Contrasting whole-tree water use, hydraulics, and growth in a co-dominant diffuse-porous vs. ring-porous species pair

Abstract

Greater transport capacity of diffuse- vs. ring-porous stem networks translated into greater water use by the diffuse-porous co-dominant, but similar growth indicated higher water use efficiency of the ring-porous species. Coexistence of diffuse- vs. ring-porous trees in north-temperate deciduous forests implies a complementary ecology. The contrasting stem anatomies may result in divergent patterns of water use, and consequences for growth rate are unknown. We investigated tree hydraulics and growth rates in two co-dominants: diffuse-porous Acer grandidentatum (“maple”) and ring-porous Quercus gambelii (“oak”). Our goals were (1) document any differences in seasonal water use and its basis in divergent stem anatomy and (2) compare annual growth rates and hence growth-based water use efficiencies. At maximum transpiration, maple trees used more than double the water than oak trees. Maple also had more leaf area per basal area, resulting in similar water use per leaf area between species. Maple had ca. double the tree hydraulic conductance than oak owing to greater conductance of its diffuse-porous stem network (leaf- and root system conductances were less different between species). Water use in maple increased with vapor pressure deficit (VPD), whereas in oak it decreased very slightly indicating a more sensitive stomatal response. Seasonably stable water use and xylem pressure in oak suggested a deeper water source. Although maple used more water, both species exhibited similar annual biomass growth of the above-ground shoot network, indicating greater growth-based water use efficiency of oak shoots. In sum, water use in maple exceeded that in oak and was more influenced by soil and atmospheric water status. The low and stable water use of oak was associated with a greater efficiency in exchanging water for shoot growth.