THE EFFECTS OF SIMULATED ACID RAIN ON THE CYANOBACTERIAL DIAZOTROPH TOLYPOTHRIX SP. (NITROGEN, FIXATION)

This study consisted of four experiments. (1) Tolypothrix was incubated in aqueous HSO(,3)('-) solutions at concentrations 0-10 ppm adjusted to pH 7.2 to 3.0 with H(,2)SO(,4). The effects on nitrogen {C(,2)H(,2)} fixation, net photosynthesis and respiration were measured. (2) Tolypothrix was grown for seven days in liquid culture adjusted to pH 6.5-4.0 with either HNO(,3) or H(,2)SO(,4). The effects on nitrogen {C(,2)H(,2)} fixation, net photosynthesis, respiration, growth rate, chlorophyll a, and phycocyanin were determined. (3) Soils were inoculated with Tolypothrix and sprayed with dilute medium adjusted to pH 6.0-2.0 with either HNO(,3) or H(,2)SO(,4). The effects on nitrogen {C(,2)H(,2)} fixation and chlorophyll a were measured. (4) Agropyron smithii seeds were planted in Tolypothrix-inoculated and noninoculated soils. Germination rates, biomass and nitrogen content of the grass were measured.;Nitrogen {C(,2)H(,2)} fixation rates declined over the 7-day incubation period at all pHs, going to zero at pH 5.0 and 4.5, as did net photosynthesis. Whereas, respiration rates remained fairly constant at pH 6.0 and increased over time at pH 5.5 and below. Tolypothrix exhibited the typical logarithmic growth curve only at pH 6.0 and pH 5.5 at pH 5.0 and pH 5.5 the optical density of the cultures remained constant during the seven-day period.;Nitrogen {C(,2)H(,2)} fixation in soil grown Tolypothrix was inhibited only at pH 2.0 where no detectable ethylene was produced. Chlorophyll a content showed a significant decrease from the other treatments only at pH 2.0.;Agropyron smithii seeds exhibited a lower germination rate in soil inoculated with Tolypothrix. The above ground biomass and nitrogen content of the grasses were similar in both Tolypothrix inoculated and noninoculated soils.;Nitrogen {C(,2)H(,2)} fixation was the most sensitive parameter to changes in pH and HSO(,3)('-) concentration. Acetylene reduction decreased from 10.0 (mu)mol C(,2)H(,4) mg Chl a('-1) hr('-1) at pH 7.2 to 0.7 (mu)mol C(,2)H(,4) mg Chl a hr('-1) at pH 4.8 and to zero at pH 4.0. Only the 10 ppm HSO(,3)('-) solution inhibited acetylene reduction, from 23 percent at pH 6.5 to 81 percent at pH 4.8 when compared to the respective controls. Net photosynthesis and respiration were less sensitive. However, there was no measureable O(,2) evolution or consumption at pH 4.0 and pH 3.0.