Soil moisture controls on phenology and productivity in a semi-arid critical zone

James Cleverly; Derek Eamus; Natalia Restrepo Coupe; Chao Chen; Wouter Maes; Longhui Li; Ralph Faux; Nadia S Santini; Rizwana Rumman; Qiang Yu; Alfredo Huete

doi:10.1016/j.scitotenv.2016.05.142

Soil moisture controls on phenology and productivity in a semi-arid critical zone

Sci Total Environ. 2016 Oct 15:568:1227-1237. doi: 10.1016/j.scitotenv.2016.05.142. Epub 2016 May 27.

Authors

James Cleverly¹, Derek Eamus², Natalia Restrepo Coupe³, Chao Chen⁴, Wouter Maes³, Longhui Li⁵, Ralph Faux⁵, Nadia S Santini⁵, Rizwana Rumman⁵, Qiang Yu⁵, Alfredo Huete³

Affiliations

¹ School of Life Sciences, University of Technology Sydney, PO Box 123, Broadway, NSW 2007, Australia; Australian SuperSite Network, University of Technology Sydney, PO Box 123, Broadway, NS 2007, Australia. Electronic address: james.cleverly@uts.edu.au.
² School of Life Sciences, University of Technology Sydney, PO Box 123, Broadway, NSW 2007, Australia; Australian SuperSite Network, University of Technology Sydney, PO Box 123, Broadway, NS 2007, Australia.
³ School of Life Sciences, University of Technology Sydney, PO Box 123, Broadway, NSW 2007, Australia; Plant Functional Biology and Climate Change Cluster, University of Technology Sydney, Australia.
⁴ CSIRO Agriculture Flagship, PMB 5, PO Wembley, WA 6913, Australia.
⁵ School of Life Sciences, University of Technology Sydney, PO Box 123, Broadway, NSW 2007, Australia.

PMID: 27241203
DOI: 10.1016/j.scitotenv.2016.05.142

Abstract

The Earth's Critical Zone, where physical, chemical and biological systems interact, extends from the top of the canopy to the underlying bedrock. In this study, we investigated soil moisture controls on phenology and productivity of an Acacia woodland in semi-arid central Australia. Situated on an extensive sand plain with negligible runoff and drainage, the carry-over of soil moisture content (θ) in the rhizosphere enabled the delay of phenology and productivity across seasons, until conditions were favourable for transpiration of that water to prevent overheating in the canopy. Storage of soil moisture near the surface (in the top few metres) was promoted by a siliceous hardpan. Pulsed recharge of θ above the hardpan was rapid and depended upon precipitation amount: 150mm storm(-1) resulted in saturation of θ above the hardpan (i.e., formation of a temporary, discontinuous perched aquifer above the hardpan in unconsolidated soil) and immediate carbon uptake by the vegetation. During dry and inter-storm periods, we inferred the presence of hydraulic lift from soil storage above the hardpan to the surface due to (i) regular daily drawdown of θ in the reservoir that accumulates above the hardpan in the absence of drainage and evapotranspiration; (ii) the dimorphic root distribution wherein most roots were found in dry soil near the surface, but with significant root just above the hardpan; and (iii) synchronisation of phenology amongst trees and grasses in the dry season. We propose that hydraulic redistribution provides a small amount of moisture that maintains functioning of the shallow roots during long periods when the surface soil layer was dry, thereby enabling Mulga to maintain physiological activity without diminishing phenological and physiological responses to precipitation when conditions were favourable to promote canopy cooling.

Keywords: Climate extremes; Ecohydrology; Evergreen Acacia; Resilience; Semi-arid woodland; Soil moisture carry-over.