Carbon isotope composition of latex does not reflect temporal variations of photosynthetic carbon isotope discrimination in rubber trees (Hevea brasiliensis)

Abstract

Latex, the cytoplasm of laticiferous cells localized in the inner bark of rubber trees (Hevea brasiliensis Müll. Arg.), is collected by tapping the bark. Following tapping, latex flows out of the trunk and is regenerated, whereas in untapped trees, there is no natural exudation. It is still unknown whether the carbohydrates used for latex regeneration in tapped trees is coming from recent photosynthates or from stored carbohydrates, and in the former case, it is expected that latex carbon isotope composition of tapped trees will vary seasonally, whereas latex isotope composition of untapped trees will be more stable. Temporal variations of carbon isotope composition of trunk latex (δ13C-L), leaf soluble compounds (δ13C-S) and bulk leaf material (δ13C-B) collected from tapped and untapped 20-year-old trees were compared. A marked difference in δ13C-L was observed between tapped and untapped trees whatever the season. Trunk latex from tapped trees was more depleted (1.6% on average) with more variable δ13C values than those of untapped trees. δ13C-L was higher and more stable across seasons than δ13C-S and δ13C-B, with a maximum seasonal difference of 0.7% for tapped trees and 0.3% for untapped trees. δ13C-B was lower in tapped than in untapped trees, increasing from August (middle of the rainy season) to April (end of the dry season). Differences in δ13C-L and δ13C-B between tapped and untapped trees indicated that tapping affects the metabolism of both laticiferous cells and leaves. The lack of correlation between δ13C-L and δ13C-S suggests that recent photosynthates are mixed in the large pool of stored carbohydrates that are involved in latex regeneration after tapping.