Infodoc : Sciences, Techniques et Culture

The [13C] values of deciduous and evergreen tree leaves were compared in open and closed- canopy environments through-out a rainy season in Panamà. Newly emerging leaves had higher [13C] values than older leaves of all seedlings and trees at all dates sampled. This was apparently not caused by a decline in water use efficiency as leaves develop because instantaneous [ci/ca] was significantly higher in newly emerging than in expanded leaves on the same twigs of trees in the field as well as on seedlings growing in a controlled, unchanging environment. Higher [13C] values in newly emerging leaves occurred across diverse environmental comparisons. For example, leaves emerging during the rainy season had higher [13C] values than corresponding mature leaves that had emerged both durin[...]

The [13C] values of deciduous and evergreen tree leaves were compared in open and closed- canopy environments through-out a rainy season in Panamà. Newly emerging leaves had higher [13C] values than older leaves of all seedlings and trees at all dates sampled. This was apparently not caused by a decline in water use efficiency as leaves develop because instantaneous [ci/ca] was significantly higher in newly emerging than in expanded leaves on the same twigs of trees in the field as well as on seedlings growing in a controlled, unchanging environment. Higher [13C] values in newly emerging leaves occurred across diverse environmental comparisons. For example, leaves emerging during the rainy season had higher [13C] values than corresponding mature leaves that had emerged both during the dry season and when water was abundant. The early enrichment in [13C] may thus reflect the translocation of carbon to initiate a new leaf. Furthermore, the lack of sensitivity of this enrichment to a microclimats suggests that it might be the result of processes that occur after carbon fixation by Rubisco. Other changes in [13C] values as leaves developed may also have resulted from carbon translocation processes. Foliar [13C] decreased significantly after most of the leaf biomass of the deciduous Apeiba membranacea had developed. The [13C] values of the evergreen Cecropia insignis were lower in the open canopy than in closed-canopy forests at the end of the rainy season. These findings suggest that the [13C] values of leaves can yield ecological information about the allocation of carbon within trees.