Acid showers and damage to plants.

Acid showers and damage to plants

In general, scientific studies so far have indicated that acid rain does not appear to damage or reduce the yield of most agricultural crops (SN: 7/18/87, p.36). "However,' says botanist Denis T. DuBay of North Carolina State University (NCSU) in Raleigh, "there are certain crops and certain situations that are a cause for concern, and that are the subject of continuing investigation.' To get a sense of how serious the problem may be, NCSU researchers recently conducted several laboratory studies designed to evaluate acid rain effects at times when plants are likely to be most sensitive.

One group of experiments focused on acid rain's effect on reproduction in corn plants. The experiments showed that corn plants subjected to acid rain showers immediately after pollination develop fewer kernels than do plants that are showered with unpolluted rain. "The more acidic the rain,' says DuBay, who headed the project, "the fewer the kernels.' Acid rain showers before pollination have no noticeable effect on kernel formation.

"Whether that means anything for the farmer is hard to say,' says DuBay, "because it was a very artificial experiment. We don't have any idea that this will happen in the field.' In the field, pollination occurs over a period of days instead of all at once, as in the experiment. Because the effect of acid rain on kernel formation appears to depend strongly on the timing, duration and frequency of acid rain showers, the chances of seeing an effect in the field are likely to be small.

In another study, NCSU researchers identified which species among 18 agricultural crops and 11 ornamental plants appear to be sensitive to acid rain during early growth. Working with seedlings that had just produced their first set of true leaves, the scientists showered the plants with acid rain for one hour, then examined the plants two days later for leaf damage. Acid rain, if it causes damage, leaves tiny white spots where plant material has dried out and died.

Of 247 species tested, the researchers detected leaf damage among plants such as tomatoes, soybeans, snap beans, tobacco, eggplant, sunflowers and cotton. Winter wheat, corn, lettuce, alfalfa, fescue and clover were among the least sensitive. Other experiments have shown that the extent of leaf injury at this early stage seems to be a good indicator of how well the plants grow if acid rain showers continue.

The overall picture is encouraging. "We saw very little injury among most of the crops we looked at,' says DuBay. "Because we set the experiments up to get the plants at the most sensitive time, we expected to see more effects than we ended up seeing.'