The effect of air pollutants on physiological processes in plants

Abstract. Important physiological processes, photosynthesis, respiration, carbon allocation and stomatal function are known to be affected by air pollutants. A wide range in sensitivity of photosynthesis both within and between species is evident from the literature for the pollutants sulphur dioxide, ozone, nitrogen oxide and hydrogen fluoride. Some of this variation is clearly due to genetic factors, but much is in response to differences in environmental conditions both prior to and during fumigation. Exposure of plants to mixtures of pollutants generally reduced the threshold at which effects were first detected and increased the level of inhibitory responses. In the majority of studies on stomatal responses to air pollutants, opening occurs at low concentrations, below the threshold for effects on photosynthesis, and closure occurs at injurious concentrations; this latter response often following the inhibition of photosynthesis. Effects on carbon allocation have been reported in response to air pollutants. Changes usually favour leaf development over root growth, which can compensate for a decline in net assimilation rate up to a certain point but may limit water uptake from soils with low moisture content. Future research into physiological effects of air pollutants should incorporate an integrated approach in which both key physiological parameters and growth parameters are measured together with estimates of the effective dose of pollutant. In this way, the underlying mechanisms to changes in growth and development will be more fully understood.     

Dynamics of plant responses to combinations of air pollutants

The focus of this review is on how plants respond to combinations of multiple air pollutants. Global pollution trends, plant physiological responses and ecological perspectives in natural and agricultural systems are all discussed. In particular, we highlight the importance of studying sequential or simultaneous exposure of plants to pollutants, rather than exposure to individual pollutants in isolation, and explore how these responses may interfere with the way plants interact with their biotic community. Air pollutants can alter the normal physiology and metabolic functioning of plants. Here we describe how the phenotypic and molecular changes in response to multiple pollutants can differ compared to those elicited by single pollutants, and how different responses have been observed between plants in the field and in controlled laboratory conditions and between trees and crop plants. From an ecological perspective, we discuss how air pollution can result in greater susceptibility to biotic stressors and in direct or indirect effects on interactions with organisms that occupy higher trophic levels. Finally, we provide an overview of the potential uses of plants to mitigate air pollution, exploring the feasibility for pollution removal via the processes of bio‐accumulation and phytoremediation. We conclude by proposing some new directions for future research in the field.     

Resource allocation by plants under air pollution stress: Implications for plant-pest-pathogen interactions

Plant growth depends on the coordinated acquisition and allocation of carbon, water, and nutrient resources to the major plant organs (root, stem, leaf, flower, and fruit) and to the major classes of metabolic function (vegetative growth, maintenance, defense, and reproduction). Air pollutants like SO₂, NO₂, and O₃ can directly damage plant tissues and disrupt normal patterns of resource acquisition and allocation. These disruptions in turn potentially will influence the plant’s ability to defend itself against pests and pathogens. This review summarizes the quantitative and qualitative changes that have been observed when plants are exposed to low levels of SO₂, NO₂, and O₃; the following generalizations emerge:

1. Root biomass is reduced more than shoot biomass in plants exposed to SO₂ or O₃, but NO₂ does not appear to induce the differential suppression of above-versus below-ground organs.
2. Quantitative allocation to leaves increases and to stem decreases under SO₂ pollution regimes; too few data are available to generalize about O₃ or NO₂ effects on leaf: stem ratio.
3. Root carbohydrate concentrations sometimes increase and sometimes decrease after SO₂ or O₃ fumigations. Leaf nitrogen concentrations tend to decrease after exposure to air pollutants, and leaf carbohydrate concentrations can increase or decrease. Too few data on leaf concentrations of lipids and secondary chemicals are available to justify any generalizations on pollutant responses.
4. Reproduction is suppressed by O₃, SO₂, and NO₂, with O₃ appearing to have the most marked effects. Seed lipid and protein composition can be altered by exposure to pollutants. While both quantitative and qualitative changes in plant resource allocation after exposure to pollutants are common, the importance of these diverse changes for plant-pest and plant-pathogen interaction requires more comprehensive study. Ideally, the time course of plant growth and of metabolite pools critical to particular pests or pathogens should be followed in plants exposed to realistic pollutant regimes and related to pest or pathogen performance on the treated plants.

     

城市化对植物生长发育的影响

 本文研究了北京市首钢工业区和樱桃沟游览区生态条件的变化及城市化对植物生长发育的影响。两个功能区的气温、相对湿度、降雨量以及雨水、飘尘、植物中的污染物质含量都有很大差异。工业区大多数植物的开花期、结果期比游览区早,而营养结束期延晚;有些植物甚至不能开花、结果;有些虽能正常开花,但花的数量少,结的果实也小等;游览区九种乔木、灌木的叶面积和四种常绿乔木的枝条年生长量都比工业区大0.5—1倍。     

Assessing the Capacity of Plant Species to Accumulate Particulate Matter in Beijing,China

Air pollution causes serious problems in spring in northern China; therefore, studying the ability of different plants to accumulate particulate matter (PM) at the beginning of the growing season may benefit urban planners in their attempts to control air pollution. This study evaluated deposits of PM on the leaves and in the wax layer of 35 species (11 shrubs, 24 trees) in Beijing, China. Differences in the accumulation of PM were observed between species. Cephalotaxus sinensis, Euonymus japonicus, Broussonetia papyriferar, Koelreuteria paniculata and Quercus variabilis were all efficient in capturing small particles. The plants exhibiting high amounts of total PM accumulation (on leaf surfaces and/or in the wax layer), also showed comparatively high levels of PM accumulation across all particle sizes. A comparison of shrubs and trees did not reveal obvious differences in their ability to accumulate particles based on growth form; a combination of plantings with different growth forms can efficiently reduce airborne PM concentrations near the ground. To test the relationships between leaf traits and PM accumulation, leaf samples of selected species were observed using a scanning electron microscope. Growth forms with greater amounts of pubescence and increased roughness supported PM accumulation; the adaxial leaf surfaces collected more particles than the abaxial surfaces. The results of this study may inform the selection of species for urban green areas where the goal is to capture air pollutants and mitigate the adverse effects of air pollution on human health.     

臭氧和气溶胶复合污染对杨树叶片光合作用的影响

由于经济的快速发展, 中国大部分地区正面临着严峻的复合型大气污染, 其中臭氧和气溶胶是两种主要污染物。已有的研究表明臭氧对叶片的氧化性伤害能够抑制光合作用, 而气溶胶可通过增加散射辐射比例或缓解高温抑制促进光合作用。但复合污染下, 臭氧和气溶胶如何共同调控叶片光合作用, 仍缺乏研究。该研究利用北京及周边地区之间的污染梯度, 选择加杨(Populus × canadensis)作为实验对象, 于2012-2013年生长季期间对叶片光合速率进行连续观测, 并同时监测臭氧浓度(AOT40)、气溶胶光学厚度(AOD)、空气温度和冠层内外光合有效辐射(PAR)等环境因子, 以期探讨大气复合污染下臭氧和气溶胶变化对植物叶片光合作用的影响及相关机制。结果表明: (1)臭氧浓度与空气温度、气溶胶浓度之间均呈显著正相关关系, 但气溶胶浓度与空气温度没有显著相关关系; (2)臭氧浓度增加显著抑制了阳生叶片的光合作用, 但气溶胶浓度上升促进了阳生叶片的光合作用; 臭氧浓度升高对阴生叶片光合作用的影响较小, 但气溶胶浓度上升促进了阴生叶片的光合作用; (3)标准化后的结果显示, 臭氧对阳生叶片光合作用的影响最大, 此时气溶胶的促进作用一定程度上补偿了臭氧浓度上升所带来的抑制效应。对于阴生叶片光合作用而言, 气溶胶则是最重要的影响因素。该研究发现复合污染下阴生叶和阳生叶光合响应不同, 这表明冠层结构可能通过影响阴生叶和阳生叶的比例, 从而对植物生长产生不同影响。该研究对理解大气复合污染如何影响光合作用提供了的机理支持, 同时也表明, 为了维持生态系统生产力及功能, 需要同时控制气溶胶和臭氧污染。     

Effects of elevated atmospheric CO(2) and temperature on leaf optical properties in Acer saccharum

Elevated partial pressures of atmospheric carbon dioxide, similar to numerous causes of plant stress, may alter leaf pigmentation and structure and thus would be expected to alter leaf optical properties. Hypotheses that elevated CO(2) pressure and air temperature would alter leaf optical properties were tested for sugar maple (Acer saccharum) in the middle of its fourth growing season under treatment. The saplings had been growing since 1994 in open-top chambers and partial shade at Oak Ridge, Tennessee under the following treatments: (1) ambient CO(2) pressure and air temperature (control); (2) CO(2) pressure approximately 30 Pa above ambient; (3) air temperatures 3 degrees C above ambient; and (4) elevated CO(2) and air temperature. Under elevated CO(2) or temperature, spectral reflectance, transmittance and absorptance in the visible spectrum (400-720 nm) tended to change in patterns that generally are associated with chlorosis, with maximum differences from the control near 700 nm. However, these changes were not significant at P=0.05. Although reflectance, transmittance and absorptance at 700 nm correlated strongly with leaf chlorophyll concentration, variability in chlorophyll concentration was greater within than among treatments. The lack of treatment effects on pigmentation explained the non-significant change in optical properties in the visible spectrum. Optical properties in the near-infrared (721-850 nm) were similarly unresponsive to treatment with the exception of an increased absorptance throughout the 739-850 nm range in leaves that developed under elevated air temperature alone. This response might have resulted from effects of air temperature on leaf internal structure.     

Effects of ozone and aerosol pollution on photosynthesis of poplar leaves

由于经济的快速发展, 中国大部分地区正面临着严峻的复合型大气污染, 其中臭氧和气溶胶是两种主要污染物。已有的研究表明臭氧对叶片的氧化性伤害能够抑制光合作用, 而气溶胶可通过增加散射辐射比例或缓解高温抑制促进光合作用。但复合污染下, 臭氧和气溶胶如何共同调控叶片光合作用, 仍缺乏研究。该研究利用北京及周边地区之间的污染梯度, 选择加杨(Populus × canadensis)作为实验对象, 于2012-2013年生长季期间对叶片光合速率进行连续观测, 并同时监测臭氧浓度(AOT40)、气溶胶光学厚度(AOD)、空气温度和冠层内外光合有效辐射(PAR)等环境因子, 以期探讨大气复合污染下臭氧和气溶胶变化对植物叶片光合作用的影响及相关机制。结果表明: (1)臭氧浓度与空气温度、气溶胶浓度之间均呈显著正相关关系, 但气溶胶浓度与空气温度没有显著相关关系; (2)臭氧浓度增加显著抑制了阳生叶片的光合作用, 但气溶胶浓度上升促进了阳生叶片的光合作用; 臭氧浓度升高对阴生叶片光合作用的影响较小, 但气溶胶浓度上升促进了阴生叶片的光合作用; (3)标准化后的结果显示, 臭氧对阳生叶片光合作用的影响最大, 此时气溶胶的促进作用一定程度上补偿了臭氧浓度上升所带来的抑制效应。对于阴生叶片光合作用而言, 气溶胶则是最重要的影响因素。该研究发现复合污染下阴生叶和阳生叶光合响应不同, 这表明冠层结构可能通过影响阴生叶和阳生叶的比例, 从而对植物生长产生不同影响。该研究对理解大气复合污染如何影响光合作用提供了的机理支持, 同时也表明, 为了维持生态系统生产力及功能, 需要同时控制气溶胶和臭氧污染。     

Increased leaf mesophyll porosity following transient retinoblastoma‐related protein silencing is revealed by microcomputed tomography imaging and leads to a system‐level physiological response to the altered cell division pattern

The causal relationship between cell division and growth in plants is complex. Although altered expression of cell‐cycle genes frequently leads to altered organ growth, there are many examples where manipulation of the division machinery leads to a limited outcome at the level of organ form, despite changes in constituent cell size. One possibility, which has been under‐explored, is that altered division patterns resulting from manipulation of cell‐cycle gene expression alter the physiology of the organ, and that this has an effect on growth. We performed a series of experiments on retinoblastoma‐related protein (RBR), a well characterized regulator of the cell cycle, to investigate the outcome of altered cell division on leaf physiology. Our approach involved combination of high‐resolution microCT imaging and physiological analysis with a transient gene induction system, providing a powerful approach for the study of developmental physiology. Our investigation identifies a new role for RBR in mesophyll differentiation that affects tissue porosity and the distribution of air space within the leaf. The data demonstrate the importance of RBR in early leaf development and the extent to which physiology adapts to modified cellular architecture resulting from altered cell‐cycle gene expression.     

Plant-insect herbivore interactions in elevated CO(2) environments

The increasing concentration of CO(2) in the atmosphere is expected to lead to global changes in the physical environment of terrestrial organisms. We are beginning to understand how these changes are transmitted into pervasive effects on the interactions between plants and their leaf-feeding insect herbivores. An elevated CO(2) atmosphere often stimulates plant carbon assimilation and growth and alters carbon allocation patterns. This, in turn, determines the quality of plants as resources for herbivorous insects. These 'quality' factors include: the concentrations of water, nitrogen and allelochemicals in host-plant leaves, and the toughness and starch and fiber content of leaf tissue. Because these parameters change in plants grown in enriched CO(2) environments, the doubled CO(2) levels anticipated for the next century will alter the dynamics of plant-insect herbivore interactions because herbivore consumption, growth and fitness are affected by the typically lower quality of plants grown under these conditions.     

Effects of Air Pollutants on the Composition of Stable Carbon Isotopes, deltaC, of Leaves and Wood, and on Leaf Injury

Air pollutants are known to cause visible leaf injury as well as impairment of photosynthetic CO₂ fixation. Here we evaluate whether the effects on photosynthesis are large enough to cause changes in the relative composition of stable carbon isotopes, δ¹³C, of plant tissue samples, and, if so, how the changes relate to visual leaf injury. For that purpose, several woody and herbaceous plant species were exposed to SO₂ + O₃ and SO₂ + O₃ + NO₂ for one month (8 hours per day, 5 days per week). At the end of the fumigations, the plants were evaluated for visual leaf lesions, and δ¹³C of leaf tissue was determined. Woody plants generally showed less visual leaf injury and smaller effects on δ¹³C of pollutant exposure than did herbaceous plants. If δ¹³C was affected by pollutants, it became, with few exceptions, less negative. The data from the fumigation experiments were consistent with δ¹³C analyses of whole wood of annual growth rings from two conifer tree species, Pseudotsuga menziesii and Pinus strobus. These trees had been exposed until 1977 to exhaust gases from a gas plant at Lacq, France. Wood of both conifer species formed in the polluted air of 1972 to 1976 had less negative δ¹³C values than had wood formed in the much cleaner air in 1982 to 1986. No similar, time-dependent differences in δ¹³C of wood were observed in trees which had been continuously growing in clean air. Our δ¹³C data from both relatively short-term artificial exposures and long-term natural exposure are consistent with greater stomatal limitation of photosynthesis in polluted air than in clean air.     

Latitudinal patterns in the phenological responses of leaf colouring and leaf fall to climate change in Japan

Aim  To estimate the potential effect of global climate change on the phenological responses of plants it is necessary to estimate spatial variations at larger scales. However, previous studies have not estimated latitudinal patterns in the phenological response directly. We hypothesized that the phenological response of plants varies with latitude, and estimated the phenological response to long-term climate change using autumn phenological events that have been delayed by recent climate change.
Location  Japan.
Methods  We used a 53-year data set to document the latitudinal patterns in the climate responses of the timing of autumn leaf colouring and fall for two tree species over a wide range of latitudes in Japan (31 to 44° N). We calculated single regression slopes for leaf phenological timing and air temperature across Japan and tested their latitudinal patterns using regression models. The effects of latitude, time and their interaction on the responses of the phenological timings were also estimated using generalized linear mixed models.
Results  Our results showed that single regression slopes of leaf phenological timing and air temperature in autumn were positive at most stations. Higher temperatures can delay the timing of leaf phenology. Negative relationships were found between the phenological response of leaves to temperature and latitude. Single regression slopes of the phenological responses at lower latitudes were larger than those at higher latitudes.
Main conclusions  We found negative relationships between leaf phenological responsiveness and latitude. These findings will be important for predicting phenological timing with global climate change.     

Exposure of cottonwood plants to ozone alters subsequent leaf decomposition

Summary Cottonwood saplings were exposed to ozone or charcoal-filtered air in a closed chamber. After leaf abscission, decomposition of individual leaf discs was measured in containers of stream water. Exposure of plants to 200 ppb ozone for 5 h caused early leaf abscission and changes in the chemical composition of leaves at time of abscission. Early-abscised leaves from O₃-exposed plants had higher nitrogen, but decomposed more slowly than leaves from control plants. Leaves from O₃-exposed plants that abscised at the normal time had lower nitrogen content and lower specific leaf mass than control leaves, but decomposed at the same rate as leaves from control plants. The results imply that O₃ exposure can alter fundamental processes important to the functioning of detritus-based aquatic ecosystems.     

THE ROLE OF PHYLLOTACTIC PATTERN AS A “DEVELOPMENTAL CONSTRAINT” ON THE INTERCEPTION OF LIGHT BY LEAF SURFACES

Computer simulations of model plants are used to assess the influence of leaf shape, size, and pattern of arrangement (= phyllotaxy) on the direct solar radiation intercepted by leaf surfaces. Changes in phyllotaxy significantly influence light interception (and, by inference, net assimilation rate) for rosette growth habits. However, changes in leaf shape and orientation and in stem length can compensate for the negative effects of leaf overlap produced by phyllotactic patterns. Phyllotaxy is viewed as a developmental limiting factor in photobiology that may necessitate compensatory changes in other morphological features not directly controlled by patterns of leaf initiation. This distinguishes it from functioning as a “developmental constraint” sensu stricto and may provide a paradigm for other features in plant evolution.     

Temperature and precipitation controls over leaf‐ and ecosystem‐level CO2 flux along a woody plant encroachment gradient

Conversion of grasslands to woodlands may alter the sensitivity of CO₂ exchange of individual plants and entire ecosystems to air temperature and precipitation. We combined leaf‐level gas exchange and ecosystem‐level eddy covariance measurements to quantify the effects of plant temperature sensitivity and ecosystem temperature responses within a grassland and mesquite woodland across seasonal precipitation periods. In so doing, we were able to estimate the role of moisture availability on ecosystem temperature sensitivity under large‐scale vegetative shifts. Optimum temperatures (T_opt) for net photosynthetic assimilation (A) and net ecosystem productivity (NEP) were estimated from a function fitted to A and NEP plotted against air temperature. The convexities of these temperature responses were quantified by the range of temperatures over which a leaf or an ecosystem assimilated 50% of maximum NEP (Ω₅₀). Under dry pre‐ and postmonsoon conditions, leaf‐level Ω₅₀ in C₃ shrubs were two‐to‐three times that of C₄ grasses, but under moist monsoon conditions, leaf‐level Ω₅₀ was similar between growth forms. At the ecosystems‐scale, grassland NEP was more sensitive to precipitation, as evidenced by a 104% increase in maximum NEP at monsoon onset, compared to a 57% increase in the woodland. Also, woodland NEP was greater across all temperatures experienced by both ecosystems in all seasons. By maintaining physiological function across a wider temperature range during water‐limited periods, woody plants assimilated larger amounts of carbon. This higher carbon‐assimilation capacity may have significant implications for ecosystem responses to projected climate change scenarios of higher temperatures and more variable precipitation, particularly as semiarid regions experience conversions from C₄ grasses to C₃ shrubs. As regional carbon models, CLM 4.0, are now able to incorporate functional type and photosynthetic pathway differences, this work highlights the need for a better integration of the interactive effects of growth form/functional type and photosynthetic pathway on water resource acquisition and temperature sensitivity.     

Municipal sludge-induced phytotoxicity

Municipal sludge (MS), containing various types of environmental pollutants, can exert phytotoxic effects in plants. Seed germination, chlorophyll content, plant weight, root and shoot growth, and metal levels, were measured as endpoints to assess the phytotoxic effects of leachates of MS from Lucknow city in three plants, Triticum aestivum, Brassica campestris and Phaseolus aureus. Among the five metals analysed, lead was found to be present at the highest concentration, and chromium at the lowest. Aqueous MS leachates had lower amounts of metals than pure MS. Seed germination was inhibited significantly in all three plants. The greatest inhibition of root and shoot growth was observed in B. campestris and T. aestivum. Total chlorophyll was depleted in all three plants, but the maximum depletion was observed in T.aestivum exposed to 10% leachate. Symptoms such as necrosis, leaf discoloration and root curling were also observed after exposure to 10% leachate, and plant weight was reduced significantly. It is evident that MS from Lucknow city exerted phytotoxic effects on all three test plant species.     

Grazing alters warming effects on leaf photosynthesis and respiration in Gentiana straminea,an alpine forb species

Aims Vast grasslands on the Tibetan Plateau are almost all under livestock grazing. It is unclear, however, what is the role that the grazing will play in carbon cycle of the grassland under future climate warming. We found in our previous study that experimental warming can shift the optimum temperature of saturated photosynthetic rate into higher temperature in alpine plants. In this study, we proposed and tested the hypothesis that livestock grazing would alter the warming effect on photosynthetic and respiration through changing physical environments of grassland plants.Methods Experimental warming was carried by using an infrared heating system to increase the air temperature by 1.2 and 1.7°C during the day and night, respectively. The warming and ambient temperature treatments were crossed over to the two grazing treatments, grazing and un-grazed treatments, respectively. To assess the effects of grazing and warming, we examined photosynthesis, dark respiration, maximum rates of the photosynthetic electron transport (J max), RuBP carboxylation (V cmax) and temperature sensitivity of respiration Q 10 in Gentiana straminea, an alpine species widely distributed on the Tibetan grassland. Leaf morphological and chemical properties were also examined to understand the physiological responses.Important findings 1) Light-saturated photosynthetic rate (A max) of G. straminea showed similar temperature optimum at around 16°C in plants from all experimental conditions. Experimental warming increased A max at all measuring temperatures from 10 to 25°C, but the positive effect of the warming occurred only in plants grown under the un-grazed conditions. Under the same measuring temperature, A max was significantly higher in plants from the grazed than the un-grazed condition. 2) There was significant crossing effect of warming and grazing on the temperature sensitivity (Q 10) of leaf dark respiration. Under the un-grazed condition, plants from the warming treatment showed lower respiration rate but similar Q 10 in comparison with plants from the ambient temperature treatment. However, under the grazed condition Q 10 was significantly lower in plants from the warming than the ambient treatment. 3) The results indicate that livestock grazing can alter the warming effects on leaf photosynthesis and temperature sensitivity of leaf dark respiration through changing physical environment of the grassland plants. The study suggests for the first time that grazing effects should be taken into account in predicting global warming effects on photosynthesis and respiration of plants in those grasslands with livestock grazing.     

RELATIVE GROWTH RATES OF VINES AND SHRUBS OF WESTERN POISON OAK,TOXICODENDRON DIVERSILOBUM (ANACARDIACEAE)

Because of the different mechanical constraints on vines and self-supporting plants, vines are thought to differ from trees and shrubs in a variety of their growth characteristics. I tested the hypotheses that vines grow faster than shrubs and that supported shoots have delayed leaf expansion relative to stem elongation, using western poison oak, Toxicodendron diversilobum (T. & G.) Greene, a plant that grows as a vine when externally supported but otherwise as a shrub. In the field, supported shoots (vines) had significantly higher aboveground biomass and relative growth rates than did their paired unsupported shoots (shrubs) growing nearby. This was not due to differences in leaf phenology, but may have resulted from vines growing into more favorable habitats for growth. In contrast, whereas 2-yr-old cloned plants in a common garden differed in their stem and internode lengths, they had the same aboveground dry weight, proportion of dry weight that was leaf, and relative rate of increase in primary stem length whether grown with stakes (vines) or without stakes (shrubs). These results suggest that there is no inherent requirement of vines to grow faster than shrubs. As hypothesized, leaf elongation was more delayed relative to stem elongation in staked than unstaked individuals in 19 paired plants (each pair cloned from a different source plant). Thus, physical cues resulting from the presence of support can alter the plant's spatial and temporal patterns of development, but do not necessarily dictate the quantity of biomass that will be produced.     

Influence of nitrogen on the production of hypericins by St. John’s wort

The effect of nitrogen supply on the production of ‘hypericins’ (hypericin and pseudohypericin) in leaves of St. John’s wort (Hypericum perforatum L.) was examined with plants grown in sand culture and soil. In sand culture, 56-d growth of St. John’s wort plants with decreased nitrogen levels resulted in increased production of hypericins in leaves. A short-term low nitrogen stress in sand culture also resulted in increased production of leaf hypericins. While growth in a low nitrogen-containing soil resulted in elevated levels of hypericins, their production was decreased by supplementation of the soil with additional nitrogen. Increased production of hypericins in St. John’s wort leaves did not require the nitrogen supply to be decreased to levels that resulted in nitrogen deficiency symptoms. Moreover, alteration in the production of leaf hypericins occurring with changes in nitrogen supply did not alter the concentration ratio of pseudohypericin and hypericin. Increased production of leaf hypericins was not associated with any significant changes in the number of dark glands on the leaves and only a weak correlation was observed between leaf dark gland number and levels of leaf hypericins. These results are discussed in terms of the biochemistry of naphthodianthrone production by St. John’s wort plants and implications for growth environment effects during cultivated growth of this medicinal plant.     

Diel growth patterns of young soybean (Glycine max) leaflets are synchronous throughout different positions on a plant

Leaf growth is controlled by various internal and external factors. Leaves of dicotyledonous plants show pronounced diel (24 h) growth patterns that are controlled by the circadian clock. To date, it is still uncertain whether diel leaf growth patterns remain constant throughout the development of a plant. In this study, we followed growth from the primary leaves to leaflets of the seventh trifoliate leaf of soybean (Glycine max) on the same plants with a recently developed imaging‐based method under controlled conditions and at a high temporal resolution. We found that all leaflets displayed a consistent diel growth pattern with maximum growth towards the end of the night. In some leaves, growth maxima occurred somewhat later – at dawn – as long as the leaves were still in a very early developmental stage. Yet, overall, diel growth patterns of leaves from different positions within the canopy were highly synchronous. Therefore, the diel growth pattern of any leaf at a given point in time is representative for the overall diel growth pattern of the plant leaf canopy and a deviation from the normal diel growth pattern can indicate that the plant is currently facing stress.