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Respiratory Activity of Hevea brasiliensis at Trunk Scale (Experiment TE01)
Bark respiratory activity of Hevea brasiliensis clone RRIM600 was monitored by the multi-channel gas exchange measurement similar to Lacointe et al. (1995). This approach was conducted at the same trees that were used for the trunk radial growth measurement. Ambient air was blown in cylindrical chambers and airflow was measured with mass flow meter (Tylan®, Millipore). The difference in the CO2 concentration of the air before and after going from the chamber was measured with an infrared gas analyzer, differential mode (LI-6200, LI-COR Inc. or Binos®1004P, Fisher-Rosemount GmbH & Co). Whole chamber CO2 exchange rate was calculated as the product of mass flow (mol. s-1) and the difference in CO2 concentration (μmol . mol-1). Gas exchange data of each chamber was collected at 57 minutes interval. The experiment was conducted continuously from December 2001 until March 2003 to cover a complete annual growth cycle.
Dynamics of Carbohydrate Reserves Based on Phenology and Latex Exploitation (Experiment TE01)
The glucose or fructose concentration in the medium is proportional to the NADPH formed during the reaction (Fig.5). The NADPH synthesis is observed, with a spectrophotometer, at 340 nm because NADPH absorbs at this wavelength contrarily to NADP. The Beer-Lambert law, a combination between the absorbance and the concentration at a fixed wavelength, is applied to evaluate NADPH concentration.
Biochemical analysis
After the core sampling was made, the sample was soaked immediately in liquid N2 and was kept in cryo-tube immersed in liquid nitrogen until transferred from the field to the laboratory and dried with freeze dryer. After, the sample was grinded and stored at -80 ºC. The powder was re-dried in the oven for 2 hrs at 65ºC. Soluble sugars were extracted from 18-23 mg aliquot samples with 1ml 80% EtOH during 30 min at 80ºC, then centrifuged. This step was repeated twice, first with 80% EtOH and then with 50% EtOH and all the supernatants were pooled. The sediment which contains starch was filled with 0.5 ml 80% EtOH and kept at -80ºC until analysis. The supernatant was filtered in the mini column added with mixture of polyvinyl polypyrrolidone and activated charcoal to eliminate pigments ad polyphenols. Ethanol was evaporated using vacuum dryer (Maxi Dry Plus, Heto,Denmark). Soluble sugars and starch were quantified by enzymatic analysis (Boehringer, 1988). Sucrose was transformed into glucose and fructose by invertase (β-fructofuranosidase), glucose and fructose were quantified using hexokinase, glucose-6-phosphate-dehydrogenase and phosphoglucose isomerase followed by spectro-photometry of NADPH at 340 nm. For starch analysis, after EtOH was evaporated, the sediment was hydrolysed with NaOH 0.02N during 1.5h at 90ºC and then with α- amyloglucosidase for 1h at 50ºC and then glucose was quantified as described above. The results were expressed as mg glucose equivalent per gram structural dry matter.
The Assessment of Trunk Radial Growth and Daily Variation
Both LVDT and RS sensor functioned well for long term continuous measurement of trunk radius under tropical condition. However, the measurement from RS sensor was overestimated when compared with trunk circumference measured by tape or with trunk diameter measured by LVDT sensor. Thus, data obtained from RS sensor needed to be adjusted with tape measurement (see in the appendix) in order to get the actual range without smoothing out the changes at fine scale. Nevertheless, RS sensor was proved to be a suitable method to follow long term radius movement, regarding its consistency, cost and the nature of the sensor that can measure directly the radius and require less space as compared to LVDT. This is particularly useful in the rubber tree where the two panels don’t have the same growth rate. However, RS was not well adapted for monitoring the reversible radius movement, unlike LVDT, since the contractions were not accurately recorded. Thus the use of both type of sensors together allowed to assess for the first time reversible changes at daily scale for untapped trees and to get a very precise figure of radius dynamics according to tapping and season.
Annual minimum respiration period
The minimum respiration of the year occurred at leaf shedding – re foliation period. Under Chachoengsao condition (mean annual rain fall 2001-2002: 1280 mm. year-1), annual leaf shedding was noticed from mid December and the complete re-foliation state was observed at the end of February (Fig. 20). No true dormancy period was noticed since the tree re-foliated just after de-foliation had completed. In some trees, the two phenomena overlapped i.e. some branches did not complete de –foliation while the others had started to re-foliate. Both tapped and untapped treatments shared a common trend of having two periods of minimum respiration; the first minimum was noticed during leaf shedding, when a significant number of leaves remained. This was during 29th December, 2001 – 3rd January, 2002 in the first year and around 11th – 14th January, 2003 in the second year. After this, a small increase of respiration was observed and continued about 3 weeks and then started a decreasing trend again until reaching the second minimum. The increase of respiration had started before bud break was noticed and then reached the peak during the stage of leaf expansion. Simultaneous increase in respiratory activity and re-foliation process suggests the requirement of energy for leaf expanding especially the translocation of reserve sugar in wood to the site of new leaves. When re-foliation process completed, the respiration rate remained in a decreasing trend until it reached the second minimum when negative radius variation was also found. This shrinkage phenomenon in concomitance to low respiration rate at the period of fully expanded canopy may suggest a stress situation when soil water content was not enough to refill the tree after transpiration, due to the absence of rainfall. Concerning the quantitative aspect, untapped tree had the lowest minimum respiration. Since no radial growth was observed at that period, the minimum respiration implied the maintenance respiration of the untapped rubber tree. The values from the 2 replicas was 6.0 and 11.4 nmol.min-1.cm-2 for the first minimum (table 3) and 3.9 and 6.3 nmol.min-1.cm-2 for the second minimum (table 4). Tapped trees showed higher respiration rate at the same period. First minimum respiration for nil stim treatment was 9.5 and 11.1 nmol.min-1.cm-2 and the second minimum was 7.2 and 9.3 nmol.min-1.cm-2. For Et 8/y treatment the first minimum was 9.6 and 12.4 nmol.min-1. cm-2 and the second 57minimum was 8.3 and 9.5 nmol.min-1.cm-2 (table 3 and 4). Thus, the difference between untapped and tapped tree was particularly clear, the second minimal respiration of untapped trees representing about 60% of value of tapped trees (table 4). Among tapped trees, three out of four showed higher respiration in tapped panel. Since tapping activity continued at that period, the respiration rate of tapped tree could account mainly for the maintenance cost and also the associated respiration for latex regeneration process. The difference in respiration between untapped and tapped tree plus the actual latex production will be further analyzed to estimate the actual respiration required for the latex regeneration process.
Table of contents :
LIST OF TABLE
LIST OF FIGURES
INTRODUCTION
1 LITERATURE REVIEW
Laticiferous System and Its Demand for Substrate and Energy Supplies.
Other Major Sinks in the Rubber Tree
MATERIALS AND METHODS
Plant Material
Methodology
RESULTS
Dynamics of Laticiferous System and Spatial Extension of Latex Regeneration Area
The Assessment of Trunk Radial Growth and Daily Variation
Respiratory Activity of Hevea brasiliensis at Trunk Scale
Dynamics of Carbohydrate Reserves based on Phenology and Latex Exploitation
DISCUSSION
Dynamics of Laticiferous System and Spatial Extension of Latex Regeneration Area
The Assessment of Trunk Radial Growth and Daily Variation
Respiratory Activity of Hevea brasiliensis at Trunk Scale
Dynamics of Carbohydrate Reserves based on Phenology and Latex Exploitation
CONCLUSION
LITERATURE CITED
APPENDIX
The Scaling Method for Validating the Over Range Output from RS System
The Use of Macro Files to Manipulate Respiration Data
