PARENT SESSION
Contributed Oral Session 124: Grassland Ecology: Water Relations; Growth
Thursday, August 11, 8:00 AM - 11:30 AM, Meeting Room 518 C, Level 5, Palais des congrès de Montréal

Rainfall regime and optimal rooting strategy in an Australian perennial grass.

Williamson, Grant^*,1, Facelli, José¹, Sadras, Victor², ¹ University of Adelaide, Adelaide, South Australia, Australia² CSIRO Land and Water, Urrbrae, South Australia, Australia

ABSTRACT- The perennial grass Austrodanthonia caespitosa H.P. Linder is common over a wide area of southern Australia, over a range that varies widely in annual rainfall total, seasonality, and event size. Seasonality is quantified using the Walsh and Lawler (1981) seasonality index, and event size bias is quantified using a statistic derived from the rainfall event size power law. Different rainfall regimes result in different distributions of water in the soil throughout the year, leading to a variety of possible optimal rooting strategies. Plants may respond to soil water availability through plasticity in root architecture, or through local genotypic differentiation, with rainfall regime acting as a selective force. An individualistic evolutionary algorithm model of plant growth and root architecture is discussed and compared with the root architecture of a number of geographically diverse genotypes of the species grown under a controlled watering regime. The model was run with both simulated rainfall with varying seasonality and event size, and with actual daily rainfall data from a number of locations across the range of the genus. Results indicate deeper roots are optimal where total annual rainfall is low, where rainfall events are large and infrequent, and where the system has a higher proportion of precipitation during the summer.

Key words: austrodanthonia caespitosa, plasticity, precipitation, modelling