其他摘要：Water transport in tall trees occurs over long-distances from roots to leaves, as well as against the gravitational hydrostatic gradient. The resulting water stress and physiological/morphological constraints of treetop leaves was considered the main cause of height-growth limitation. In tall trees, there is functional trade-off of xylem hydraulic efficiency relative to hydraulic safety and water-stress adaptation. In addition, xylem hydraulic properties affect photosynthetic production by regulating CO2 uptake through stomata and resource allocation. Because the well-illuminated treetop environment can yield potentially high photosynthetic production, researchers have suggested mechanisms that allow tall trees to adapt/acclimate to, or compensate for, hydraulic limitation. Recent research has revealed new insights, such as structural characteristics of xylem cells for hydraulic efficiency and safety, adaptation/acclimation of xylem structure and function to increasing height, and hydraulic capacitance of leaf and sapwood that compensates for hydraulic limitation. New findings have revealed variability of hydraulic architecture due to high phenotypic plasticity and short-term changes in hydraulic conductivity within tall trees. In tall trees, the water transport pathway connecting soil-plant-atmosphere is not a simple circuit consisting only of resistances, but includes circuit-breaker-like safety buffers and capacitor-like storage mechanisms. Further research should elucidate, in its entirety, the hydraulic architecture of tall trees, and lead to integrated understanding tall-tree ecophysiology.
