基于光谱特征分析的苹果树叶片营养素预测模型构建

该文旨在利用光谱分析技术建立高精度苹果叶片营养素预测模型,为苹果树的精细管理提供技术支持。在苹果树年度生长周期的坐果期、生理落果期和果实成熟期等重要物候期,采集了180个果树叶片样本并测量了果树叶片在可见光和近红外波段的反射光谱,同时在实验室采用化学方法获取了果树叶片的氮素以及叶绿素含量。对于聚类后样本,分别分析了果树叶片反射光谱以及经小波滤波后的反射光谱与叶绿素以及氮素之间的相关关系,而后利用偏最小二乘和支持向量机（SVM,support vector machine）方法分别建立了果树叶片叶绿素和氮素含量的回归模型。研究发现,随着生长阶段的推进,在可见光处的反射率逐渐升高,在近红外处的反射率逐渐降低,且基于小波滤波反射光谱的营养素SVM回归模型精度最高：建立的叶绿素回归模型,其测定系数R2达到0.9920,均方根误差 RMSE为0.0039,验证精度R2达到0.9036,RMSE为0.1979;建立的氮素回归模型,其测定R2和验证R2也达到0.74以上,模型的回归RMSE为0.0554,验证RMSE为0.1215。结果表明,采用支持向量机回归模型可以精确估计果树叶片叶绿素含量,对氮素含量的估计精度也达到了实用化水平。     

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。     

基于反射光谱预处理的苹果叶片叶绿素含量预测

以苹果叶片叶绿素含量为研究对象,定量研究了光谱数据预处理方法对光谱特征提取及叶绿素含量预测模型的影响。首先,比较了苹果叶片原始反射率光谱、小波包去噪反射率光谱、反射率一阶差分光谱、先小波包去噪后一阶差分光谱、先一阶差分后小波包去噪光谱这5种光谱的波段间相关系数以及光谱与叶绿素含量间的相关系数,建立了叶绿素含量预测逐步回归模型并对建模结果进行了比较分析。结果表明单纯3层sym8小波包去噪可使光谱曲线平滑,但不会明显提高模型精度;一阶差分虽然放大了局部噪声,但是消除了基线漂移影响,可提高模型精度;先差分后小波包去噪比先小波包去噪后差分具有更高的峰值信号噪声比,更低的均方误差与最大误差,建模结果也显示出同样的结果。因此,先差分后小波包去噪算法可认为是一种有效的苹果叶片叶绿素含量预测光谱预处理方法。利用这一方法建立了苹果叶片叶绿素含量预测模型,获得了较高的预测精度。该研究可用于对苹果树营养状态的评价并指导按需施肥。     

小波包-局部最相关算法提高土壤有机碳含量高光谱预测精度

高光谱遥感可以实现水稻土排水期有机碳含量的快速预测,但土壤反射率受多种噪声的影响,有机碳光谱信号探测受阻,预测模型性能低下,如何在去除噪声的同时最大限度地保持有机碳光谱信号十分重要。以原状新鲜水稻土为研究对象,采用Bior1.3小波系对反射光谱进行1~7层小波包变换,通过相关分析确定最大分解层;将原始反射率至最大分解层以内的各层光谱相关系数组成相关系数集,采用局部最相关算法(local correlation maximization,LCM)构造土壤有机碳最优光谱;最后基于最优光谱建立有机碳含量偏最小二乘预测模型并进行分析。结果显示:1)随着小波包分解层数的增加,土壤反射率与有机碳含量的相关性不断增强,到第6层达到最高,确定为小波包最大分解层;2)基于LCM构造的最优光谱比未去噪光谱平滑,比小波包去噪光谱保留了更多光谱细节;3)未去噪光谱、小波包去噪光谱和LCM最优光谱有机碳预测模型的验证决定系数分别为0.693、0.727和0.781,均方根误差为1.952、1.840和1.679 g/kg,残留预测偏差为1.85、1.97和2.17。小波包-局部最相关算法在去噪同时有效保持了土壤有机碳光谱信号,可提高水稻土有机碳含量高光谱预测精度。     

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。     

基于高光谱的柑橘叶片钾含量快速诊断模型

及时准确地监测柑橘树体钾营养状况,有助于科学施肥,提高柑橘果实的品质和产量。试验对采集的W·默科特叶片钾含量及叶片光谱信息进行相关性分析,利用主成分分析和连续投影算法进行降维处理,同时结合偏最小二乘回归和最小二乘支持向量机回归分别建立了叶片钾含量预测模型。结果显示,柑橘叶片钾含量特征波长主要集中在450～600 nm、700 nm左右、980～1030 nm区域;最小二乘支持向量机回归模型的预测效果明显优于偏最小二乘回归模型,预测集相关系数达0.91。结果表明,利用高光谱成像技术结合最小二乘支持向量机回归可实现对柑橘叶片钾含量的快速诊断。     

傅立叶变换中红外光谱估测水稻叶片氮素含量的研究

通过不同氮素水平的水稻田间试验,在分析测定了水稻叶片叶绿素、氮素等农学参数后,采用傅立叶中红外光谱仪测定了水稻孕穗期叶片干样的透射光谱,利用协同偏最小二乘算法（siPLS）分析选取了傅立叶变换红外光谱估测水稻氮素含量的敏感波段及其组合。结果表明,其最优主成分数是9个,最佳估测建模的波段组合分别为1350.89～1586.57, 1587.53～1822.40 和 3709.41～3943.72 cm-1;建立的水稻氮素预测模型的精度较高,交互验证均方根误差（RMSECV）和预测均方根误差（RMSEP）分别为0.1538和0.1933,预测值与化学分析获得的叶片总氮浓度之间的交互相关系数和独立检验相关系数分别为0.9393和0.6649,高于中红外光谱指数NFS和NFSA的预测精度。说明利用傅立叶红外光谱作为水稻氮含量的诊断技术是可能的,值得进一步验证和完善。     

区域水稻穗期叶片氮素的遥感估测初探

快速、无损、准确地监测水稻穗期氮素状况,对于诊断水稻生殖生长特征、提高氮肥运筹水平具有重要意义。本研究在浙江省海宁市晚稻试验点进行田间取样试验,并获取同时期CBERS-1遥感数据,分析了试验点晚稻穗期叶片氮素与CBERS-1影像冠层光谱信息之间的关系。结果表明,水稻穗期叶片氮素含量与同期CBERS-1影像的光谱信息NDVI之间有良好的相关性,可以建立水稻穗期叶片氮素含量反演的相关统计模型。但由于遥感影像特征与水稻穗期叶片氮素含量之间存在较复杂的非线性关系,因此统计模型反演精度不够理想。因而,又尝试运用BP人工神经网络方法来反演水稻穗期叶片氮素含量,发现BP人工神经网络模型具有很强的非线性拟合能力,与统计模型相比,其水稻穗期叶片氮素含量的反演精度有显著提高。由此表明,利用CBERS-1遥感影像可以对水稻穗期叶片氮素含量进行建模并反演,能够在较大的范围里估测水稻的氮素营养状况。     

调亏灌溉合理滴灌频率提高大棚西瓜产量及品质

在调亏灌溉条件下,该试验研究了不同膜下滴灌频率对早春大棚西瓜植株生长、果实产量、品质及水分利用效率的影响,从而确定西瓜整个生育期的最佳灌溉频率方案。试验在各生育期设置3个不同的灌溉频率水平,分别为高频(每2 d灌溉1次)、中频(每4 d灌溉1次)和低频(每6 d灌溉1次),并做4因素3水平正交实验设计,共9个处理,各处理总灌水量相等。结果表明:各处理中,苗期中频、开花坐果期高频、果实膨大期中频、成熟期低频灌溉处理植株在生长势上表现最好,该处理植株的叶绿素含量、净光合速率、气孔导度、蒸腾速率以及叶片水分利用效率在全生育期中均能保持较高水平,且该处理植株具有较高的坐果率、单果质量,果实总产量和灌溉水分利用效率最高,分别达到63.72 t/hm2和303.64 kg/(hm2·mm)。品质方面,苗期中频、开花坐果期高频、果实膨大期中频、成熟期低频灌溉处理的果皮最薄,仅有8.30 mm,且具有较高含量的总维生素C和最高含量的可溶性蛋白质和中心边可溶性固形物。综合考虑生长势、产量、品质和灌溉水分利用效率,适用于西北地区早春大棚西瓜调亏灌溉的最佳灌溉频率方案为苗期中频、开花坐果期高频、果实膨大期中频、成熟期低频灌溉。该研究可为实现西北地区早春设施西瓜栽培高效节水灌溉提供理论与技术参考。     

水分胁迫对日光温室葡萄叶片生理变化及果实发育的影响

为探究鲜食日光温室葡萄高效节水生产的水分管理方式,选取日光温室6a生葡萄‘红地球’为试验材料,以充分灌溉为对照[CK,土壤含水率为75%～100%的田间持水率(θf)],分别在萌芽期、新梢生长期、开花坐果期、果实膨大期、着色成熟期设置土壤含水率为55%θf(其他4个生育期为75%～100%θf)的5个水分胁迫处理,调查叶片超氧化物歧化酶(SOD)活性及膜质过氧化物丙二醛(MDA)和脯氨酸(Pro)含量、果实纵横径、果实硬度、单粒重量和产量,研究日光温室葡萄叶片生理和果实产量对水分胁迫的响应机制。结果表明,在果实膨大期、着色成熟期施加水分胁迫均会显著降低葡萄叶片SOD活性和Pro含量,导致MDA含量大量积累,对叶片产生不利影响。在萌芽期、新梢生长期、开花坐果期进行水分胁迫对葡萄叶片SOD活性、Pro含量影响不大,但对叶片MDA含量的影响具有滞后效应。果实膨大期水分胁迫葡萄产量仅为14 830kg·hm–2,较CK和萌芽期、新梢生长期水分胁迫显著减产20%以上。因此,水分胁迫显著降低果实膨大期SOD活性及渗透调节物质含量,增加膜质过氧化物含量,并导致产量降低,该时期不宜进行亏水处理;生长前期的水分胁迫对葡萄叶片的生理和果实的影响不显著。     

“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。     

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.     

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.     

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.     

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.     

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.