THE WATER RELATIONS OF RUBBER (HEVEA BRASILIENSIS): A REVIEW

摘要: SUMMARY The results of research done on water relations rubber are collated and summarised in an attempt to link fundamental studies crop physiology management practices. Background information is given the centres origin (Amazon Basin) production (humid tropics; south-east Asia), but now being grown drier regions. effects stress development processes summarised, followed by reviews its relations, requirements productivity. majority recent published international literature has been conducted Asia. tree a single straight trunk, growth which restricted ‘tapping’ for latex. Increase stem height discontinuous, period elongation ‘rest’ during emergence leaves takes place. Leaves produced tiers separated lengths bare stem. Trees older than three four years shed senescent (a process known as ‘wintering’). ‘Wintering’ induced dry, or less wet, weather; trees may remain (nearly) leafless up weeks. more pronounced dry season shorter defoliation. Re-foliation begins before rains start. supply latex dependent pressure potential vessels, whereas rate flow negatively correlated with saturation deficit air. Radial declines tapped relative untapped within two weeks start tapping. Roots can extend depth 4 m laterally 9 from trunk. roots found 0.3 soil surface. Root depressed leaf growth, while root branching enhanced. Stomata only lower surface leaf, at densities 280 700 mm −2 . xylem vessels under drought vulnerable cavitation, particularly petiole. By closing, stomata play essential role limiting cavitation. Clones differ their susceptibility occurs potentials range −1.8 −2.0 MPa. Clone RRII 105 capable maintaining higher other clones because stomatal closure, supporting reputation tolerance. photosynthetic rates. Light inhibition photosynthesis occur, young plants, when shade be beneficial. Girth measurements have used identify drought-tolerant clones. Very little reported, it difficult judge validity assumptions made some methodologies described. actual evapotranspiration rates reported generally might expected growing tropics (< 3m d −1 ). Virtually no yield responses and, regions, this surprising. In these areas, irrigation reduce immaturity 10 six years. important that plays livelihoods smallholders, integrated farming systems practised Asia, summarized.