叶片上下表面的光谱特性

绿色植物的光合作用、生产量及能量关系受叶片及整个群落的光学特性的强烈制约。叶片的光谱特性包括对光的吸收、反射和透过等几个方面。对光合作用有效辐射[400—700nm(纳诺米),可见光区域]的吸收是光合作用的第一个步骤。叶片对光的反射可以降低叶温、减少叶片的水分丧失,在一个植株或植物群落中,上部叶片对光的反射和透过通常可以调节群落中的光能利用。一般而言,绿色植物的上表面吸收太阳可见辐射能的80—85%,反射约10%,透过5—     

植物叶片的延迟发光光谱特性

实验采用滤光片及ＩＣＣＤ图像探测系统对白菜叶及其叶绿体的超弱发光光谱进行了研究。实验方法 :选取 2 1片窄带滤光片 (波长范围 :4 70～ 75 4ｎｍ ,带宽小于 15ｎｍ) ,白光照射样品 2分钟 ,延迟 2 0秒后连续采集 6幅图像 ,每幅曝光时间为 10秒 ,每换一片滤光片都进行同样记录。数据处理结果发现 ,叶绿体与叶片的光诱导的延迟发光光谱为相似 ,二者在 5 91ｎｍ、6 35ｎｍ等处均存在较强的峰值。这证实植物的超弱发光主要来自叶绿体。另外 ,延迟发光的光谱特征不随延迟时间的增长而变化。这似乎意味着诱导的延迟发光与植物自发的超弱发光的…     

植物叶片延迟发光的光谱特性

采用生物超微弱发光探测技术,对绿宝石喜林芋成熟叶片在特定波长下的延迟发光特性进行了测量和分析,得到在400 nm~640 nm波长范围内其延迟发光衰减参数"1/P"随波长变化的光谱特性。实验结果表明:叶片在各个特定波长下"1/P光谱"特性不同;植物叶片延迟发光主要集中在大于500 nm的长波波段,在这个波段内延迟发光强度最大;衰减参数1/P随波长的增加而上升,当波长大于500 nm时,衰减参数1/P相对稳定,在这个波段条件下衰减参数1/P最大。     

小麦叶片氮素状况与光谱特性的相关性研究

 系统分析了不同时相下两个小麦(Triticum aestivium)品种叶片含氮量及叶片氮积累量与冠层光谱反射特征的关系。结果表明,随施氮水平的增加,小麦冠层在可见光区的反射率逐渐降低,而近红外波段的反射率逐渐升高。小麦叶片氮素状况与比值指数或归一化指数显著相关,两个品种表现极为一致,可以用一个指数方程来拟合。分阶段建模并没有提高模型的精度,因此可以建立一个适用于整个生育时期的通用氮素诊断方程。叶片含氮量同光谱指数在整个生育期内的关系要优于叶片氮积累量的,其中,与叶片含氮量关系最佳的指数为红波段(660 nm)和蓝波段(460 nm)的组合(R2>0.80);与叶片氮积累量关系最佳的光谱指数为中红外波段(1 220 nm)与红波段(660 nm)的组合(R2>0.62)。     

土壤镉污染对水稻叶片光谱反射特性的影响

水稻移栽于添加不同量镉(50、100、200和400 ppm)的土壤上,叶片反射光谱特性发生变化:可见光区反射率增加,其中550—680nm波段反射率的增加更突出;反射光谱的一次微分图和二次微分图上叶绿素吸收边缘明显蓝移。这些变化以分蘖期最为显著。镉害水稻可见光区反射特性的变化与叶片中叶绿素含量的降低相一致。初步确定几个波段可用于区分镉毒害的和正常的水稻的光谱反射特性。     

橡胶树叶片高光谱特征分析

从光谱曲线特征和光谱变换特征分析橡胶树(Hevea brasiliensis)叶片反射曲线特征.结果表明,蓝边、红边、黄边位置特征分别出现于525 nm、725 nm、550 nm波段附近,红谷位置特征变化较大,并提取了红边积分面积等重要光谱变量特征.叶片氮含量与反射光谱的相关分析表明橡胶树叶片氮素敏感波段为700～1300 nm,其中730 nm处相关性最好,达到0.8422的极显著水平,以730 nm处的反射率与叶片氮含量建立线性模型,其复相关系数R2达到0.7094.     

大豆叶片淀粉酶的特性

大豆叶片的α—淀粉酶对SH—反应剂不敏感,在pH3.6时失活Ca~(2 )使它的耐热性提高至70℃.β—淀粉酶对SH—反应剂敏感,耐酸至pH 2.3,耐热至60℃. 随着叶龄的增长α—淀粉酶的同工酶数目增加,此酶在一般情况下不需要添加Ca~(2 ),EDTA对它起不可逆的失活作用,β—极限糊精及Ca~(2 )可排除EDTA对酶的影响。此酶可能是Ca—金属酶,Ca~(2 )与酶结合紧密,它位于酶的活性中心或附近。 在体外,大豆叶片α—淀粉酶可被自身的淀粉粒吸附,但容易被 pH5的醋酸缓冲液洗脱。     

小麦叶片色素含量的高光谱监测

连续两年采用不同小麦品种在不同施氮水平下进行大田试验,建立了小麦叶片色素含量的光谱定量监测模型.结果表明,叶片色素含量随着施氮水平的增加而提高,品种间存在差异,叶绿素(Chl) a+b相对含量随生育时期的变化较Chl b和类胡萝卜素(Car)更为明显.群体叶片色素含量的敏感波段主要存在于可见光区,其中,红边区域表现显著.红边位置参数REP_LE和REP_IG与叶绿素关系较为密切,REP_LE的表现较好.以REP_LE为变量对Chl a、Chl b和Chl a+b进行方程拟合,决定系数R²分别为0.835、0.841和0.840;对Car含量进行方程拟合,其R²显著下降,且光谱参数间差异较小.经独立数据的检验表明,红边位置的估算结果较好,以REP_IG为变量对Chl b进行预测,模型测试的R²和RE分别为0.632和18.2%;以REP_LE为变量对Chl a、Chl a+b和Car含量进行预测,R²分别为0.805、0.744和0.588,RE分别为9.0%、9.7%和14.6%.表明红边位置与叶片色素含量关系密切且表现稳定,利用REP_LE可以对小麦叶片Chl a和Chl a+b含量进行可靠的监测.     

基于光谱参数对小白菜叶片镉含量的高光谱估算

为实现利用高光谱技术快速、准确、无损地检测叶类蔬菜叶片重金属镉污染情况,通过采用室内盆栽试验,检测了小白菜在6个不同的镉浓度梯度0 mg/kg(CK)、0.5 mg/kg(T1)、1 mg/kg(T2)、5 mg/kg(T3)、10 mg/kg(T4)和20 mg/kg(T5)下的叶片高光谱反射率及其镉含量。利用相关分析和逐步回归的统计方法对叶片原光谱、一阶导数光谱和光谱参数与镉含量进行统计分析,确定了反演叶片镉含量的敏感光谱参数,并建立了估算叶片镉含量的参数模型。结果表明:(1)在540 nm附近和红外区域,叶片光谱反射率随着处理浓度的增加呈下降趋势。T1组叶片光谱与对照组的光谱没有明显的变化差异;(2)原光谱与镉含量的敏感波段主要在690—1300 nm,相关系数最高的波段是782 nm。一阶微分光谱与镉含量的敏感波段在黄边、红外、近红外和远红外范围均有分布;(3)反映植物色素、水含量和细胞结构的参数MCARI(叶绿素吸收反射修正指数Modified Chlorophyll Absorption Reflectance Index),SDy(黄边面积Yellow Edge Area),WI(水质指数Water Index),DCWI(病态水分胁迫指数Disease Water Stress Index),SDr(红边面积Red Edge Area)和Dr(红边幅值The Amplitude of the Red Edge)可分别作为反演镉含量的敏感光谱参数,其倒数回归模型能够较好地反演镉污染下小白菜叶片的镉含量;(4)镉胁迫处理15 d时,建立的SDr的倒数模型估算处理30 d时小白菜叶片镉含量的效果最优。研究表明红边面积参数可以用于估算小白菜叶片的镉含量,可为评价小白菜的食用安全提供科学方法。     

Leaf Pubescence: The Significance of Lower Surface Hairs for the Spectral Properties of the Upper Surface

The fraction of the global radiation incident on the upper surfaceof leaves of Tussilago farfara L. which is reflected, variesaccording to the presence or absence of hairs on the lower surface.Calculations of the radiation fluxes at 550 and 1000 nm wavelengthsprove that these differences arise from a partial reflectionof the radiation emerging from the lower epidermis by the haircover.     

The Spectral Sensitivity of Light-induced Leaf Movements

White, blue, green, red, and deep red illumination were usedto shorten a dark period for plants of Bauhinia monandra under12 hour: 12 hour alternations of white light and darkness. Redalone imitated the effect of white light in advancing the cycleof leaf movement. Deep red did not counteract the effect ofprevious illumination with white light.     

Photosynthesis and Stomatal Conductance of Potato Clones (Solanum tuberosum L.) : Comparative Differences in Diurnal Patterns, Response to Light Levels, and Assimilation through Upper and Lower Leaf Surfaces

A few potato clones, such as A6948-4, had higher rates of photosynthesis in the field than the Russet Burbank and were able to maintain higher rates not only during mid-day but also in the early morning and late evening hours. In addition, they maintained higher carbon assimilation rates over a range of photosynthetic photon flux density from 400 to 2,000 microeinsteins per square meter per second.

Stomatal conductance increased linearly as irradiance increased from 500 to 2,000 microeinsteins per square meter per second with all four potato clones that were examined. Obviously, comparative measurements of stomatal conductance or diffusive resistance with potato must be taken at a known and constant photosynthetic photon flux density.

The upper (adaxial) leaf surface of some potato clones provided a surprising contribution to total carbon assimilation. Neither stomatal conductance, number of stomata per unit area, total area of the stomatal apparatus, nor chlorophyll content appear to account for differences in carbon assimilation rates among clones.

     

Spatial Organization of Dual-Species Bacterial Aggregates on Leaf Surfaces

The spatial organization of cells within bacterial aggregates on leaf surfaces was determined for pair-wise mixtures of three different bacterial species commonly found on leaves, Pseudomonas syringae, Pantoea agglomerans, and Pseudomonas fluorescens. Cells were coinoculated onto bean plants and allowed to grow under moist conditions, and the resulting aggregates were examined in situ by epifluorescence microscopy. Each bacterial strain could be localized because it expressed either the green or the cyan fluorescent protein constitutively, and the viability of individual cells was assessed by propidium iodide staining. Each pair of bacterial strains that was coinoculated onto leaves formed mixed aggregates. The degree of segregation of cells in mixed aggregates differed between the different coinoculated pairs of strains and was higher in mixtures of P. fluorescens A506 and P. agglomerans 299R and mixtures of P. syringae B728a and P. agglomerans 299R than in mixtures of two isogenic strains of P. agglomerans 299R. The fractions of the total cell population that were dead in mixed and monospecific aggregates of a gfp-marked strain of P. agglomerans 299R and a cfp-marked strain of P. agglomerans 299R, or of P. fluorescens A506 and P. agglomerans 299R, were similar. However, the proportion of dead cells in mixed aggregates of P. syringae B728a and P. agglomerans 299R was significantly higher (13.2% ± 8.2%) than that in monospecific aggregates of these two strains (1.6% ± 0.7%), and it increased over time. While dead cells in such mixed aggregates were preferentially found at the interface between clusters of cells of these strains, cells of these two strains located at the interface did not exhibit equal probabilities of mortality. After 9 days of incubation, about 77% of the P. agglomerans 299R cells located at the interface were dead, while only about 24% of the P. syringae B728a cells were dead. The relevance of our results to understanding bacterial interactions on leaf surfaces and the implications for biological control of pathogenic and other deleterious microorganisms is discussed.     

Lognormal Distribution of Epiphytic Bacterial Populations on Leaf Surfaces

Total populations of epiphytic bacteria and selected components thereof were determined on sets of 24 to 36 individual leaves (corn, rye) or leaflets (snap bean, soybean, tomato) of field-grown plants by washing and dilution plating. In general, levels of component populations (e.g., bacteria that are ice nucleation active) were quantitatively more variable from leaf to leaf within a set than were total epiphytic bacterial populations. Populations of a given component frequently varied by a factor of 100 to 1,000 within a set of leaves. Total bacterial populations usually varied by a factor of about 10. For each set of leaves, total and component epiphytic bacterial populations were found to approximate a lognormal distribution by the Shapiro-Wilk test for normality. Due to the lognormal distribution of epiphytic bacterial populations, estimates of population size based on the common practice of using bulked samples (wherein several leaves are washed together) will overestimate the population median by a factor of approximately 1.15σ². From the known probability distribution of bacterial populations, the frequency with which a given bacterial population size is met or exceeded on individual leaves can be estimated. If the bacterial component is phytopathogenic, the frequency estimates could be used to relate quantitatively pathogen populations and disease incidence.     

Factors Affecting Survival of Bacteriophage on Tomato Leaf Surfaces

The ability of bacteriophage to persist in the phyllosphere for extended periods is limited by many factors, including sunlight irradiation, especially in the UV zone, temperature, desiccation, and exposure to copper bactericides. The effects of these factors on persistence of phage and formulated phage (phage mixed with skim milk) were evaluated. In field studies, copper caused significant phage reduction if applied on the day of phage application but not if applied 4 or 7 days in advance. Sunlight UV was evaluated for detrimental effects on phage survival on tomato foliage in the field. Phage was applied in the early morning, midmorning, early afternoon, and late evening, while UVA plus UVB irradiation and phage populations were monitored. The intensity of UV irradiation positively correlated with phage population decline. The protective formulation reduced the UV effect. In order to demonstrate direct effects of UV, phage suspensions were exposed to UV irradiation and assayed for effectiveness against bacterial spot of tomato. UV significantly reduced phage ability to control bacterial spot. Ambient temperature had a pronounced effect on nonformulated phage but not on formulated phages. The effects of desiccation and fluorescent light illumination on phage were investigated. Desiccation caused a significant but only slight reduction in phage populations after 60 days, whereas fluorescent light eliminated phages within 2 weeks. The protective formulation eliminated the reduction caused by both of these factors. Phage persistence was dramatically affected by UV, while the other factors had less pronounced effects. Formulated phage reduced deleterious effects of the studied environmental factors.     

Non-Smooth Morphologies of Typical Plant Leaf Surfaces and Their Anti-Adhesion Effects

The micromorphologies of surfaces of several typical plant leaves were investigated by scanning electron microscopy（SEM）. Different non-smooth surface characteristics were described and classified. The hydrophobicity and anti-adhesion of non-smooth leaf surfaces were quantitatively measured. Results show that the morphology of epidermal cells and the morphology and distribution density of epicuticular wax directly affect the hydrophobicity and anti-adhesion. The surface with uniformly distributed convex units shows the best anti-adhesion, and the surface with regularly arranged trellis units displays better anti-adhesion. In contrast, the surface with randomly distributed hair units performs relatively bad anti-adheslon. The hydrophobic models of papilla-ciliary and fold-setal non-smooth surfaces were set up to determine the impacts of geometric parameters on the hydrophobicity. This study may provide an insight into surface machine molding and apparent morphology design for biomimetics engineering.     

Responses of Net Photosynthesis and Conductance to Independent Changes in the Humidity Environments of the Upper and Lower Surfaces of Leaves of Sunflower and Soybean

A dual-surface leaf chamber was used to investigate the responsesof net photosynthesis and leaf conductance to independent changesin the humidity environments of the upper and lower surfacesof leaves of sunflower and soybean. In sunflower decreasingthe humidity around the upper leaf surface while maintainingthat of the lower surface constant and high reduced both thephotosynthetic rate and the conductance of the lower surface.These reductions could not be attributed to changes in bulkleaf water potential since the transpiration rate of the wholeleaf remained constant. Similarly, the reductions were not relatedto localized water deficits in the lower epidermis or lowermesophyll since the transpiration rate of the lower surfacewas reduced. Possible mechanisms whereby the gas exchange characteristicsof the lower leaf surface of sunflower respond to the humidityenvironment of the upper surface are discussed. In contrastto sunflower, the photosynthetic rate of the lower surface ofsoybean was insensitive to the humidity environment of the uppersurface. In leaves of sunflower grown under a moderate temperature anda medium light level, simultaneous decreases of humidity atboth leaf surfaces reduced the photosynthetic rate of the wholeleaf without affecting the substomatal partial pressure of CO₂.In contrast, with leaves developed under a cool temperatureand a high light level, both the photosynthetic rate and thesubstomatal partial pressure of CO₂ were reduced. Evidently,the occurrence in sunflower of the response pattern suggestinga non-stomatal inhibition of photosynthesis by low humiditydepends upon the environment during growth. The possibilitythat this non-stomatal inhibition may be an artifact due toan error in the assumption of water vapour saturation withinthe leaf airspace is considered. Key words: Vapour pressure deficit, photosynthesis, conductance, non-stomatal inhibition, Helianthus annuus, Glycine max