Herbivory of wild Manduca sexta causes fast down-regulation of photosynthetic efficiency in Datura wrightii: an early signaling cascade visualized by chlorophyll fluorescence

Plants experiencing herbivory suffer indirect costs beyond direct loss of leaf area, but differentially so based on the herbivore involved. We used a combination of chlorophyll fluorescence imaging and gas exchange techniques to quantify photosynthetic performance, the efficiency of photochemistry, and heat dissipation to examine immediate and longer-term physiological responses in the desert perennial Datura wrightii to herbivory by tobacco hornworm, Manduca sexta. Herbivory by colony-reared larvae yielded no significant reduction in carbon assimilation, whereas herbivory by wild larvae induced a fast and spreading down-regulation of photosynthetic efficiency, resulting in significant losses in carbon assimilation in eaten and uneaten leaves. We found both an 89?% reduction in net photosynthetic rates in herbivore-damaged leaves and a whole-plant response (79?% decrease in undamaged leaves from adjacent branches). Consequently, herbivory costs are higher than previously estimated in this well-studied plant-insect interaction. We used chlorophyll fluorescence imaging to elucidate the mechanisms of this down-regulation. Quantum yield decreased up to 70?% in a small concentric band surrounding the feeding area within minutes of the onset of herbivory. Non-photochemical energy dissipation by the plant to avoid permanent damage was elevated near the wound, and increased systematically in distant areas of the leaf away from the wound over subsequent hours. Together, the results underscore not only potential differences between colony-reared and wild-caught herbivores in experimental studies of herbivory but also the benefits of quantifying physiological responses of plants in unattacked leaves.     

Evaluating the effect of rootstocks and potassium level on photosynthetic productivity and yield of pear trees

In this experiment, leaf gas exchange, photosynthetic efficiency, area index, and chlorophyll content were measured in pear (Pyrus communis L.) trees grown on different rootstocks and potassium fertilization doses. Our results showed that trees budded on the Pyrodwarf rootstock had the biggest leaf area and the highest photosynthetic efficiency, photosynthesis rate, and chlorophyll content. There was no correlation between the applied potassium fertilization dosage and the photosynthetic efficiency of the trees. This paper is addressed to discuss various mechanisms and selected factors responsible for pear tree photosynthetic productivity.     

Spatial association of photosynthesis and chemical defense in Arabidopsis thaliana following herbivory by Trichoplusia ni

Because they share common precursors and require significant amounts of energy, photosynthesis and defense against herbivores and pathogens may be inversely related. This relationship was examined in Arabidopsis thaliana exposed to herbivory by Trichoplusia ni neonates. The spatial pattern of photosynthesis was compared statistically with that of induction of the defense-related cinnamate-4-hydroxylase (C4H) gene across individual leaves exposed to herbivory in transgenic plants harboring a C4H:GUS gene fusion. In portions of the leaf where C4H:GUS expression was upregulated, photosynthesis was depressed, while non-photochemical quenching was increased, suggesting a trade-off between these two processes. However, photosynthetic damage spread further into surrounding areas than the induction of C4H:GUS expression. Photosynthetic depression was observed up to 1 mm from the edges of holes, whereas C4H:GUS induction typically was limited to about 0.5 mm or less from edges. Other mechanisms may be responsible for the spread of photosynthetic damage beyond where C4H-related defense was induced. Alternatively, C4H induction may reflect a subset of defensive responses more limited in their spatial distribution than the downregulation of photosynthesis. The suppression of photosynthesis in remaining leaf tissue represents a 'hidden cost' of herbivore damage.     

The differential effects of herbivory by first and fourth instars of Trichoplusia ni (Lepidoptera: Noctuidae) on photosynthesis in Arabidopsis thaliana

The effect of different feeding behaviours of 1st and 4th instar Trichoplusia ni on photosynthesis of Arabidopsis thaliana var. Columbia was characterized using spatially resolved measurements of fluorescence and leaf temperature, as well as leaf gas exchange,. First instars made small holes with a large perimeter-to-area ratio and avoided veins, while 4th instars made large holes with a low perimeter-to-area ratio and consumed veins. Herbivory by 1st instars reduced photosynthesis more strongly in the remaining leaf tissue than that by 4th instars. Photosystem II operating efficiency (PhiPSII) was correlated with the rate of CO2 exchange, and reductions in PhiPSII in areas around the missing tissues contributed to a 15.6% reduction in CO2 assimilation on the first day following removal of 1st instars. The corresponding increases in non-photochemical quenching and greater rates of non-stomatal water loss from these regions, as well as the partial reversal of low PhiPSII by increasing the ambient CO2 concentration, suggests that localized water stress and reduced stomatal conductance contributed to the inhibition of photosynthesis. Damage by 1st but not 4th instars reduced the maximum quantum efficiency of photosystem II photochemistry (Fv/Fm) by 4-8%. While herbivory by both 1st and 4th instars increased dark respiration rates, the rates were too low to have contributed to the observed reductions in CO2 exchange. The small holes produced by 1st instars may have isolated patches of tissue from the vascular system thereby contributing to localized water stress. Since neither 1st nor 4th instar herbivory had a detectable effect on the expression of the Rubisco small subunit gene, the observed differences cannot be attributed to changes in expression of this gene. The mode of feeding by different instars of T. ni determined the photosynthetic response to herbivory, which appeared to be mediated by the level of water stress associated with herbivore damage.     

The usefulness of the chlorophyll fluorescence parameters in harvest prediction in 10 genotypes of winter triticale under optimal growth conditions

The aim of the experiment was to detect differences in the activity of the photosynthetic apparatus in 10 genotypes of winter triticale. Measurements of gas exchange and chlorophyll fluorescence were performed. Among the tested genotypes, the photosynthetic apparatus of Timbo and Piano was the most active, while the photosynthesis of both Babor and Boreas was highly reduced. Additionally, we have found significant correlations between the yield and some parameters of chlorophyll fluorescence and leaf gas exchange. Parameters of chlorophyll fluorescence are useful for estimation of the functional state of the photosynthetic apparatus and could become selection criteria in plant breeding. Moreover, such parameters permit definition of the effectiveness of the utilization of chlorophyll a excitation energy and co‐operation of the light phase reactions, with reactions occurring during the dark phase of photosynthesis.     

Biomass and photosynthetic productivity of water hyacinth (Eichhornia crassipes) as affected by nutrient supply and mirid (Eccritotarus catarinensis) biocontrol

The biological control of water hyacinth is affected by water nitrogen and phosphorus content and this was investigated experimentally at five levels of nutrient supply by measuring plant photosynthetic and growth responses, and mirid reproduction and herbivory of nutrient treated plants. Low nitrogen (2–0.2 mg L⁻¹) and phosphorus (0.2–0.01 mg L⁻¹) supply decreased hyacinth photosynthesis, growth and biomass accumulation relative to plants supplied 200 mg L⁻¹ N and 20 mg L⁻¹ P. This effect depended more on nitrogen supply than phosphorus supply. Chlorophyll fluorescence showed that the photosynthetic light reactions of low nutrient plants were affected and leaves had decreased chlorophyll content, density of functional photosystems II and dissipated a greater proportion of absorbed energy as heat. Gas exchange parameters showed reduced carboxylation efficiency, rates of RuBP regeneration and light saturated photosynthetic rates, but not quantum yields. Effects on photosynthesis translated into lower plant dry biomass. Mirid herbivory exacerbated the effects of low nutrients noted for chlorophyll fluorescence, gas exchange parameters and biomass accumulation, however, these effects were not always significant and there was no obvious correlation between the level of nutrients supplied and the effect of mirid herbivory. Low nutrient supply did, however, affect mirid performance reducing the number of adult insects, nymphs and herbivory intensity suggesting that in the long-term mirid populations would be significantly affected by water nutrient status.     

Indirect effects of insect herbivory on leaf gas exchange in soybean

Herbivory can affect plant carbon gain directly by removing photosynthetic leaf tissue and indirectly by inducing the production of costly defensive compounds or disrupting the movement of water and nutrients. The indirect effects of herbivory on carbon and water fluxes of soybean leaves were investigated using gas exchange, chlorophyll fluorescence and thermal imaging. Herbivory by Popillia japonica and Helicoverpa zea (Boddie) caused a 20–90% increase in transpiration from soybean leaflets without affecting carbon assimilation rates or photosynthetic efficiency (Φ_PSII). Mechanical damage to interveinal tissue increased transpiration up to 150%. The spatial pattern of leaf temperature indicated that water loss occurred from injuries to the cuticle as well as from cut edges. A fluorescent tracer (sulforhodamine G) indicated that water evaporated from the apoplast approximately 100 µm away from the cut edges of damaged leaves. The rate of water loss from damaged leaves remained significantly higher than from control leaves for 6 d, during which time they lost 45% more water than control leaves (0.72 mol H₂O per cm of damaged perimeter). Profligate water loss through the perimeter of damaged tissue indicates that herbivory may exacerbate water stress of soybeans under field conditions.     

叶角、光呼吸和热耗散协同作用减轻大豆幼叶光抑制

研究了大豆叶片逐步展开过程中的色素组成、气体交换、荧光动力学以及叶片角度等特性。随着叶片展开程度的增加 ,叶绿素含量和叶绿素 a/ b比值增加 ;光合速率 (Pn)也增加 ,揭示叶片展开过程中光合机构是逐步完善的。自然状态下 ,不同展开程度的叶片均未发生明显的光抑制 ;但将叶片平展并暴露在 12 0 0μmol/ (m2 · s)光下时幼叶发生严重的光抑制 ,伴随叶面积的增加光抑制程度减轻。强光下 ,尽管幼叶光呼吸 (Pr)的测定值较低 ,但幼叶光呼吸与总光合之比 (Pr/ Pm)较高。将叶片平展置于强光下时 ,幼叶的实际光化学效率 (ΦPSII)明显下调 ,非光化学猝灭 (NPQ)大幅增加 ;幼叶叶黄素库较大 ,光下积累较多的脱环氧化组分 ,揭示幼叶依赖叶黄素循环的热耗散增强。自然条件下测量叶片角度 ,观察到在叶片展开过程中叶柄夹角逐渐增加 ;日动态过程中幼叶的悬挂角随光强增加而明显减小 ,完全展开叶的悬挂角变化幅度很小。叶片角度的变化使实际照射到幼叶叶表的光强减少。推测较强的光呼吸、依赖叶黄素循环的热耗散以及较大的叶角变化可能是自然状态下幼叶未发生严重光抑制的原因     

Photosynthesis within isobilateral Eucalyptus pauciflora leaves

Adult Eucalyptus pauciflora leaves are vertically displayed. They have multiple palisade cell layers beneath both surfaces, interrupted by numerous oil glands. Here, we characterized light absorption, chlorophyll, photosynthetic capacity and CO2 fixation profiles through these leaves. Multiple chlorophyll fluorescence images of leaves viewed in cross-section were made by applying light from different directions. 14CO2 labelling, followed by paradermal cryosectioning, was used to measure profiles of photosynthesis. Photosynthetic capacity peaked 75 microm into the mesophyll beneath each surface and was lowest in the centre of the 600-microm-thick leaf. Predictions by a multilayer model using Beer's law matched the observed profiles of 14C fixation. When constrained to the horizontal, a vertically acclimated leaf gains only 79% of the daily photosynthesis achieved by a horizontally acclimated leaf. However, it outperforms the horizontally acclimated leaf when both are oriented vertically. Each half of the observed profile of photosynthetic capacity closely matches the profile of light absorption through the leaf with unilateral illumination to that surface. Derivation of biochemical parameters from gas exchange measured under unilateral illumination would underestimate the real photosynthetic capacity of these leaves by 21%.     

Transitions in photosynthetic parameters of midvein and interveinal regions of leaves and their importance during leaf growth and development

Abstract: The areal development of photosynthetic efficiency and growth patterns in expanding leaves of two different dicotyledonous species - Coccoloba uvifera and Sanchezia nobilis - was investigated by imaging both processes repeatedly over 32 days. Measurements were performed using combined imaging systems for chlorophyll fluorescence and growth, with the same spatial resolution. Significant differences in potential quantum yield of photosynthesis (F_v/F_m), a parameter indicating the functional status of photosystem II, were found between midvein and interveinal tissue. Although base-tip gradients and spatial patchiness were observed in the distribution of relative growth rate, neither midvein nor interveinal tissue showed such patterns in F_v/F_m. In young leaves, F_v/F_m of the midvein was higher than F_v/F_m of interveinal tissue. This difference declined gradually with time, and upon cessation of growth, F_v/F_m of interveinal regions exceeded those of midvein tissue. Images of chlorophyll fluorescence quenching showed that ΔF/F_m' in the different tissues correlated with F_v/F_m, indicating that, in these uniformly illuminated leaves, transitions in photosynthetic electron transport activity follow those of predawn quantum efficiency. We explore the implications of these observations during leaf development, discuss effects of sucrose delivery from veins to interveinal areas on relative rates of photosynthetic development in these tissues, and propose that the initially higher photosynthetic activity in the midvein compared to the intervein tissues may supply carbohydrates and energy for leaf growth processes.     

Changes in Leaf Gas Exchange Properties of Cloned Betula pendula Saplings after Partial Defoliation

The effects of partial defoliation on the gas exchange characteristicsof the remaining leaves were studied in cloned Betula pendulaL. saplings grown in pots on two different soil types: prefertilizedpeat and unfertilized sand (Experiment 1). The responses ofundamaged leaves to different damage modes of leaf laminae werealso studied using saplings grown on prefertilized peat only(Experiment 2). In Experiment 1, removal of the upper leaves,which represented about half the total leaf area, approximatelydoubled the mean net photosynthetic rates of the remaining lowerleaves on both soil types and at both measuring dates (12–13d and 34 d after assigning the treatments). However, when thelower leaves were removed there was a temporary increase inthe mean net photosynthetic rates of the remaining expandedupper leaves only in the plants grown on sand. In Experiment2, the removal of laminae caused a similar increase in the light-saturatednet photosynthetic rates of the remaining leaves, irrespectiveof whether the laminae were removed totally immediately or graduallyin three stages. The magnitude of the photosynthetic responsewas determined by the amount of leaf tissue removed and wasindependent of the way in which it was removed. We concludethat the increase in the photosynthetic rates of the remainingleaves after partial defoliation may be attributed to the alleviatedcompetitive status among the leaves rather than to the decreasedsource/sink ratio within a plant. Key words: Partial defoliation, net photosynthesis, Betula pendula, birch sapling, herbivory     

Photosynthetic capacity of field-grown durum wheat under different N availabilities: A comparative study from leaf to canopy

The effect of N availability on photosynthetic capacity, growth parameters and yield was studied in field-grown durum-wheat plants at both the leaf and canopy levels. Two contrasting nitrogen levels (120 and 0 kg ha^?1) were assayed in a randomised block design with nine replicates each. Total biomass was measured at anthesis and yield and its agronomical components at maturity. Photosynthetic measurements were performed 2 weeks after anthesis in two plots of each N treatment. Flag leaves were measured, using a LI-COR 6400 combined with the chlorophyll fluorescence meter, and the whole canopy by measuring CO₂ and H₂O fluxes in an innovative canopy-chamber system. We showed a clear increase in photosynthetic gas exchange and chlorophyll contents with N fertilisation at both canopy and leaf levels. As a consequence the increase in yield as response to N fertilisation seems the result of a larger green leaf area combined with a higher photosynthetic capacity of the leaves attributable to an increase in the maximum carboxylation velocity of Rubisco. Moreover gas-exchange measurements of the flag leaf during grain filling seem to provide a realistic characterisation, not just of the photosynthetic performance of the crop, but also about the impact of N availability on yield. Thus, measurements performed on the flag leaf matched those at the canopy level, with proportional increases in terms of gas exchange and chlorophyll content, providing a fast, cheap and reliable estimation of canopy photosynthesis and the grain yield attained by the crop.     

Causes of reduced leaf‐level photosynthesis during strong El Niño drought in a Central Amazon forest

Sustained drought and concomitant high temperature may reduce photosynthesis and cause tree mortality. Possible causes of reduced photosynthesis include stomatal closure and biochemical inhibition, but their relative roles are unknown in Amazon trees during strong drought events. We assessed the effects of the recent (2015) strong El Niño drought on leaf‐level photosynthesis of Central Amazon trees via these two mechanisms. Through four seasons of 2015, we measured leaf gas exchange, chlorophyll a fluorescence parameters, chlorophyll concentration, and nutrient content in leaves of 57 upper canopy and understory trees of a lowland terra firme forest on well‐drained infertile oxisol. Photosynthesis decreased 28% in the upper canopy and 17% in understory trees during the extreme dry season of 2015, relative to other 2015 seasons and was also lower than the climatically normal dry season of the following non‐El Niño year. Photosynthesis reduction under extreme drought and high temperature in the 2015 dry season was related only to stomatal closure in both upper canopy and understory trees, and not to chlorophyll a fluorescence parameters, chlorophyll, or leaf nutrient concentration. The distinction is important because stomatal closure is a transient regulatory response that can reverse when water becomes available, whereas the other responses reflect more permanent changes or damage to the photosynthetic apparatus. Photosynthesis decrease due to stomatal closure during the 2015 extreme dry season was followed 2 months later by an increase in photosynthesis as rains returned, indicating a margin of resilience to one‐off extreme climatic events in Amazonian forests.     

Chlorophyll a fluorescence: can it shed light on fundamental questions in photosynthetic carbon dioxide fixation?

Abstract A close, immediate and precise relationship between chlorophyll a fluorescence and photosynthetic carbon assimilation in vivo is demonstrated. The examples discussed include kinetics displayed during dark to light transitions plus oscillations and transients observed during changes in the gas phase surrounding the leaf. Remaining uncertainties surrounding the relationship between chlorophyll fluorescence and photosynthesis are attributed to the underlying complexity of the regulatory mechanisms involved. Examples are also given that show how multiple simultaneous measurements of different aspects of the photosynthetic process may contribute to the resolution of these uncertainties. The practical relevance of these matters is also discussed, particularly in relation to the limitations of the photosynthetic process and to the use of chlorophyll fluorescence as a diagnostic probe of chemical and genetic manipulation and stress.     

Complex regulation of gene expression, photosynthesis and sugar levels by pathogen infection in tomato

The infection of plants with pathogens results in the induction of defence reactions as well as changes in carbohydrate metabolism. On the one hand, the pathogen attempts to manipulate the carbohydrate metabolism of the plant for its own advantage. On the other, the plant has to reorganize carbon fluxes to ensure fight against the pathogen. In order to further investigate the connection between pathogen infection and carbohydrate metabolism, the effects of two types of pathogen, biotrophic and necrotrophic, on gene expression, endogenous sugar levels and photosynthesis of tomato plants were analysed. Photosynthetic gene expression was downregulated on infection with Pseudomonas syringae and Botrytis cinerea . In contrast, expression of a sink-specific gene encoding a cell wall invertase and of defence genes was induced by both pathogens. These results provide evidence for a co-regulation of defence, sink and photosynthetic gene expression in planta in response to both types of pathogen. The brassinosteroid-containing plant restorative ComCat enhanced resistance against B. cinerea and counter-regulated the repression of photosynthetic gene expression. Endogenous sugar levels decreased and the hexose to sucrose ratio increased on treatment with B. cinerea . The application of chlorophyll fluorescence imaging revealed the spatio-temporal heterogeneity of the pathogen response. At 24 h after infection, inhibition of photosynthetic electron transport was restricted to the direct vicinity of the infection site, which was surrounded by a circle of increased photosynthetic activity. The photosynthesis of the remaining leaf was not affected at this stage. These results show the usefulness of chlorophyll fluorescence imaging for the assessment of the complex spatio-temporal changes and for the definition of the areas relevant for other types of determination, e.g. gene expression.     

Gas Exchange and Emission of Chlorophyll Fluorescence during the Monocycle of Rust, Angular Leaf Spot and Anthracnose on Bean Leaves as a Function of their Trophic Characteristics

Measurements related to gas exchange and chlorophyll fluorescence emission were taken from healthy and diseased bean leaves with rust, angular leaf spot, and anthracnose during lesion development for each disease. The experiments were performed at different temperatures of plant incubation, and using two bean cultivars. The main effect of temperature of plant incubation was in disease development. There was no significant difference between cultivars in relation to disease development and in magnitude of physiological alterations when disease severity was the same for each cultivar. These diseases reduced the net photosynthetic rate and increased the dark respiration of infected leaves after the appearance of visible symptoms and the differences between healthy and diseased leaves increased with disease development. The transpiration rate and stomatal conductance were stable during the monocycle of rust, however, these two variables decreased in leaves with angular leaf spot and anthracnose beginning with symptom appearance and continuing until lesion development was complete. Carboxylation resistance was probably the main factor related to reduction of photosynthetic rate of the apparently healthy area of leaves with rust and angular leaf spot. Reduction of the intercellular concentration of CO₂, due to higher stomatal resistance, was probably the main factor for leaves with anthracnose. Chlorophyll fluorescence assessments suggested that there was no change in electron transport capacity and generation of ATP and NADPH in apparently healthy areas of diseased leaves, but decreases in chlorophyll fluorescence emission occurred on visibly lesioned areas for all diseases. Minimal fluorescence was remarkably reduced in leaves with angular leaf spot. Maximal fluorescence and optimal quantum yield of photosystem II of leaves were reduced for all three diseases. Bean rust, caused by a biotrophic pathogen, induced less damage to the regulation mechanisms of the physiological processes of the remaining green area of diseased leaves than did bean angular leaf spot or anthracnose, caused by hemibiotrophic pathogens. The magnitude of photosynthesis reduction can be related to the host–pathogen trophic relationships.     

高温对仁用杏光合特性及PSⅡ光化学活性的影响

为探讨高温胁迫下仁用杏叶片的光合适应机制,以科尔沁沙地生长的4年生'超仁'仁用杏为试材,设置环境温度为25℃、30℃、40℃和50℃处理,利用气体交换技术和快速叶绿素荧光诱导动力学曲线分析技术(JIP-test),研究了仁用杏叶片光合特性和PSⅡ光化学活性.结果表明:在一定温度范围内,随着温度升高,仁用杏通过提高光合色素含量和比例来维持光能的吸收、传递和转换能力,从而保证光合机构正常运转;当高温超过叶片自身生理调节限度后,叶绿素发生分解、净光合速率(Pn)明显下降、胞间CO2浓度(Ci)上升,说明光合作用的下降是由叶肉因素造成的.温度40℃导致单位面积有活性反应中心数量(RC/CSo)显著下降;而50℃高温下荧光诱导曲线中K点(Wk)和J点(Vj)明显增加,高温对仁用杏叶片放氧复合体(OEC)、受体侧和PsⅡ反应中心造成了伤害.此外,50℃高温还导致初始荧光(Fo)显著升高,为对照的2.26倍,PSⅡ最大光化学效率(Fv/Fm)和光化学性能指数(PI/ABS)分别下降为对照的37.9%和10.3%.高温损害了PSⅡ供体侧和受体侧的功能,造成光合效率下降,这是高温胁迫对仁用杏叶片光合机构伤害的主要机制之一.     

Little strokes fell great oaks: minor but chronic herbivory substantially reduces birch growth

Modern concepts of plant tolerance to herbivory are primarily based on studies of short‐term severe damage, whereas the effects of minor chronic damage to long‐lived woody plants, corresponding to background herbivory (2–15% annual loss of foliar biomass in boreal and temperate forests), remain poorly understood. In our experiment, the annual removal of 2, 4, 8 and 16% of the leaf area from naturally growing mountain birch Betula pubescens subsp. czerepanovii saplings during a seven‐year period resulted in a pronounced reduction of plant vertical growth (–30, –34, –45 and –78%, respectively). Leaf size decreased first (already after one year of the 16% treatment), resulting in the reduction of the total leaf area. This effect was followed by a considerable decrease in the length of long shoots in all treatments. Leaf number on the plant was maintained for a longer time, being reduced by the end of the experiment in 16% treatment only; no changes in specific leaf area or chlorophyll fluorescence were observed in either of the treatments. This pattern may indicate that the plant reallocates resources from the growth of the woody parts to the maintenance of the photosynthetic area, and can be seen as a strategy of tolerance to minor herbivory, whereas compensatory responses typical of severe herbivory (increased photosynthesis rates and shoot regrowth) have not been detected. The predicted 2–5% increase in background herbivory due to climate warming can potentially produce previously unrecognised negative impacts on tree growth. We conclude that in the long term, background herbivory is likely to impose stronger effects on the growth of woody plants than short‐term devastating outbreaks of defoliators, thus contributing more to the development of plant evolutionary adaptations to herbivory than severe but episodic bouts of damage.     

Kinetic imaging of chlorophyll fluorescence using modulated light

Fluorometers that measure the kinetics of chlorophyll fluorescence have become invaluable tools for determining the photosynthetic performance of plants. Many of these instruments use high frequency modulated light to measure the rate, efficiency and regulation of photosynthesis. The technique is non-invasive and is effective under diverse environmental conditions. Recently, imaging fluorometers have been introduced that reveal variability in photosynthesis over the surface of a leaf or between individual plants. Most imaging instruments depend on continuous light or low frequency modulated light for fluorescence excitation, which imposes serious limitations on measurements of the fluorescence parameters, especially the minimum fluorescence (F₀) and variable fluorescence (F_V). Here, we describe a new instrument that combines the advantage of high frequency modulated light with two-dimensional imaging of chlorophyll fluorescence. The fluorometer produces dynamic images of chlorophyll fluorescence from leaves or plants, providing accurate mapping of F₀ and F_V, and non-photochemical quenching. A significant feature of the instrument is that it can record fluorescence images of leaves in daylight under field conditions. This revised version was published online in June 2006 with corrections to the Cover Date.     

Elevated CO2 interacts with herbivory to alter chlorophyll fluorescence and leaf temperature in Betula papyrifera and Populus tremuloides

Herbivory can influence ecosystem productivity, but recent evidence suggests that damage by herbivores modulates potential productivity specific to damage type. Because productivity is linked to photosynthesis at the leaf level, which in turn is influenced by atmospheric CO(2) concentrations, we investigated how different herbivore damage types alter component processes of photosynthesis under ambient and elevated atmospheric CO(2). We examined spatial patterns in chlorophyll fluorescence and the temperature of leaves damaged by leaf-chewing, gall-forming, and leaf-folding insects in aspen trees as well as by leaf-chewing insects in birch trees under ambient and elevated CO(2) at the aspen free-air CO(2) enrichment (FACE) site in Wisconsin. Both defoliation and gall damage suppressed the operating efficiency of photosystem II (ΦPSII) in remaining leaf tissue, and the distance that damage propagated into visibly undamaged tissue was marginally attenuated under elevated CO(2). Elevated CO(2) increased leaf temperatures, which reduced the cooling effect of gall formation and freshly chewed leaf tissue. These results provide mechanistic insight into how different damage types influence the remaining, visibly undamaged leaf tissue, and suggest that elevated CO(2) may reduce the effects of herbivory on the primary photochemistry controlling photosynthesis.