Effects of simulated acid rain on nitrogenase activity (acetylene reduction) in the lichen Stereocaulon paschale (L.) Hoffm., with special reference to nutritional aspects

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Abstract
The effects of SAR (simulated add rain using H2 SO4 and HNO3 singly and combined) on ARA (acetylene reduction activity), and concentrations of N, K4 , Mg2+ and Ca2- was investigated in Sterecaulon paschale (L.) Hoffm. ARA was significantly decreased after 4 months of SAR at pH 3.0. One year after spraying treatments had ceased, lichens treated at pH 3.0. showed no clear signs of recovery of ARA. After 5 y of acidification. ARA in lichens sprayed with combined H2 SO4 and HNO3 at pH 2.9. was comparable to that observed after 4 months of pH 3.0.enhanced rain, i.e. close to zero. SAR at pH 4.0. had no marked effect on nitrogenase activity after 4 months' exposure, but ARA was significantly decreased after 5 y-of pH 4.1. (H2 SO4 ) treatment. There were no clear relationships between the inhibitory effects of acid additions and alterations in nutritional status in the lichen caused by SAR. Furthermore, no correlation between thallus N concentration and nitrogenase activity was observed.