The vegetation of the Roodeplaat Dam Nature Reserve. V. Photosynthesis and transpiration of a deciduous tree Berchemia zeyheri

The rates of photosynthesis and transpiration of Berchemia zeyheri (Sond.) Grubov were studied on a daily and seasonal basis. Variations in photosynthetic photon flux density (PPFD) and wind speed had the greatest influence on the daily course of the photosynthetic rate, transpiration rate and diffusion resistance. The rate of photosynthesis usually varied between 3 and 13 mg CO2 dm− 2 h− 1 and the maximum rate occurred at approximately 10h00. This coincided with the maximum transpiration rate which was usually between 09h00 and 13h00. Seasonal variations in the rates of photosynthesis and transpiration are related to PPFD as well as soil moisture availability and relatively high air and leaf temperatures (> 28°C). Transpiration is enhanced by high leaf temperatures but high air temperatures lead to a decline in photosynthetic activity. Die fotosintese- en transpirasietempo van Berchemia zeyheri (Sond.) Grubov is op ’n daaglikse en seisoenale basis ondersoek. Die fotosintetiese foton-vloeddigtheid (FFV) en windspoed oefen die grootste invloed op die daaglikse verloop van die fotosintesetempo, transpirasietempo en diffusieweerstand uit. Die fotosintesetempo varieer meesal tussen 3 en 13 mg CO2 dm− 2 h− 1 en die maksimum tempo word teen ongeveer 10h00 aangetref. Dit stem ooreen met die maksimum transpirasietempo wat gewoonlik tussen 09h00 en 13h00 voorkom. Seisoenale variasies in die fotosintese- en transpirasietempo toon ’n verband met FFV sowel as die beskikbaarheid van grondvog en relatief hoë lug- en blaartemperature (> 28°C). Transpirasie word onder andere deur hoë blaartemperature bevoordeel terwyl hoë lugtemperature ’n verlaging in die fotosintesetempo veroorsaak.