Sornprach Thanisawanyangkura

Leaf orientation and sunlit leaf area distribution in cotton

The diurnal leaf orientation behaviour of row-planted cotton plants (Gossypium hirsutum L. cv. ‘DES 119’) and its relationship to sunlit leaf area distribution at three stages of development were studied in the field. Electromagnetic digitizing was used for plant geometrical structure measurement for three periods of 2 h during the day. Cotton leaves showed a diaheliotropic response throughout the day. This heliotropic behaviour varied according to growth stage. In addition to changes in orientation, leaves also moved in space. The distance moved by a leaf between two observation times increased with stage of development, in agreement with petiole and blade lengths. Sunlit leaf area distribution varied according to stage of development. Analysis of interception showed that probability of light interception was greater in the morning and in the afternoon than at noon. Without a diurnal change in canopy structure, cotton plants would intercept less direct radiation in the morning and in the afternoon. Leaf dispersion was regular during the first and last stage of development, but it was clumped during the intermediate stage. Leaf dispersion was more regular in the morning and the afternoon than at noon.. Leaf dispersion, however, changed primarily with sun direction and not with canopy structure. This would indicate that small changes in leaf location do not significantly affect light interception. Finally, the ecological significance of diaheliotropism and the implications for modelling light interception in cotton plants are discussed.

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

When the current level of carbohydrates produced by photosynthesis is not enough to meet the C demand for maintenance, growth or metabolism, trees use stored carbohydrates. In rubber trees (Hevea brasiliensis Muell. Arg.), however, a previous study (Silpi U., A. Lacointe, P. Kasemsap, S. Thanisawanyangkura, P. Chantuma, E. Gohet, N. Musigamart, A. Clement, T. Améglio and P. Thaler. 2007. Carbohydrate reserves as a competing sink: evidence from tapping the rubber tree. Tree Physiol. 27:881-889) showed that the additional sink created by latex tapping results not in a decrease, but in an increase in the non-structural carbohydrate (NSC) storage in trunk wood. In this study, the response of NSC storage to latex tapping was further investigated to better understand the trade-off between latex regeneration, biomass and storage. Three tapping systems were compared to the untapped Control for 2 years. Soluble sugars and starch were analyzed in bark and wood on both sides of the trunk, from 50 to 200 cm from the ground. The results confirmed over the 2 years that tapped trees stored more NSC, mainly starch, than untapped Control. Moreover, a double cut alternative tapping system, which produced a higher latex yield than conventional systems, led to even higher NSC concentrations. In all tapped trees, the increase in storage occurred together with a reduction in trunk radial growth. This was interpreted as a shift in carbon allocation toward the creation of reserves, at the expense of growth, to cover the increased risk induced by tapping (repeated wounding and loss of C in latex). Starch was lower in bark than in wood, whereas it was the contrary for soluble sugars. The resulting NSC was twice as low and less variable in bark than in wood. Although latex regeneration occurs in the bark, changes related to latex tapping were more marked in wood than in bark. From seasonal dynamics and differences between the two sides of the trunk in response to tapping, we concluded that starch in wood behaved as the long-term reserve compartment at the whole trunk level, whereas starch in bark was a local buffer. Soluble sugars behaved like an intermediate, ready-to-use compartment in both wood and bark. Finally, the dynamics of carbohydrate reserves appears a relevant parameter to assess the long-term performance of latex tapping systems.

Effect of leaf age and position on light-saturated CO2 assimilation rate, photosynthetic capacity, and stomatal conductance in rubber trees

Shoots of the tropical latex-producing tree Hevea brasiliensis (rubber tree) grow according to a periodic pattern, producing four to five whorls of leaves per year. All leaves in the same whorl were considered to be in the same leaf-age class, in order to assess the evolution of photosynthesis with leaf age in three clones of rubber trees, in a plantation in eastern Thailand. Light-saturated CO2 assimilation rate (Amax) decreased more with leaf age than did photosynthetic capacity (maximal rate of carboxylation, Vcmax, and maximum rate of electron transport, Jmax), which was estimated by fitting a biochemical photosynthesis model to the CO2-response curves. Nitrogen-use efficiency (Amax/Na, Na is nitrogen content per leaf area) decreased also with leaf age, whereas Jmax and Vcmax did not correlate with Na. Although measurements were performed during the rainy season, the leaf gas exchange parameter that showed the best correlation with Amax was stomatal conductance (gs). An asymptotic function was fitted to the Amax-gs relationship, with R2 = 0.85. Amax, Vcmax, Jmax and gs varied more among different whorls in the same clone than among different clones in the same whorl. We concluded that leaf whorl was an appropriate parameter to characterize leaves for the purpose of modelling canopy photosynthesis in field-grown rubber trees, and that stomatal conductance was the most important variable explaining changes in Amax with leaf age in rubber trees.

Impact of tapping and soil water status on fine root dynamics in a rubber tree plantation in Thailand

Fine roots (FR) play a major role in the water and nutrient uptake of plants and contribute significantly to the carbon and nutrient cycles of ecosystems through their annual production and turnover. FR growth dynamics were studied to understand the endogenous and exogenous factors driving these processes in a 14-year-old plantation of rubber trees located in eastern Thailand. FR dynamics were observed using field rhizotrons from October 2007 to October 2009. This period covered two complete dry seasons (November to March) and two complete rainy seasons (April to October), allowing us to study the effect of rainfall seasonality on FR dynamics. Rainfall and its distribution during the two successive years showed strong differences with 1500 and 950 mm in 2008 and 2009, respectively. FR production (FRP) completely stopped during the dry seasons and resumed quickly after the first rains. During the rainy seasons, FRP and the daily root elongation rate (RER) were highly variable and exhibited strong annual variations with a total FRP of 139.8 and 40.4 mm-2 and an average RER of 0.16 and 0.12 cm day-1 in 2008 and 2009, respectively. The significant positive correlations found between FRP, RER, the appearance of new roots, and rainfall at monthly intervals revealed the impact of rainfall seasonality on FR dynamics. However, the rainfall patterns failed to explain the weekly variations of FR dynamics observed particularly during the rainy seasons. At this time step, FRP, RER, and the appearance of new FR were negatively correlated to the average soil matric potential measured at a depth of between 30 and 60 cm. In addition, our study revealed a significant negative correlation between FR dynamics and the monthly production of dry rubber. Consequently, latex harvesting might disturb carbon dynamics in the whole tree, far beyond the trunk where the tapping was performed. These results exhibit the impact of climatic conditions and tapping system in the carbon budget of rubber plantations.

3-D maps of tree canopy geometries at leaf scale

The geometrical structure of plant canopies has many implications for plant functioning, microclimatic conditions, and plant-pathogen/herbivore interactions. Plant geometry can be described at several scales. At the finest scale, canopy structure includes the shape, size, location, and orientation of each organ in the canopy. This data set reports the three-dimensional (3-D) geometry of a set of fruit and rubber trees at the leaf scale. A 3-D magnetic digitizer was used to measure the spatial coordinates and the orientation angles of each leaf, namely, the midrib azimuth and inclination angles, and the rolling angle of leaf lamina around the midrib. In addition, for most trees, branching or flush order is given as well as the ranking of leaves along branches and the leaf identity of leaflets in compound-leaved trees. Leaf length was also measured for most trees. Leaf width was measured or estimated based on allometric relationships. Leaf area was derived from allometric relationships with leaf length and width. The data set includes the 3-D geometry of six trees: one apple, two mangos, two rubbers, and one walnut. Plant height ranged from 1.6 m for mango trees to 5.3 m for the large rubber tree. The number of leaves ranged from 895 for the small rubber tree to 26,283 for the apple tree. Total leaf area ranged from 3.6 m2 for the small rubber tree to 36.4 m2 for the apple tree. Most of the data were used to show how canopy geometry determines light interception and subsequently plant primary production and fruit yield. The data set was also used to test the quality of innovative methods for canopy structure description at tree scale. The apple tree was used to study the thermal environment of a leaf miner insect, to show how canopy geometry leads to a strongly heterogeneous risk of mortality, in particular under heat-wave conditions. Overall, our data set provides explicit plant architectures suitable for spatial modeling of plant physiological ecology and plant–herbivore interactions, allowing us to determine the mechanisms through which climate impacts biological and ecological processes involved in these functions.