柑橘叶片叶绿素含量高光谱无损检测模型

针对柑橘叶片叶绿素含量的传统化学检测,不仅耗时长且损伤柑橘叶片,还依赖检测者实操技术,无法集成于精细农业中变量喷施农机具的诸多弊端,该文探讨快速无损检测柑橘叶片叶绿素含量方法。以117棵园栽萝岗甜橙树为研究对象,选用ASD Field Spec 3光谱仪对萌芽期、稳果期、壮果促梢期、采果期共4个生长时期的柑橘叶片进行高光谱反射率采集,并同步采用分光光度法测得叶片的叶绿素含量;以原始光谱及其变换形式作为模型输入矢量,分别在主成分分析(principle component analysis,PCA)降维的基础上利用支持向量机回归(support vector regression,SVR)算法和在小波去噪的基础上利用偏最小二乘回归(partial least square regression,PLSR)算法对柑橘叶片叶绿素含量进行建模预测,全生长期整体建模的校正集和验证集最佳模型决定系数R2分别为0.8713和0.8670,均方根误差RMSE(root-mean-square error)分别为0.1517和0.1544,试验结果表明,高光谱可快速无损地对柑橘叶片叶绿素含量进行精确的定量检测,为柑橘不同生长期的营养监测提供理论依据。     

不同生长期柑橘叶片磷含量的高光谱预测模型

针对传统柑橘叶片磷含量检测耗时费力、操作繁琐且损伤叶片等弊端,该研究引入高光谱信息探索柑橘叶片磷含量快速无损检测与预测模型,选ASD Field Spec 3光谱仪采集柑橘4个重要生长期的叶片反射光谱,同步采用硫酸-双氧水消煮-钼锑抗比色法测定叶片的磷含量;先用正交试验确定小波去噪的最佳去噪参数组合,再分别选拉普拉斯特征映射(laplacian eigenmaps,LE)、局部线性嵌入(locally-linear embedding,LLE)、局部切空间对齐(local tangent space alignment,LTSA)、等距映射(isometric mapping,Isomap)和最大方差展开(maximum variance unfolding,MVU)5种典型的流形学习算法对去噪后的光谱数据进行降维和特征提取,进而建立基于支持向量机回归(support vector regression,SVR)的柑橘叶片磷含量预测模型。结果表明,基于一阶导数谱的Isomap-SVR建模结果最佳,全生长期校正集和验证集模型决定系数分别为0.9430和0.8949。试验表明,5种流形学习算法皆适用于对柑橘叶片磷含量的预测,为高光谱检测技术用于柑橘树长势监测和营养诊断提供了参考。     

波段比算法结合高光谱图像技术检测柑橘果锈

为克服柑橘表面不平整导致光线反射不均匀的影响,研究提出了波段比算法,使高光谱图像技术能够快速有效地检测柑橘果锈。首先根据Sheffield指数（SI）确定最佳波段（625 nm和717 nm）,经比值变换后得到第一幅比值图像;然后选取特征波长625 nm的邻近波段（621 nm）,与其比值变换后得到第二幅比值图像,提取轮廓,构建掩膜以消除第一幅比值图像的背景噪声,最后进行阈值分割和数字形态学运算,完成果锈区域的特征检测。试验结果表明,基于波段比算法的高光谱图像技术可有效检测柑橘果锈,检测率达到92%。研究表明波段比算法在高光谱图像技术快速无损地检测柑橘果锈中,能够有效地降低光照反射不均匀的影响,增强谱间差异,提高检测的精度。     

基于高光谱图像的茶树LAI与氮含量反演

为了对茶树进行实时、快速、无损的叶面积指数LAI和氮含量检测,该文以英红九号茶树为试验对象,利用便携式高光谱成像仪采集光谱数据、人工破坏性采摘叶片进行叶面积指数的计算以及传统化学方法测量叶片氮含量,比较不同高光谱特征变换形式与LAI和氮含量之间的相关性,并选择其中相关系数较高的高光谱特征变量作为自变量,分别采用线性、指数、对数和抛物线表达式建立LAI和氮含量的回归模型。结果显示:在多种高光谱数据变量建立的模型中,以绿峰反射率R_g为自变量的对数拟合模型最佳,其拟合样本的决定系数R~2和验证样本的均方根误差RMSE值分别为0.9和0.087 6。以植被指数变量VI_4(红边面积/黄边面积)与氮含量建立的指数模型为最佳建模效果,拟合样本的决定系数R~2和验证样本的均方根误差RMSE值分别为0.830 3和0.102 9,研究结果可为茶树叶面积指数LAI和营养成分的无损检测提供参考。     

水稻叶片氮素及籽粒蛋白质含量的高光谱估测模型

研究水稻叶片氮素和籽粒蛋白质含量的高光谱快速、无损监测方法,对于水稻营养诊断、籽粒品质监测及氮肥高效利用具有重要意义。本文通过水稻盆栽试验,测定水稻叶片氮素、籽粒蛋白质含量和冠层光谱,采用不同的光谱建模方法来提高氮素、籽粒蛋白质含量的估测精度。先用主成分分析(PCA)方法进行特征波段的提取,再用多元线性回归(MLR)、人工神经网络(ANN)和偏最小二乘回归(PLSR)进行建模。结果表明,水稻叶片氮素和籽粒蛋白质含量与特征光谱存在很好的模型关系,3种模型预测的决定系数(R2_p)均在0.847以上,并以PLSR模型的预测效果为最好,可以实现水稻氮素营养和籽粒品质的高光谱估测。     

库尔勒香梨叶片全钾含量高光谱估算模型研究

为实现库尔勒香梨养分状况的无损、实时、快速监测,利用便携式光谱仪(SVC HR-768)测定不同钾肥施用量的20年树龄库尔勒香梨叶片光谱反射率,并结合叶片全钾含量的室内分析,对叶片全钾含量与原始光谱、一阶导数光谱、高光谱参数之间相关性进行分析。结果表明:在425 nm处原始光谱与叶片全钾含量构建的线性模型,调整决定系数R2值达到0.913;在630 nm处一阶微分光谱与全钾含量构建的线性模型,调整决定系数R2值为0.986。叶片全钾含量与高光谱特征变量中绿峰位置变量(Rg)和红谷位置变量(Ro)的相关性极显著,由此构建的线性模型调整决定系数R2值均达到0.96以上。通过模型检验,确定基于630 nm的光谱一阶微分(X630)模型Y=1 136.835X630+50.709为库尔勒香梨叶片全钾含量(Y)的最优估测模型。     

基于高光谱图像的黄瓜叶片叶绿素含量分布检测

植物叶片叶绿素含量及分布是植物营养信息表达的重要指标。为了给大棚黄瓜营养元素的控制提供理论依据,该研究利用高光谱图像建立简单实用的光谱值和叶绿素含量关系的模型,从而实时、无损地检测叶片的叶绿素分布。选取黄瓜叶片的高光谱图像数据块中450~850 nm波段作为研究波段。选取8个具有代表性的植被指数,建立特征波长λ下相应的光谱反射值Rλ与黄瓜叶片叶绿素含量之间的关系模型。结果显示,基于最优指数(R695–705)-1-(R750–800)-1的模型可以很好地预测黄瓜叶片叶绿素的含量,校正集和预测集相关系数r分别为0.8410和0.8286,最小均方根误差RMSE分别为0.2045和0.2190 mg/g。最后根据最优模型预测叶片上任意位置叶绿素的含量,并通过伪彩手段描述叶绿素含量的分布。研究结果表明,利用高光谱图像技术分析黄瓜叶片叶绿素含量及其在叶面上的分布是可行的。另外,该研究确定的最优植被指数所包含的695~705和750~800 nm 2个波段可用于搭建更加简便实用的快速检测叶片叶绿素的便携式多光谱设备。     

基于光谱特征参量的核桃叶片氮素含量估测模型

建立基于光谱特征参量的新温185号(Juglans regia‘Xinwen185’)核桃叶片氮素含量估测模型,旨在为快速监测新温185号核桃叶片N素营养状况提供技术途径。基于肥料效应田间试验,测定N肥不同施用量水平下新温185号核桃果实坐果期、速生生长期、脂化期和近成熟期的叶片光谱反射率和N素含量,采用Pearson相关分析方法筛选与叶片N素含量呈极显著相关的光谱特征参量,并应用回归分析方法建立叶片N素含量光谱特征参量估测模型。结果表明:与叶片N素含量呈极显著相关(P0.01)的光谱特征参量在果实坐果期有绿峰反射率和红色比值指数,在果实速生生长期有黄边位置、红谷反射率和绿色比值指数、红色比值指数、绿色归一化差值指数、红色归一化差值指数,在果实脂化期有绿峰反射率和红色比值指数,在果实近成熟期有绿峰反射率、黄边幅值和红边面积。分别以绿峰反射率、黄边位置、红色比值指数和黄边幅值为自变量采用三次函数建立的果实坐果期、速生生长期、脂化期和近成熟期叶片N素含量回归估测模型的拟合度R2均在0.99以上,且模型具有很好的稳定性和很高的估测精度。表明可采用三次函数建立果实不同生育时期叶片N素含量光谱特征参量估测模型对新温185号核桃树体N素营养水平进行监测。光谱技术在核桃树体N素营养信息探测方面有较大的应用潜力。     

利用Stacking集成学习估算柑橘叶片氮含量

准确估算柑橘叶片氮含量对于科学合理的施肥具有重要的指导作用,该研究利用Landsat8OLI卫星遥感影像和地面采样实测数据,以K-近邻(K-Nearest Neighbors,KNN),随机森林(Random Forest,RF)和自适应增强(Adaptive boosting,Adaboost)模型为基础,构建Stacking集成学习框架,实现对柑橘叶片氮含量(Leaf Nitrogen Content,LNC)的估算。首先分析不同氮含量下的光谱反射特征,构建植被指数(Vegetation Indices,VIs)并计算其与柑橘LNC的相关系数;接着利用格网搜索、交叉验证训练模型,最后将Stacking模型与包括Bagging(Bootstrap Aggregating,Bagging)、人工神经网络(Artificial Neural Network,ANN)在内的多个经典机器学习模型试验结果进行对比分析,并生成柑橘果园的氮含量分布图。结果表明:1)构建的光谱指数与LNC具有较好的相关性,大部分指数相关系数在0.55以上;2)相比KNN、RF、Adaboost等多个单一模型,Stacking模型的估算效果最佳,决定系数达到0.761,均方根误差为1.366 g/kg,平均绝对百分比误差为3.494%;同时,Stacking模型的赤池信息准则(Akaike Information Criterion,AIC)值最低,是观测期内LNC估算的最优模型;3)研究区内LNC值整体上处于30.5～31.5 g/kg左右,接近柑橘种植的理想区间,模型估算与实测值趋于一致。总体上,该研究采用的光谱特征能够有效表征柑橘冠层叶片氮含量,并证明Stacking集成学习能综合多个基模型的优点,提高模型的准确性,为利用卫星遥感展开作物参数估算提供新的思路。     

基于高光谱图像光谱与纹理信息的生菜氮素含量检测

高光谱图像包含丰富的光谱与图像信息,该文基于此试图构建生菜氮素检测模型。利用高光谱图像采集系统获取可见-近红外(390~1 050 nm)范围内的生菜叶片高光谱图像,同时利用凯氏定氮法获取对应叶片的氮素值。将光谱反射值较大波长图像与反射值较小波长图像相除并用阈值化法构建掩膜图像,获取感兴趣区域(ROI,region of interest)。由于高光谱数据量大、且数据间冗余性强,因此如何有效的提取一些特征波长十分重要。该文采用主成分分析(PCA,principal component analysis)对原始高光谱图像进行处理,根据前3个主成分图像(PC1、PC2、PC3)在全波长下的权重系数分布图选出662.9、711.7、735.0、934.6 nm 4个特征波长及对应的光谱特征,并且分别提取4个特征波长图像、主成分图像PC1、PC2、PC3在ROI下的基于灰度共生矩阵的纹理特征,最后利用支持向量机回归(SVR,support vector machine regression)分别建立生菜叶片基于特征波长光谱特征、特征波长图像与主成分图像的纹理特征及光谱纹理融合特征与对应氮素值之间的关系模型。结果表明,在校正性能指标决定系数R2C上,基于光谱特征+特征波长图像纹理特征的模型较好,R2C=0.996,校正集均方根误差RMSEC为0.034;在预测性能指标决定系数R2P上,基于光谱特征的模型较好,R2P=0.86,预测集均方根误差RMSEP为0.22。该研究结果可为农作物氮素的快速、无损检测提供一定的参考价值。     

Potential of wild species for genetic enhancement of some semi-arid food crops

Discovery and incorporation of genes from wild species provide means to sustain crop improvement, particularly when levels of resistance in the cultigens are low and virulent strains of pests and pathogens overcome the host plant resistance. The extent of utilization and the potential of the wild genepool for genetic enhancement were reviewed in five important food crops viz. sorghum, pearl millet, chickpea, pigeonpea and groundnut grown in the semi-arid tropics. Introgression from compatible wild germplasm in the primary gene pool resulted in transfer of new cytoplasmic male sterility systems in pearl millet and pigeonpea, development of high protein, cleistogamous flower and dwarf pigeonpea lines and foliar disease resistant groundnut cultivars. Utilization of wild species in secondary and tertiary gene pools has been generally limited due to sterility, restricted recombination or cross incompatibility. Nevertheless, these species are extremely important as they contain high levels of resistance to several important biotic and abiotic stresses. Several of them, like those belonging to the Parasorghum section and the rhizomatous Arachis species are sources of multiple resistances and hold great promise to sustain crop productivity.     

“绿色革命”以来大气CO2浓度升高对C3作物营养品质的影响

自20世纪60年代"绿色革命"以来,育种技术和农耕技术的发展促进了农作物产量的大幅提升,然而作物的营养品质出现下降趋势。在相似的遗传背景下,大气CO_2浓度升高会使单位体积农作物产品的营养元素含量下降,因此"绿色革命"至今,农作物产品的营养元素下降可能受大气CO_2浓度升高影响。通过植物生长箱模拟"绿色革命"初期和目前的大气CO_2浓度水平(310μmol/mol和400μmol/mol),针对主要C_3作物水稻、小麦和大豆,研究"绿色革命"以来大气CO_2浓度升高对其籽粒的C、N、Fe、Zn元素含量的影响,结果表明:CO_2浓度升高对3种作物籽粒的C元素含量几乎没有影响,变化幅度在±1.5%之间;籽粒的N、Fe、Zn元素含量普遍呈现下降趋势,但均未达到显著水平。     

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     

Collection and preliminary evaluation of native turfgrass accessions in Italy

Despite a raising interest on turfs in Italy, all theavailable varieties of this kind in the Country are of foreign origin, and areoften poorly adapted to the prevailing climatic conditions. This prompted tobegin a collection activity of indigenous turfgrass species, with the ultimategoal of identifying promising materials for future breeding based on localgenetic resources. The collection was carried out in three areas of Italy, viz.the northern Po Plain, the coastal region of Liguria, and the island of Sardiniathat are characterised, respectively, by subcontinental, warm temperate, andtypical Mediterranean climate. Altogether, 141 sites were visited, yielding 226accessions belonging to eight species of potential interest for turfs:Poa pratensis, Poa trivialis,Festuca rubra, Festuca arundinacea,Lolium perenne, Agrostis stolonifera,Agrostis tenuis, and Cynodon dactylon,this last being a warm-season grass. Poa pratensis andCynodon dactylon were mostly collected in northern Italyand Sardinia, respectively, whereas Festuca arundinacea andLolium perenne were rather ubiquitous. The collection sitesranged from 0 to 1040 m asl, but sites over 750 m wereonly visited in the inner part of Sardinia. All the accessions, collected aswhole plants, were transplanted at Lodi, northern Italy, where they are beingevaluated. Their preliminary evaluation for traits of importance for turf use,such as sward colour and overall quality, highlighted the great variation andthe occurrence of interesting accessions in all species. Other characters wererecorded, bearing specific importance in individual species, and in all casespromising accessions were identified. The germplasm of Festucarubra, Festuca arundinacea, and Loliumperenne proved highly infected by endophytic (symbiotic) fungi of thegenus Neotyphodium.     

Leaf position and genotype differences for mineral element concentrations in sorghum grown on tropical acid soil 1

Mineral element deficiencies and toxicities are common problems associated with sorghum [Sorghum bicolor (L.) Moench] production on acid soils. To better understand some of the mineral element problems and the analysis of plant tissue of sorghum plants grown on acid soils, four sorghum genotypes were grown on an acid Oxisol at Carimagua, Colombia limed with dolomite at 2 and 6 Mg ha^‐1.

Samples for mineral element analyses were obtained from leaves at different positions on the four genotypes. Concentrations of P and Mg were highest in the flag leaf (Leaf No. 1) and decreased as the position on the plant declined from the top of the plant for plants grown at 2 Mg lime ha^‐1. Similar decreases in P, Mg, K, and Zn concentrations occurred in plants grown with 6 Mg lime ha^‐1. Concentrations of Ca, S, Si, Mn, Fe, Cu, and Al increased as leaf position declined from the flag leaf for plants grown at 2 and 6 Mg lime ha^‐1. The higher lime supply enhanced Ca and reduced Mn and Fe concentrations in leaves. Differences in mineral element concentrations for the four genotypes used were fairly extensive. The elements to show the greatest range among genotypes were Al and Si and the elements to show the least range among genotypes were P, K, and S. Care should be used in collecting leaf samples for plant analysis and genotypic differences for accumulation of mineral elements should be considered in interpretation of results.     

Short-term variation in the concentration of selected ions within individual tropical rainstorms

Rainwater was collected at the campus of the University of Brunei Darussalam in Bandar Seri Begawan, Brunei Darussalam, using a funnel-in-bottle sampler. Polypropylene bottles were changed at intervals during rainstorm events. The pH and conductivity were determined immediately after collection on aliquots of the sample. Samples were refrigerated at 5°C for subsequent chemical analysis. Analyses for Na, Mg, Ca, Zn and Fe were carried out by means of inductively coupled plasma atomic emission spectroscopy (ICP-AES); Cu and Mn were analysed by graphite furnace atomic absorption spectroscopy (GFAAS); K was analysed using flame atomic emission spectroscopy (FAES); and Cl^–, NO₃ ^– and SO₄ ^2– were analysed by ion chromatography (IC). Concentration versus time profiles are reported for three rainstorm events. All ions exhibited a decrease in concentration during the rainstorm. The first sample contained the highest concentration of ions, consistent with a first-flush effect. The contribution of the initial stages of the shower to the total quantity of ion deposited during the entire rainstorm is quite overwhelming; in many cases 20 to 30% of the mass was deposited in less than 5% of rainstorm duration. On the other hand, the pH and conductivity variation during rainstorms did not exhibit a consistent pattern.     

Leaf litter selection by detritivore and geophagous earthworms

Summary Litterbag experiments with 10 different kinds of leaf litter showed that detritivore (Lumbricus species) and geophagous (Aporrectodea species) earthworms prefer certain litter types over others, since different numbers of worms were found below the litter after 50–52 days of exposure in a pasture. The detritivores preferred Fraxinus, Tilia, and predecomposed Ulmus and Fagus litter to Fagus litter and paper, while geophages preferred Tilia litter to Alnus and Ulmus litter, so that the two groups of earthworms showed different preferences. The detritivores seemed to be more selective than the geophages. The palatability of the litter was examined in relation to the C: N ratio, the lignin concentration and the initial and final polyphenol concentration. The numbers of detritivores were significantly correlated with the C: N ratio and the final polyphenol concentration, so that selection of litter seems to be related to palatability. The numbers of geophages were not significantly correlated with any of the parameters for palatability. The disappearance of litter after 50–52 days appeared to be due to detritivore activity, since the numbers found below the litter were positively and significantly correlated with the litter disappearance. There was no significant correlation with geophage activity. This indicates that detritivores use litter as food, and therefore influence the composition of the litter layer.     

The 5S rRNA gene diversity in the genus <Emphasis Type="Italic">Secale</Emphasis> and determination of its closest haplomes

We analyzed 127 rDNA sequences (5S DNA units) obtained from 23 seed accession samples from more or less 10 taxa in wild and cultivated rye, genus Secale L. The sequences fell into two known groups, here assigned to two unit classes, viz. long R1 and short R1 (designations to reflect on R haplome of rye). The different taxa could not be fully differentiated based on the 5S DNA units. We searched for 5S DNA sequences from known unit classes most closely similar to the long R1 and the short R1. One set with the long R1 unit class contained sequences of the long P1 unit class from Agropyron (P haplome) and from Kengyilia (StYP haplome), long J1 from Thinopyrum (J haplome), whereas the set with the short R1 included the long S1 from Pseudoroegneria (St haplome) and Kengyilia (StYP haplome), the short J1 from Thinopyrum (J haplome) and the short V1 from Dasypyrum (V haplome). Each of the two sets was analyzed separately by maximum likelihood (ML) phylogenetic analysis from which we were able to infer that the 5S DNA units of Secale differentiated in a non-clock fashion and followed the HKY substitution model in the gene tree with the long R1 unit class and the HKY + G in the gene tree with the short R1 unit class. A complementary Bayesian analysis yielded identical tree topologies to the ML ones for each of the two sequence sets. In the tree with the long R1 units the long P1 and long J1 unit classes were closest to the long R1 unit class, whereas in the tree with the short R1 units the long S1 and short J1 unit classes were closest to the short R1 unit class, indicating possibly a close relationship between the St, J and R haplomes.     

Nematode succession and microfauna-microorganism interactions during root residue decomposition

The quality of plant material affects the vigor of the decomposition process and composition of the decomposer biota. Root residues from hairy vetch (Vicia villosa Roth), rye (Secale cereale L.) and vetch+rye, packed in litterbags were placed in pots of soil at 15 C and the content of the bags was analyzed after 2, 4, 8 and 12 weeks. Bacterial biomass did not differ between residues with contrasting composition. Among bacterivores groups of nematodes that require high bacterial production dominated in fast decomposing resources whereas flagellates with smaller requirements prevail in slower decomposing resources. Biomass of bacterial feeding nematodes correlated positively with early phase (0-2 wk) decomposition that increased in the order: rye< vetch+rye<vetch. Bacterial biomass therefore seems to be under top-down (predation) control during early decomposition. In contrast, the fungal biomass differed between resources with highest values for rye. Moreover, this increase in fungal biomass occurred later during succession and was correlated with decomposition activity for rye in that period. Fungal biomass therefore seems to be under bottom-up (resource) control. The composition of the nematode assemblages (composed of 25 taxa) showed a clear relationship to initial plant resource quality as well as decomposition phase. Early successional microbivorous nematodes vary according to resource quality with demanding bacterivores+predators (Neodiplogasteridae) dominating in vetch and less demanding bacterivores (Rhabditidae) and fungivores (Aphelenchus) being equally common in vetch and rye. Later in the succession (2-4 wk) bacterivorous Cephalobidae and fungivorous Aphelenchoides prevailed similarly on the different root materials whereas bacterivorous protozoa and the amoebal fraction thereof dominated in rye. At week 12 no species dominated the nematode assemblages that were similar between the resources. The differences between nematode assemblages among plant resources at 2 week were similar to the results of a field study sampled after 6 weeks with the same soil and plant resources. This lends support to the relevance of the successional patterns observed in this incubation study.     

Cycling of extracellular DNA in the soil environment

Upon entering the soil environment, extracellular DNA is subjected to dynamic biological, physical, and chemical factors that determine its fate. This review concerns the fate of both recombinant and non-recombinant sources of DNA. A schematic of DNA cycling coupled with genetic transformation is presented to understand its behavior in soil. Extracellular DNA may persist through cation bridging onto soil minerals and humic substances, be enzymatically degraded and restricted by DNases of microbial origin, and/or enter the microbial DNA cycle through natural transformation of competent bacteria. Lateral gene transfer may disseminate DNA through the microbial community. An understanding of DNA cycling is fundamental to elucidating the fate of extracellular DNA in the soil environment.