In conclusion, the good news is that your plants will likely not be harmed by the smoke, especially if you give them a bath. The bad news is that the smoke is still hazardous to us humans.
Luckily, we have the plants to help us out by cleaning the air for us. Humans can find out current air quality conditions online at airnow. The Backyard Gardener. How is Smoke Affecting my Plants? Author: Trina Tobey.
Tags: smoke 1. No Comments Posted. Share Print. Recent Posts Blog Home. Archives All Archives. Tags All Tags. With continued exposure the necrotic areas increase in size, spreading inward to the midrib on broad leaves and downward on monocotyledonous leaves.
Fluoride injuries to plum foliage [ 26 ]. The fluoride enters the leaf through the stomata and is moved to the margins where it accumulates and causes tissue injury. Note, the characteristic dark band separating the healthy green and injured brown tissues of affected leaves.
Studies of susceptibility of plant species to fluorides show that apricot, barley young , blueberry, peach fruit , gladiolus, grape, plum, prune, sweet corn and tulip are most sensitive. Resistant plants include alfalfa, asparagus, bean snap , cabbage, carrot, cauliflower, celery, cucumber, eggplant, pea, pear, pepper, potato, squash, tobacco and wheat. Chlorine Cl 2. Older plants are more sensitive to chlorine than seedlings. The age of tissue has little effect on the sensitivity and older as well as young tissues are almost equally afected by chlorine pollution.
Injury symptoms: Chlorine injury symptoms can appear from 18 hours to 8 days after exposure. In most plant species, recovery from chlorine injury can occur 3 to 4 days after exposure is stopped. Chlorine injury symptoms are quite variable in different species.
Most common visible symptoms in conifers are chlorosis, tip burn and necrosis is needles. In angiosperm leaves, marginal or intraveinal necrosis, water-soaked appearance, leaf cupping and abscission are common. Hydrogen chloride HCl. The HCl injury can be caused to plants even at a distance of meter from the source.
Like fluorides, the chloride from HCl is accumulated in the leaves and translocated towards their margins and tips. Symptoms of HCl injury appear after a critical concentration is reached, usually between 24 and 72 hours after the exposure. Impact of HCl pollution decreases with increase in humidity, deficiency of Mg and excess of Ca. Mature plants are more sensitive to HCl than seedlings. Similarly, young fully expanded leaves are more sensitive than immature unexpanded leaves.
Injury symptoms: Most common visible injury symptoms in conifer needles are red or brown discolouration and tip burn. In angiosperm leaves, common symptoms are intraveinal water-soaked streaks, yellow or brown necrosis, tip necrosis, bleached areas around the necrosis and shot-holing. Tip burn, necrotic stipple and discolouration in sepals and petals are also observed.
Ammonia NH 3. Impact of ammonia on plants generally increases with humidity and decreases with drought. Effect of darkness on ammonia sensitivity is highly variable among species. Some species are more sensitive to low concentrations of ammonia than to its high concentration. Age of tissue has little effect on sensitivity and both young and old tissues are equally sensitive to ammonia. Injury symptoms: Most common visible symptoms in conifers are black discolouration, usually sharply bordered tip burn and abscission of needles.
Ammonia injury to vegetation has been observed frequently in Ontario in recent years following accidents involving the storage, transportation or application of anhydrous and aqua ammonia fertilizers.
These episodes usually release large quantities of ammonia into the atmosphere for brief periods of time and cause severe injury to vegetation in the immediate vicinity. Complete system expression on affected vegetation usually takes several days to develop, and appears as irregular, bleached, bifacial, necrotic lesions.
Grasses often show reddish, interveinal necrotic streaking or dark upper surface discolouration. Flowers, fruit and woody tissues usually are not affected, and in the case of severe injury to fruit trees, recovery through the production of new leaves can occur fig. Sensitive species include apple, barley, beans, clover, radish, raspberry and soybean. Resistant species include alfalfa, beet, carrot, corn, cucumber, eggplant, onion, peach, rhubarb and tomato.
Severe ammonia injuries to apple foliage and subsequent recovery through the production of new leaves following the fumigation [ 26 ]. Organic gases Ethylene. Ethylene injury symptoms develop in plants only in exposure to high concentrations and take several days to develop.
After exposure to the gas is stopped, level of recovery is variable in different species. Generally, younger plant parts recover but older parts do not. Injury symptoms: In injuriously high concentrations of ethylene, growth of plants is stopped. In low concentrations, growth abnormalities appear. In conifers, yellow tips in needles and abscission of branches and cones are common.
In angiosperms, common symptoms are epinasty or hyponasty, loss of bark, abscission of leaves and flowers, premature flower opening and fruit ripening. Ethylene affects the growth hormones and regulatory process that takes place in the plant and results in a number of outward manifestations of infection.
Leaves can begin to curl and die; ethylene causes the leaves of plants to curl down and fold under as they shrivel and are stuck with necrosis. On flowering plants, buds can stop opening or flowers can begin to show signs of discoloration or die and drop sooner than expected.
Even in more resistant plants like evergreen conifers, growth of the plant will be stunted, needles will be small and few pine cones will be produced. Plants such as peach trees, marigolds, blackberries and tomatoes are extremely vulnerable to damage from exposure to ethylene. Hydrogen sulphide H 2 S. Plants show wilting on exposure to this gas but the symptoms develop after about 48 hours. No injury occurs below the exposure of 40 ppm for 4 hours.
Carbon monoxide CO. Like ethylene this gas produces epinasty, chlorosis and abscission. However, concentration of over times that of ethylene is needed to produce same degree of damage.
No injury to plants occurs below exposure of ppm for 1 week. Studies show these gases are highly toxic to plants. HI and I 2 are readily absorbed and accumulated by plants producing visible injury symptoms similar to those of SO 2.
Injury occurs at exposure of 0. Common injury symptoms of bromine in angiosperms are necrosis of leaf margins, leaf tips and tendrils; brown discoloration and black spots later spreading to entire leaf.
Mercury vapors Hg. Unlike other pollutants, flowers are more sensitive to Hg than leaves. Injury symptoms usually appear within 24 hours of Hg exposure but often go on increasing up to 5 days. Common injury symptoms due to Hg-vapors pollution are abscission of oldest leaves, interveinal necrosis, chlorosis around veins, flower abscission, loss of petal colors, buds remaining closed and later becoming necrotic, blackening of stamens, pistils and peduncles. Particulate pollutants.
Different types of solid particulate materials are also important air pollutants. Each of these affects the plants in characteristic manner. Some common particulate air pollutants have been discussed below. Cement-kiln dust. In generals, plants having hairy surface of leaves trap more dust and are, therefore, damaged more than the plants with shiny leaf surface.
The cement dust forms crusts on the surface of leaves, twigs and flowers. This inhibits gaseous exchange from the surfaces of plant parts. Such crust on the leaves also inhibits light penetration and consequently reduces photosynthesis. Such crusts are especially thicker in conditions of dew, mist or light rains.
In dry conditions, dust blowing with wind is highly abrasive and damages the cuticle of leaves. Cuticle is also damaged due to alkalinity of cement dust.
Due to damaged cuticle plants become more susceptible to infection by pathogens. Lime and gypsum. Lime and gypsum deposited on the soil from the air, these change the pH of the soil and thus affect the nutrient availability to plants. Such deposition usually causes appearance of various nutrient deficiency symptoms in the plants. Lime and gypsum are less adhering as compared to cement-kiln dust. However, these are also trapped and deposited on the surface of plant parts particularly the leaves with hairy surfaces and produce injury symptoms similar to cement dust.
Lime and gypsum particles blowing with wind are also highly abrasive for cuticle. Soot deposited on the surface of leaves may be washed away by rains so its damage may be reduced. However, in bright sunlight and high temperature, the damage is increased.
Soot deposited on the surface of leaves inhibits light penetration, increased surface temperature due to absorption of heat and clogging of stomata.
The result of these is reduced gaseous exchange, reduced photosynthesis and general weakening of the plant growth. Necrotic spots also develop in many species due to soot deposition. Magnesium oxide. Deposited on the soil these compounds can soon increase the soil pH to levels injurious to plants. Deposition of these substances on the soil prevents germination of seedlings. In areas of heavy pollution, composition of the vegetation changes completely.
Severe injury to plants is observed even at a distance of meters from the source and mild injury may be observed up to meters in all the directions from the source. Impact of boron pollution is more severe on older leaves than on younger leaves. Boron is also accumulated in the leaves and produces injury symptoms quite similar to fluoride pollution.
Chlorides of sodium, potassium and calcium Injury symptoms produced by these chlorides in plants are very similar to those produced by SO 2 and fluoride pollution.
Sodium sulphate dust can cause necrosis of leaves of the plants. The damage increases in moist condition. Pesticides, insecticides and herbicides. A large variety of such chemicals are sprayed on the crops these days. These substances may drift with wind to nearby areas. Generally, these chemicals are deposited on the soil and form important soil pollutants.
However, in frosty conditions when crops and other plants damaged by early frost are quite susceptible to foliar spray of these chemicals, these may also be injurious air pollutants.
Injury symptoms vary with the plant species and the type of chemical. Generally, the symptoms are produced on foliage and are quite similar to those produced when these substances act as soil pollutants.
Many of the primary pollutants under specific environmental conditions may interact with each other and produce secondary environmental pollutants or certain complex environmental conditions that are injurious to plants. Such secondary pollutants and pollution conditions are discussed below. The common visible symptoms of exposure to PAN are chlorosis and necrosis in leaves. It also interferes with photosynthesis, respiration and absorption and synthesis of carbohydrates and proteins.
It inhibits photorespiration, NADP reduction, carbon dioxide fixation, cellulose synthesis and the enzymes associated with photosynthesis and respiration. Ozone O 3 is released into the atmosphere from the burning of fossil fuels and is one of the most harmful pollutants to plants. It can be carried for long distances and is readily absorbed as a part of the photosynthetic process. Plants exposed to large amounts of ozone can develop spots on their leaves.
These spots are irregular and often tan, brown or black. Some leaves can take on a bronze or red appearance, usually as a precursor to necrosis. Depending on the concentration of ozone in the environment, plants can show different amounts of discoloration before the leaves begin to die. Studies by the National Crop Loss Assessment Network show that ozone in the environment also has a detrimental effect on crop production. While crops such as cotton, soybeans and other dicots are more sensitive than monocot crops, all crops sampled over the decades-long studies show significant loss of productivity when exposed to ozone.
Cotton crops show significantly less yield when exposed to levels of ozone in the atmosphere. Common symptoms of ozone pollution are yellowing, flecking and blotching in leaves, premature senescence and early maturity.
It interferes with pollen formation, pollination, pollen germination and growth of pollen tubes. Increase in the level of RNA, starch, polysaccharides and number of polysomes is observed in ozone pollution. Ozone stimulates respiration, inhibits oxidative phosphorylation and changes membrane permeability. In some species, it inhibits the synthesis of glucon and cellulose and reduces the level of reducing sugars, ascorbic acid and ATP while in other species the effect is opposite to it.
The impact of ozone on plants increases with humidity and decreases with drought, darkness, low temperature, high soil salinity, deficiency of soil phosphorus and excess of soil sulphur. Throughout the growing season, particularly July and August, ozone levels vary significantly. Periods of high ozone are associated with regional southerly air flows that are carried across the lower. Localized, domestic ozone levels also contribute to the already high background levels.
Injury levels vary annually and white bean, which are particularly sensitive, are often used as an indicator of damage. Other sensitive species include cucumber, grape, green bean, lettuce, onion, potato, radish, rutabagas, spinach, sweet corn, tobacco and tomato.
Resistant species include endive, pear and apricot. Ozone injuries to soybean foliage [ 26 ]. Ozone symptoms fig. Although yield reductions are usually with visible foliar injury, crop loss can also occur without any sign of pollutant stress. Conversely, some crops can sustain visible foliar injury without any adverse effect on yield. Susceptibility to ozone injury is influenced by many environmental and plant growth factors. High relative humidity, optimum soil-nitrogen levels and water availability increase susceptibility.
Injury development on broad leaves also is influenced by the stage of maturity. The youngest leaves are resistant. With expansion, they become successively susceptible at middle and basal portions.
The leaves become resistant again at complete maturation. Ground-level ozone causes more damage to plants than all other air pollutants combined. This web page describes the ozone pollution situation, shows classical symptoms of ozone injury and shows how ozone affects yield of several major crops. Ozone enters leaves through stomata during normal gas exchange.
As a strong oxidant, ozone or secondary products resulting from oxidation by ozone such as reactive oxygen species causes several types of symptoms including chlorosis and necrosis. It is almost impossible to tell whether foliar chlorosis or necrosis in the field is caused by ozone or normal senescence.
Several additional symptom types are commonly associated with ozone exposure, however. These include flecks tiny light-tan irregular spots less than 1 mm diameter , stipples small darkly pigmented areas approximately mm diameter , bronzing, and reddening. Ozone symptoms usually occur between the veins on the upper leaf surface of older and middle-aged leaves, but may also involve both leaf surfaces bifacial for some species.
The type and severity of injury is dependent on several factors including duration and concentration of ozone exposure, weather conditions and plant genetics. One or all of these symptoms can occur on some species under some conditions, and specific symptoms on one species can differ from symptoms on another.
With continuing daily ozone exposure, classical symptoms stippling, flecking, bronzing, and reddening are gradually obscured by chlorosis and necrosis. Studies in open-top field chambers have repeatedly verified that flecking, stippling, bronzing and reddening on plant leaves are classical responses to ambient levels of ozone. Plants grown in chambers receiving air filtered with activated charcoal CF to reduce ozone concentrations do not develop symptoms that occur on plants grown in non-filtered air NF at ambient ozone concentrations.
Foliar symptoms shown on this web site mainly occurred on plants exposed to ambient concentrations of ozone either in NF chambers or in ambient air. Yield Loss Caused by Ozone. Field research to measure effects of seasonal exposure to ozone on crop yield has been in progress for more than 40 years.
Most of this research utilized open-top field chambers in which growth conditions are similar to outside conditions. At each location, numerous chambers were used to expose plants to ozone treatments spanning the range of concentrations that occur in different areas of the world. The strongest evidence for significant effects of ozone on crop yield comes from NCLAN studies [ 18 ] fig.
The results show that dicotyledonous species soybean, cotton and peanut are more sensitive to yield loss caused by ozone than monocot species sorghum, field corn and winter wheat. Particulate Matter. Particulate matter such as cement dust, magnesium-lime dust and carbon soot deposited on vegetation can inhibit the normal respiration and photosynthesis mechanisms within the leaf. Cement dust may cause chlorosis and death of leaf tissue by the combination of a thick crust and alkaline toxicity produced in wet weather.
The dust coating fig. In addition, accumulation of alkaline dusts in the soil can increase soil pH to levels adverse to crop growth. Effect of ozone on yield of crops [ 18 ]. Cement-dust coating on apple leaves and fruit.
The dust had no injurious effect on the foliage, but inhibited the action of a pre-harvest crop spray [ 26 ]. Because the crop plants are mostly annual plants they can not show the long-term effects produced by air pollutants. Therefore to monitor the effects of air pollution are recommended the trees, the changes in forest structure highlight the harmful effects of different air pollutants.
The evident decline of the health state of the forest in Europe since the beginning of the due to the negative impact of air pollution were illustrated by numerous publication from this period see litt. In the efforts to obtain objective and comparable data concerning the health of the European forests were developed a common methodology for the assessment of the forest state under the influence of air pollution. The poor health status of the forests in Central Europe concerns all the Europe.
The pictures of the forests on large area were dominated by tree with defoliated crowns and an increasing rate of the death trees fig Under the umbrella of ICP Forest Programme, were developed and implemented an European network of plots for the assessment of the parameters of the trees crowns condition known as Level I plots. In comparison with the national grids used by each country the obtained data were relevant for the evaluation of the forest health state at European level.
After were put in function the Level II monitoring plots used for the intensive monitoring and collection of comparable data related to the changes in forest ecosystems which are directly connected to specific environment at factors such as atmosphere pollution and acid deposition.
Such data can help in a better understanding at the relation causes and effects in the forests decline. General aspects of silver fir crowns affected by decline in the border of the northern Carpathians Forest District Solca. Fifteen years of monitoring forest condition and two decades of forest damage research have shown, however, that the discussion of recent forest damage must not be confined to the effects of air pollution alone. The comprehensive monitoring programme corresponds to the complex interrelations between natural and anthropogenic factors in forest ecosystems.
Infrastructure and data of the programme are thought to be relevant for other processes of international forest policies, e. The monitoring results obtained each year are summarized in annual Executive Reports. Methodology for the crown health condition assessment of forests. The state of health of forest trees can be determined by assessing the foliage loss. With a little practice, this can be accurately estimated by the foresters or other trained personnel.
The development of forest damage can be traced through repeated assessments of the same trees. Loss of needles or leaves should be assessed after sprouting in spring or early summer and before broadleaves and larch display autumn coloration, at best in July and August.
Evergreen conifers fig. Assessments should be made under good light conditions in good weather: rain and fog render assessments inaccurate. Leaf or needle loss is estimated for the entire crown. The crown is considered to reach from the peak of the tree to, the lowest strong green branch forming part of the crown as such; epicormic shoots on the stem are not considered, while those in the crown are. A forest tree can spread its crown to a greater or lesser extent depending on the room available within the stand.
Consequently, spatial conditions must be considered in crown assessment; that is, the maximum foliage that each tree could possibly produce must be taken as a basis. The photo series fig. It is therefore applicable to trees of the middle and lower strata only to a limited extent. Foliage loss may be determined by comparing the tree under consideration with the corresponding photo series. The appearance of the crown is matched with one of the photos and the foliage loss estimated to a degree of 5 percent accuracy.
Assessments should be made with field-glasses from a distance of at least one tree-length. Field-glasses permit precise identification of bare branches and twigs and discoloration. In subsequent surveys it is important that the tree always be observed from the same side; this should either be marked on the tree itself or noted in terms of compass direction.
Leaf or needle loss due to known causes, e. The draft long-term strategy of WGE specifies the following long-term aims to which all ICP are expected to contribute:.
The present status, long-term trends and dynamics, and the degree and geographical extent of the impact of air pollution, particularly, but not exclusively, its long range trans-boundary impact.
Derivation of exposure-response functions for chemical and biological effects of air pollutants including investigation of nutrient nitrogen, acidifying compounds and ozone effects on ecosystem functions and on biodiversity, including combinations with other stresses e. Further development of models and mapping procedures, particularly for effects of nitrogen and ozone on the environment and for the description of dynamic processes of damage and recovery acidification, eutrophication, heavy metal accumulation by including to a larger extent biological effects;.
Objective 1: A periodic overview on the spatial and temporal variation of forest condition in relation to anthropogenic and natural stress factors in particular air pollution by means of European-wide and national large-scale representative monitoring on a systematic network. Objective 2: A better understanding of the cause-effect relationships between the condition of forest ecosystems and anthropogenic as well as natural stress factors in particular air pollution by means of intensive monitoring on a number of selected permanent observation plots spread over Europe and to study the development of important forest ecosystems in Europe.
These objectives imply in accordance with the long-term priorities of WGE contributions to calculations of critical loads and levels and the assessment of their exceedances. They imply also dynamic modeling of the response of forest ecosystems to deposition scenarios expected for the future.
Additional insight is gained by compiling available studies from the National Focal Centers NFCs and from related programmes inside and outside of Convention on Long-range Trans-boundary Air Pollution. Monitoring activities. In order to meet its data generation and reporting obligations, ICP Forests employs data collection at two levels. Large-scale monitoring Level I provides a periodic overview of the spatial and temporal variation in a range of attributes related to forest condition.
Level I plots, national forest inventory NFI plots, and other related inventory plots may be combined when appropriate, feasible and necessary, according to defined and agreed procedures. Intensive monitoring Level II is carried out on plots installed in important forest ecosystems. These plots are dedicated to in-depth investigation of the interactive effects of anthropogenic and natural stress factors on the condition of forest ecosystems.
Quality assurance and control. All monitoring activities are harmonized by ICP Forests among the participating countries and are laid down in this Manual. This ensures a standard approach for data collection and evaluation and can form the nucleus for a future common European forest monitoring programme. A consistent quality assurance approach is applied within the programme covering the set up of methods, data collection, submission and investigation as well as reporting.
Quality assurance and control is supervised by the Programme Coordinating Group through its Quality Assurance Committee. A set of Expert Panels cares for data quality assurance within the specific surveys and for the further development of monitoring methods and standards.
This includes field checks, inter-calibration courses, laboratory ring tests, and data validation. Data evaluation and reporting. A range of monitoring variables is required to meet the information requirements of Convention on Long-range Trans-boundary Air Pollution and other international institutions. The Programme Coordinating Group and the Expert Panels are responsible for a data evaluation and reporting approach which takes the medium term work-plan of Working Group on Effects of Atmospheric Pollution into account.
International and national data from other programmes and institutions should be included in combined analysis. The main topics for data analysis are:.
Trends in deposition and their interactive effects on the adaptation and vulnerability of forest ecosystems are evaluated. This includes spatial and temporal changes and cause-effect relationships with special emphasis on critical loads and their exceedances.
Dynamic models and transfer functions derived from suitably selected intensive monitoring plots are used to investigate the effects of climatic factors and greenhouse gases on forest ecosystems and applied to the large scale monitoring plots.
These models are validated against measured data collected at the plots. Furthermore, data gathered at the plots are used in an integrated manner to investigate the carbon sequestration potential of forests, ozone fluxes to forests and contribute to assess status and trends of forest biodiversity at the pan-European level.
This facilitates an understanding of the effects of deposition on the role and functioning of forest ecosystems in protecting soils and water. Furthermore the programme surveys can contribute to the understanding and forecast of climate change effects on forests and can be used to supply information on the sequestration of carbon and are going to provide information on forest biodiversity as an integral part of forest ecosystems. ICP Forests aims to provide periodic overviews on the spatial and temporal variation of forest condition in relation to man-made and natural stress factors particularly air pollution ; to contribute to a better understanding of the cause-effect relationships between the condition of forest ecosystems and man-made and natural stress factors particularly air pollution ; and to study the development of important forest ecosystems in Europe.
More specifically, to support harmonized forest monitoring by linking existing and new monitoring mechanisms at the national, regional and EU level tab. Surveys and number of plots for Level II monitoring. Conclusions after 25 years of forest monitoring at European level. The system combines an inventory approach with intensive monitoring. It provides reliable and representative data on forest ecosystem health and vitality and helps to detect responses of forest ecosystems to the changing environment.
The data collected so far provide a major input for several international programmes and initiatives, such as the Convention on Long-range Trans-boundary Air Pollution and the Ministerial Conference for the Protection of Forests in Europe. Forest surveys and defoliation classes for all tree species in European countries Results of national surveys as submitted by National Focal Centres after www. In the early s, a dramatic deterioration in forest condition was observed in Europe and this initiated the implementation of forest condition monitoring under Convention on Long-range Trans-boundary Air Pollution.
Today, the monitoring results indicate that, at the large scale, forest condition has deteriorated far less severely than was feared at that time. Stress factors like insects, fungi and weather effects have been shown to affect tree health.
The drought in the Mediterranean region in the mids and the extremely warm and dry summer across large parts of Europe in led to increased levels of defoliation as a natural reaction of trees to this type of stress. The programme has also reported on acidifying deposition which is regionally correlated with defoliation and on atmospheric inputs that are accentuating other stress factors.
In the past three years there has been little change in the mean levels of defoliation for the main European tree species. However, long-term trends show more deterioration than improvement tab. The health status of forest trees in Europe is monitored over large areas by surveys of tree crown condition. Trees that are fully foliated are regarded as healthy.
The Ministerial Conference on the Protection of Forests in Europe uses defoliation as one of four indicators for forest health and vitality. In , crown condition data were submitted for plots in 30 countries. In total, trees were assessed. In , This represents no change relative to Of the main tree species, European and sessile oak had the highest levels of damaged and dead trees, at There were no significant changes in crown condition over the past ten years on two-thirds of the plots, but deterioration prevailed on the remaining third.
Trends vary between species, with European and sessile oak the most frequently damaged species. Ozone symptoms Figure 1 characteristically occur on the upper surface of affected leaves and appear as a flecking, bronzing or bleaching of the leaf tissues.
Although yield reductions are usually with visible foliar injury, crop loss can also occur without any sign of pollutant stress. Conversely, some crops can sustain visible foliar injury without any adverse effect on yield. Susceptibility to ozone injury is influenced by many environmental and plant growth factors. High relative humidity, optimum soil-nitrogen levels and water availability increase susceptibility.
Injury development on broad leaves also is influenced by the stage of maturity. The youngest leaves are resistant. With expansion, they become successively susceptible at middle and basal portions. The leaves become resistant again at complete maturation. Major sources of sulfur dioxide are coal-burning operations, especially those providing electric power and space heating. Sulfur dioxide emissions can also result from the burning of petroleum and the smelting of sulfur containing ores.
Sulfur dioxide enters the leaves mainly through the stomata microscopic openings and the resultant injury is classified as either acute or chronic.
Acute injury Figure 2 is caused by absorption of high concentrations of sulfur dioxide in a relatively short time. The symptoms appear as 2-sided bifacial lesions that usually occur between the veins and occasionally along the margins of the leaves.
The colour of the necrotic area can vary from a light tan or near white to an orange-red or brown depending on the time of year, the plant species affected and weather conditions. Recently expanded leaves usually are the most sensitive to acute sulfur dioxide injury, the very youngest and oldest being somewhat more resistant.
Figure 2. Acute sulfur dioxide injury to raspberry. Note that the injury occurs between the veins and that the tissue nearest the vein remains healthy. Chronic injury is caused by long-term absorption of sulfur dioxide at sub-lethal concentrations. The symptoms appear as a yellowing or chlorosis of the leaf, and occasionally as a bronzing on the under surface of the leaves.
Different plant species and varieties and even individuals of the same species may vary considerably in their sensitivity to sulfur dioxide. These variations occur because of the differences in geographical location, climate, stage of growth and maturation. The following crop plants are generally considered susceptible to sulfur dioxide: alfalfa, barley, buckwheat, clover, oats, pumpkin, radish, rhubarb, spinach, squash, Swiss chard and tobacco.
Resistant crop plants include asparagus, cabbage, celery, corn, onion and potato. Fluorides are discharged into the atmosphere from the combustion of coal; the production of brick, tile, enamel frit, ceramics, and glass; the manufacture of aluminium and steel; and the production of hydrofluoric acid, phosphate chemicals and fertilizers.
Fluorides absorbed by leaves are conducted towards the margins of broad leaves grapes and to the tips of monocotyledonous leaves gladiolus. Little injury takes place at the site of absorption, whereas the margins or the tips of the leaves build up injurious concentrations.
The injury Figure 3 starts as a gray or light-green water-soaked lesion, which turns tan to reddish-brown. With continued exposure the necrotic areas increase in size, spreading inward to the midrib on broad leaves and downward on monocotyledonous leaves.
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