下的土地利用空间分布;构建景观生态风险评价模型,进而分析广州市景观生态风险状况及其对土地利用变化的时空响应。[结果] 2001—2017年,建设用地的面积大幅增加,其他用地类型面积均不断减少;建设用地、草地和未利用地的变化幅度较大。相较于2017年,广州市2025年自然发展情景下建设用地持续扩张;而"三线"约束情景下建设用地的扩张得到制约,林地、水域等用地面积减少幅度有所缓和,耕地反而略微增加。2001—2017年,广州市景观生态风险指数不断上升,风险等级空间分布呈现圈层状结构,由中心城区向外围递减,低、较低生态风险区规模总体缩小,而较高、高生态风险区规模逐渐增大。[结论]与2017年相比,2025年两种情景下的景观生态风险指数均有所提高,而"三线"约束情景下生态风险指数增幅较小,更符合广州市未来城市建设和生态保护的需要。     

基于景观结构的黄河沿岸土地利用生态风险时空变化分析——以河南省为例

[目的] 探究黄河流域沿岸城市土地利用生态风险时空变化特征,为土地景观资源保护、生态系统优化与生态环境保护、管控措施制定等提供理论依据。[方法] 以河南省黄河沿岸7个城市为研究区,在GIS与Fragstats软件技术支持下,基于2005,2010,2015以及2018年4期土地利用数据,将研究区划分为1 737个6 km×6 km的生态评价单元,根据景观扰动指数与景观脆弱指数构建生态风险评价模型,借助土地转移矩阵与空间自相关分析方法,对研究区内土地利用变化、生态风险时空变化特征及空间关联格局进行评价。[结果] ①2005—2018年,研究区域内建设用地面积增加,且增长趋势较快;其他几类用地面积均有不同程度的减少;耕地是建设用地增加的主要来源,林地、草地和水域主要转化为耕地。②在研究时段内,研究区域土地利用生态风险在空间上呈现出显著的正相关性,存在空间集聚特征,且“高—高”、“低—低”是生态风险主要的空间聚集模式。③2005—2018年,生态风险最小值和最大值大致呈N形变化;4个时期内高风险区分布区域大致相同,呈条状和块状分布,条状高风险区大多分布在黄河沿岸,块状高风险区大多分布在农村居民点零散分布的平原区;低和较低风险区大多分布在研究区域四周以及西南大部分区域。[结论] 研究时段内,低风险区和中等风险区面积在逐年增加,较低风险区面积先减少后增加,高风险区和较高风险区面积在逐年减少。各风险区主要向相邻风险区转化,仅有少量地区出现跨区转移,说明研究区土地利用生态风险变化相对稳定,生态风险急剧变化的区域较小。     

生态脆弱区景观生态风险时空分异及其地形梯度分析——以陕西省米脂县为例

目前,生态脆弱区已成为景观生态风险评价研究的热点区域之一。以黄土丘陵沟壑区陕西省米脂县为研究区,以2009年、2015年土地利用数据为基础数据,将研究区划分为耕地、林地、草地、果园、水域、城镇工矿用地和荒地7类土地利用类型,基于干扰度与脆弱度构建生态风险模型,并结合地形分布指数进一步分析了生态风险随高程和坡度梯度的动态变化规律,得出如下结论:(1)米脂县土地利用格局变化明显,耕地面积减少3 168.45 hm~2,林地与荒地面积分别增加1 102.95,1 609.47 hm~2;(2)米脂县2009年、2015年景观生态风险指数分别为0.221 7,0.228 9,且呈现西高东低,中间高南北低的空间分布格局。Ⅰ级风险主要转化为Ⅱ级风险,面积比例由28.17%降为13.59%;Ⅲ风险达到研究区面积的1/3,主要由Ⅱ风险区转化而来;Ⅳ与Ⅴ风险区面积变化不大,面积比例整体上升3.9%;(3)生态风险等级时空分布随高程和坡度梯度变化显著。Ⅰ级风险向低海拔、低坡度转移的趋势明显;Ⅱ与Ⅲ级风险均向高海拔转移;Ⅳ与V级风险在地形梯度上无明显的风险转移。     

基于生态服务价值的沱江流域土地景观生态风险时空分异研究

[目的]探究沱江流域基于生态服务价值的生态风险时空分异的特征,为基于生态服务价值的沱江流域生态风险管控决策提供一定依据。[方法]借助ArcGIS,GeoDa,GS~+和Conefor Sensinode等软件,以沱江流域为研究区,基于2000,2005,2010和2015年4期遥感土地利用数据,计算研究区生态服务价值,对生态风险计算方法进行改进,构建基于生态服务价值的生态风险评价指标体系,运用空间自相关分析和地统计分析方法,探讨位于快速城市化地区的沱江流域生态风险的时空分异规律。[结果]①沱江流域土地利用动态变化显著,用地类型以耕地转建设用地和林地转耕地为主。②沱江流域生态服务价值总量先增后降,耕地、林地对生态服务价值的贡献最大。③生态风险值总体呈上涨趋势,生态风险等级由以较低、中等生态风险为主向以中等生态风险为主转移,中等生态风险区域面积大幅增加。④研究区生态风险等级分布差异明显,高风险区和较高风险区主要分布在研究区北部,中等和较低风险区分布在研究区中部和南部,生态风险总体北大于南。[结论]土地利用变化会对生态服务价值产生重要影响,进而对沱江流域的生态风险产生影响。     

辽宁省抚顺市2000-2020年土地利用格局变化与生态环境效应

[目的] 探讨辽宁省抚顺市退耕还林以来土地利用格局时空变化特征及生态环境效应,揭示土地利用格局变化对环境的影响,为该区土地利用结构优化提供科学依据。[方法] 以2000,2010和2020年3期遥感影像为基础数据,通过土地利用动态度、土地利用程度综合指数、土地利用转移矩阵、NDVI差值分析、区域生态环境质量指数等方法定量分析抚顺市土地利用格局时空变化特征及生态环境效应。[结果] ①2000—2020年研究区各种土地类型存在相互转化的关系,其中林地和耕地变化较为明显。20 a间,耕地面积减少825.59 km²,增长率-7.32%;林地面积增加591.14 km²,增长率5.24%;城镇用地面积增加182.36 km²,增长率1.62%; ②2000,2010和2020年研究区土地利用程度综合指数分别为224.48,225.57和226.12,同比增长0.49%和0.24%,研究区土地开发利用强度缓慢上升; ③研究区20 a间植被覆盖整体呈上升趋势,NDVI减少的区域与城镇用地的扩张区域基本重合; ④3个时期土地利用类型转化的生态环境质量指数分别为0.744 8,0.775 4和0.782 6,10 a间环境质量生态指数分别上升4.11%和0.93%,环境质量整体呈上升趋势。[结论] 20 a间研究区快速推进城镇化进程的同时环境质量整体向好,局部范围内生态环境质量改善与恶化并存。城镇用地、耕地、林地之间的转化为主要原因,退耕还林等环境保护政策使研究区环境质量不断上升,但随着时间的推移,上升趋势趋于平缓。     

福建省碳储量时空特征及其对土地利用变化的响应

[目的] 研究福建省生态系统碳储量及其对土地利用变化的响应,为生态系统保护提供参考。[方法] 基于土地利用数据和碳密度数据,运用InVEST模型模拟福建省1980,2000,2020年碳储量;利用冷热点分布、转移图谱和矩阵分析碳储量和土地利用的时空特征;最后分析碳储量对土地利用变化的响应。[结果] ①福建省碳储量整体均较高,82.5%以上区域的碳储量为中等以上(＞3 000 t),主要分布在山地丘陵地区,也是高碳储量的热点集中区;高(热点)低(冷点)碳储量集中区转移较少;1980—2020年总碳储量波动略升高,2000—2020年不同碳储量等级彼此之间转移相对较多。②福建省土地利用/覆被以林地为主(61.4%~62.9%),其次是耕地(16.9%~18.3%)和草地(15.2%~17.2%);土地利用/覆被变化在1980—2000年较稳定,在2000—2020年较剧烈。③林地、草地和耕地的总碳储量较高,水域、建设用地和未利用地总碳储量较少;耕地总碳储量减少,建设用地总碳储量增加,林地和草地有增加也有减少;由土地利用/覆被变化导致的总碳储量转出和转入最多均为林地,其次是草地和耕地;总碳储量净转移为负的是林地,其他为正,林地转移引起的碳亏损最多。[结论] 耕地、林地和草地是福建省的主要土地利用类型,它们贡献了较高碳储量,并相互转移引起了碳储量变化。     

2000—2020年湖北省土地利用变化对植被覆盖度的影响

[目的] 土地利用及其对陆地生态系统的影响是当前全球变化研究的重要内容。科学分析土地利用变化对植被覆盖度的影响,促进社会经济与生态环境质量的协调发展及地区经济的平衡发展,为政府部门对区域生态保护和恢复管理提供借鉴和参考。[方法] 以湖北省为研究对象,利用2000,2020年2期Landsat遥感影像、土地利用遥感数据,利用遥感数据的空间处理、像元二分模型、土地利用转移矩阵等方法,分析研究湖北省植被覆盖的时空变化、土地利用类型变化特征及其对植被覆盖度的影响。[结果] ①2000-2020年,湖北省耕地、草地和未利用地面积减少,水域以及建设用地面积增加,林地面积基本保持不变,其面积大小顺序为:林地>耕地>水域>建设用地>草地>未利用地。②湖北省植被覆盖度平均值上升了6.50 %。林地、耕地、草地和未利用地的平均植被覆盖度均有所增加,建设用地的平均植被覆盖度有所降低。③湖北省植被覆盖度总体呈现增加的趋势。植被覆盖度增大的区域主要集中在湖北省的西部和东南部地区,局部地区也存在植被退化的区域,主要集中在湖北省中南部及襄阳北方部分区域。④不同土地利用类型FVC转移过程中,耕地较高植被覆盖与高植被覆盖之间的转移过程最为剧烈,林地不同等级植被覆盖的转移量占转移总量的47.87 %,草地不同水平植被覆盖度的转移量占转移总量比例较小,仅为3.40 %。[结论] 2000-2020年湖北省土地利用变化较大,不同土地利用类型的植被覆盖度相互转移,尤其是林地、耕地及草地的平均植被覆盖度均有所增加,使得湖北省近20 a来整体植被覆盖度呈现出上升趋势。     

浙江省海岸带景观生态风险格局演变研究

海岸带景观生态风险格局演变分析,对建立生态风险预警机制、降低生态风险概率,促进海岸带地区景观格局优化具有重要意义。以1990年、2000年、2010年3个时期的TM遥感影像为景观格局分析主要数据源,构建景观生态风险格局演变模型,分析浙江省海岸带景观生态风险格局时空变化特征。结果表明:(1)1990—2010年,研究区内景观结构发生了较大的变化,耕地、海域、林地以及水域面积均呈现出下降趋势,建设用地、未利用地以及养殖用地呈现出不断增加的趋势;(2)1990年,浙江省海岸带景观以低和较低等级生态风险区为主,分别占全区总面积的50.30%和35.94%,2000年低、较低等级生态风险区面积均有不同程度减少,而中等生态风险区面积则有显著增加。至2010年,低生态风险区面积进一步减少,而高与较高生态风险区面积增加明显;(3)从风险格局演变来看,1990—2010年海岸带景观低和较低等级生态风险区的分布范围不断向陆侧后退,面积呈现下降趋势,中等、较高和高生态风险区在沿海地区不断扩展,侵占生态风险等级相对较低区域,以沿海平原的淤泥质海岸尤为典型;(4)2000—2010年生态风险等级上升的速率明显低于前10a,表明人类在加速海岸带景观开发利用的同时,已开始关注生态环境的保护,正在逐步追求经济与生态环境的协调发展。     

陕西省2000-2018年土地利用时空演变及驱动因素

[目的] 分析陕西省土地利用变化及驱动因素,为促进该省土地资源综合优化配置和社会经济可持续发展提供科学依据。[方法] 基于2000,2010和2018年陕西省的土地利用遥感监测数据,通过土地利用动态度、土地利用转移矩阵、空间自相关等方法定量分析陕西省土地利用的时空演变特征,并利用主成分分析法对其土地利用变化的驱动力进行分析。[结果] 各土地利用类型面积均有不同程度的变化。其中,耕地面积下降最多,工矿建设用地面积增速最快,水域面积变化最小。土地利用类型受自然条件的影响,空间差异性显著。农村居民用地、未利用地、耕地、林地、草地的空间聚集性强,水域、城镇居民用地和工矿生产用地的空间集聚性性相对较弱,草地、工矿建设用地形成新的集聚区。陕北高原和关中平原土地利用转移相对频繁,陕南山区土地利用转换相对较小。榆林市和延安市主要表现为耕地向林地和草地转移以及未利用地和草地向工矿建设用地转移,西安市主要表现为耕地和农村居民用地向城镇居民用地转移。土地利用变化的主要因素是城市化发展过程中社会经济的发展以及产业结构的调整。[结论] 陕西省土地利用变化区域差异较大,应因地制宜制定土地利用规划,促进人口—经济—生态之间的协调发展。     

秦巴山区土地利用时空格局及地形梯度效应

自然景观的垂直地带性为区域土地利用的垂直景观格局奠定了基础,同时也决定了垂直景观带上土地利用的强度及其变化情况。该文采用地形位指数、分布指数、土地利用程度综合指数和土地利用信息图谱法等,分析了1989-2010年秦巴山区土地利用格局的地形梯度效应和图谱信息,揭示地形控制下土地利用时空格局和土地转移的变化规律。结果表明:1)秦巴山区土地利用以林地和耕地为主,呈西林东耕分布;1989-2010年间林地减少显著,建设用地增加明显,其中耕地是建设用地主要转入来源,林、草地是耕地主要转入来源。2)秦巴山区各生态亚区用地类型差异明显,各生态亚区土地利用转移方向也存在差异性。3)秦巴山区土地利用强度指数呈东高西低,中高周低的态势;土地利用强度变化率稳定少动,增加趋势不明显;土地利用动态度呈中高周低的态势,整体变化不大。4)水域、建设用地和耕地主要集中在地形起伏度小和坡度小的低地形位,且耕地主要转移为其他两种用地类型,建设用地有向中低地形位分布的趋势。林地和草地集中在地形起伏大、坡度陡的中高地形位,且存在着相互转移演替现象,中低地形位往往是耕地、林地、草地间的相互转换,未来势必加强坡耕地和低山丘陵区林草地的管治工作。     

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.