Responses of maternal siblings ofPinus densiflora to simulated add rain

Because most research on acid rain does not consider the genetic composition of seeds and the inherent variations in seed mass and germination date, the potentially diverse patterns of plant response are neglected within a population. Therefore, we examined the effects of both family identity and simulated acid rain onPinus densiflora seedlings over a 34-week period, beginning at germination. We were able to evaluate the importance of family and pH treatment independent of seed mass and germination date by considering the latter two variables as covariates. Seeds were collected from six randomly chosen trees that were assumed to represent different genotypes. After germination in a controlled environment, the seedlings were moved outdoors. Each was then subjected twice a week to 40 mL of simulated acid rain, at a pH of either 3.0 or 5.6. We examined variations in germination date, seedling height, needle numbers and lengths, and root and shoot masses. The maternal family effect was significant for all characters over the entire test period. Strong effects of pH treatment were detected only at the later growth stages. Artificial rain with a pH of 3.0 enhanced growth rates, particularly aboveground, compared with seedlings treated with pH 5.6 rain. However, regardless of pH, certain groups of maternal siblings consistently performed better in almost all parameters. The exception was for mean germination date, which differed among families only at a pH of 3.0. Therefore, although we demonstrated that acid rain affected both the date of germination as well as seedling growth rates inP. densiflora, the responses differed among maternal families, and were also associated with seed mass and germination date.