GROWTH AND PARTITIONING OF C AND FIXED N IN THE SHRUB LEGUME ACACIA-LITTOREA IN THE PRESENCE OR ABSENCE OF THE ROOT HEMIPARASITE OLAX-PHYLLANTHI

Nodulated plants of Acacia littorea were pot cultured singly in minus nitrogen sand culture in the presence or absence of a transplanted see dling of the root hemiparasite Olax phyllanthi and harvests of culture s made 4 and 8 months after introducing the parasite. Parasitism decre ased host shoot growth while increasing root growth to a similar exten t. Final shoot:root dry weight ratio was 2.2 for parasitized versus 4. 3 for unparasitized Acacia. Partitioning of fixed N showed 4-fold larg er N increments in shoots than roots of unparasitized plants, whereas parasitized plants lost a small amount of shoot N, made a root gain of N double that of unparasitized plants and lost over half of their N t o Olax. The increment of fixed N in the host:parasite association was similar to that of unparasitized Acacia. Data on dry matter gain per u nit foliage area and mean CO2 assimilation rates per shoot of Olax and Acacia (parasitized or unparasitized) were discussed in relation to a n estimated heterotrophic gain of xylem C from the host equivalent to 40% of the increment of dry matter C made by the parasite. Growth of O lax was accompanied by large increases in numbers of haustoria, 9% of which were attached to root nodules as opposed to roots, Structural an d nutritional features of direct parasitism of nodules are described. Models of flow and utilization of C and N in the Acacia : Olax associa tion and unparasitized Acacia are discussed in relation to published d ata for other host:parasite associations.