一种基于图像分析提取作物冠层生物学参数的方法与验证

利用图像分析方法,通过准确识别冠层和背景像素进行棉花冠层生物学产量和叶面积系数估测。采用Olympus C740 Ultra Zoom数码相机拍摄棉花不同生育期冠层图像,在棉花冠层数码照片特征分析的基础上提出了棉花冠层图片计算机自动判读的方法,即混合采用图像色度(H)、绿光(G)、红光(R)灰度值构造提取条件,通过多重判断识别棉花冠层和背景,并编写了相应的计算机程序。利用该程序分析棉花不同施氮量下、不同生育期提取地面覆盖度参数与棉花生物学产量、叶面积系数间的关系,发现棉花冠层地面覆盖度指标可以有效预测棉花生物学产量和叶面积系数,二者间指数相关系数达到r=0.97以上,为极显著相关。     

基于小波变换的带状套作玉米叶面积指数光谱估测

【目的】为构建带状套作种植下玉米全生育期叶面积指数光谱估测模型。【方法】基于玉米-大豆带状套作种植模式下的大田玉米氮素试验,测定带状套作玉米不同生育时期的冠层光谱反射率及叶面积指数,比较多种植被指数及小波系数与叶面积指数之间的关系,构建并筛选出最佳叶面积指数估测模型。【结果】带状套作玉米叶面积指数随施氮水平增加而增加,且在各生育时期下差异显著;冠层反射光谱曲线的"绿峰"位置(550 nm)及高反射率平台(760～1 000 nm)反射率在不同施氮水平上差异显著。叶面积指数与冠层光谱反射率在波长范围(400～725 nm、742～1 000 nm)内显著相关(P0.05);叶面积指数与植被指数及小波系数相关性均达到极显著水平(P0.01),其中与自由组合比值植被指数RVI(762,747)相关性最好,相关系数为0.900 4。通过估测模型的构建及筛选,构建了基于db3(750,10)下的小波系数作为光谱变量x的带状套作玉米全生育期叶面积指数估测模型y=-5.84x2+8.417 8x+2.231 1(R2=0.85,RMSE=0.49,RE=19.43%)。【结论】不同施氮水平下玉米冠层光谱和叶面积指数存在差异性,利用高光谱遥感技术可以实现带状套作玉米叶面积指数的实时监测。     

喀斯特石漠化地区枇杷冠层结构特征

[目的]分析喀斯特石漠化地区枇杷的冠层结构特征,为经济果林种植与管理提供科学依据.[方法]采用CI-110植物冠层分析仪测定石漠化地区种植枇杷树的冠层光合有效辐射(PAR)、叶面积指数和散射辐射透过系数,计算PAR透过率、消光系数(K)和林分空隙度,并对冠层结构各参数进行相关性分析.[结果]枇杷冠层的平均林分空隙度、PAR、叶面积指数、叶倾角和散射透过系数分别为0.241、38.245[mol/(m2·d)]、1.648、10.197°和0.228,其中林分空隙度与叶面积指数和PAR呈极显著相关(P<0.01,下同),相关系数分别为-0.852和0.852,散射辐射透过系数与PAR呈极显著正相关,相关系数为0.872,说明林分空隙度、叶面积指数和散射辐射透过系数对枇杷的光截获能力具有较大影响;平均叶倾角与林分空隙度、PAR、散射辐射透过系数和叶面积指数等参数无显著相关性(P>0.05);K和PAR透过率的最小值分别为0.697和0.070%,说明枇杷冠层的光截获能力较强.[结论]喀斯特石漠化地区枇杷冠层内光能利用与光照情况主要受冠层结构特征的深度影响,冠层对光的截获能力较强,生产中应对枇杷冠层结构进行适当修剪调整.     

温室番茄源库协调下冠层光分布特征及群体光合生产的研究

[目的]研究番茄源库协调下冠层叶面积分布、叶倾角、光透过系数等指标的变化,探讨叶片空间配置对冠层结构的影响及与群体光合生产,为温室番茄“矮、密、早”高产栽培提供理论支持.[方法]通过源库协调整枝,系统测定源库协调期叶面积指数、叶倾角、光透过系数等指标的空间分布,结合冠层群体光合速率的变化及光合生产与分配.分析温室番茄源库协调下冠层光分布特征及群体光合生产.[结果]源库协调下,从第2穗花序下换头冠层叶面积指数(LAI)在上层叶、中层叶均在2以上,叶面积指数分布比例高,平均叶簇倾斜角表现为:下层叶＞上层叶＞中层叶＞发育叶,下部茎叶夹角相对较大,群体直射辐射和散射辐射透过系数较小,番茄冠层群体辐射透过系数一直处于较适宜的范围,在0°～360°内叶分布较为均匀,消光系数从下层叶至表层叶逐渐减小,表层叶位没有“午休”现象,上层叶表现出轻微午休特性,中、下部叶位光合速率明显高于对照(CK);植株鲜物质分配到根和果实中的比例分别比对照(CK)高19.2;、8.2;,干物质主要分配到果实,其干重分配比例比对照(CK)果实中高18.6;,群体光合在根和果实中生产,在果实中累积较多,有利于经济产量的形成.[结论]从第2穗花序下换头群体叶面积配置光分布较均匀,源库协调下冠层中部有较好的透光性,冠层底部漏光损失较小,整个冠层仍维持了较高的群体光合速率.促进了光合物质积累,冠层各层次的叶源与光分布的比例吻合程度高,保证了光能的有效利用,温室番茄冠层光合生产效率的继续提高主要依赖于冠层光照条件的改善,可通过整枝技术的改良来实现.     

长白落叶松人工林叶面积指数测定

通过测定三江平原丘陵区13～40年生长白落叶松人工林中55株标准木的针叶生物量,建立了单木针叶生物量模型,结合每木检尺结果和比叶面积,估算和建立了不同立地条件(立地指数11～17)、不同林龄(13～40 a)和不同密度(556～3 122株.hm-2)人工林的针叶生物量、叶面积指数和叶面积指数模型,给出了植被冠层分析仪(LAI-2000)间接测定叶面积指数时的校正系数和校正系数模型。结果表明:长白落叶松比叶面积为12.93m2.kg-1,95%的区间估计为[12.23,13.63]m2.kg-1,单木针叶生物量模型为幂函数模型,叶面积指数为5.76～11.04,针叶生物量为4 455.52～8 535.69 kg.hm-2;LAI-2000测得的叶面积指数为1.77～4.02,低于实测叶面积指数,LAI-2000测量长白落叶松人工林叶面积指数的校正系数为1.45～3.63。林龄、密度、立地条件及其综合作用能够影响长白落叶松人工林叶面积指数和LAI-2000测量叶面积指数时的校正系数,它们能够解释叶面积指数和校正系数变异的99.9%。     

多层离散各向异性辐射传输模型在玉米叶面积指数垂直分布反演中的应用

为更准确地监测玉米叶面积指数(leaf area index, LAI)垂直分布,以多层离散各向异性辐射传输(discrete anisotropic radiative transfer, DART)模型构建的模拟数据集为基础,提出一种条件约束的LAI垂直分布反演方法。首先,基于3层垂直分布场景,评价DART模型对玉米冠层反射率和光合有效辐射(photosynthetically active radiation, PAR)的模拟效果,并构建相应的模拟数据集。其次,基于模拟数据集构建LAI和PAR单参数反演模型。最后,以单参数反演模型为先验知识,通过求解约束化问题实现基于高光谱植被指数的玉米冠层LAI垂直分布反演。结果表明:相较于单参数反演模型,约束优化条件下的反演模型精度更高。玉米上层LAI反演结果的决定系数(R2)提高0.022,均方根误差(root-mean-square error, RMSE)降低0.016 m~2/m~2,归一化均方根误差(normalized root-mean-square error, NRMSE)降低1.3%;玉米中层LAI反演结果的R2提高0.08,RMSE降低0.219 m~2/m~2,NRMSE降低10.1%;玉米下层LAI反演结果的R2提高0.069,RMSE降低0.041 m~2/m~2,NRMSE降低4.6%。说明利用条件约束优化的方法进行玉米冠层LAI的垂直分布反演,能有效提高反演精度。     

基于CFD的植物工厂管道通风模拟及优化

针对植物工厂中传统通风模式难以实现内部气流均匀分布的问题,在满足合适的管孔径比情况下,通过计算设计了管道通风方案,利用计算流体力学CFD(Computational fluid dynamics)仿真软件对不同方案的作物冠层气流场进行模拟,探究管孔直径、管孔数量及进风口风速对作物冠层气流分布的影响,确定最佳管道通风方案。结果表明:所有的管道通风方案气流均匀性均优于传统通风模式,且进风口风速为3m/s的25孔管道通风方案最佳,此时作物冠层表面平均风速为0.55m/s,适宜区(风速范围为0.3～1.0m/s)面积占冠层表面总面积的86.1%。     

几种丛生竹叶性状随冠层高度的垂直变化规律

[目的]了解几种丛生竹叶的平均叶面积(MLA)、比叶面积(SLA)和叶干物质含量(LDMC)沿冠层高度的垂直变化规律。[方法]对福建农林大学百竹园内12种丛生竹不同冠层高度叶片MLA、SLA和LDMC进行调查,分析丛生竹不同冠层MLA、SLA和LDMC的垂直空间结构与差异。[结果]不同丛生竹的上、中、下冠层MLA与LDMC变化较小,SLA变化较大,MLA与LDMC均以唐竹最高(上、中、下冠层MLA均值分别为26.0、33.7、27.4 cm~2;LDMC分别为766.0、814.8、792.4 m~2/kg),LDMC以大黄苦竹最低(上、中、下冠层分别为528.4、548.5、479.0 mg/g);SLA均以高节竹最高(上、中、下冠层分别为629.0、284.9、440.7 m~2/kg);同竹种不同冠层间MLA差异不显著(P0.05);除白哺鸡竹外,其他11种竹种3个冠层间的SLA差异不显著(P0.05)。[结论]光照、水分资源及养分在冠层不同高度的分配,共同导致MLA、SLA和LDMC沿冠层垂直方向发生变化。     

杏树冠层内光合有效辐射(PAR)分布规律及结构优化初探

以杏树为试材,为了解杏树冠层内透光率随树龄和叶面积指数的变化,采用LP-80型冠层分析仪测定了光合有效辐射PAR (Photosynthetically Active Radiation)在不同树龄杏树冠层三维空间上的分布情况,研究了杏树冠层内透光率随树龄(2～6 a)和叶面积指数的变化.结果表明,杏树冠层内部平均PAR的垂直分布具有随着向下累计叶面积指数的增加而递减的趋势,在冠层中上部,透光率较高,PAR递减很明显,冠层下部则维持较低水平,变化不大,在相同的天气和时间条件下不同树龄冠层内PAR同一相对高度的透光率有随树龄增加而递减的趋势,但在不同时刻不同天气条件下,即使同一棵树相同高度同一方位冠层内也具有不同的消光系数,影响杏树冠内光分布的因素是多样的,它们之间存在着复杂的关系; 2～6年生杏树冠层中部的全天平均透光率分别为49.5;、30.0;、27.5;、13.4;和7.8;,冠层下部的平均透光率分别为29.1;、12.1;、10.9;、6.4;和5.9;;杏树冠层叶面积指数LAI (Leaf Area Index)与透光率呈极显著指数相关关系,其表达式为Y=131.39 e-0.896 3X(R2=0.907**);试验结果也可为果树冠层内PAR三维空间分布的模拟研究及冠层结构的优化提供试验方法和理论验证上的参考.     

不同水稻品种各层叶片光合能力的比较

以亚种间两系组合培矮 6 4S/E32、培矮 6 4S/ 9311、X0 7S/紫徽 10 0及三系杂交组合冈优 881、汕优 6 3和中粳 95 16为材料 ,研究水稻不同生育期单株的叶面积和 2 2 5m2 小区的叶面积系数、不同叶层的光合速率和叶绿素含量、叶绿素荧光特性 (叶绿体PSⅡ的原初光化学效率Fv/Fm、光化学猝灭参数 qP和非光化学猝灭参数qN)等的变化 ,分析上述水稻品种的群体冠层结构 ,截光特点以及不同叶层的光合生理特性。结果表明 ,参试的 6个高产水稻品种 (组合 )的冠层结构均具有分层的特点 ,形成了分层的群体光合作用特性 :上层为光合速率限制区、中层为光能截获限制区、下层为光合速率和光能截获双限区 ,但与汕优 6 3相比 ,除培矮 6 4S/E32的株型显著改善 ,类似于粳稻的冠层结构外 ,其他两系或三系杂交稻的冠层结构改善不大     

Assessing effect of wind tunnel sizes on air velocity and concentration boundary layers and on ammonia emission estimation using computational fluid dynamics (CFD)

The objective of this study was to investigate the effect of different geometric sizes of wind tunnels on aerial boundary layers above the emission surface and therefore their effect on ammonia emission using CFD tool. Five wind tunnels of different sizes were used for the CFD simulation. Detail experimental measurements on air velocity and concentration profiles above the emission surface were realised using average inlet velocities of 0.1, 0.2, 0.3, and 0.4 m s⁻¹ in two wind tunnels under isothermal condition. The TAN (Total Ammoniacal Nitrogen) and pH of ammonia aqueous solution were kept constant during the experiments. The boundary conditions necessary for the CFD study were obtained from the measured experimental data. The CFD model used for simulations was first validated using the data from the two wind tunnel experiments. For assessing the effects of wind tunnel size, the air velocity range of 0.1-0.6 m s⁻¹ was used in CFD investigations. It was found that the velocity and concentration boundary layer thickness decreased with the increase of inlet air velocity where the concentration boundary was thinner than the corresponding velocity boundary layer. Wind tunnel sizes affected both velocity and concentration boundary layer thicknesses (P < 0.001). The velocity and concentration boundary layer was thicker in a wind tunnel with larger heights than in small height. The over estimation of ammonia emission of smaller wind tunnels were observed comparing to the largest wind tunnel or open field situation (P < 0.001). Non-linear regression equations were developed using four wind tunnels data for velocity boundary layer thickness (δ_u), concentration boundary layer thickness (δ_c), and ammonia mass transfer coefficient (k_G) as a function of wind tunnel height (H) and average inlet velocity (u_m), which given clear quantitative indication of effects of H, and u_m on δ_u, δ_c, and k_G, respectively.     

Aerodynamic analysis and CFD simulation of several cellulose evaporative cooling pads used in Mediterranean greenhouses

The present work makes an aerodynamic analysis and computational fluid dynamics (CFD) simulation of the four commercial models of corrugated cellulose evaporative cooling pads that are most widely used in Mediterranean greenhouses. The geometric characteristics of the pads have been determined as well as the volume of water they retain at different flows of water, thus obtaining the mean thickness of the sheet of water which runs down them and their porosity. By means of low velocity wind tunnel experiments, the pressure drop produced by the pads has been recorded at different wind speeds and water flows. In this way it has been possible to obtain the relationship of the permeability and the inertial factor with pad porosity using a cubic type equation. Finally, a CFD simulation with a 3D model has been carried out for both dry pads (Q_w = 0 l s⁻¹ m⁻²) and wet ones (Q_w = 0.256 l s⁻¹ m⁻²), finding good correlation between the simulated and experimental pressure drop, with maximum differences of 9.08% for dry pads and 15.53% for wet ones at an airspeed of 3 m s⁻¹.     

A new integrated CFD modelling approach towards air-assisted orchard spraying. Part I. Model development and effect of wind speed and direction on sprayer airflow

The current trend in modelling flow phenomena within trees such as in orchards follows the assumption of the space occupied by the trees as a porous and horizontally homogeneous medium to avoid the flow details associated with the individual plants. This being sufficient at a larger field or regional scale much has to be done at a plant scale to analyse the flow details within the plant and its elements especially for sensitive agricultural operations such as spraying. This article presents an integrated 3D computational fluid dynamics (CFD) model of airflow from a two-fan air-assisted cross-flow orchard sprayer through non-leafed orchard pear trees of 3 m average height. In this model the effect of the solid part of the canopy on airflow was modelled by directly introducing the actual 3D architecture of the canopy into the CFD model. The effect of small canopy parts, such as very short and thin branches and flowers that were not incorporated in the geometrical model, on airflow was simulated by introducing source-sink terms in the Reynolds averaged Navier-Stokes (RANS) momentum and k-? turbulence equations in a sub-domain created around the branches. This model was implemented in a CFD code of ANSYS-CFX-11.0 (ANSYS, Inc., Canonsburg, PA, USA). In this work it was possible to link the real 3D architecture of pear canopy into a CFD code of CFX. The model was able to capture the local effects of the canopy and its parts on wind and sprayer airflow directly by inserting the tree structure into the model which gave realistic results. The model showed that within the injection region of the sprayer there was an average reduction of the jet velocity by 1 m s⁻¹ for a distance of 2.3 m from the sprayer outlet due to the presence of leafless pear canopy. This reduction was variable at different vertical positions due to the difference in the canopy density. Maximal effect of the canopy was observed in the middle height of the trees between 0.25 m and 2.5 m which is the denser region with a bunch of several branches. The maximum velocity difference observed between these two positions was 1.35 m s⁻¹ at 1.75 m height. Thus, regions of high and low air velocity zones of the sprayer due to the variable branch density of the pear tree were predicted. The effects of wind speed and direction on the air jet from the sprayer were investigated using the model. For a cross- (direction of 90°) wind speed of 5 m s⁻¹ there was about 2 m s⁻¹ reduction in the sprayer jet velocity at the jet centre and 0.5 m horizontal shift of the jet centre towards the wind direction. Generally there was a decrease in the jet velocity with increasing cross-wind and decreasing wind direction with respect to the jet direction.     

油菜抗倒伏测试风洞关键部件仿真与试验

为解决现有油菜抗倒伏品种选育周期长、难度大等问题，依托计算流体力学软件Fluent建立油菜抗倒伏测试风洞模型，对风洞扩散段、稳定段、收缩段等关键部位进行参数设计及仿真试验，分析该模型对风洞流场品质的影响，最终通过正交试验选择最佳设计方案。结果显示，单因素试验中，收缩段长度Lc增加，风洞出口风速变异系数增加，气流品质下降；随稳定段长度Lw增加，风洞出口风速变异系数先减小后增加，稳定段长度1 000 mm时，风速变异系数最低，气流品质最佳；阻尼网距稳定段出口长度增加，风洞出口风速变异系数先降低后增加，阻尼网距稳定段出口0.65Lw时，风速变异系数最小。正交试验结果显示，收缩段长度600 mm、稳定段800 mm、阻尼网距风洞出口0.65Lw时，对应风洞试验区风速平均变异系数为0.139，风速较其他方案更稳定，气流品质最佳。实测验证发现，与仿真结果相比，实测风速大小无明显差别，且实测结果中各截面风速变异系数略优于仿真值，整体仿真结果与实测效果拟合较好。     

侧向风对航空植保无人机平面扇形喷头雾滴飘移的影响

目的 侧向风是影响植保无人机航空喷施雾滴飘移和作业效果的主要因素。探究航空植保喷施过程中侧向风对雾滴沉积和飘移的影响,为植保无人机航空喷施作业参数的选择和作业关键部件的改进提供数据支持和理论指导。方法 以常用平面扇形喷头Lechler系列的LU 120-015和LU 120-03标准压力喷头为研究对象,基于计算流体力学离散相模型的粒子跟踪技术,在适宜的边界条件下对喷施作业过程中风洞内雾滴流场和农药喷洒离散相进行模拟试验;通过仿真模拟对平面扇形喷头喷施的雾滴沉积和飘移分布情况进行可视化分析,探究雾滴粒子在不同侧风风速条件下的飘移特性;在农业航空专用风洞中,采用近似条件对雾滴的沉积飘移特性进行试验验证和分析。结果 仿真模拟结果表明,随着侧向风速的增加,离散相雾滴粒子飘移程度越严重,雾滴水平飘移越明显。随着侧向风速的增加,模拟离散相雾滴粒子的准确沉积率(R_a)呈指数下降,由14.11%下降到0.66%;水平飘移率(R_h)呈线性增加,由14.25%增加到60.58%。风洞试验结果表明,在侧风风速分别为1、3和6 m/s的条件下,雾滴的R_h分别为0.4%、48.1%和75.1%,且雾滴在风洞内部会随着侧风风速的增加发生一定程度的卷扬现象。仿真模拟与风洞测试试验的R_h具有显著相关性(R²=0.963,P<0.05)。结论 仿真模拟对航空喷施条件下的雾滴飘移具有较好的预测效果;采用仿真模拟辅助风洞试验测试的方法,可以比较准确地得出航空植保无人机作业中常用平面扇形喷头的雾滴沉积与飘移情况。     

头孢菌素C对蔬菜种子萌发的毒理效应

为探究头孢菌素菌渣无害化处置与肥料化利用过程中残留的头孢菌素C对蔬菜生长的毒理效应，通过恒温保湿培养法，采用生菜（Lactuca sativa Linn.var.ramosa Hort.）、油麦菜（Lactuca sativa var.longifoliaf.Lam）、白菜（Brassica pekinensis（Lour.）Rupr.）及油菜（Brassica campestris L.） 4种蔬菜种子为研究对象，以种子发芽率、幼苗的鲜质量、胚轴长、胚根长为毒性敏感指标，研究了7种浓度头孢菌素C溶液胁迫下4种蔬菜毒性的剂量-效应关系，比较了不同蔬菜在头孢菌素C毒害下的生态毒性差异和相对敏感的指标。结果表明：头孢菌素C溶液对4种蔬菜种子毒性敏感指标的影响程度依次为胚根 > 鲜质量 > 胚轴 > 发芽率；头孢菌素C溶液浓度与4种蔬菜胚根生长率呈显著的线性关系（P<0.01）；头孢菌素C对生菜、油麦菜、白菜以及油菜的最大无响应浓度（NOEC）分别为868.10、727.25、796.27 mg·L^-1和629.277 mg·L^-1，4种蔬菜对头孢菌素C的毒性敏感度依次为油菜 > 油麦菜 > 白菜 > 生菜，其中油菜IC₅₀值为1 538.36 mg·L^-1。研究表明，与油麦菜、白菜和生菜相比，油菜更适合作为后续实验的生态毒性指示植物。     

粳稻冠层叶绿素含量PSO-ELM高光谱遥感反演估算

目的 叶绿素含量是表征粳稻生长状态的重要指示信息，利用无人机高光谱遥感技术及时获取区域尺度的粳稻叶绿素含量。方法 以2016—2017年沈阳农业大学辽中水稻实验站粳稻无人机遥感试验数据为基础，利用连续投影算法(SPA)进行有效波段的提取，提取的特征波段分别为410、481、533、702和798 nm。将提取出的特征波段作为输入，利用极限学习机(ELM)和粒子群优化的极限学习机(PSO-ELM)分别建立粳稻冠层叶绿素含量反演模型。在PSO-ELM模型中，针对PSO算法的种群规模(p)、惯性权重(w)、学习因子(C₁、C₂)、速度位置相关系数(m)这5个参数进行了优化。结果 确定了最优参数：p为80，w为0.9~0.3线性递减，C₁和C₂分别为2.80和1.10，m为0.60。利用优化后的ELM和PSO-ELM所建立的粳稻冠层叶绿素含量模型的决定系数分别为0.734和0.887，均方根误差分别为1.824和0.783。结论 利用优化后的PSO-ELM建立的粳稻叶绿素含量反演模型精度要明显高于单纯利用ELM建立的反演模型，前者具有较好的粳稻叶绿素含量反演能力。本研究为东北粳稻叶绿素含量反演无人机遥感诊断提供了数据支撑和应用基础。     

干旱区棉花水分胁迫指数对滴灌均匀系数和灌水量的响应

为了修订和完善滴灌均匀系数的设计与评价标准,在新疆干旱区研究了滴灌均匀系数和灌水量对作物水分胁迫指数（CWSI）的影响。供试作物为棉花,试验中滴灌均匀系数（C_u）设置0.65（C1）、0.78（C2）和0.94（C3）三个水平,灌水量设置充分灌水量的50%、75%和100%三个水平。结果表明：棉花冠层温度和CWSI表现出随灌水量增加而降低的趋势;冠层温度和CWSI均匀系数的变化范围分别为0.91～0.98和0.65～0.91,均随滴灌均匀系数增加而增大;灌水量对冠层温度和CWSI均值的影响达到极显著水平（α=0.01）,滴灌均匀系数对冠层温度和CWSI均匀系数的影响达到显著水平（α=0.05）或极显著水平。CWSI与皮棉产量呈显著或极显著的负相关关系;滴灌均匀系数越低,水分亏缺引起的减产幅度越小。     

The positive function of selenium supplementation on reducing nitrate accumulation in hydroponic lettuce (Lactuca sativa L.)

High nitrate(NO_3~- ) in vegetables, especially in leaf vegetables poses threaten to human health. Selenium(Se) is an important element for maintaining human health, and exogenous Se application during vegetable and crop production is an effective way to prevent Se deficiency in human bodies. Exogenous Se shows positive function on plant growth and nutrition uptake under abiotic and/or biotic stresses. However, the influence of exogenous Se on NO_3~- accumulation in hydroponic vegetables is still not clear. In the present study, hydroponic lettuce plants were subjected to six different concentrations(0, 0.1, 0.5, 5, 10 and 50 μmol L–1) of Se as Na2 Se O3. The effects of Se on NO_3~- content, plant growth, and photosynthetic capacity of lettuce(Lactuca sativa L.) were investigated. The results showed that exogenous Se positively decreased NO_3~- content and this effect was concentration-dependent. The lowest NO_3~- content was obtained under 0.5 μmol L–1 Se treatment. The application of Se enhanced photosynthetic capacity by increasing the photosynthesis rate(Pn), stomatal conductance(Cs) and the transpiration efficiency(Tr) of lettuce. The transportation and assimilation of NO_3~- and activities of nitrogen metabolism enzymes in lettuce were also analysed. The NO_3~- efflux in the lettuce roots was markedly increased, but the efflux of NO_3~- from the root to the shoot was decreased after treated with exogenous Se. Moreover, Se application stimulated NO_3~- assimilation by enhancing nitrate reductase(NR), nitrite reductase(Ni R), glutamine synthetase(GS) and glutamate synthase enzyme(GOGAT) activities. These results provide direct evidence that exogenous Se shows positive function on decreasing NO_3~- accumulation via regulating the transport and enhancing activities of nitrogen metabolism enzyme in lettuce. We suggested that 0.5 μmol L–1 Se can be used to reduce NO_3~- content and increase hydroponic lettuce yield.     

基于CFD的蛋鸭舍内环境模拟分析与验证

为优化4层层叠式笼养鸭舍舍内环境,基于计算流体动力学(computational fluid dynamics,CFD)对鸭舍内气流场、温度场及CO_2浓度场进行模拟。将笼架简化,考虑其对气流的阻挡作用,将鸭笼及鸭只视为多孔介质。模拟结果显示,进风口为湿帘时,侧墙湿帘与端墙之间存在通风死区,风速低于0.5 m·s~(-1)。进风口为通风小窗时,鸭舍未安装通风小窗区域风速小,CO_2浓度大。改变纵墙湿帘位置对鸭舍结构进行改进,改进后气流不均匀系数降低了17%。改进通风小窗布置发现,提升通风小窗分布均匀性显著降低舍内温差;提升通风小窗安装高度将显著降低舍内CO_2浓度。该研究可为蛋鸭舍结构设计提供参考。