The effects of acid rain and ozone on biomass and leaf area parameters of shortleaf pine (Pinus echinata Mill.)

Abstract

Shortleaf pine (Pinus echinata Mill.) seedlings in 24 open-top chambers were exposed to combinations of ozone (carbon-filtered (control), ambient, 1.7 x ambient, and 2.5 x ambient) and acidic precipitation (pH 5.3, 4.3 and 3.3) for 16 months (1989 harvest) or 28 months (1990 harvest). Although the effects of acid rain were generally not significant, there was a trend toward increased aboveground biomass and leaf area in seedlings subjected to the low pH treatments. Because N concentrations in the soils generally increased with decreasing pH, we concluded that the effects of acid rain on aboveground biomass and leaf area were a consequence of an increasing concentration of soil N. In the 1989 harvest, seedlings in the 2.5 x ambient ozone treatment had significantly less biomass in all aboveground plant components and significantly less total leaf area than seedlings in the 1.7 x ambient ozone treatment. In the 1990 harvest, there were no significant effects of ozone on total aboveground biomass, although there was a trend toward reduced biomass in seedlings in the 2.5 x ambient ozone treatment. Both total leaf area and leaf biomass were significantly less in seedlings exposed to 2.5 x ambient ozone for 28 months than in both control seedlings and seedlings in the 1.7 x ambient ozone treatment. The greater, but not always significant, aboveground biomass and leaf area of seedlings in the 1.7 x ambient ozone treatment compared with control seedlings may be associated with the observed increase in soil nitrate concentration as a result of increased rates of leaf senescence and litterfall.

Some foliar characteristics of ash trees (Fraxinus excelsior) exposed to ozone episodes

“…The 8-h mean ozone exposure regime used in this experiment was severe in comparison with ambient ozone concentrations in the UK and northern Europe, In the UK, the 8-h mean ozone concentration exceeded 150 ppb only four times at any of the sites in the national monitoring network in the period 1972-1990(Fowler et aL, 1993, On the other hand, the experimental exposures never exceeded 160 ppb, and hourly means commonly exceed this figure throughout southern Europe and in parts of the USA, In general, other workers have reported that the effects on leaf area of exposure to low or moderate concentrations of ozone have been mediated by premature abscission (Byres et aL, 1992;Stow etal., 1992;Shelburne et aL, 1993) or by impaired plant growth and, therefore,, impaired leaf production (Paakkonen et al, 1993), In this study, the leaf number data indicated that there was no detectable ozone-induced premature leaf loss outside the usual leaf-fall period, and no effects of ozone exposure on whole-tree leaf area were observed. It is not surprising that we were unable to attach statistical confidence to the possible effects we report on leaf size and stomatal density, at least in 1992 and 1993, These parameters could only be affected early in the season, during leaf differentiation, when most leaves would have been exposed to few or no ozone episodes.…”

“…Sheiburne, Reardon & Paynter, 1993). Less well Ozone concentrations have increased in Europe characterized are effects of ozone exposure on leaf during the last decade by about 1-2% per year size and leaf production.…”

The Effects of Acid Mist Environment on Plant Growth: A Review

“…However, the combinations of ozone (carbon-filtered (control), ambient, 1.7 x ambient, and 2.5 x ambient) and acidic precipitation (pH 5.3, 4.3 and 3.3) for 16 months (1989 harvest) or 28 months (1990 harvest) showed trend of increased in aboveground biomass in seedlings of Shortleaf pine (Pinus echinata Mill.) and concluded that because N concentrations in the soils generally increased with decreasing pH [SHELBURNE & al. 1993].…”