The influence of acid rain and drought on early growth and development of jack pine and balsam poplar

The influence of "acid rain" (watering with tap water acidified to pH 3.0 ) and drought on jack pine seedlings and balsam poplar cuttings growing in two different soil types was studied in a short-term greenhouse experiment. Changes in soil chemistry were assessed and a number of growth parameters and physiological processes measured. Irrigation with "acid rain" led to rapid soil acidification. It resulted in decreased soil pH, cation exchange capacity and base saturation, and altered concentrations of the basic exchangeable ions; the level of Al’” increased, while the levels of Ca*', Mg”and K’ decreased. There was a slight decrease in total soil organic matter and a slight increase in soil nitrogen. Drought generally enhanced the adverse effects of the soil acidification process. “Acid rain" had a beneficial effect on seedling and cutting growth and development. Height and diameter growth, development of root surface area, production of aboveground and belowground biomass were stimulated by "rain" with pH 3.0. Seedlings and cuttings watered with "acid rain" also had lower water saturation deficit, lower diffusive resistance and higher transpiration rates. Changes in leaf chlorophyll fluorescence indicated slight stimulation of photosynthesis. Drought reduced seedling and cutting growth and development, but "rain" with pH 3.0 significantly reduced these adverse effects. Both tree species responded in a similar way to the stress factors. Plants performed better in the lighter soil because of better growth conditions. For early tree growth and development, "acid rain" was not directly harmful even when combined with drought