吕梁山地区植被物候变化及对气候的响应

吕梁山地区地形垂直差异明显,植被对气候变化反应敏感,研究吕梁山地区植被物候变化,探索植被物候变化与气候的响应关系,旨在为高海拔山区植被物候研究和生态治理提供借鉴。基于2000—2015年MODIS NDVI时间序列数据,通过动态阈值法提取吕梁山地区的植被物候,对气温、降水进行空间插值,并对植被2个关键物候期与气候因素进行偏相关分析。结果表明：（1）植被生长季开始日期(the start of the growing season,SOS)提前的区域约占85.7%,其中16.2%显著提前;植被生长季结束日期(the end of the growing season,EOS)推迟的区域约占90.6%,其中33.3%显著推迟。（2）区内74.8%、87.7%植被SOS分别与气温、降水呈负相关,气温升高或降水增加,植被SOS提前。植被SOS在高海拔山区受4月气温影响显著,而低海拔地区受4月降水影响显著。（3）区内72.6%、65.1%植被EOS分别与气温、降水呈正相关,气温升高或降水增加,植被EOS推迟。植被EOS在北部和西部地区受11月气温影响显著,而高海拔地区受9月降水影响显著。2000—2015年吕梁山地区植被物候发生显著变化,各地区对气温、降水的响应不同,研究结果可为区域物候、气候变化研究和陆地生态治理提供科学依据。     

基于BP神经网络的柴油发动机特性建模

建立连续的发动机燃油特性和调速特性数学模型作为液压机械无级变速器虚拟试验平台的动力源。根据虚拟平台对不同特性区域的精度需求对柴油发动机不同特性区域的试验数据进行不同的密度选取、乱序和归一化处理,采用单隐层BP神经网络对试验数据进行训练,对比不同隐层节点数网络的训练误差和测试误差,选取误差最小的网络,求解出网络的数学表达式。通过该方法以ISLe310柴油发动机为例建立燃油特性和调速特性的连续数学模型,这两个简单的数学表达式准确反映了发动机万有特性和外特性,连续模型避免了虚拟试验中出现信号的突变和奇异点。通过和经典的最小二乘法拟合得到的最优特性模型进行对比,其具有更小的误差、更强的泛化能力,能够更好地反映柴油发动机的相关特性。     

新疆部分地区苹果、核桃和杨树腐烂病的病原鉴定

 树木腐烂病在新疆主林果种植区均有不同程度的发生,近年呈加重趋势。本研究在调查了新疆阿克苏、和田、伊犁、喀什和库尔勒等地区苹果树、核桃树和杨树3种林果腐烂病田间发病情况的基础上,重点对14个样本点的样品进行病原物的分离与鉴定。结果表明,各样本点3种林果均有不同程度的腐烂病发生,分离鉴定结果为引起苹果树腐烂病病原菌主要为Valsa mali var. mali(分离频率为64.5%),其次是V. mali var. pyri(25.8%)、V. malicola(3.2%)和V. nivea(6.5%);引起核桃树和杨树腐烂病病原菌为V. sordida(分离频率为83.3%和96%)和V. nivea(分离频率为16.7%和4%)。离体枝条及苹果果实上的致病性测定结果表明,3种林果上分离得到的病原菌均能感染原寄主。引起新疆部分地区苹果树腐烂病的主要病原菌是Valsa mali var. mali,核桃树和杨树腐烂病的主要病原菌是V. sordida。同时,基于实际生产中存在感病枯死杨树枝干作为苹果园、核桃园树体支撑木的现象,推测3种林果腐烂病菌间可能存在交叉感染的潜在风险。     

Assessing the utility of topographic variables in predicting structural complexity of tree stands in a reforested urban landscape

The transformation of natural landscapes into impervious built-up surfaces through urbanization is known to significantly interfere with the ecological integrity of urban landscapes and accelerate climate change and associated impacts. Although urban reforestation is widely recognised as an ideal mitigation practice against these impacts, it often has to compete with other lucrative land uses within an urban area. The often limited urban space provided for reforestation therefore necessitates the optimization of the ecological benefits, which demands spatially explicit information. The recent proliferation of tree stands structural complexity (SSC) and topographic data offer great potential for determining the ecological performance of reforested areas across an urban landscape. This study explores the potential of using topographic datasets to predict SSC in a reforested urban landscape and ranks the value of these topographic variables in determining SSC. Tree structural data from a reforested urban area was collected and fed into a tree stand structural complexity index, which was used to indicate ecological performance. Topographic variables (Topographic Wetness Index, slope, Area Solar Radiation and elevation)- were derived from a Digital Elevation Model (DEM) and used to predict SSC using the Partial Least Squares (PLS) regression technique. Results show that SSC varied significantly between the topographic variables. Results also show that the topographic variables could be used to reliably predict SSC. As expected, the Topographic Wetness Index and slope were the most important topographic determinants of SSC while elevation was the least valuable. These results provide valuable spatially explicit information about the ecological performance of the reforested areas within an urban landscape. Specifically, the study demonstrates the value of topographic data as aids to urban reforestation planning.     

基于连续投影算法和光谱变换的冬小麦生物量高光谱遥感估算

为探索基于全波段冠层高光谱以及变换光谱的冬小麦地上部生物量的遥感估算方法，以2016、2017年冬小麦田间试验为基础，通过对冠层光谱和地上部生物量的相关性分析，筛选拔节期、抽穗期的冬小麦冠层光谱、一阶导数光谱、对数变换光谱和连续统去除光谱对地上部生物量的敏感波段，并结合偏最小二乘法(PLS)分别建立拔节期和抽穗期基于SPA算法的冬小麦地上部生物量估测模型，再与基于任意两波段组合的最佳归一化光谱指数、比值光谱指数、差值光谱指数和已报道光谱指数的冬小麦地上部生物量估测模型进行比较。结果表明：(1)SPA算法较好地利用了全波段冠层光谱信息，并显著降低了光谱维度，不同变换光谱的地上部生物量敏感波段个数在4~14之间；(2)拔节期和抽穗期冠层光谱与地上部生物量的相关性高于开花期和灌浆期，各生育时期一阶导数光谱与地上部生物量之间的相关性优于连续统去除光谱、对数变换光谱和光谱指数；(3) 利用抽穗期一阶导数光谱敏感波段建立的预测模型和验证模型达到了较高的精度，其预测模型的决定系数和均方根误差分别为0.78和0.87 t·hm^-2，验证模型的决定系数和均方根误差分别为 0.84和0.69 t·hm^-2，预测相对偏差为2.74。这说明，抽穗期是估算地上部生物量的最佳生育时期，且基于冠层一阶导数变换光谱，结合连续投影算法和偏最小二乘回归方法所构建抽穗期地上部生物量估算模型具有最优的精度和预测能力，可用于地上部生物量的定量估算。     

油棕叶梗重组方材制备工艺

以油棕叶梗为原材料、酚醛树脂为胶黏剂，采用正交试验方法研究重组方材密度、施胶量、热压时间和热压温度对油棕叶梗重组方材力学性能的影响。结果表明，密度对油棕叶梗重组方材性能的影响较大，密度和施胶量越大，重组方材力学性能越好；热压温度和热压时间对油棕叶梗重组方材性能的影响比较复杂。综合考虑确定油棕叶梗重组方材的较优制备工艺条件为:密度0.7 g/cm³，施胶量12%，热压温度180℃，热压时间40 min；较优工艺条件下油棕叶梗重组方材的弹性模量为7 185 MPa，静曲强度为68.7 MPa，顺纹抗压强度为35 MPa，内结合强度为0.21 MPa。密度为0.7 g/cm³的油棕叶梗重组方材的弹性模量、静曲强度、顺纹抗压强度高于了杉木的性能。     

假眼小绿叶蝉与其天敌的空间关系及最佳样方确定

为了分析在聚块大小不同时天敌对假眼小绿叶蝉Empoasca vitis Gothe空间上跟随关系的密切程度、聚集原因和聚集范围,为评价假眼小绿叶蝉的天敌优势种提供科学依据,用聚块样方方差分析法、灰色关联度法、空间聚集强度指数、种群聚集均数法和ρ指数法对安徽省合肥市‘乌牛早’和‘白毫早’茶园不同大小聚块条件下的假眼小绿叶蝉及其7种蜘蛛类的天敌空间关系进行分析。假眼小绿叶蝉与其7种蜘蛛类天敌均方差峰值时的聚块样方数的关联度分析结果表明:‘乌牛早’茶园中与假眼小绿叶蝉空间上跟随关系密切的前四种天敌依次是茶色新圆蛛Neoscona theisi(0.753 5)、八斑球腹蛛Theridion octomaculatum(0.720 1)、锥腹肖蛸Tetragnatha maxillosa(0.681 3)和草间小黑蛛Erigonidium graminicolum(0.644 2)。‘白毫早’茶园中与假眼小绿叶蝉空间上跟随关系密切的前四种天敌依次是粽管巢蛛Clubiona japonicola(0.823 5)、鳞纹肖蛸Tetragnatha squamata(0.800 9)、锥腹肖蛸(0.794 2)和茶色新圆蛛(0.794 2)。两种茶园前四种天敌中相同的天敌是茶色新圆蛛和锥腹肖蛸。假眼小绿叶蝉在聚块内基本样方数k为1、2、4、8时,随着聚块内基本样方数的增多,聚集分布格局时的扩散系数C不断增大,均匀和随机格局时扩散系数不断减小。聚块内基本样方数k为2、4、8时与k为1时的假眼小绿叶蝉的空间分布聚集程度差异均不显著。假眼小绿叶蝉的种群聚集均数λ多数情况均大于2,其聚集是该虫本身原因引起的,假眼小绿叶蝉在种群聚集均数λ为正值时,随着聚块内基本样方数的增加,则种群聚集均数λ不断增大。用假眼小绿叶蝉不同大小聚块的ρ指数判断个体群聚集时的最小范围是聚块中有1个基本样方,即本文的4 m~2。该研究为该虫抽样时确定样方大小提供了科学依据。     

2003-2017年陕西省NDVI时空变化及其影响因素

[目的] 研究影响陕西省植被覆盖主导气候类和非气候类因子，为区域生态文明建设提供科学依据。[方法] 基于2003—2017年MODIS NDVI数据，利用趋势分析和地理探测器模型等方法，研究了气候类和非气候因素对陕西省植被覆盖的影响。[结果] ①2003—2017年陕西省NDVI空间分布总体上为改善趋势，但在不同植被类型区和生态区有所差异。②降水是影响陕西省植被覆盖空间分布的主导气候类因素，其他因素对当地植被覆盖影响程度有所差异。③降水与气温、日照、风速、相对湿度的交互作用对陕西省植被覆盖空间分布起主导作用。且气温的作用只有在和降水的交互作用下才能体现出来。④植被类型和地貌是陕西省植被覆盖空间分布的主导非气候类因素，其他因素的影响有所差异。⑤植被类型、地貌和土壤类型之间的交互作用对陕西省植被覆盖空间分布起主导作用。人口、GDP的影响也只有在与其他因素的交互作用下才能显现出来。[结论] 气候类因素的影响大于非气候类因素，气候类和非气候类因素的共同作用能够充分的解释植被覆盖空间分布。     

Technical efficiency of different farm sizes for tilapia farming in China

China is the world's largest tilapia producer. This study uses the stochastic frontier function in the Cobb–Douglas model to evaluate a production frontier for tilapia aquaculture and analyses the relationship between farm size and production efficiency in China. A random sample of 300 tilapia farmers was surveyed in the main tilapia‐producing areas to study their economic efficiencies. The percentage distribution of tilapia farm technical efficiency was determined, with an average efficiency of 79%, which showed that the sample tilapia farmers operate at 21% below the production frontier and hence that they still have a chance to achieve targeted yields. The technical efficiencies of two categories (≤1 ha and >1 ha) were 78.82% and 79.27% respectively. A second‐stage analysis investigated the relationship between farm size and technical efficiency and showed a positive relationship between farm size and production efficiency based on the ordinary least‐squares model. The optimal farm size was found to be 7.50 ha. This study proposes strategies such as enlarging the farming scale moderately, thereby achieving the advantage of economies of scale, and enhancing the competitiveness of the tilapia industry in China.     

Feasibility analysis of NIR for detecting sweet corn seeds vigor

This paper explores the feasibility of particle-based detection and grading of seed vigor based on a self-built seed single-granulation device using near infrared spectroscopy (NIRS). Sweet corn with uniform kernel size was used for this study. The seed samples were divided into three types, they were normal seeds, artificially aged seeds and heat-damaged seeds. A 2-part spectral acquisition of each seed were performed, one for the collection of seeds that fall into the detection zone within the separation pipe, another was on the static platform, whose collection was performed on 5 faces of each seed. Partial least squares discriminant analysis (PLS-DA) was used to classify the original data of the seeds. In the 2 parts, the discriminant results of the unprocessed normal seeds and the artificial accelerated aging seeds, the untreated normal seeds and the heat-damaged seeds showed that classification accuracy was higher than 98%. The research indicates that the spectral data of different positions of seeds can reflect their activity information, and it is feasible to detect and classify seeds in real time in the detection area of the separation pipeline.