La composition isotopique en carbone est-elle un indicateur écophysiologie pertinent de l’efficience d’utilisation de l’eau de l’hévéa ?

The rubber (Hevea brasiliensis) plantations extend to non-traditional area in Thailand where dryer conditions has been reported to impair the growth of rubber trees and latex production. Physiological parameters helpful for breeding adapted genotypes are required, such as water use efficiency (WUE). Carbon isotope discrimination is widely used as a proxy for WUE that can easily be used for selection and breeding programs for drought tolerance. Leaf [delta]13C and leaf gas exchange were measured on young saplings of 10 rubber clones growing in pot in a common garden. The range of leaf [delta]13C among 10 clones was narrow and the correlation between [delta]13C and WUEi was significant under high vapour pressure deficit only, which means the prediction of WUE by [delta]13C would have low precision. There were large [delta]13C variations among the genotypes at all seasons in a collection of 49 wild genotypes of rubber in Northeastern Thailand. [delta]13C was rather stable with a good correlation between rainy and dry season. The genetic variability of [delta]13C is promising for breeding if a good correlation between [delta]13C of leaf and WUE can be established. The lack of correlation between [delta]13C of latex ([delta]13C-L) and of leaf soluble compounds ([delta]13C-S) collected from tapped and untapped 20 year-old rubber trees suggests that recent photosynthates are mixed in the large pool of stored carbohydrates that are involved in latex regeneration after tapping. Thus [delta]13C of latex is not a relevant indicator of WUE of rubber treesLes plantations d’hévéa (Hevea brasiliensis) s’étendent vers des zones non traditionnelles de production en Thaïlande où des conditions plus sèches ont pu conduire à une diminution de la croissance des arbres et de la production de latex. Des paramètres physiologiques utiles pour sélectionner des génotypes adaptés sont nécessaires, comme l’efficience d’utilisation de l’eau (WUE). La discrimination isotopique du carbone est largement utilisée comme proxy pour WUE et peut être aisément utilisée dans des programmes de sélection pour la tolérance à la sécheresse. [delta]13C des feuilles et les échanges gazeux foliaires ont été mesurés sur de jeunes plants de dix clones d’hévéa cultivés en pot dans une pépinière. La gamme de [delta]13C des feuilles entre ces dix clones était restreinte et la corrélation entre [delta]13C et WUEi était significative que sous fort déficit de pression de vapeur saturante, ce qui signifie que la prédiction de WUE par [delta]13C serait peu précise. Il y avait une large gamme de [delta]13C entre les génotypes dans une collection de 49 génotypes sauvages d’hévéa cultivés dans le nord-est de la Thaïlande en saison sèche et en saison des pluies. [delta]13C était relativement stable avec une bonne corrélation entre les saisons. Cette étude montre que la variabilité génétique de [delta]13C est prometteuse pour des futurs programmes de sélections si une bonne corrélation entre of [delta]13C et WUE peut être établie. L’absence de corrélation entre de [delta]13C du latex ([delta]13C-L) et des composés solubles extraits des feuilles ([delta]13C-S) prélevées sur des arbres saignés et non saignés âgés de 20 ans suggère que photosynthétats récemment produits se mélangent à un stock important d’hydrate de carbone impliqués dans la régénération du latex après la saignée. Donc, [delta]13C du latex n’est pas un indicateur pertinent de WU

Is carbon isotope composition a relevant ecophysiological indicator of genetic variation in water use efficiency of rubber trees?

Les plantations d’hévéa (Hevea brasiliensis) s’étendent vers des zones non traditionnelles de production en Thaïlande où des conditions plus sèches ont pu conduire à une diminution de la croissance des arbres et de la production de latex. Des paramètres physiologiques utiles pour sélectionner des génotypes adaptés sont nécessaires, comme l’efficience d’utilisation de l’eau (WUE). La discrimination isotopique du carbone est largement utilisée comme proxy pour WUE et peut être aisément utilisée dans des programmes de sélection pour la tolérance à la sécheresse. δ13C des feuilles et les échanges gazeux foliaires ont été mesurés sur de jeunes plants de dix clones d’hévéa cultivés en pot dans une pépinière. La gamme de δ13C des feuilles entre ces dix clones était restreinte et la corrélation entre δ13C et WUEi était significative que sous fort déficit de pression de vapeur saturante, ce qui signifie que la prédiction de WUE par δ13C serait peu précise. Il y avait une large gamme de δ13C entre les génotypes dans une collection de 49 génotypes sauvages d’hévéa cultivés dans le nord-est de la Thaïlande en saison sèche et en saison des pluies. δ13C était relativement stable avec une bonne corrélation entre les saisons. Cette étude montre que la variabilité génétique de δ13C est prometteuse pour des futurs programmes de sélections si une bonne corrélation entre δ13C et WUE peut être établie. L’absence de corrélation entre de δ13C du latex (δ13C-L) et des composés solubles extraits des feuilles (δ13C-S) prélevées sur des arbres saignés et non saignés âgés de 20 ans suggère que photosynthétats récemment produits se mélangent à un stock important d’hydrate de carbone impliqués dans la régénération du latex après la saignée. Donc, δ13C du latex n’est pas un indicateur pertinent de WUEThe rubber (Hevea brasiliensis) plantations extend to non-traditional area in Thailand where dryer conditions has been reported to impair the growth of rubber trees and latex production. Physiological parameters helpful for breeding adapted genotypes are required, such as water use efficiency (WUE). Carbon isotope discrimination is widely used as a proxy for WUE that can easily be used for selection and breeding programs for drought tolerance. Leaf δ13C and leaf gas exchange were measured on young saplings of 10 rubber clones growing in pot in a common garden. The range of leaf δ13C among 10 clones was narrow and the correlation between δ13C and WUEi was significant under high vapour pressure deficit only, which means the prediction of WUE by δ13C would have low precision. There were large δ13C variations among the genotypes at all seasons in a collection of 49 wild genotypes of rubber in Northeastern Thailand. δ13C was rather stable with a good correlation between rainy and dry season. The genetic variability of δ13C is promising for breeding if a good correlation between δ13C of leaf and WUE can be established. The lack of correlation between δ13C of latex (δ13C-L) and of leaf soluble compounds (δ13C-S) collected from tapped and untapped 20 year-old rubber trees suggests that recent photosynthates are mixed in the large pool of stored carbohydrates that are involved in latex regeneration after tapping. Thus δ13C of latex is not a relevant indicator of WUE of rubber tree

Data from: Trait evolution in topical rubber (Hevea brasiliensis) trees is related to dry season intensity

1. Drought shapes the distribution and survival of trees even in tropical wet forests, and the wood and leaf trait spectra are used to understand drought adaptations. However, trait variation may result from ontogenetic adjustment or be related to tree size, and not reflect evolutionary adaptations. 2. Intraspecific variation in adaptations to drought can be an important factor in a species’ distribution and response to climate change, but excluding potentially confounding factors and proving adaptive evolution is challenging. Provenance trials can identify hereditary variability. 3. We analysed wood and leaf traits in rubber (Hevea brasiliensis) tree clones from 15 locations in the Amazon basin that were planted in northern Thailand, controlled for tree size, tested for genetic relatedness and the phylogenetic signal in traits, and compared trait variations with the climate at the location of origin. 4. Correlations between traits and tree size were low. Intra-specific trait variation was similar to relationships in published among-species comparisons and correlations among wood traits and correlations among leaf traits were stronger than between wood and leaf traits. Genotype explained 30 – 70% of the trait variation, and traits differed in how much of this variation was controlled by location or the relatedness among clones. 5. There was no correlation with mean temperature or total annual rainfall. However, rainfall in the driest quarter (19 – 199 mm) was strongly related to leaf mass per area, carbon isotopic composition and area-based nitrogen content(r2 = 0.54 - 0.70) and weaker to wood traits (vessel density and vessel lumen fraction). Trees from locations with a stronger dry season also had higher growth rates in Thailand. 6. All traits correlating with climate showed a significant phylogenetic signal. We found no evidence of increased drought tolerance, but the trait spectrum and higher growth in trees from drier locations suggests that deciduous rubber trees have adapted via drought avoidance rather than tolerance. Our study also underlines the importance of looking at a suite of traits rather than individual ones to understand adaptive strategies

Functional traits of Hevea brasiliensis clones

wood and leaf traits and tree size for Hevea brasiliensis clones from Brazil planted in a provenance trial in Thailan

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

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 (δ(13)C-L), leaf soluble compounds (δ(13)C-S) and bulk leaf material (δ(13)C-B) collected from tapped and untapped 20-year-old trees were compared. A marked difference in δ(13)C-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 δ(13)C values than those of untapped trees. δ(13)C-L was higher and more stable across seasons than δ(13)C-S and δ(13)C-B, with a maximum seasonal difference of 0.7‰ for tapped trees and 0.3‰ for untapped trees. δ(13)C-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 δ(13)C-L and δ(13)C-B between tapped and untapped trees indicated that tapping affects the metabolism of both laticiferous cells and leaves. The lack of correlation between δ(13)C-L and δ(13)C-S suggests that recent photosynthates are mixed in the large pool of stored carbohydrates that are involved in latex regeneration after tapping