Agriculture and Environment最新文献

Tests were conducted on the viability and vigor of soybean seed harvested from plants grown in field chambers and treated with simulated acidic rain at two levels of photochemical oxidant. The plants (Glycine max [L.] Merr. cv ‘Beeson’ and ‘Williams’) were treated with simulated rain at pH values of 4.0, 3.4, or 2.8 in chambers supplied either with charcoal-filtered or unfiltered ambient air. At harvest, Beeson, a maturity class II cultivar, was at full maturity whereas Williams, a maturity class III cultivar, had not yet attained full maturity. There were no visual symptoms of acidic rain injury, but symptoms of oxidant injury were observed on all plants grown in unfiltered air.

In Beeson the germination of seeds was not affected by filtering the ambient air or by the acidity of simulated rain. Seeds from Williams had a lower germination rate than Beeson and were more sensitive to artificial aging stress. At each level of acidity, the proportion of seeds that germinated in Williams was greater in those obtained from plants grown in filtered air than in those from unfiltered air. Germination was greater at pH 4.0 than at pH 2.8 in both filtered and unfiltered air. In both cultivars, the average percentage of seed with green cotyledons approximated the average proportion of ungerminated seed. In Williams, the occurrence of green cotyledons was negatively correlated with viability. Therefore, coloration of the cotyledon was a good measure of seed maturity.

The results observed with Beeson agreed with previous reports that at full plant maturity, there are no measurable effects of oxidant on seed viability. However, the data obtained with Williams indicate that at earlier stages of plant growth oxidant or simulated acidic rain have a measurable effect on seed development.

Studies were conducted in a controlled environment chamber to determine the association between plant water status and ozone sensitivity. Bean plants were subjected to various water stress regimes for 4 to 10 days using a semipermeable membrane system which controlled plant water status and then exposed to ozone. Ozone sensitivity was measured using stress ethylene which was highly correlated with foliar injury. Plant water stress decreased plant sensitivity to ozone; complete protection was attained within 1 to 3 days depending on the level of water stress. When water stress was removed, the plants regained ozone sensitivity equal to nonwater stressed plants within 6 days. The decreased ozone sensitivity was associated with only a small changes in leaf water potential. The reduced sensitivity following water stress was apparently associated with a decreased leaf conductance reducing ozone uptake.

A soil-plant-atmosphere model was used to evaluate the effects on ammonia (NH₃) exchange of changing leaf NH₃ compensation concentration, atmospheric NH₃ concentration, and soil surface NH₃ flux density. An increase in NH₃ compensation concentration from 0.5 to 5.0 μg/m³ resulted in a small, constant decrease in the NH₃ uptake rates by the crop canopy under all conditions simulated. Ambient concentration and soil flux density proved to be the most critical variables in influencing net vegetative-soil NH₃ exchange. Variation in soil flux density determined whether the system evolved or consumed NH₃. Consequently, differences between systems in soil flux density may result in NH₃ transfer via the atmosphere from agricultural lands to natural lands.

A computerized open-top field chamber fumigation system is described for exposing plants to ozone and sulfur dioxide. The exposure system is capable of operating unattended for several days, maintaining and monitoring pollutant concentrations in the chambers as desired. Pollutants are dispensed to the chambers through mass flow controllers, operated by a microcomputer. Inputs to the microcomputer consist of monitored pollutant concentrations, weather and hardware function signals, feedback from mass flow controllers, and operator input via a terminal. Pollutant monitors are time-shared through solenoid valves controlled by the computer, and information is recorded by data loggers.

Exposing Bel W₃ tobacco plants for 12 h to 0.03 ppm ozone did not cause any visible injury. However, subsequent exposure to 0.08 and 0.1 ppm ozone caused the earlier appearance of leaf injury, greater number of injured leaves and a larger proportion of chlorotic leaf surface than in previously untreated plants. A quantitative injury index was defined, enabling statistical testing of the injury differences between the two plant groups, and the differences were found to be significant. These effects should be taken into consideration in assessing crop damage and loss induced by ambient air pollution.

Experiments were performed to determine the effects of simulated acidic rain on yields of garden beet and radish grown under standard agronomic practices. Plots were exposed to small additions of simulated rain with pH levels of 5.7, 4.0, 3.1, and 2.7. The spray-to-wet simulated rain applications had volumes similar to those of most ambient summer rainfalls. Some plots received no simulated rain applications. All plants were exposed to ambient rainfalls at Brookhaven National Laboratory (Upton, NY, U.S.A.) which had a mean weighted pH of 4.06 during the summer of 1980. Root mass of radishes was not significantly affected by simulated acidic rain exposures. Root yields of beets exposed to simulated rain applications at pH 5.7, 4.0, 3.1, and 2.7 were 110, 70, 84 and 86% of beets receiving ambient rainfalls only. Foliar injury observed on beets was attributed to exposure to both simulated acidic rain and ambient rainfalls with a mean weighted pH of 3.88. This is the first experiment where visible foliar injury has occurred due to both ambient rain and simulated rain applications above pH 3.1 under standard agronomic conditions.

Amounts of atmospheric sulphur compounds including the gaseous sulphur dioxide, hydrogen sulphur and methyl mercaptan, and particulate sulphate depend upon the activities of man, volcanic emissions, releases from waterlogged soils and anaerobic estuarine and marine environments 3. The gases are transferred to vegetation, soil and other surfaces by dry deposition whereas particulate pollutants are removed mainly in, or on, raindrops, snowflakes 3. i.e. wet deposition.

The balance of dry to wet deposition varies regionally, SO₂ being the predominant sulphur pollutant near emission sources, particulate sulphate and acid rain gaining in importance at greater distances. Amounts of deposited sulphur may minimise the occurrence of sulphur deficiencies when crops are cultivated intensively.

Although effects of SO₂ have been assessed in series of controlled fumigations, few observations have relevance to field conditions where concentrations fluctuate diurnally and seasonally, and where episodic extreme concentrations may be more important than protracted exposures to mean concentrations. Additionally SO₂ usually occurs in mixtures with oxides of nitrogen (NO_x), also ozone; changes in U.K. concentrations of NO_x, but not ozone, tend to parallel those of SO₂. Little is known about the effects of mixtures; there is, however, evidence showing that damage done by mixtures of SO₂ and NO_x, also SO₂ and ozone, is sometimes greater than the summation of the damage done by each constituent. Plant growth can be decreased by concentrations of pollutants which do not cause blemishes.

In parts of Scandinavia, the U.K., the U.S.A. and probably elsewhere in the industrialised world, rain is commonly acid (pH 4.5, sometimes 4.0). Where it contained biologically significant concentrations of bisulphite (HSO₃⁻) ions, vegetation (Sphagnum spp.) seems to have been damaged: in the absence of these concentrations, rain, unless it is more acid than pH 3.0, neither blemishes foliage nor decreases yields of field-grown crops including trees. The role of acid rain in areas with relatively large concentrations of mixed atmospheric pollutants has not been identified. Acid inputs are, it seems, beginning to affect some mechanisms/processes in field soils. These need to be quantified in relation to plant production. Lakes and streams (a) lacking dissolved calcium and magnesium (as happens when they are dependent upon slowly weathering granitic and porphyritic bedrocks) and (b) subject to acid rain, have become more acid in recent years with a progressive switch from carbon dioxide/bicarbonate to aluminium/strong acid buffering systems. With increasing acidity, assemblages of plankton and macrophytes change but without greatly affecting plant biomass. Similarly there is a change among species of invertebrat