Shade-tolerance as a predictor of responses to elevated CO2 in trees

Evidence from 10 studies comparing angiosperm trees and 5 studies comparing conifers or differing shade-tolerance was analysed. The number of intraphyletic comparisons in which the more shade-tolerant species showed the greater relative increase of biomass in elevated CO2 was significantly higher than would be expected by chance alone. It is suggested that more shade-tolerant species are inherently better disposed. in terms of plant architecture and partitioning of biomass and nitrogen, to utilise resources (light, water, nutrients) that are potentially limiting in elevated CO2 and that these traitu are responsible for the interaction between shade-tolerance and CO2 concentration. Compared with less shade-tolerant angiosperm trees, more shade-tolerant angiosperm species generally have a lower lear area ratio in ambient CO2 and show a smaller relative reduction in elevated CO2. Furthermore, leaf nitrogen content is usually lower in more shads-tolerant angiosperm species and tends to be more strongly reduced by elevated CO2 in those species. Within angiosperm trees, more shade-tolerant species showed a stronger stimulation of net leaf photosynthetic I ate in most experiments, but this trend was not significant