Respiration and net photosynthesis of cotyledons during establishment and early growth of propagules of the mangrove, Avicennia marina, at three temperatures

Respiration and net photosynthesis of discs excised from cotyledons of Avicennia marina (Forssk.) Vierh. were measured at temperatures of 17, 21 and 25 °C in a Gilson Respirometer. Cotyledonary material was also analysed for TNC (total non-structural carbohydrates). Rates of respiration and net photosynthesis were significantly different at the three temperatures, with the lowest rates recorded in each case at 17 °C and the highest at 25 °C. TNC values revealed an initial decrease, followed by a small increase, and thereafter a drop to fairly constant low levels. While seedlings at 25 °C grew well, very little growth was recorded at 17 °C. Growth at the different temperatures was related to the relative excess of photosynthesis over respiration. The ecological implications of these results are discussed. Respirasie en netto fotosintese van snitte van die saadlobbe van Avicennia marina (Forssk.) Vierh. is by temperature van 17, 21 en 25 °C in ’n Gilson Respirometer gemeet. Saadlobmateriaal is ook vir TNC (totale nie-gestruktureerde koolhidrate) ontleed. Die tempo’s van respirasie en netto fotosintese het betekenisvol by die drie temperature verskil, met die laagste tempo’s in elke geval by 17 °C en die hoogste by 25 °C. TNC- waardes het ’n aanvanklike afname getoon, gevolg deur ’n klein toename, en daarna ’n daling na redelik konstante lae vlakke. By 25 °C het saailinge goed gegroei, terwyl baie min groei by 17 °C aangeteken is. Dit blyk dat groei by die verskillende temperature verband hou met die mate waarin fotosintese respirasie oorskry. Die ekologiese implikasies van hierdie resultate word bespreek.