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UV Effects on Pigments and Assimilation of 15 N‐Ammonium and 15 N‐Nitrate by Natural Marine Phytoplankton of the North Sea
Author(s) -
Döhler G.,
Hagmeier E.
Publication year - 1997
Publication title -
botanica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.871
H-Index - 87
eISSN - 1438-8677
pISSN - 0932-8629
DOI - 10.1111/j.1438-8677.1997.tb00666.x
Subject(s) - nitrogen , nitrate , phytoplankton , ammonium , irradiation , environmental chemistry , fucoxanthin , pigment , chemistry , chlorophyll a , nuclear chemistry , photochemistry , nutrient , biochemistry , organic chemistry , physics , nuclear physics
Effects of ambient solar UV radiation in the field and of artifical UV irradiation under controlled laboratory conditions were studied with natural phytoplankton populations from Helgoland, German Bight, North Sea. The pattern of pigments varied after UV‐A or UV‐B plus a low dose of UV‐A radiation: UV‐A usually induced a stimulation of pigment biosynthesis; whereas UV‐B plus UV‐A led to a reduction of the contents of chlorophyll a, diadinoxanthin, fucoxanthin, peridinin and an unknown carotenoid; content of diatoxanthin was significantly enhanced. The damaging effect on nitrogen assimilation by UV was more pronounced after artificial UV‐B plus UV‐A irradiance compared to the influence of ambient solar UV under field conditions. The uptake of inorganic nitrogen was dependent on the dose and exposure time of UV radiation as well as on the species composition. The uptake of 15 N‐nitrate by natural phytoplankton collected in spring was more sensitive to UV irradiation than the assimilation of 15 N‐ammonium. UV‐A radiation with a small part of shorter wavelengths at 315 nm (Philips‐lamps in conjunction with the cut‐off filter WG 320) caused a reduction of up to 12% whereas a stimulation of the 15 NH 4 + uptake was observed after exposure to UV‐A without any UV‐B (Philips lamps TL 60W/09N). Pattern of 15 N‐incorporation into free amino acids and pool sizes varied in dependence on the applied nitrogen compound and on the irradiation conditions. The impact of UV radiation on the pattern of 15 N‐Iabelled free amino acids and the pool sizes was different. 15 N enrichment into all the tested amino acids was reduced after 5 h UV‐B plus UV‐A exposure and after application of 15 NH 4 + . A depression of the glutamate and glutamine pools was observed after addition of 15 N‐nitrate alone. Pools of all main amino acids from phytoplankton in summer 1993/94 were inhibited by UV irradiance. Results are discussed with reference to the UV target (e.g. enzymes, pigments) and the adaptation to the environmental conditions.