Pushing the limits to tree height: could foliar water storage compensate for hydraulic constraints in Sequoia sempervirens?

Abstract

Summary The constraint on vertical water transport is considered an important factor limiting height growth and maximum attainable height of trees. Here, we show evidence of foliar water storage as a mechanism that could partially compensate for this constraint in Sequoia sempervirens, the tallest species. We measured hydraulic and morpho‐anatomical characteristics of foliated shoots of tall S. sempervirens trees near the wet, northern and dry, southern limits of its geographic distribution in California, USA. The ability to store water (hydraulic capacitance) and saturated water content (leaf succulence) of foliage both increased with height and light availability, maintaining tolerance of leaves to water stress (bulk‐leaf water potential at turgor loss) constant relative to height. Transverse‐sectional area of water‐storing, transfusion tissue in leaves increased with height, while the area of xylem tissue decreased, indicating increasing allocation to water storage and decreasing reliance on water transport from roots. Treetop leaves of S. sempervirens absorb moisture via leaf surfaces and have potential to store more than five times the daily transpirational demand. Thus, foliar water storage may be an important adaptation that helps maintain physiological function of treetop leaves and hydraulic status of the crown, allowing this species to partially compensate for hydraulic constraints and sustain turgor for both photosynthesis and height growth.