Rytidosperma species (formerly Austrodanthonia) are native grasses common in temperate grasslands of southern Australia. Nine Rytidosperma species, Lolium perenne and Bromus hordeaceus were grown as microswards in pots in a glasshouse, and their growth response to six levels of applied P was measured. Shoot yield differed up to twofold between the highest-and lowest-yielding Rytidosperma species. Some Rytidosperma species were slow growing with minimal ability to respond to increased soil P availability. However, three species, Rytidosperma duttonianum, Rytidosperma racemosum and Rytidosperma richardsonii, had a similar shoot yield to L. perenne. Species that grew well at high P also grew well at low P, except B. hordeaceus, which was the lowest-yielding species at low P, but had among the highest yields at high P. No species showed evidence of P toxicity. The species exhibited a range in critical external P requirement (i.e. amount of P applied for 90% maximum yield). Among the fast-growing Rytidosperma species, R. richardsonii was notable because it had a low critical external P (16Á3 mg P pot À1 ) and high agronomic Puse efficiency (94Á1 g DW g À1 P applied). In contrast, R. duttonianum had a higher critical external P requirement (22Á4 mg P pot À1 ) and lower agronomic P-use efficiency (85 g DW g À1 P applied). It was concluded that it is important to know which Rytidosperma species are present in a grassland to understand how it may respond to P fertilization. The results help to explain the diverse opinions expressed about the productivity of pastures containing Rytidosperma species.
Perennial plants such as lucerne are now widely acknowledged as one means of controlling the expansion of dryland salinity in southern Australia. However, their inclusion in farming systems is limited by poor seedling vigour, thought to be associated with greater allocation of biomass to perennating organs in roots, and poor adaptation to some soils and climatic conditions in south-western Australia. For this reason, interest in other perennial options such as perennial wheat is increasing. In this research we compared early (29-day) seedling growth and root : shoot ratios for annual and perennial medics (Medicago truncatula and M. sativa), and for annual and perennial wheat (Triticum aestivum and Triticum × Agropyron cross). For the medics, the annual reached the 6-leaf stage after 29 days and produced more root and shoot biomass than lucerne (4-leaf stage after 29 days), but there was no difference in root : shoot ratio or depth of root growth. For wheat, there were no differences in root growth, shoot growth, or root : shoot ratio between the annual and perennial lines (Zadoks growth stages 23 and 21, respectively, after 29 days). The poor competitive performance of M. sativa seedlings relative to M. truncatula was not due to changed allocation of biomass to shoots, but was related more to seed size (2.7 and 5.0 mg, respectively). This does not seem to occur to the same extent in perennial wheat lines, suggesting that their seedling performance may be more competitive.
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