Inter-specific differences in the dynamics of water use and pulse-response of co-dominant canopy species in a dryland woodland

- We captured the response of three species of Acacia to a simulated rainfall pulse.
- Tree water relations were anisohydric and tightly coupled to soil water availability.
- Branch water potential increased from ∼−8 MPa to > −1 MPa within 5 days.
- Phyllode relative water content increased from 43.4% to 98.6% within 5 days.
- There was no evidence of temporal resource partitioning among the canopy species.

Differences in the magnitude and timing of rainfall pulse-response among plant species in dryland ecosystems may facilitate the maintenance of species diversity, but this hypothesis remains untested among species that appear to occupy the same ecological niche. Here, we examined the pulse-response of co-dominant Acacia species forming the canopy of a dryland woodland. Trees received natural precipitation and supplemental irrigation equivalent to a ∼105 mm rainfall pulse over four days. The pulse-response was large and rapid irrespective of species or differences in minimum water potential during drought. Branch water potential increased from ∼−8 MPa to > −1 MPa at pre-dawn and foliage relative water content increased from 43.4% to 98.6% within five days of drought-break. Differences in midday water potential among species following the water pulse reflected differences in rates of stomatal conductance (gs) and likely as a consequence of differences in specific leaf area (SLA). We conclude there is no temporal partitioning of resources among the canopy species in the study woodland. Instead, water relations in these three closely related species were anisohydric and tightly coupled to soil water availability.