Phosphorus management of Australian native plants

The export market for the Australian species Caustis blakei and Sticherus flabellatus has mostly been met by bush-harvesting. Consolidation of the export market for these species is dependent upon their domestication, which will depend upon understanding their responses to fertiliser phosphorus (P). Two greenhouse experiments were conducted to investigate the P nutrition of the Australian native species Sticherus flabellatus, waxflower (Chamelaucium uncinatum x C.floriferum) 'Wanneroo' and Caustis blakei 'M63' and 'B84'. Caustis did not show deficiency symptoms at no added P, but showed P toxicity symptoms at P application rates > 11 g p m(-3) medium as MCP. The critical P concentration in the plant tops associated with a 10% decrease in yield from the maximum was 0.26% for Caustis 'M63' and 0.33% for Caustis 'B84'. The two Caustis cultivars did not develop P toxicity symptoms or show any decline in tops dry weight when fertilised with RP. Growth of Caustis 'M63' in growth substrates with different P adsorption capacity and fertilised with MCP showed that the severity of P toxicity increased with a decrease in P adsorption capacity of the growth substrate which was in the order Palmwoods soil > Mt Cotton soil > potting medium. Waxflower grown under non-leaching conditions showed reduced tops weight at no added P or when fertilised with RP. The external P requirement for production of 90% of the maximum dry weight of tops of waxflower was estimated to be 110 g p m(-3) medium when P was applied as MCP. However, waxflower did not develop P toxicity symptoms even at rates of 352 g P m(-3) medium. Sticherus did not respond significantly to P application as either MCP or RP. However, Sticherus grew much better when grown under leaching conditions than when grown under non-leaching conditions. Although leaching conferred some advantages in the growth of Sticherus and in the reduction of P toxicity in Caustis, it also caused a considerable loss of P and other nutrients.