Lance S. Evans

Biological effects of acidity in precipitation on vegetation: A review☆

Abstract Acidic precipitation, wet or frozen deposition with a hydrogen ion concentration greater than 2.5 μeq/1 is a significant air pollution problem in the United States and Canada. The chief anions accounting for the hydrogen ions in rainfall are nitrate and sulfate. Although visible injury to foliage has been documented in a variety of greenhouse studies, no experimental evidence demonstrates loss of field crop value or reduction in plant productivity due to visible foliar injury. Acidic precipitation can contribute nutrients to vegetation and could also influence leaching rates of nutrients from vegetation. Although these processes occur, there are no data that show changes in nutrient levels in foliage that relate to crop or natural ecosystem productivity. Experimental results show that fertilization of ferns is inhibited by present levels of acidic precipitation in the north-eastern United States. However, the overall impacts of inhibited fertilization on perpetuation of the species or ecosystem productivity have not been evaluated. Simulated acidic precipitation has been shown to affect plant pathogens in greenhouse and field experiments. Simulated acidic precipitation inhibited pathogen activities under some circumstances and promoted pathogen activities under other circumtances. No general conclusions can be drawn about the effects of current levels of precipitation acidity on plant pathogen-host interactions under field conditions. Few experiments have been aimed at determining the impacts of acidic precipitation on crop and forest yields. Most of these studies are inadequate because they are not conducted in nature with adequate randomization of treatments coupled with vigorous statistical analyses. From the above information, it must be concluded that research on the effects of acidity in precipitation on terrestrial vegetation is too meager to draw definitive conclusions about the effects of ambient and/or anticipated levels of acidity.

Botanical aspects of Acidic precipitation

Acidic precipitation can be characterized as wet or frozen atmospheric deposition with a hydrogen ion concentration greater than 2.5 μeq liter-1. Acidic precipitation is perceived as a significant air pollution problem derived chiefly from combustion of fossil fuels, smelting of sulfide metals, and other industrial processes. Precipitation data from the northeastern United States show a mean pH of between 4.0 and 4.2 with a range of from 3.0 to 6.0 among individual events. Although visible injury to plant foliage has been documented in a variety of studies only one case of visible foliar injury from the acidity in ambient rainfalls has been documented. Acidic precipitation can contribute nutrients to vegetation and could also influence nutrient leaching rates from vegetation. Although these processes occur, there are no data that show changes in nutrient levels in foliage that relate to crop or natural ecosystem productivity. Although no consistent patterns are presently known, acidic precipitation may affect host-plant pathogen interactions. Few experiments with field-grown crops or vegetation under natural conditions have been performed. Many of the studies are inadequate because they have been conducted with inadequate replication of treatments coupled with vigorous statistical analyses. Studies with field-grown crops are evaluated. Acidification of fresh waters of the northeastern United States is caused by acid deposition. Such regions in which this acidification occurs have in common, volume weighted mean H+ concentrations of 25μeq liter-1 or higher and slow weathering of granitic or Precambrian bedrock with thin soils deficient in minerals that provide buffering capacity. As freshwater acidification occurs, many plants, invertebrates, and vertebrates are progressively eliminated. Generally, fisheries are severely impacted when lake pH falls below 5.0. Fish are almost always eliminated when the lake pH is below 4.8.ResuméLa précipitation atmosphérique acide a comme caractéristique que la concentration d’ions hydrogène dans son contenu liquide ou solide est de plus de 2,5 μeq litre-1 précipitation acide contribue en grande mesure aux problèmes de la pollution de l’air. Elle provient principalement de la combustion de carburants, de la fonte de sulfures et d’autres procédés industriels. Dans le nord-est des Etats-Unis, d’après les données, le pH moyen varie entre 4,0 et 4,2. Dans des cas séparés il va de 3,0 à 6,0. Dans plusieurs études ont a déterminé que des dommages visibles se font au feuillage, mais ce n’est que dans un seul cas que la documentation est suffisante pour attribuer les dommages visibles à l’acidité de la pluie de cette région. La précipitation acide peut fournir des éléments nutritifs à la végétation et pourrait aussi influencer le taux de filtrage des éléments nutritifs de la végétation. Bien que nous sachions que ces processus ont lieu, il n’y a pas de données, se rapportant à la productivité de la culture agricole ou celle du système écologique naturel, qui nous montrent des changements dans le niveau nutritif des feuilles. La précipitation acide peut avoir de l’influence sur l’interaction pathogène des plantes affectées, mais, jusqu’à présent, on n’en a pas trouvé de manifestations uniformes. Peu d’expériences scientifiques sur la végétation ont été faites dans les champs où dans son habitat. Plusieurs études sont inadéquates: elles ont été faites sans reproduire adéquatement les traitements et sans analyses statistiques solides. Suit une évaluation d’études faites sur des cultures dans les champs. L’acidification des eaux douces dans le nord-est des Etats-Unis est causée par des dépôts acides. Les régions affectées ont toutes une concentration poids/volume moyenne de H+ de 25 μeq litre-1 ou davantage. Là où la couche du sol est mince et ne contient pas de minéraux qui puissent servir de tampon, la désagrégation lente des roches de fond granitiques ou précambiennes suit. L’acidification des eaux douces produit la disparition de beaucoup de plantes et d’animaux invertébrés et vertébrés. La pêche est sévèrement atteinte quand le pH des lacs tombe sous 5,0. Il ne reste plus de poisson quand le pH descend sous 4,8.

Chemical Characterization of a Hormone That Promotes Cell Arrest in G2 in Complex Tissues

A G2|factor in the cotyledons of Pisum sativum, which arrests the growth of cells in both roots and shoots in the G2 stage of the cell cycle, has been isolated and identified as trigonelline (N-methylnicotinic acid). To our knowledge, trigonelline is the first hormone that effects cell arrest in complex tissues of plants and animals to be chemically identified.

Effect of nutrient medium pH on symbiotic nitrogen fixation byRhizobium leguminosarum andPisum sativum

SummaryExperiments were performed to measure the pH-sensitive steps in nodulation and symbiotic fixation byPisum sativum and isolate RP-212-1 ofRhizobium leguminosarum. An aeroponic system with rigorous pH control was used to obtain numerous effective nodules. After exposure to various pH levels, the following responses were measured: (1) legume root growth and development, (2) survival and growth rate of a single effective bacterial isolate, (3) degree of nodulation, (4) rate of nitrogen fixation, (5) plant biomass, and (6) nitrogen content of plants. Both bacterial growth and root development were adequate at all pH levels from 4.4 to 6.6, but efficient nodulation and nitrogen fixation did not occur at pH 4.8 and below. The processes required for symbiosis were about 10 times as sensitive to acidity as either bacterial growth or root growth alone. Nodulation was the most acid-sensitive step.

Cell arrest in G2 in root meristems: A control factor from the cotyledons

Abstract A substance promoting cell cycle arrest in G 2 in the root meristem is demonstrated. This substance is produced in the cotyledons and is transported to the root.

Relationships between cellular injury, visible injury of leaves, and ozone exposure levels for several dicotyledonous plant species at Great Smoky Mountains National Park

Abstract Ozone is a ubiquitous air pollutant in the troposphere that can significantly affect terrestrial vegetation. Great Smoky Mountains National Park (GRSM), in eastern Tennessee and in western North Carolina, is experiencing ozone concentrations that may be sufficient to injure vegetation. The purpose of this research was to determine (1) if the percentages of dead palisade parenchyma cells were correlated with the percentages of leaf area that exhibited stippling (necrosis) and (2) if percentages of dead palisade parenchyma cells were correlated with cumulative ozone exposure for leaves of native plants in field chamber ozone exposures at GRSM. Such relationships between cells and leaf injuries with cumulative ozone exposure level may eventually provide an understanding of the leaf anatomical parameters that confer sensitivity of foliage to ozone insult. Using linear regression models, percentages of dead palisade parenchyma cells were correlated positively with percentages of leaf areas with visible injuries for Sassafras albidum, Rudbeckia laciniata , and Rubus canadenis for two growing seasons. For each of the three species there were positive relationships with r 2 values between 0.52 and 0.90 with probability values below 0.001 in all cases. No statistically significant relationships for these parameters occurred for Aster divaricatus, Magnolia tripetela, Liquidamber styraciflua, Rhus copallina , and Platanus occidentalis . The lack of relationships for these five species between percentage of dead cells and percentage of leaf area with visible leaf injury was attributed to large percentages of palisade cell death with only small amounts of visible leaf injuries during fumigation. In addition to the above relationships, percentages of dead palisade parenchyma cells were positively correlated by linear regression with cumulative ozone exposure for S. albidum ( r 2 =0.83) and R. canadensis ( r 2 =0.64). Both had probability values below 0.001. The results are discussed with regard to the factors that may confer such levels of sensitivity which need to be tested quantitatively. To our knowledge this is the first report to demonstrate statistically significant quantitative relationships among percentage of dead palisade parenchyma cells, percentage of leaf area with visible injuries, and cumulative ozone exposure of foliage of broad-leaved plant species.

Perturbations of upper leaf surface structures by simulated acid rain

Abstract Lesions on leaves of Phaseolus vulgaris and Helianthus annuus subjected to simulated sulfate acid rain were initially localized near trichomes and stomata on adaxial leaf surfaces. Scanning electron micrographs showed that 75% of all lesions began at the bases of spiked and glandular trichomes while 20% originated at or near stomata. Very few (5%) lesions began in areas unassociated with these structures. These results may eventually help explain differential responses of plant taxa to acid rain.

Growth, development and yield responses of pinto beans and soybeans to hydrogen ion concentrations of simulated acidic rain

Abstract Greenhouse experiments were performed to determine changes in seed yield of soybeans (Glycine max L.) and pinto beans (Phaseolus vulgaris L.), exposed to simulated rain of 2, 398, 794, 1259, 1995 and 3162 μeq 1−1 H+ (pH 5.7, 3.1, 2.9, 2.7 and 2.5, respectively). Simulated acidic rain of 794 μeq l−1 H+ (pH 3.1) and above decreased the dry mass of seeds, leaves, and stems of pinto beans compared with plants exposed to rain of 2 μeq 1−1 H+. On a percentage mass basis the decrease in seed yield was comparable to reductions in biomass of leaves and stems. The decrease in yield of pinto beans by simulated acidic rain was attributed to a decrease in the number of seeds per pod. In soybeans, simulated acidic rain of 794 and 3162 μeq l−1 H+ (pH 3.1 and 2.5, respectively) decreased the dry mass of both stems and leaves. However an increase in seed yield occurred when plants were exposed to rain of 794 μeq l−1 H+ (pH 3.1) which resulted from ȧ larger dry mass per seed. In general, simulated acidic rain decreased leaf enlargement of the first-produced leaves of pinto beans but had no effect on enlargement of leaves produced later in development. In soybeans, a decrease in leaf enlargement occurred in leaves produced later in development than in the first-produced leaves. Rain acidity response functions were established between the responses of various plant parameters and the hydrogen ion concentration of the simulated rainfalls. These rain acidity response functions are used to better understand (1) the sensitivity of various processes to simulated acidic rain and (2) how the differences in sensitivity of these various processes affect plant productivity.

Relationship between trigonelline concentration and promotion of cell arrest in G2 in cultured roots of Pisum sativum

Abstract Trigonelline, G2 Factor, present in cotyledons of Pisum sativum is transported to roots and shoots after germination. This hormone promotes prefere

Acidic precipitation: Considerations for an air quality standard

Acidic precipitation, wet or frozen precipitation with a H+ concentration greater than 2.5 μeq l−1, is a significant air pollution problem in the United States. The chief anions accounting for the H+ in rainfall are nitrate and sulfate. Agricultural systems may derive greater net nutritional benefits from increasing inputs of acidic rain than do forest systems when soils alone are considered. Agricultural soils may benefit because of the high N and S requirements of agricultural plants. Detrimental effects to forest soils may result if atmospheric H+ inputs significantly add to or exceed H+ production by soils. Acidification of fresh waters of southern Scandinavia, southwestern Scotland, southeastern Canada, and northeastern United States is caused by acid deposition. Areas of these regions in which this acidification occurs have in common, highly acidic precipitation with volume weighted mean annual H+ concentrations of 25 μeq l−1 or higher and slow weathering of granitic or precambrian bedrock with thin soils deficient in minerals which would provide buffer capacity. Biological effects of acidification of fresh waters are detectable below pH 6.0. As lake and stream pH levels decrease below pH 6.0, many species of plants, invertebrates, and vertebrates are progressively eliminated. Generally, fisheries are severely impacted below pH 5.0 and are completely destroyed below pH 4.8. At the present time studies documenting effects of acidic precipitation on terrestrial vegetation are insufficient to establish an air quality standard. It must be demonstrated that current levels of precipitation acidity alone significantly injure terrestrial vegetation. For aquatic ecosystems, current research indicates that establishing a maximum permissible value for the volume weighted annual H+ concentration of precipitation at 25 μeq l−1 may protect the most sensitive areas from permanent lake acidification. Such a standard would probably protect other systems as well.