Repository logo
 

Search Results

Now showing 1 - 3 of 3
  • High nitrogen and phosphorous acquisition by belowground parts of Caulerpa prolifera (Chlorophyta) contribute to the species' rapid spread in Ria Formosa lagoon, Southern Portugal
    Publication . Alexandre, Ana; Santos, Rui
    Despite worldwide proliferation of the genus Caulerpa and subsequent effects on benthic communities, little is known about the nutritional physiology of the Caulerpales. Here, we investigated the uptake rates of ammonium, nitrate, amino acids, and phosphate through the fronds and rhizoids + stolon, the internal translocation of nitrogen, and developed a nitrogen budget for the rapidly spreading Caulerpa prolifera in Ria Formosa lagoon, southern Portugal. Caulerpa prolifera acquired nutrients by both aboveground and belowground parts at similar rates, except nitrate, for which fronds showed 2-fold higher uptake rates. Ammonium was the preferential nitrogen source (81% of the total nitrogen acquisition), and amino acids, which accounted for a significant fraction of total N acquisition (19%), were taken up at faster rates than nitrate. Basipetal translocation of 15 N incorporated as ammonium was nearly 3-fold higher than acropetal translocation, whereas 15 N translocation as nitrate and amino acids was smaller but equal in either direction. The estimated total nitrogen acquisition by C. prolifera was 689 μmol · m-2 · h-1 , whereas the total nitrogen requirement for growth was 672 μmol · m-2  · h-1 . The uptake of ammonium and amino acids by belowground parts accounted for the larger fraction of the total nitrogen acquisition of C. prolifera and is sufficient to satisfy the species nitrogen requirements for growth. This may be one reason explaining the fast spreading of the seaweed in the bare sediments of Ria Formosa where it does not have any macrophyte competitors and the concentration of nutrients is high.
  • Impacto da actividade de marisqueio na floração e no esforço de reprodução sexual em Zostera noltii Hornemann na Ria Formosa
    Publication . Alexandre, Ana; Santos, Rui
    A angiospérmica marinha Zostera noltii cresce e reproduz-se sexualmente nas zonas intertidais da Ria Formosa. A época de floração ocorre entre Março e Novembro. O desenvolvimento das flores ao longo da época de floração, desde a formação da inflorescência até à produção da semente, foi observado e organizado numa escala de maturação. A razão entre o número de flores masculinas e femininas determinado para a Z. noltii foi de 1:1 (4±0.14 S.E. flores masculinas para 4±0.13 S.E. flores femininas). O impacto da actividade de marisqueio na reprodução sexual da espécie foi avaliado. Valores mais elevados de esforço reprodutivo (6.38±3.91%), bem como da densidade de rebentos reprodutores (2200 rebentos por m2), foram observados nos campos mariscados em relação aos campos de controlo (1.85±1.14% de esforço reprodutivo; 1062 rebentos por m2). Os resultados obtidos mostram que a Z. noltii aumenta o seu esforço na reprodução sexual como resposta ao distúrbio provocado pela actividade de marisqueio. No entanto, devido ao rápido crescimento clonal da Z. noltii e aos constrangimentos existentes no seu ciclo reprodutor, a recuperação dos campos mariscados na Ria Formosa é provavelmente efectuada através do desenvolvimento vegetativo da espécie.
  • Competition for nitrogen between the seaweed Caulerpa prolifera and the seagrass Cymodocea nodosa
    Publication . Alexandre, Ana; Santos, Rui
    The rhizophytic seaweed Caulerpa prolifera has been expanding rapidly in the Ria Formosa lagoon, southern Portugal, taking over deeper unvegetated areas and mixing with the native seagrass Cymodocea nodosa in shallower areas. In the Ria Formosa lagoon, belowground ammonium uptake from the sediment represents the main source of nitrogen for the 2 macrophytes, except during the ammonium pulses from the sediment to the water column that are incorporated through aboveground plant parts. We examined the competition for inorganic and organic nitrogen between C. prolifera and C. nodosa through a series of N-15-ammonium and N-15-amino acid surge uptake experiments combining single-species and mixed incubations at a range of nutrient concentrations. Our results showed that C. prolifera is generally faster than C. nodosa in the acquisition of ammonium and amino acids by both above- and belowground parts, and that the uptake rates of ammonium and amino acids of one species were not affected by the presence of the other species. The exception was the amino acid uptake through the rhizoids of C. prolifera, which was slightly enhanced in the presence of C. nodosa. In this situation, the aboveground ammonium uptake becomes the main contributor to the nitrogen budget of C. nodosa but not to that of C. prolifera. When ammonium pulses are considered, C. nodosa is more competitive for nitrogen than C. prolifera. In this case, the leaf uptake of ammonium is the largest contributor to the total nitrogen (ammonium plus amino acids) budget of the seagrass. Our results showed that the different nutritional strategies of the 2 macrophytes allow their coexistence in the Ria Formosa lagoon.