title: Water loss regulation in mature Hevea brasiliensis: effects of intermittent drought in the rainy season and hydraulic regulation.
abstract: Effects of soil and atmospheric drought on whole-tree transpiration (E(T)), leaf water potential (Ψ(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 (ET(0)) ~2.2 mm day(-1) or maximum vapor pressure deficit ~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 (Ψ(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.
authors: Faculty of Agriculture, Khon Kaen University, Khon Kaen 40002, Thailand. isupat@kku.ac.th
authors: Supat
authors: S
authors: Isarangkool Na Ayutthaya
authors: Frederic C
authors: FC
authors: Do
authors: Krirk
authors: K
authors: Pannangpetch
authors: Junya
authors: J
authors: Junjittakarn
authors: Jean-Luc
authors: JL
authors: Maeght
authors: Alain
authors: A
authors: Rocheteau
authors: Herve
authors: H
authors: Cochard
mesh_terms: D000388:Air / Q000032:analysis; D002940:Circadian Rhythm; D055864:Droughts; D028482:Hevea / Q000502:physiology*; D007700:Kinetics; D008954:Models, Biological; D018515:Plant Leaves / Q000502:physiology; D018526:Plant Transpiration; D011891:Rain; D012621:Seasons; D012987:Soil / Q000032:analysis; D014867:Water / Q000032:analysis / Q000502:physiology*
chemical_list: D012987:Soil; D014867:Water