Relative growth rate, resource allocation and root morphology in the perennial legumes, Medicago sativa, Dorycnium rectum and D. hirsutum grown under controlled conditions

Perennial pastures are needed in farming systems in southern Australia to combat environmental problems such asdryland salinity. The mediterranean climate in southern Australia imposes constraints to the growth and survivalof perennial plants. The aim of this study was to compare growth rates, resource allocation and root distributionin three perennial legumes, Medicago sativa L., Dorycnium hirsutum (L.) Ser. and Dorycnium rectum (L.) Ser.,to identify different plant traits and their ecological and agronomic significance. Plants were grown in 1-m deepsplit tubes and destructive harvests were made every 2 weeks after plant emergence for 10 weeks. Leaf area andleaf, stem and root fresh and dry weights were measured. Maximum root depth and the root distribution werealso determined. Seedlings of Dorycnium were slower to emerge and had a lower relative growth rate (RGR) thanM. sativa. The slower RGR was associated with a lower specific leaf area (SLA) in D. hirsutum and a lower netassimilation rate (NAR) in D. rectum. Although all species allocated a similar proportion of biomass to roots,D. rectum had a shallower root distribution and took longer to produce deep roots. The slow growth rates ofDorycnium seedlings suggest that they are more prone to establishment problems due to competition from weedsor other pastures, and because they have less access to water at greater depth during summer drought. However, D.hirsutum displayed characteristics of a plant that is adapted to stressful environments and therefore may be able togrow in conditions where other perennial legumes cannot.