SHORT-TERM EFFECTS OF BISULFITE ON POLLUTION-TOLERANT AND POLLUTION SENSITIVE POPULATIONS OF SPHAGNUM-CUSPIDATUM EHRH (EX HOFFM)

Moss tissue from two distinct populations of Sphagnum cuspidatum from N. Wales ('unpolluted') and the S. Pennines ('polluted') was exposed to 0.2 mM HSO3- over a 24-26 h period. The rates of HSO4- disapperance in the bathing solution were monitored in conjunction with tissue dark respiration, net photosynthetic rate and chlorophyll a fluorescence induction kinetics. Slow disappearance of HSO3- in the presence of moss tissue from N. Wales (40 % of initial concentration remaining after 24 h) resulted in a rapid (< 2 h) loss of photosynthetic oxygen evolution, and a gradual marked decline in tissue dark respiration and chlorophyll fluorescence quenching. In the S. Pennine tissue, rapid HSO3- disappearance in the growth medium (complete after < 4 h) resulted in a marked recovery of photosynthetic and respiratory pathways after the initial inhibitory effects of HSO3- on these processes. Pretreating S. Pennine moss tissue with EDTA prior to exposure increased HSO3- residence time with consequent rapid decline in net photosynthetic rate, rendering the response of the moss similar to that from N. Wales ('unpolluted' site). In a second experiment, identical moss samples from the two study sites were exposed to 0.2 mM HSO3- for a period of 24 d. One set of plants from each population was prewashed in 5 mM EDTA to remove extracellularly-bound cations prior to HSO3- exposure. Growth decrease was greater in the unpretreated moss from N. Wales (74 % with respect to tissue not exposed to HSO3-) than that from the S. Pennines (45.5 %). After 10 days the pigments of the former were visibly bleached. No bleaching was observed in the latter. In the moss from N. Wales, removal of the extracellular cations with EDTA only slightly enhanced the effect of HSO3- on growth, whilst in the S. Pennine plants EDTA pretreatment resulted in a further growth reduction of 13 %. The differential response of the moss from the two sites is discussed as a function of the extracellular transition metal concentration (notably Fe) associated with the plants.