SHADE-TOLERANCE AS A PREDICTOR OF RESPONSES TO ELEVATED CO2 IN TREES

Evidence from 10 studies comparing angiosperm trees and 5 studies comp aring conifers or differing shade-tolerance was analysed. The number o f intraphyletic comparisons in which the more shade-tolerant species s howed the greater relative increase of biomass in elevated CO2 was sig nificantly higher than would be expected by chance alone. It is sugges ted that more shade-tolerant species are inherently better disposed. i n 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 w ith less shade-tolerant angiosperm trees, more shade-tolerant angiospe rm species generally have a lower lear area ratio in ambient CO2 and s how a smaller relative reduction in elevated CO2. Furthermore, leaf ni trogen content is usually lower in more shads-tolerant angiosperm spec ies and tends to be more strongly reduced by elevated CO2 in those spe cies. Within angiosperm trees, more shade-tolerant species showed a st ronger stimulation of net leaf photosynthetic I ate in most experiment s, but this trend was not significant.