Ozone stimulates protonematal growth and gametophore production in Polytrichum commune

In order to assess the effects of O-3 an the early growth and developmental phases of the gametophyte of Polytrichcum commune Hedw., young protonemata were grown far Jive weeks under the following concentrations of ozone (O-3 ): 11 (ambient-control), 50, 100, and 150 ppb. Protonematal growth was ass essed weekly by measuring total area of the colony and gametophore (bud) pr oduction was estimated as area of the colony occupied by young gametophores . No O-3 effect on protonematal growth or gametophore production was detect ed until the final two wet ks of treatments. Calculated slopes of protonema tal and gametophore growth, based on log-transformed data, were significant ly affected by exposure to O-3. Protonematal colonies exposed to 50, 100, a nd 150 ppb O-3 had slopes that were 114, 100, and 90%, respectively of the ambient O-3 treated colonies. Gametophore production of colonies exposed to 50, 100, and 150 ppb O-3 had slopes that were 189, 173, and 125%, respecti vely of those colonies exposed to ambient air. After 35 days of treatment, final protonematal growth at 50 ppb was nearly double (193%) that of ambien t and gametophore area was nearly tripled (276%) that of ambient. At 100 pp h, O-3 protonematal growth was 127% and gametophore area was 202% of the co ntrol. At 150 ppb O-3 protonematal and gametophore growth were 76% and 91% respectively of the control. We suggest that O-3 may interfere with the hor monal controls of the early gametophytic development of P. commune resultin g in the stimulation of both protonematal growth and gametophore production . If these growth and developmental increases of P. commune, induced at 50 ppb under laboratory conditions are also occurring in nature, then P. commu ne, a common and abundant bryophyte, may be out-competing other species ass ociates at current ambient oxidant levels. However, if O-3 levels were to i ncrease as currently predicted the growth and competitiveness of P, commune could be impaired.