我国西南岩溶地区自然植被群落与小生境耦合关系研究

生境是植物生长的具体环境,而群落环境是有机体和生境共同作用的结果。关于岩溶地区植物对不同生境的利用已成为近年来研究的热点。文中系统地总结了岩溶地区小生境类型特征、不同石漠化等级、坡位等因素对自然植被群落分布特征的影响,结合前人研究成果进一步分析了岩溶地区不同生境条件、坡位以及石漠化等级下自然植被群落结构、优势种、物种多样性、生物量以及生活型谱结构的差异,以期为岩溶地区植被与生境耦合程度以及不同生境下植被资源的配置提供理论参考,对岩溶生态环境保护、石漠化防治和石漠化地区植被恢复具有重要意义。     

基于ITS和trnL-F序列鉴定边陲黄耆为独立的物种

乌拉特黄耆(Astragalus hoantchy Franch.)、边陲黄耆(A.dshimensis Gontsh.)和A.coluteocarpus Bioss.为形态上相似的3个近缘物种。为了明确它们之间的分子亲缘关系,探讨分子证据是否支持边陲黄耆为一个独立的物种,测定了这3个物种共33个样本的ITS和trn L-F序列。基于ITS+trn L-F联合序列,运用Mega 6.06软件计算了种内和种间的遗传距离,并利用Mega 6.06和Mr Bayes 3.2软件分别构建了最大似然(ML)树和贝叶斯(BI)树。结果显示:乌拉特黄耆、边陲黄耆和A.coluteocarpus Bioss.的种内平均遗传距离分别为0.000、0.001和0.003;乌拉特黄耆和边陲黄耆之间平均遗传距离为0.010,而这2个物种与A.coluteocarpus Bioss.之间的平均遗传距离分别为0.015和0.016;乌拉特黄耆和边陲黄耆种间的平均遗传距离远大于其物种内的遗传距离;ML树和BI树具有相似的拓扑结构,均分成了3个分支,其中每个物种的所有个体都聚集在一个单独的分支上且不存在种间交叉现象。本研究揭示了这3个近缘物种的分子亲缘关系,分子证据说明边陲黄耆应该是一个独立的种。     

EFFECTS OF IMAGE PLANE,PATIENT POSITIONING,AND FORAMINAL ZONE ON MAGNETIC RESONANCE IMAGING MEASUREMENTS OF CANINE LUMBOSACRAL INTERVERTEBRAL FORAMINA

Degenerative lumbosacral stenosis has been suspected to have a dynamic component, especially regarding encroachment of the L7 nerve roots exiting the lumbosacral foramina. Angled cross‐sectional imaging of the neuroforamina has been found improve the accuracy of the diagnosis of stenosis in humans. In this anatomic study, foraminal apertures were evaluated by MRI at the entry, middle, and exit zones of the nerve roots in 30 dogs that were clinically affected by lumbosacral disease. Standard vs. oblique planar orientation and neutral vs. hyperextended positioning of the lumbosacral area were compared by measuring the median values for entry, middle, and exit zones. The neuroforaminal area acquired using oblique plane acquisition was significantly smaller than standard parasagittal measurements. Furthermore, standard parasagittal neuroforaminal dimensions in the hyperextended position were significantly smaller than standard parasagittal measurements in the neutral position. This statistical difference was even more pronounced for neuroforaminal dimension evaluated in the oblique plane and hyperextended position. Positioning of the dog during imaging has a significant effect on neuroforaminal dimension, corroborating the notion that spinal position may influence neural claudication in clinically affected patients. Reductions in neuroforaminal dimension are more evident on oblique planar image acquisition, suggesting that this approach may be more useful than parasagittal imaging as a tool for identifying subtle changes in L7 neuroforaminal dimensions in cases of canine lumbosacral stenosis.     

中低海拔烟区黑膜开孔位置及大小对膜下烤烟生长的影响

为解决膜下烤烟人工开孔破膜费工耗时和破膜不及时导致烟苗素质差、高温高湿蒸死烟苗、烟苗成活率低的问题,在云南省楚雄州中低海拔烟区研究了黑膜不同开孔位置及大小对膜下烤烟生长的影响。结果表明:中海拔烟区膜下烤烟移栽后,在烟苗正上方开孔2cm(孔直径),移栽至掏苗期间14:00时膜内温度较对照(不开孔)降低5~10℃;与对照比较,烟苗成活率提高3%,烟株早生快发,病害较轻,大田生育期提早5d,产量和产值比对照分别提高292.5kg/hm~2、9 271.2元/hm~2,经济效益明显。     

采用不同红边位置提取技术估测蔬菜叶绿素含量的比较研究

红边位置常被用来估测植被的叶绿素/氮素含量、叶面积以及探测植被胁迫,其精确计算十分重要.目前其计算主要是基于导数光谱或曲线拟合技术,但哪种方法能更有效地探测植被的叶绿素/氮素含量,还没有一个定论.本研究以菠菜的叶片高光谱为例,详细比较了目前常用的6种红边位置提取方法与叶片叶绿素之间的关系,并从其对叶绿素含量预测的准确度、计算的难易程度、所需数据的精度及适用范围等几个方面进行了讨论.结果表明,叶片红边位置的计算结果对选择方法的依赖性很大,几种计算方法提取的红边位置与叶绿素含量的相关性均较好.四点线性内插法计算的红边位置往往偏大,最大一阶导数法与叶绿素含量的关系存在着明显的不连续性,拉格朗日内插法、倒高斯模犁法在一定程度上存在着对高叶绿素含量的饱和现象,多项式拟合法对拟合波段区间、最高项次及光谱分辨率等比较灵敏而导致结果不够稳定,而线性外推法计算出的红边位置对叶绿素含量最为敏感,预测的准确度最高,且计算相对比较简单,并能适用于较宽波段的遥感数据.在实际应用时还应根据具体情况而选择合适的红边位置提取方法.     

Soil distribution in valleys according to stream order

While much research has been done on predicting the occurrence of waterlogged soils in small catchments, we need to improve our knowledge of the extension of these soils in large catchments. The aim of this study is to analyse the extent of soils with redoximorphic features in the valley bottomland domain as a function of the stream order.This study concerns a 10,000 km² catchment (River Vilaine, Armorican massif, north-western France) where valley bottomland soils commonly associated with hydromorphic characteristics cover up to 20% of the basin area. To describe the catchment organisation, we used the stream order classification of Strahler to test the behaviour of the topographic index in a large range of landscape morphological settings. Two methods were used to define the extent of the hydromorphic zone (HZ) in each valley bottomland according to stream order: (i) A field study based on mapping the HZ according to the occurrence of redoximorphic features along 60 transects; (ii) a modelling approach linking a DEM-derived topographic index to the digitized stream network of the River Vilaine.In view of the topographic factors, progressive valley widening may represent an enhancing factor of HZ extent. Thus, simple topographic index modelling predicts an increase in waterlogging in high-order channel settings (orders 6–7). By contrast, field mapping suggests that HZ extent remains stable with increasing order and decreases significantly for high-order settings (orders 6–7). Therefore, topographic index modelling appears effective in upper catchment settings (1st, 2nd and 3rd order). On the contrary, modelling efficiency is limited in high-order settings where the indices prove to be inappropriate: in such contexts, interactions between adjacent hillslope and HZ are of secondary importance. Along the longitudinal profile of the catchment, soil material near the streams shifts from having a colluvial origin in low-order to an alluvial origin in high-order settings. In high-order settings, the fine-scale valley bottomland topography and the spatial organisation of deposits control waterlogging duration and possibly play a major role in HZ extent. Finally, the integration of stream order data should considerably improve the efficiency of modelling the spatial distribution of soils over large catchments.     

试论行商园林海山仙馆的历史地位

从商帮发展的角度介绍行商园林的历史背景,引出由广州十三行行商潘仕成购置兴创并精心经营的著名行商园林——海山仙馆。其为岭南古典园林的高峰之作,既有古意,又有新创,具有水际安塔、碑林胜景、长廊高架、舟车游览的景观特点。海山仙馆在中外交往活动中具有重要地位,是外交、外贸活动的举办场地和在粤洋人被允许外出消遣的场所,且园主人还在此汇编、出版和收藏中西著作经典。故彰显海山仙馆精神灵魂、探索其艺术精华、复兴其文化景观具有非常重要的意义。     

基于红边位置的马铃薯植株氮浓度估测方法研究

【目的】高光谱遥感技术可以用于植被生长状况的监测和研究光谱与植被理化性质间的关系。红边位置是与作物氮素营养关系较为密切的光谱参数,常用于作物叶绿素或氮素的含量监测,监测参数以及数据的计算都影响着该方法的准确性和实用性。为此,本研究优化了红边位置方法的参数,比较了六种方法对所得马铃薯氮浓度预测数据的翻译的准确性和精确度。【方法】于2014—2016年在内蒙古阴山北麓,进行了三个马铃薯品种、不同施氮量的田间试验。在马铃薯苗期、块茎形成期、块茎膨大期、淀粉积累期和收获期,使用红边位置获取了马铃薯冠层反射光谱,采用六种方法计算了该数据翻译的马铃薯地上部氮浓度,并分别与实测值进行了相关性分析。【结果】马铃薯生育后期一阶导数光谱中双峰现象较为明显。不同生育时期中苗期由于受到噪声光谱的影响氮浓度,与红边位置相关性较差,块茎形成期至淀粉积累期的氮浓度与红边位置相关性较高,其中块茎膨大期相关性最高。最大一阶导数法和拉格朗日内插法所得红边位置无连续性;线性外推法所得红边位置变幅与标准差最高,最大分别可达到44.6和9.3;多项式拟合法次之,变幅和标准差分别为15.1和2.6;倒高斯拟合法和线性四点内插法的变幅和标准差较小。在六种方法所得红边位置与马铃薯地上部氮浓度的预测模型中,线性外推法决定系数最高(R^2=0.55),预测值与观测值相关性最好(R^2=0.44,RMSE=3.96 g/kg,RE=11.46%);倒高斯拟合法与多项式拟合法模型决定系数相近,R^2均在0.40左右,倒高斯拟合法对氮浓度的预测能力更高一些(R^2=0.31,RMSE=4.33 g/kg, RE=12.03%)。【结论】红边位置能够对块茎形成期至淀粉积累期的植株氮浓度进行诊断,花期红边位置有轻微的饱和现象,但并不影响整体的预测,在花期和块茎膨大期采集光谱时需要注意传感器与植物冠层的距离,保证采集数据的准确性。线性外推法是最适合马铃薯冠层光谱的红边位置计算方法,所得红边位置变幅大,对马铃薯地上部氮浓度的变化较为敏感,回归模型决定系数和预测精度也最高,而且对于高氮浓度处的饱和现象有较好的缓解作用。     

液压驱动并联加载机构正弦位置/力幅相控制

液压驱动并联加载机构对试件进行多自由度位置/力加载时,受到液压系统非线性因素和试件耦合作用的影响,其位置和力加载自由度的频宽难以提高,导致正弦位置/力响应信号的幅值衰减和相位滞后。为提高系统对正弦位置/力信号的跟踪精度,提出一种改进幅相控制方法。对正弦信号幅值、相位、均值3个特征参数进行评估,将评估后的3个特征参数作为控制变量分别进行控制,给出相应的幅相控制器设计和参数整定方法。实验结果表明,该方法能有效提高正弦位置/力信号的跟踪精度,具有控制结构简单、调节参数少、参数整定方便的特点。     

黄土高原北部生长季土壤氮素矿化对植被和地形的响应

氮素矿化是陆地生态系统氮循环的重要过程,对氮素有效性有着重要影响。本文在黄土高原北部六道沟小流域选取退耕年限相近的油松和柠条坡地,用原位培养法测定生长季节(4—10月)不同坡位冠层下和冠层外0~10 cm和10~20 cm土层土壤氮素矿化速率,以确定该区氮素矿化的季节动态特征和主要影响因素。结果表明,研究区生长季土壤矿质氮以铵态氮为主,其含量在0~10 cm和10~20 cm土层分别占矿质氮总量的61%和70%,并随生长季的推移而升高。油松林上坡位和中坡位土壤铵态氮显著高于下坡位土壤,柠条林不同坡位铵态氮差异不显著。土壤硝态氮和矿质氮不受坡位的影响,但与林型和采样位置有关,冠层下硝态氮在油松林与冠层外相近,在柠条林则高于冠层外。生长季土壤氮素矿化在0~10 cm土层由硝化作用引起,在10~20 cm土层则由硝化和铵化作用共同引起。铵化速率在生长季初期较高,中期较低,并受坡位、林型和采样位置的影响。土壤硝化和矿化速率在油松林不受采样位置影响,但是在柠条林则以冠层下较高。硝化和矿化速率在冠层下以下坡位土壤最高,在冠层外则以下坡位土壤最低。柠条林促进了冠层下土壤氮素的硝化和矿化过程,有利于矿质氮的积累;油松林对矿质氮和氮素矿化的影响不受采样位置影响。