Carbohydrate storage in wood and bark of rubber trees submitted to different level of C demand induced by latex tapping

Summary When the current level of carbohydratesproducOO by photosynthesis is not enough to meet theC demand for maintenance, growth or metabolism, treesuse stored carbohydrates. In rubber trees (Hevea brasili­ensis Muell. Arg.), however, a previous study (Silpi D.,A. Lacointe, P. Kasemsap, S. Thanisawanyangkura,P. Chantuma, E. Gohet, N. Musigamart, A. Clement,T. Ameglio and P. Thaler. 2007. Carbohydrate reserves asa competing sink: evidence from tapping the rubber tree.Tree Physiol. 27:881-889)showed that the additional sinkcreated by latex tappingresults notin a decrease, butin anincrease in the non-structuralcarbohydrate(NSC) storagein trunk wood. In this study, the response ofNSCstorageto latex tapping was further investigated to better under­stand the trade-offbetween latex regeneration, biomassand storage. Three tapping systems were compared to theuntapped Control for 2 years. Soluble sugars and starchwere analyzOO in bark and wood on both sides of thetrunk, from 50 to 200 cm from the ground. The resultsconfirmed over the 2 years that tapped trees stored moreNSC, mainly starch, than untapped Control. Moreover, adouble cut alternative tapping system, which produced ahigher latex yield than conventional systems, 100 to evenhigher NSC concentrations. In ail tapped trees, theincrease in storage occurred together with a rOOuction intrunk radial growth. This was interpretOO as a shift incarbon allocation toward the creation of reserves, at theexpense ofgrowth, to coyer the increased risk induced bytapping(repeated woundingand loss ofCin latex). Starchwas lower in bark than in wood, whereas it was thecontrary for soluble sugars. The resulting NSC was twiceas low and less variable in bark than in wood. Althoughlatex regeneration occurs in the bark, changes relatOO tolatex tapping were more marked in wood than in bark.From seasonal dynamics and differences between the twosides of the trunk in response to tapping, we concludOOthat starch in wood behavOO as the long-term reservecompartment at the whole trunk leve1, whereas starch inbark was a local buffer. Soluble sugars behaved like anintermOOiate, ready-to-usecompartment in both woodand bark. Finally, the dynamics ofcarbohydrate reservesappears a relevant parameter to assess the long-termperformance oflatex tapping systems.