• Pollination;
  • pollen germination;
  • acid rain;
  • Oenothera parviflora


Effects of simulated acid precipitation on pollination in Oenothera parviflora L. from different populations were examined both in vitro and in vivo. The responses of pollen to acidity (pH 5.6 to 2.6) in standing drop cultures and the stigma receptivity of flowers under field simulations of acid rain were observed. The response of pollen in vitro indicated significant inhibitory effects of pH, and demonstrated that pH values ≤ 3.6 were inhibitory to both germination and tube growth, when compared with the treatment of pH 5.6. Dosages of LD50 for in vitro pollen germination, taken as the initial pH of cultures for the different pollens, ranged from pH 3.49 to 3.72. Stigma receptivity assessed by germination and initial tube growth on the stigmatic surface also declined significantly (P < 0.01) in response to acid rain simulation prior to hand pollinations. Again simulants ≤ pH 3.6 significantly reduced stigma receptivity compared with the treatment at pH 5.6. Here LD 50, dosages, taken as the pH of the simulant, were pH 3.45 and 4.66 for the failure of potentially viable pollen to germinate, or produce tubes three times the length of the grain, respectively. These results are discussed in relation to rain chemistry in Southern Ontario, Canada.