Interactive effects of macronutrients and metals (Mn, Co, Zn) on the ephemeral green alga Ulva rigida C. Agardh (Chlorophyta, Ulvophyceae, Ulvales)
Munda, Ivka M.; Veber, Marjan
Interactive effects of excess macronutrients (phosphates, nitrates) and metals (Mn, Co, Zn) which act as micronutrients, on the ephemeral green alga Ulva rigida were studied under controlled conditions "in vitro". Nitrate and phosphate were applied singly or in a dual combination together with the single metals. Three experimental series with plants belonging to spring and autumn populations were carried out. In control samples, lacking metals, spring plants exhibited a higher growth in phosphate than in nitrate-enriched media, while the opposite was found for the autumn plants. The presence of metals (Mn, Co) changed the sequence of growth responses to ambient nutrients. Modifications of growth responses were dependent on the time when the plants were collected. Results indicated that metal accumulation was dependent on the presence of nutrients in the media. It was the highest for Mn and lowest for Zn, and higher in autumn than in spring plants of Ulva rigida. In two of the experimental series a positive relationship between growth expressions and Mn accumulation was indicated. The relationship between Co or Zn accumulation and growth did not follow definite trends. The nitrogen content of the experimental plants suggested a correlation with the ambient metals, Mn promoting nitrogen uptake in nitrate enriched media, while Zn was inhibitory. Results indicated that Ulva rigida has a greater ability to accumulate phosphorus than nitrogen and that the presence of metals depressed the phosphorus uptake in phosphate enriched media. The carbon content of the plants exhibited irregular variations related to the presence of nutrients and their interactions with ambient metals. It was usually elevated in the presence of nitrate and its combinations with Mn and Co. A maximum in carbon content found simultaneously with maxima in nitrogen uptake, Mn accumulation and growth suggests that Mn plays a central role in macro-micronutrient interactions.