The relative importance of photosynthesis and respiration in determining plant growth rate

Abstract

The underlying physiological and biomass allocation parameters associated with differences in (RGR) among plant species characteristic of contrasting habitats have been well characterised. When grown at a single temperature under controlled environment conditions, plant species characteristic of unfavourable habitats exhibit lower RGR values than species from favourable environments. Slow growing species also exhibit lower rates of photosynthesis and respiration per unit plant mass. We examine the impact of different growth temperatures on photosynthesis and respiration and how this affects the RGR of some fast and slow growing species. Photosynthesis and respiration are both temperature sensitive in short-term experiments. Continued exposure to contrasting temperatures can, however, result in acclimation of respiration and photosynthesis. We examine the impact of different growth temperatures on photosynthesis and respiration and how this affects the RGR of a range of fast and slow growing species. Measurements of leaf level photosynthesis, leaf respiration (dark and light) and root respiration were made on 16 plant species that differed in RGR. Plants were grown hydroponically at 18, 23 and 28oC and measurements were made at the respective growth temperature. Photosynthesis and root respiration achieved homeostasis when plants were grown at the three temperatures. Leaf respiration however increased with temperature. There was a negative correlation between RGR and the percentage of daily photosynthesis respired, this relationship was maintained at all temperatures. RGR was reduced at 28oC due to a lack of acclimation of leaf respiration, which lead to an increase in ratio of respiration to photosynthesis. The importance of respiration and photosynthesis on ultimate growth rate will be discussed.