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International audience; Rubber Flux aims at providing a complete picture of CO2, water and energy budget of a rubber plantation in Eastern Thailand. Beyond the evaluation of the fluxes, our purpose is to partition them among the different components of the plantation ecosystem (canopy, trunks, roots, under storey, soil) and the different functions (photosynthesis, respiration. evapotranspiration ) in order to understand the factors controlling the carbon, water and energy budgets of the ecosystem. The experiment is situated at the Chachoengsao Rubber Research Station located in Phanom Sarakham district, about 140 km east of Bangkok The observation site is located in a 6 ha plot at the center of the 350 ha station. The plot itself is planted with a monoclonal stand (clone RRIM 600). Trees were 13 years old in 2007. The average height was 20 m and average girth at 1.7 in was 60 cm. Initial planting density was 500 trees/ha and actual stand density was 454 trees/ha in June 2006. Trees are tapped for latex production for 5 years. Carbon fluxes of rubber plantation ecosystem are continuously measured by the eddy covariance method (ED). Evapo-transpiration (ET) is measured by ED and water balance together. Meanwhile, amounts of carbon (C) stored in the trees will be evaluated by measuring biomass increment of the plantation, in combination with estimations of the carbon content at the different compartments. ED methodology was adapted from a similar experiment developed by our research group on another tropical tree crop plantation, coconut tree, in Vanuatu islands. The flux tower is 25 in high. Three-demensional (3-D) sonic anemometer Young 81000V 20 Hz is used together with alt open path gas analyser (LI-7500; LI-COR, Inc., Lincoln, Nebraska, USA). Raw data are collected and pre-processed by the "Tourbillon" software (INRA-Bioclimatologie, Bordeaux, France) for a time-integration period of 300 s. Raw data are post-processed using EdiRe software (University of Edinburgh, UK) into half-hourly values. All data are despiked according to variance filters, planar fit is applied (parameters are calculated monthly), and vapour is corrected for buoyancy. Weather station measures semi-hourly net radiation (Rn), photosynthetically active radiation (PAR), diffuse PAR (PARdiff), reflected PAR (PARreflected), global radiation (Rg), Air temperature (Ta), Relative humidity (Rh), wind speed, wind direction, rainfall, vertical profile of air temperature (TCs). Energy balance will be assessed by measurements of net radiation (Rn) and estimation of the energy partitioning among heat fluxes and heat storage. Results obtained at the ecosystem scale by these methods will be compared to gas exchanges measured at the level of the different compartments (canopy, trunk, root system, soil, etc). Thereby, the validated CO2 and H2O fluxes will be used to model gas exchanges of rubber plantation ecosystem according to climate and other environmental parameters as well as crop management.

International audience; In Thailand, rubber is the major tree crop covering more than 2 millions hectares. Its impact on environment, and particularly CO2 balance and water use, is a major issue. A complete flux-measuring system has been installed in a 13 years old tubber plantation (clone RRIM 600) in eastern Thailand (Chachoengsao Rubber Research Center, RRIT-DOA) in 2006. Carbon fluxes of rubber plantation ecosystem are continuously measured by eddy-covariance method (CO2 exchanges between the ecosystem and the atmosphere). Evapo-transpiration (ET) are measured by eddy-covariance and water balance together and partitioned between tree transpiration and soil evaporation. Sapflow is measured by heat dissipation method (Granier 1985, 1987) using home-made 20 mm-long radial probes, continuously heated (0.2 W). Meanwhile, amounts of C stored in the trees are evaluated by measuring biomass increment along the life cycle of the plantation, in combination with estimations of the carbon content of the different compartments. These measurements will provide the annual balance of C within plantations at different ages. Results obtained at ecosystem scale by these methods will be compared to gas exchanges measured at the level of the different compartments (canopy, trunk, root system, soil...). Particularly, Farquhar's photosynthesis model (Farquhar et al. 1980) is parameterized across the canopy. Leaf water potential, sapflow and canopy transpiration are computed to calculate canopy conductivity. Thereby, validated CO2 and H2O fluxes will be used to model gas exchanges of rubber plantation ecosystem according to climate and other environmental parameters as well as crop management.

The aim of study was assessed clonal variability of starch and sugar soluble (SS) in trunk of rubber tree. The two experiments were set up, the first field compared 25 clones tested in an international clone exchange program which is now 30 years old. A second field clone trial was used for 15 years trees, with 18 clones. The results showed that an average starch in wood 71 mgGLUg/SDM and SS wood 21 mgGLU/gSDM recorded 25 clones exchange trial at 30 years were similar to the average obtained the same season in the previous study on standard clone RRIM600 age 11 years, starch 76 mgGLU/gSDM and SS 16 mgGLU/gSDM. However, mean contents SS bark 37 mgGLU/gSDM, and particularly starch in bark 25 mgGLU/gSDM were higher in the 30 years tree than the previous study SS 22 mgGLU/gSDM and starch 11 mgGLU/gSDM. The 15 years trial with 18 clones, mean content in wood were a bit higher for both starch 94 mgGLU/gSDM and SS 28 mgGLU/gSDM than the previous study. The bark SS 22 mgGLU/gSDM was similar as above but starch 41 mgGLU/gSDM was much higher than RRIM 600 age 11 years. Starch and SS in wood seems not much variable with age, However, carbohydrate contents in bark varied widely. The main source of variation may be the status of the bark Nevertheless, there was a negative correlation between cumulative yield and starch content in the bark Carbohydrate contents in clones had a high variability and heritability. Some interesting trends linking contents in the different forms of carbohydrate to clonal origin or to a well known metabolic characteristic were also detected.

In order to assess water balance of rubber plantations at plot scale, accurate dynamic measurements of tree transpiration is required. Sapflow was measured in a 12 years old plantation (RRIM 600) in eastern Thailand, by heat dissipation method (Granier 1985, 1987) using home-made 20 mm-long radial probes, continuously heated (0.2 W), and connected to a data logger. The calibration of the homemade probes was checked in the laboratory with reference to the gravimetric method. We adjusted the experimental devices to rubber field conditions and evaluated the different sources of variability to design the appropriate monitoring process. Natural thermal gradient was not significant. Vertical variation along the trunk below canopy was low. Conversely a significant azimuthal variation was recorded, though without specific trend. Accordingly 2 probes (one on the North face, one on the South face), located above the tapping panel were used for monitoring. Radial distribution of sapflow was recorded, using a long probe, and our results showed significant variations of sapflow along the radius. A function was derived from these radial variations to estimate total tree sapflow from measurements within the outer 2 cm of sapwood. Finally to evaluate stand transpiration (mm h-1), trees were sampled according to trunk diameter. Such data will be used to partition evapotranspiration measured on the same plot by eddy-correlation between tree transpiration, T, and soil and understorey evaporation, E. (Texte intégral)

Carbon sequestration potential of rubber plantations may provide opportunities to increase the profitability and acceptability of plantations. Thus, carbon exchange of the plantations has to be assessed accurately. A complete system has been installed in eastern Thailand (Chachoengsao Rubber Research Center, RRIT-DOA) in 2006. Carbon fluxes of rubber plantation ecosystem are continuously measured by eddy-correlation method (CO2 exchanges between the ecosystem and the atmosphere). Evapo-transpiration (ETR) are measured by eddy-correlations and water balance together and partitioned between tree transpiration and soil evaporation. Meanwhile, amounts of C stored in the trees will be evaluated by measuring biomass increment along the life cycle of the plantation, in combination with estimations of the carbon content of the different compartments. These measurements will provide the annual balance of C within plantations at different ages. Energy balance will be assessed by measurements of net radiation (Rn) and estimation of energy partitioning among heat fluxes and heat storage. Results obtained at ecosystem scale by these methods will be compared to gas exchanges measured at the level of the different compartments (canopy, trunk, root system, soil...). Thereby, validated CO2 and H2O fluxes will be used to model gas exchanges of rubber plantation ecosystem according to climate and other environmental parameters as well as crop management. (Texte intégral)

After two years of tapping in Chachoengsao province, uprooting of 12 trees (clones RRIM 600, PB 235, GT1, 4 trees per clone) provided estimations of the relations existing between the total dry biomass of rubber trees and their trunk girth. These relations were found linear at least inside the studied range (trunk girth varying from 45 cm to 65 cm), but different between clones. A general model, able to estimate in one location the biomass of all clones might perhaps be set up by taking into account not only the trunk girth but also some other variables describing canopy structure, as the canopy biomass cannot be described by the trunk girth only. Nevertheless, finding and parameterizing such a model requires further survey. Thanks to the linear regression models obtained between biomass and trunk girth, biomass of the trees could be estimated at the moment of opening and after two years of tapping. Biomass partition variables could be calculated, allowing estimation of the harvest index and k factor, accounting for rubber production efficiency. Nevertheless, as these models rely on the uprooting of only 4 trees per clone, an extended survey is required to confirm their accuracy. Competition between growth and production was found linear for all three clones, confirming numerous previous studies. Clone GT1 showed a rather bad behavior regarding the competition between growth and rubber production. Clones PB 235 and RRIM 600 showed much better behaviors with lower competition between growth and production. Moreover, RRIM 600 seemed to maintain a significant growth compared to other clones during the tapping stop period (February to April 2000, dry season), sign of a better water use effectiveness. Rubber breeders in rather dry areas should aim at such a characteristic .and systematic survey of clonal girth increments during the dry season could provide a reliable picture of clonal susceptibility to draught and water stress.