干旱胁迫下雷竹叶片叶绿素的高光谱响应特征及含量估算

植物叶片的反射光谱特征与叶绿素含量密切相关。以重要的笋用竹种雷竹(Phyllostachys violascens)为研究对象,采用盆栽及控水试验方法研究了2年生雷竹在干旱胁迫条件下冠层叶片反射光谱的响应特征,分析了叶片叶绿素含量与不同波段光谱反射率一阶微分值以及光谱特征参数之间的相关关系,并以雷竹叶绿素含量敏感波段及构建的植被指数与叶绿素含量进行了拟合。结果表明,重度缺水处理后雷竹叶片叶绿素含量显著降低,在可见光区叶片光谱反射率随叶绿素含量的降低而增加,以波长493、639、693、756 nm等处的光谱反射率一阶微分值与叶绿素含量的相关性较高。雷竹叶片叶绿素含量与光谱特征参数如绿峰反射率、红谷反射率、蓝边面积、绿峰面积之间的相关性较高。与已有的植被指数相比基于雷竹叶绿素含量敏感波段修正后的植被指数与叶绿素含量相关性优于原植被指数。基于反射率一阶微分值构建的多元回归方程以及修正的绿色归一化植被指数(m GNDVI)构建的回归方程拟合效果较好,为雷竹叶绿素含量的较优估算方程。研究结果可以为雷竹叶绿素含量的快速无损测定以及季节性干旱条件下雷竹林的科学经营及灾后评估提供依据。     

水稻冠层高光谱特征变量与叶片叶绿素含量的相关性研究

为了探讨水稻冠层光谱对叶片叶绿素含量的响应规律,以双季早稻为材料,设置不同施氮量处理的田间试验,测定水稻冠层光谱和叶片叶绿素含量,计算基于冠层反射光谱的特征变量,研究水稻冠层高光谱特征变量与叶片叶绿素含量之间的关系。结果表明:施用氮肥对反射光谱有明显的影响,在可见光范围内,不施氮处理的反射率高于施氮处理,尤其在波长550 nm左右的绿峰处显著增加,在近红外区反射率随施氮量的增加而增加;与叶绿素含量相关性较好的光谱位置参数是红边位置和红谷反射率,随着叶绿素含量的增加,红谷反射率降低,红边位置向长波方向移动;比值植被指数R800/R550、R750/R553和R990/R553,以及色素比值指数PSSRa、PSSRb与chla、chlb、chl(a+b)呈极显著正相关,可以作为水稻冠层叶片叶绿素监测的特征变量。     

烤烟冠层光谱参数与叶片叶绿素含量的相关分析

为了明确烤烟冠层光谱参数与叶片叶绿素含量的相关性,测定了不同氮肥施用量条件下烤烟冠层光谱特征和烤烟鲜烟叶片叶绿素a(Chl-a)、叶绿素b(Chl-b)、类胡萝卜素(Cars)含量,并对光谱参数与叶绿素含量进行了相关分析和回归分析。结果表明:随着氮肥施用量增加,团棵期和旺长期鲜烟叶片的Chl-a、Chl-b和Cars含量均增加,可见光波段反射率降低、近红外波段反射率增加;而打顶期叶片的3种色素含量和光谱特征的变化规律不明显。可见光460～670nm范围内,460nm反射率与叶片叶绿素含量呈显著正相关,其他波段反射率与叶片叶绿素的含量呈显著负相关;近红外780～1260nm范围内,所有波段与叶片叶绿素含量的都呈显著正相关,1480nm反射率与叶片叶绿素含量呈显著负相关。反映Chl-a、Chl-b、Cars含量与光谱参数——比值植被指数(ratio vegetation index,RVI)定量关系的最佳回归方程分别为幂函数、幂函数和指数函数:Chl-a=0.250RVI(730,550)1.511,Chl-b=0.049RVI(730,550)1.841,Cars=0.0998e0.379RVI(730,550)。     

稻麦叶片氮积累量与冠层反射光谱的定量关系

作物氮素积累动态是评价作物群体长势及估测产量和品质的重要指标,对于作物氮素的实时监测和精确管理具有重要意义。该文以5个小麦(Triticum aestivum)品种和3个水稻(Oryza sativa)品种在不同施氮水平下的3年田间试验为基础,综合研究了稻麦叶片氮积累量与冠层反射光谱的定量关系。结果表明,不同试验中拔节后叶片氮积累量均随施氮水平呈上升趋势;稻麦冠层光谱反射率在不同施氮水平下存在明显差异,可见光区(460~710 nm)反射率一般随施氮水平的增加逐渐降低,近红外波段(760~1 220 nm)反射率却随施氮水平的增加逐渐升高;就单波段而言,810和870 nm处的冠层光谱反射率均与稻麦叶片氮积累量具有相对较高的相关性;在光谱参数中,比值植被指数(Ratio vegetation index, RVI)(870,660)和RVI(810,660)均与稻麦叶片氮积累量具有高度的相关性,且相关系数明显高于单波段反射率,尤其是水稻作物;对于小麦和水稻,均可以利用统一的波段和光谱指数来监测其叶片氮积累量,并可以采用统一的回归方程来描述其叶片氮积累量随单波段反射率和反射光谱参数的变化模式,但若采用单独的回归系数则可以提高稻麦叶片氮积累量估测的准确性。     

稻麦叶片氮含量与冠层反射光谱的定量关系

作物氮素含量是评价作物长势、估测产量与品质的重要参考指标,叶片氮素含量的无损快速监测对于指导作物氮素营养的精确管理及生产力的预测预报具有重要意义.以5个小麦品种和3个水稻品种在不同施氮水平下的3a田间试验为基础,综合研究了稻麦叶片氮含量与冠层反射光谱的定量关系.结果显示：（1）不同试验中拔节后稻麦叶片氮含量均随施氮水平呈上升趋势;（2）稻麦冠层光谱反射率在不同施氮水平下存在明显差异,在可见光区（460～710 nm）的反射率一般随施氮水平的增加逐渐降低,而在近红外波段（760～1100 nm）却随施氮水平的增加逐渐升高;（3）就单波段光谱而言,610、660 nm和680 nm处的冠层反射率均与稻麦叶片氮含量具有较好的相关性;（4）在光谱指数中,归一化差值植被指数NDVI（1220,610）与水稻和小麦叶片氮含量均具有较好的相关性,且相关性好于单波段反射率;（5）对于小麦和水稻,可以利用共同的波段和光谱指数来监测其叶片氮含量,采用统一的回归方程来描述其叶片氮含量随单波段反射率和冠层反射光谱参数的变化模式,但若采用单独的回归系数则可以提高稻麦叶片氮含量估测的准确性.     

不同水氮条件下水稻冠层反射光谱与植株含水率的定量关系

研究了不同土壤水氮条件下水稻 (Oryzasativa) 冠层光谱反射特征和植株水分状况的量化关系。结果表明, 水稻冠层近红外光谱反射率随土壤含水量的降低而降低, 短波红外光谱反射率随土壤含水量的降低而升高。相同土壤水分条件下, 高氮水稻的冠层含水率高于低氮水稻的冠层含水率 ;同一水分条件下, 高氮处理的可见光区和短波红外波段光谱反射率低于低氮处理, 近红外波段光谱反射率高于低氮处理。发现拔节后比值植被指数 (R810 /R460 ) 与水稻叶片含水率和植株含水率呈极显著的线性相关, 模型的检验误差 (RootmeansquareError, RMSE) 分别为 0.93和 1.5 0。表明比值植被指数R810 /R460 可以较好地监测不同生育期水稻叶片和植株含水率。     

水稻高光谱变化特征与叶绿素含量监测研究

叶绿素含量是评价水稻光合效率的重要指标,实时无损监测叶绿素含量对水稻生长诊断具有重要意义。以水稻P88S(绿叶)和黄1S(黄叶)为试验材料,分析高光谱指数与水稻叶绿素含量的关系,并构建冠层反射光谱与水稻叶绿素含量监测模型。研究结果表明:水稻不同叶色的冠层光谱反射率随着植株生长而不断变化,在绿叶材料P88S的502-711 nm和黄叶材料黄1S的487-716 nm可见光波长范围内,叶绿素含量与一阶微分光谱的相关系数呈极显著正相关。以P88S RVI(363,675)和黄1S DVI'(639,680)作为光谱参数,与叶绿素含量建立估算模型拟合效果最佳,说明利用高光谱技术结合一阶微分光谱的方法可以监测水稻叶绿素含量。     

UV-B辐射胁迫下杨梅幼苗的高光谱响应

设置UV-B滤光减弱、UV-B辐射增强和自然光(对照)3组模拟大田试验,比较了不同UV-B辐射处理下,亚热带典型木本植物杨梅幼苗的叶绿素含量、光谱反射率及光谱特征参数,研究UV-B辐射变化对亚热带森林树种的影响.结果表明:增强UV-B辐射可降低杨梅幼苗的叶绿素含量,而降低辐射则会显著促进叶绿素的增加,并且这种胁迫反应于光谱反射率中.3种不同梯度UV-B辐射作用下,可见光部分光谱反射率间的差异主要集中在绿光反射峰及红边附近,同时红边所在波长位置“红移”.UV-B辐射对杨梅的胁迫在时间上具有积累性.用反高斯模型参数R0、λ0、λp、Rs、6指示杨梅受UV-B胁迫,以Rs最显著.不同UV-B辐射水平下植物叶片光谱反射率上的差异,可通过较窄波段光谱反射率或特定波长光谱反射率所构建的植被指数加以有效区分.     

水稻叶片光谱对亚铁胁迫的响应

在湖泊富营养化治理过程中,除了要注意控制氮、磷的输入,还应考虑铁（Fe）的调控作用．本文基于“Fe^2＋假说”,探索性地将植物光谱效应应用于湖泊水体富营养化遥感预警机制研究．在水培条件下分析了亚铁（Fe^2＋）胁迫对水稻（Oryza sativa L．）体内Fe含量、叶绿素浓度及可见一近红外特征光谱的影响,并对其相关关系进行了深入探讨;同时,应用3个光谱定量化指标A1（Fe^2＋胁迫水稻叶片在460～670nm波段反射率变化积分值）、A2（Fe^2＋胁迫水稻叶片在760～1000nm波段反射率变化积分值）、S（Fe^2＋胁迫水稻叶片光谱曲线红边“蓝移”强度）分别建立了水稻叶片Fe含量与叶片光谱之间的定量相关关系模型．结果表明,随培养液中Fe^2＋浓度的升高,水稻体内Fe含量逐渐增加,叶绿素浓度降低,叶片光谱反射率在可见光波段升高,在近红外波段降低,同时红边发生“蓝移”．水稻叶片的3个光谱指标A1,A2,S与叶片中Fe含量都具有显著相关性,相关系数分别为0．933（P〈0．01）,-0．965（P〈0．01）和0．946（P〈0．01）,且A1,A2和S3个参数都能够较好地模拟（复相关系数R^2〉0．96）和估测水稻叶片Fe含量。     

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。     

重金属对黄瓜籽苗发育影响的研究

选用黄瓜(Cucumis sativus)籽苗为材料,硫酸铜、醋酸铅、硫酸锌、氯化镉和氯化镍为化学处理试剂,研究它们对黄瓜籽苗的生长及其根尖细胞有丝分裂的影响。发现随着化学处理试剂浓度的增大,黄瓜籽苗根长度、苗高度、侧根数和最长侧根的长度均有所下降,其中下降最明显的是根长度。同样,根尖细胞有丝分裂的细胞数量明显减少,细胞分裂速率减慢。5种重金属盐中,硫酸铜的毒性最甚,氯化镉,醋酸铅次之。     

Interaction of benzo[a]pyrene, 2,3,3',4,4',5 hexachlorobiphenyl (PCB 156) and cadmium on biomarker responses in flounder (Platichthys flesus L.)

Interactive effects of a mixed pollutant exposure on biomarker responses were studied in European flounder (Platichthys flesus L.). The model chemicals, benzo[a]pyrene (BaP, 2.5 mg kg^-1), 2,3,3',4,4'5 hexachlorobiphenyl (PCB-156, 2.5 mg kg^-1), and cadmium (cadmium, 1 mg kg^-1), were administered to fish by subcutaneous injections. Biomarker responses were quantified both following administration of single chemicals and sequential combinations of the chemicals in pairs. Significant induction of CYP1A protein levels and corresponding ethoxyresorufin-O-deethylase (EROD) activities was observed in BaP and PCB treated flounder after 2 and 8 days, respectively. The strongest induction (44 fold) was caused by BaP. No further induction was observed after additional treatment with PCB 156. CYP1A induction caused by BaP was inhibited (40% compared with BaP treatment alone) in flounder pre treated with cadmium, whereas induction by PCB 156 appeared to be unaffected by pre treatment with cadmium. Flounder treated with cadmium only had significantly elevated hepatic levels of metallothionein (MT) after 15 days. Pre treatment with BaP and PCB prior to cadmium inhibited the MT induction (30-50%) compared with cadmium alone. Furthermore, significantly higher glutathione S transferase activities were observed in flounder administered cadmium alone, and in flounder treated with BaP or PCB 156 prior to cadmium. GST selenium independent peroxidase activities appeared to be unaffected by any of the treatments in the present study. The results indicate that chemical mixtures may affect biomarker responses differently from compounds administered alone, and that the sensitivity of both CYP1A and MT are influenced by pollutants other than their primary inducers.     

Role of S-adenosyl-L-methionine in potentiating cadmium mobilization by diethylenetriamine penta acetic acid in mice

The beneficial effects of S-adenosyl-L-methionine (SAM) in potentiating the mobilization of cadmium by cadmium trisodium diethylenetriamine penta acetic acid (DTPA) from the major target organs and restoration of depleted tissue glutathione (GSH), zinc and copper concentration, were determined in cadmium-exposed mice. The results indicated a significant depletion of cadmium concentration from the blood in DTPA plus SAM treated animals compared with DTPA or SAM alone treated groups. The treatment with SAM alone was also effective in correcting the zinc and GSH concentrations. The results indicated few beneficial effects of concomitant SAM administration during chelation of cadmium with DTPA.     

ENZYMATIC SURFACE HYDROLYSIS OF POLYAMIDE 6,6 WITH MIXTURES OF PROTEOLYTIC AND LIPOLYTIC ENZYMES

This study investigated the changes induced on nylon 6,6 fabric by a mixture of proteolytic and lipolytic enzymes. Technical measurements were studied including those of Fourier-transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), weight loss (WL), bending lengths (BL), scanning electron microscopy (SEM), moisture absorbency (MA), and reflectance spectroscopy (RS). For this purpose, nylon 6,6 fabrics were treated separately with different concentrations of protease and lipase mixtures in solution. The dyeing process was then carried out on the treated fabrics with two reactive and acid dyes. The intensity of major peaks in the FTIR spectra of the protease-treated samples is in favor of chemical changes the polypeptide functional groups in the fabrics. Thermal studies also show a significant decrease in the thermal degradation temperature of the treated polymer at temperatures higher than 400°C. The protease and lipase mixtures decreased the sample weight, while lipase intensified the weight loss comparing with protease. It was observed that the concentration of lipase enzyme had a direct influence on the darkness of dyed samples.     

Interaction of benzo[a]pyrene, 2,3,3′,4,4′,5 hexachlorobiphenyl (PCB 156) and cadmium on biomarker responses in flounder (Platichthys flesus L.)

Interactive effects of a mixed pollutant exposure on biomarker responses were studied in European flounder (Platichthys flesus L.). The model chemicals, benzo[a]pyrene (BaP, 2.5 mg kg^-1), 2,3,3′,4,4′5 hexachlorobiphenyl (PCB-156, 2.5 mg kg^-1), and cadmium (cadmium, 1 mg kg^-1), were administered to fish by subcutaneous injections. Biomarker responses were quantified both following administration of single chemicals and sequential combinations of the chemicals in pairs. Significant induction of CYP1A protein levels and corresponding ethoxyresorufin-O-deethylase (EROD) activities was observed in BaP and PCB treated flounder after 2 and 8 days, respectively. The strongest induction (44 fold) was caused by BaP. No further induction was observed after additional treatment with PCB 156. CYP1A induction caused by BaP was inhibited (40% compared with BaP treatment alone) in flounder pre treated with cadmium, whereas induction by PCB 156 appeared to be unaffected by pre treatment with cadmium. Flounder treated with cadmium only had significantly elevated hepatic levels of metallothionein (MT) after 15 days. Pre treatment with BaP and PCB prior to cadmium inhibited the MT induction (30-50%) compared with cadmium alone. Furthermore, significantly higher glutathione S transferase activities were observed in flounder administered cadmium alone, and in flounder treated with BaP or PCB 156 prior to cadmium. GST selenium independent peroxidase activities appeared to be unaffected by any of the treatments in the present study. The results indicate that chemical mixtures may affect biomarker responses differently from compounds administered alone, and that the sensitivity of both CYP1A and MT are influenced by pollutants other than their primary inducers.     

Cadmium inhibits the protein degradation of Sml1 by inhibiting the phosphorylation of Sml1 in Saccharomyces cerevisiae

Cadmium is a toxic metal, and the mechanism of cadmium toxicity in living organisms has been well studied. Here, we used Saccharomyces cerevisiae as a model system to examine the detailed molecular mechanism of cell growth defects caused by cadmium. Using a plate assay of a yeast deletion mutant collection, we found that deletion of SML1, which encodes an inhibitor of Rnr1, resulted in cadmium resistance. Sml1 protein levels increased when cells were treated with cadmium, even though the mRNA levels of SML1 remained unchanged. Using northern and western blot analyses, we found that cadmium inhibited Sml1 degradation by inhibiting Sml1 phosphorylation. Sml1 protein levels increased when cells were treated with cadmium due to disruption of the dependent protein degradation pathway. Furthermore, cadmium promoted cell cycle progression into the G2 phase. The same result was obtained using cells in which SML1 was overexpressed. Deletion of SML1 delayed cell cycle progression. These results are consistent with Sml1 accumulation and with growth defects caused by cadmium stress. Interestingly, although cadmium treatment led to increase Sml1 levels, intracellular dNTP levels also increased because of Rnr3 upregulation due to cadmium stress. Taken together, these results suggest that cadmium specifically affects the phosphorylation of Sml1 and that Sml1 accumulates in cells.     

Cadmium-induced alterations in ocular trace elements

The present report demonstrates, for the first time, that feeding rats 50 ppm cadmium for just 7 wk results in detectable levels of cadmium in the eye of rats. Furthermore, these ocular cadmium concentrations affect significant alterations in the levels of the essential trace elements selenium, calcium iron, and copper in the eye. Rats were fed a low-selenium (<0.02 ppm selenium), high-copper basal diet (50 ppm copper) supplemented with 0, 0.1, and 0.5 ppm selenium. The animals were either untreated or treated with 50 ppm cadmium admixed with their feed. Cadmium treatment resulted in significant reductions (up to 50%) in ocular selenium. Furthermore, rats fed the basal diet and given 100 ppm cadmium via their feed for 6 wk exhibited a 69% reduction in the activity of the selenoenzyme, glutathione peroxidase, in the eye. Cadmium treatment also resulted in reductions of up to 50% in ocular calcium, irrespective of dietary selenium supplementation. Iron levels were increased by 30% in rats fed the low-selenium diet and decreased by as much as 40% in rats fed the selenium-supplemented diets, compared to animals fed identical levels of selenium without cadmium. Ocular copper levels were significantly increased only in rats fed the low-selenium diet and treated with cadmium. Ocular zinc levels were not significantly affected by dietary cadmium or selenium.     

铜或镉胁迫对海洋青鳉生理生化指标及产卵量的影响

通过研究海水中不同浓度重金属胁迫对海洋青鳉(Oryzias melastigma)生理生化的影响, 探讨与分析各指标间的相互关系, 为海洋重金属污染的生物监测提供参考。按海水水质标准分别设定铜(Cu)和镉(Cd)离子各3个浓度梯度, 测定海洋青鳉中乳酸(LA)、乳酸脱氢酶(LDH)、睾酮(T)、促卵泡素(FSH)、促黄体生成素(LH))及产卵量的动态变化。海洋青鳉中的LA含量随铜胁迫时间的延长而显著降低, 随镉胁迫浓度的增加而升高; LDH活性在铜胁迫下变化不大, 而随镉胁迫时间的延长略有上升; T含量在短期铜胁迫下有所升高, 但随胁迫时间的延长呈显著下降趋势, 却随镉胁迫浓度升高及胁迫时间延长而上升; FSH与LH含量随铜胁迫浓度增加呈显著下降, 随镉胁迫浓度增加呈先降后升趋势, 两者的含量变化与T的动态密切相关。与此同时, 随铜胁迫时间的延长和胁迫浓度的增加, 青鳉的产卵量也呈显著下降趋势。综合表明, 铜或镉胁迫均能显著影响雌性青鳉的LA含量, 增加能量消耗, 进而影响性激素水平, 最终影响到产卵量, 但两类离子的影响存在较大的差异性。因此, 一定浓度的铜或镉胁迫会导致海洋青鳉鱼体内生理生化的变化, 且存在两性差异性, 雌鱼对铜或镉胁迫的响应敏感强, 可选择雌鱼开展相关污染监测。     

Toxicity of S-metolachlor containing formulation and heavy metals to chicken embryos

Environmental pollution of metal modelled by copper sulphate, cadmium sulphate and a 960 g/l S-metolachlor containing herbicide formulation (Dual Gold 960 EC) were studied on chicken embryos after administration as a single compounds or in combination. The test materials were injected into the air-chamber in a volume of 0.1 ml/egg on day 0 of incubation. The concentration of copper, and cadmium sulphate was 0.01%. The applied concentration of Dual Gold 960 EC was 0.375%. Evaluation was done on day 19 of the hatching period. In comparison with the values of the control group, the rate of embryomortality also increased significantly in the groups which were treated by herbicide and heavy metals individually. When the herbicide (Dual Gold 960 EC) was used individually, one quarter of the treated animals died in comparison with the values measured in the control group. In the groups which were treated with cadmium sulphate and Dual Gold 960 EC embryomortality increased significantly in comparison with both the control and individually treated groups. In the groups, which were treated together, the occurrence of development disorders remained as low level as in the case individual treatments. Looking at the types of development disorders, the most frequent problems were the oedema, the shortening of the beak mandible, and the incorrect posture of the feet and the neck. As the collective result of the treatment with cadmium sulphate and Dual Gold 960 EC, the body mass of the treated embryos decreased significantly in comparison with the control and individually treated groups, therefore we can conclude that the combined treatment resulted in increased embryo toxic effect in comparison with the individual embryo damaging effect of the used components.     

RESPONSES OF LEAF SPECTRAL REFLECTANCE TO PLANT STRESS

Leaf spectral reflectances were measured to determine whether leaf reflectance responses to plant stress may differ according to the agent of stress and species. As a result of decreased absorption by pigments, reflectance at visible wavelengths increased consistently in stressed leaves for eight stress agents and among six vascular plant species. Visible reflectance was most sensitive to stress in the 535–640-nm and 685–700-nm wavelength ranges. A sensitivity minimum occurred consistently near 670 nm. Infrared reflectance was comparatively unresponsive to stress, but increased at 1,400–2,500 nm with severe leaf dehydration and the accompanying decreased absorption by water. Thus, visible rather than infrared reflectance was the most reliable indicator of plant stress. Visible reflectance responses to stress were spectrally similar among agents of stress and species.