Sulfur dioxide plant growth

Sulfur has four unique characteristics related to its occurrence and chemistry in soil. As sulfate, it is one of the principle counterions that keep the soil electrically neutral. Soil receives constant additions of sulfur through volcanic activity around the world and industrial pollution, usually in the form of acid rain. This means that soils usually have sufficient sulfur for plant growth. Lastly, plants can take and use sulfur dioxide from the air as a source of sulfur for growth [22,38],... 

Another area where improved air quaUty has impacted on sulfur use is ia agriculture. As sulfur dioxide emissions have decreased, sulfur content of soils has also decreased. Sulfur, recognized as the fourth most important plant nutrient, is necessary for the most efficient use of other nutrients and optimum plant growth. Because many soils are becoming sulfur-deficient, a demand for sulfur-containing fertilizers has been created. Farmers must therefore apply a nutrient that previously was freely available through atmospheric deposition and low grade fertilizers. 

Plant nutrient sulfur has been growing in importance worldwide as food production trends increase while overall incidental sulfur inputs diminish. Increasing crop production, reduced sulfur dioxide emissions, and shifts in fertilizer sources have led to a global increase of crop nutritional sulfur deficiencies. Despite the vital role of sulfur in crop nutrition, most of the growth in world fertilizer consumption has been in sulfiir-free nitrogen and phosphoms fertilizers (see Fertilizers). 

Economic Aspects. U.S. capacity for production of merchant sodium dithionite (soHds basis) was estimated at 93,000 metric tons in 1994. There are three North American producers of sodium dithionite. Hoechst Celanese is the largest producer (68,000 tons capacity) with two formate production locations and one zinc process location. Olin (25,000 t capacity) produces solution product only at two locations using both the amalgam and electrochemical processes. In 1994, Vulcan started a small solution plant in Wisconsin using the Olin electrochemical process. In addition, it is estimated that 13,000 t/yr is produced at U.S. pulp mills using the Borol process from sulfur dioxide and sodium borohydride. Growth is estimated at 2—3%/yr. The... 

D. Weber (personal communication) reported reductions in plant growth and nematode populations firom mixtures of ozone and sulfur dioxide, but these changes were similar to those caused by ozone alone. 

TABLE 11-18 Growth Response of Selected Plants to Sulfur Dioxide and Ozone Mixtures"... 

Adedipe, N. O., R. E. Barrett, and D. P. Ormrod. Phytotoxkity and growth responses of ornamental bedding plants to ozone and sulfur dioxide. J. Amer. Soc. Hort. Sci. 97 341-345, 1972. 

Tingey, D. T., and R. A. Reinert. The effect of ozone and sulfur dioxide singly and in combination on plant growth. Environ. Pollut. 9 117-126, 1975. 

Ting, D. T., R. A. Reinert, C. Wickliff, and W. W. Heck. Chronic ozone or sulfur dioxide exposures or both, affect the early vegetative growth of soybeans. Can. J. Plant Sci. 53 875-879, 1973. 

Beneficial and Harmful Effects. At low levels, sulfur dioxide in the atmosphere is not harmful to crops, but damage can occur at excessive levels (305—309). Crops differ gready in their sensitivity. Forest damage attributed to acid rain is often cited but the observed symptoms seem to have multiple causes and the contribution of sulfur acids is unspecified. The sulfur in precipitation is, up to a point, beneficial to plant growth because sulfur is an essential nutrient. Lessening the sulfur content of the atmosphere requires that supplementary sulfur be provided in fertilizer to some crops some crops already require supplementary sulfur. Sulfur dioxide itself has been found useful in drip irrigation systems (310,311) and in calcareous soils (308). Small field generators have been developed for this purpose. 

A possible function of this intracellular sulfur cycle is to buffer, i.e. to homeostatically regulate, the cysteine concentration of the cells. Irrespective of whether sulfate, cysteine, or sulfur dioxide is available as sulfur source, the intracellular sulfur cycle would allow a plant cell to use as much of these compounds as necessary for growth and development. At the same time, it would give a plant cell the possibility to maintain the cysteine pool at an appropriate concentration by emitting excess sulfur into the atmosphere. Thus, emission of hydrogen sulfide may take place when the influx of sulfur in the form of sulfate, cysteine, or sulfur dioxide exceeds the conversion of these sulfur sources into protein, glutathione, methionine, and other sulfur-containing components of the cell. 

These data and those of others (1, 5, 6, 26, 27) indicate a change in growth rate and/or a reduction in leaf area after prolonged exposure to sulfur dioxide. These effects indicate possible alterations in the normal physiological functioning of the plant, and therefore probably have both a visible (ultrastructure) and biochemical basis. 

Costonis et al. (33) were unable to demonstrate a positive correlation between ambient sulfur dioxide levels and inorganic sulfur ion accumulation in the needles of pines which are injured by relatively low levels of sulfur dioxide in the air. White pines growing in air polluted with more than 0.25 ppm of sulfur dioxide are often stunted, and a direct correlation can be obtained between plant growth and ambient S02 levels (34). However, tissue analysis does not reveal a measurable rise in sulfur level as inorganic sulfate ions. It is posible that the excess sulfur is incorporated into cell protein, but the data conflict (28, 35). For these reasons, it is not possible to follow sulfur accumulation in plants chronically exposed to low levels of ambient S02 without resorting to labeled S02. 

However, this does not preclude following the effects on plant growth of chronic exposure to low levels of sulfur dioxide. Injury is manifested in altered growth rates, reduction in plant size, and alteration in reproductive capacity, all of which are visible only if the plants can be compared with others of the same variety growing under nonpolluted condi-... 

Fligh concentrations of air pollutants are known to kill many annual plants and trees. This amounts to a coarse biological indicator. Less severe exposures can cause premature senescence (early leaf drop) of sensitive species of trees and shrubs [39], which can be used as an indicator [40]. For example, the aspen poplar, Populus tremuloides, drops its leaves after exposure to as little as 0.34 ppm of sulfur dioxide for 1 hr. Early leaf drop slows tree growth, which can be qualitatively assessed by examining the growth ring widths from the tree cores. Several leaf drops in quick succession can kill trees or annual plants. 

The insertion reaction of sulfur dioxide is of interest since it could lead to metal sulfinates which possess potential catalytic, bacterial, and plant growth regulator activities This reaction is known for iron, gallium, and indium porphyrins ... 

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