Water Relations, Shoot and Root Architecture, and Phenology of Three Co-Occurring Banksia Species: No Evidence for Niche Differentiation in the Pattern of Water Use

Abstract

The niches of three co-dominant Banksia shrub species were determined by examining their water relations, architecture and vegetative phenology. Dawn and dusk xylem pressure potentials were similar in the three species, decreasing almost three fold from early summer to mid-autumn. All species showed similar daily patterns of stomatal conductance. Peak conductances decreased almost three fold over the summer period, corresponding with increased aerial and edaphic water deficits. The horizontal and vertical root patterns were similar, providing equal access to soil-stored water, with much intermingling of root systems. Vegetative growth of the three species occurred almost exclusively in summer even though surface root growth was restricted to winter-spring. Despite marked differences in life history and leaf sizes, no variations in water use patterns that might promote co-existence of the three species were evident. It is concluded that co-occurrence of these species cannot be attributed to their differential partitioning of this apparently limiting resource.