Short term effects of latex tapping on micro-changes of trunk girth in [i]Hevea Brasiliensis[/i]

Latex tapping has a well-known negative effect on the long term radial growth of rubber trees (Hevea Brasiliensis). The additional carbon sink induced by latex yield is considered as the main cause. However the potential contribution of a tapping induced water stress has received little attention. In Northeast Thailand, we applied an exploring approach comparing the diel cycle of girth change between days of rest and days with tapping in conditions of relatively stable evaporative demand and soil water availability. Trees were tapped at dark in the early morning for two consecutive days and rested for one day. Five standard trees were equipped with high accuracy girth bands above the tapping panel. The sampling included one tree with additional measurements, one below the tapping cut and the other at the trunk bottom. Data were recorded at 30 min interval over 14 days at the onset of the dry season in November. Results demonstrated a significant short-term shrinkage within two hours after tapping. However, the nighttime expansion maximum diurnal shrinkage and midnight recovery were not significantly influenced by the tapping cycle. As a result the daily growth was not negatively impacted on tapping days. Finally, in conditions of low average growth, our results refute the hypothesis of a negative impact of tapping on radial growth at a daily scale through a simple dehydration. A substantial loss of turgor was confirmed but trees seem to quickly react and smooth the consequences on nighttime recovery and diurnal shrinkage

Nutrient uptake of peanut genotypes under different water regimes

Abstract Drought is a serious environmental stress limiting growth and productivity in peanut and other crops. Nutrient uptake of peanut is reduced under drought condition, which reduces yield. The objectives of this study were to investigate nutrient uptake of peanut genotypes in response to drought and to estimate the relationship between nutrient uptake and peanut yield under different water regimes. Pot experiment was conducted in a greenhouse in the dry season 2002/03 and the rainy season 2003. Three soil moisture levels [field capacity (FC), 2/3 available soil water (2/3 AW) and 1/3 available soil water (1/3 AW)] were assigned as factor A and 11 peanut genotypes as factor B. Total nutrient uptake was determined at harvest. Season×water regime interactions and differences in seasons, water regimes and genotypes were significant for all nutrient uptakes. The interactions between season and genotype were significant for N and K uptakes. The nutrient uptakes of peanut plants grown under FC were higher than those plants grown under water stress treatments. Tifton 8 was the highest genotype for all nutrient uptakes in both dry and rainy seasons, while ICGV 98303 and KK 60-3 had high nutrient uptake under water stress condition. The nutrient uptake of peanut in the rainy season was higher than the dry season. The relationships between nutrient uptake parameters, biomass and pod dry weight were positive and significant in both seasons. This information is important for peanut breeder interested in developing peanut lines with reasonably high nutrient uptake under drought condition

Process-based environmental models tree transpiration: A case study of rubber tree (Hevea brasiliensis)

Nowadays, tree transpiration (ETree) limitation is investigated in several plant species especially the commercial trees such as the rubber tree. Exceptional tree physiology responds to droughts, the modeling for prediction of ETree is also interest. The aim of this investigation was to evaluate the environmental model for ETree estimation in all leaf phenology under a wide range of soil water availability and evaporative demand. The results showed that the environmental model called ‘Fsoil_Emax’ (which considered only soil water available affect) produced a reduction of estimated ETree the same as the reducing pattern of actual measured in drought conditions. But there was no variability of estimated ETree when evaporative demand changed. The improving of the environmental model by added the reference evapotranspiration (ET0 ) which alternated in minimum value between ET0 and Emax, called Fsoil*MIN(Emax;ET0 ) model, produced a reduction in estimated ETree in both soil drought and low evaporative demand conditions at fully mature leaves stage. Therefore, this model was optimum for estimating transpiration under various conditions. Moreover, the annual accumulated ETree of the improved model slightly overestimated the measured value by 20 mm. However, this model produced estimated ETree at fully mature leaves stage better than during leaf shedding-flushing stage

Effect of trunk locations on micro-change of trunk girth in mature rubber trees (Hevea brasiliensis)

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Transpiration, growth and latex production of a Hevea brasiliensis stand facing drought in northeast Thailand : the use of the WaNuLCAS model as an exploratory tool

International audienceIn order to get the benefit of the growing world demand for natural rubber, Hevea brasiliensis is increasingly planted in drought-prone areas, such as in the southern part of northeast Thailand. Modelling can be a useful approach in identifying key points of improvement for rubber tree cultivation in such waterlimited areas. The first objective of this study was to test the possibility of using the Water Nutrients and Light Capture in Agroforestry Systems (WaNuLCAS) model as an exploratory tool to simulate water use, growth and latex production in a pure stand on a daily basis. The second was to evaluate the relative accuracy of predictions with the current model version. Finally, the third aim of this study was to identify particular parameterisations that may be adapted to improve overall prediction quality. Model outputs were compared to measurements recorded in a mature rubber tree stand of RRIM 600 clones growing in the water-limited area of northeast Thailand. The period of analysis concerned seven months of full foliation, from May to November, including a severe drought spell. Whole-tree transpiration was estimated by xylem sap flow measurement from 11 trees. The results show that the model was able to simulate daily and seasonal change of soil water content, tree transpiration, girth increment and latex production within plausible ranges. However, under detailed scrutiny, the predictions show large inaccuracies compared to the observations: soil water content (determination coefficient (R2) = 0.461, relative root mean square error (RMSErel) = 35%), tree transpiration (R2 = 0.104, RMSErel = 94%), tree girth increment (R2 = 0.916, RMSErel = 208%) and latex production (R2 = 0.423, RMSErel = 169%). As soil water content was overestimated during the driest periods, no water stress was predicted and transpiration, growth and latex production were logically overestimated during such periods. However, tree transpiration was also largely overestimated in conditions of non-limiting soil water availability with high evaporative demand. Hence, two key points of parameterisation and improvement are identified for better simulation in our conditions: the soil water balance and particularly the ratio between water infiltration and run-off, and the regulation of transpiration under high evaporative demand. In conclusion, the WaNuLCAS model is usable as an exploratory model to simulate water use, growth and production for a pure rubber tree stand. However, in our conditions of much degraded soil and high evaporative demand, the modules of soil water balance and tree transpiration require particular parameterisations and improvement

Vapour pressure deficit affects diurnal girth fluctuation of rubber trees (Hevea brasiliensis)

Diurnal variation in stem girth as affected by three different ranges (0.43, 1.78 and 2.11 kPa) of air vapour pressure deficit (VPD) under minimum soil water stress was studied in mature rubber trees (Hevea brasiliensis) in Northeast Thailand. Diurnal cycle of shrinkage and swelling of stem girth was observed in all ranges of VPD. Stem girth as expressed by maximum daily trunk shrinkage (MDS) decreased during the day in association with high sap flow and high VPD, and then stem girth increased during the night when VPD and sap flow were low. Stem girth fluctuation was inversely related to VPD and sap flow, especially at higher ranges of VPD. A positive and significant correlation of MDS on VPD (r = 0.42, p <= 0.01) and negative correlation of MDS on sap flow (r = 0.41, p <= 0.01) were observed, whereas positive correlations of trunk growth rate (TGR) on VPD (r = 0.19) and of TGR on sap flow (r = 0.18) were not significant. This indicates that MDS was sensitive to air moisture conditions. Measurement of MDS could be easily automated and MDS signal intensity could be used as a tool for predicting plant water status and utilizing crop modeling

Water loss regulation in mature Hevea brasiliensis : effects of intermittent drought in the rainy season and hydraulic regulation

Effects of soil and atmospheric drought on whole-tree transpiration (E-T), leaf water potential (psi(L)) and whole-tree hydraulic conductance (K-T) were investigated in mature rubber trees (Hevea brasiliensis, clone RRIM 600) during the full canopy stage in the rainy season in a drought-prone area of northeast Thailand. Under well-watered soil conditions, transpiration was tightly regulated in response to high evaporative demand, i.e., above reference evapotranspiration (ETo) similar to 2.2 mm day(-1) or maximum vapor pressure deficit similar to 1.8 kPa. When the trees experienced intermittent soil drought E-T decreased sharply when relative extractable water in the top soil was < 0.4. The midday leaf water potential (psi(md)) on sunny days did not change as a function of soil drought and remained stable at approximately -1.95 MPa, i.e., displaying isohydric behavior. The decrease in E-T was mainly due to the change in K-T. K-T remained constant over a wide range of environmental conditions and decreased sharply at low soil water availability. A simple hydraulic model incorporating critical minimum water potential and the response of whole-tree hydraulic conductance to relative extractable water correctly simulated patterns of transpiration over 6 months. We conclude that an explicit and simplified framework of hydraulic limitation hypothesis was sufficient to describe water use regulation of a mature rubber tree stand in water-limited conditions. Given the complexity of constraints in the soil-plant-atmosphere pathway, our results confirm the relevance of this approach to synthesize the overall behavior of trees under drought