Effects of light on the performance of shade-tolerant tropical rainforest tree seedlings

• Main Author: Bloor, J.
• Published: University of Cambridge 2001
• Subjects: 634.9
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596725

This thesis set out to investigate the light responses of shade-tolerant tropical tree species, and to assess whether or not there was a trade-off between shade tolerance and responsiveness to high light. Shadehouse experiments indicated that low-light relative growth rate was positively correlated with that of high light across species, and all seedlings showed typical 'sun' and 'shade' characteristics when grown in high- and low-light survival amongst the species studied. These trends were mirrored in forest-growth plants. Seedling mortality rate in the forest varied across species and was driven by vertebrate herbivory rather than light availability. In the shadehouse studies, seedling light responses did not appear to be confounded by nutrient limitation. Some evidence was found for phylogenetic effects across species, particularly in root morphology. Ontogenetic effects were also found for a number of plant traits, although the significance of these effects was not consistent across species. Species showed changes in growth ranking both across light levels and over time, suggesting a role for shifting competitive hierarchy in promoting species coexistence. The shade-tolerant species studied also varied significantly in the flexibility of their plant traits in response to changes in light conditions. Nonetheless, all species showed significant acclimation to an increase in light in terms of growth, photosynthesis, morphology and architecture. Acclimation to a decrease in light involved a significant decrease in photosynthetic rate and growth across species, but changes in morphology were limited.