Anisohydric but isohydrodynamic: seasonally constant plant water potential gradient explained by a stomatal control mechanism incorporating variable plant hydraulic conductance.

摘要: Isohydric and anisohydric regulations of plant water status have been observed over several decades field, glasshouse laboratory studies, yet the functional significance mechanism both remain obscure. We studied seasonal trends in hydraulic properties a natural stand Eucalyptus gomphocephala through cycles varying environmental moisture (rainfall, groundwater depth, evaporative demand) order to test for isohydry provide physiological information mechanistic interpretation status. Over 16 month period monitoring, spanning two summers, midday leaf potential (Ψleaf) correlated with predawn Ψleaf, which was table depth below ground level, turn total monthly rainfall. therefore not seasonally isohydric. Despite strong stomatal down-regulation transpiration rate response increasing demand, this insufficient prevent Ψleaf from falling levels −2 MPa driest month, well into region likely induce xylem air embolisms, based on vulnerability curves obtained study. However, even though varied by 1.2 across seasons, hydrodynamic (transpiration-induced) gradient roots shoots (ΔΨplant), measured as difference between relatively constant averaging 0.67 MPa. This unusual pattern regulation, referred here isohydrodynamic, is explained hydromechanical control model where conductance dependent rate.