PARTITIONING OF DRY-MATTER AND MINERAL NUTRIENTS DURING A REPRODUCTIVE-CYCLE OF THE MISTLETOE AMYEMA-LINOPHYLLUM (FENZL) TIEGHEM PARASITIZING CASUARINA-OBESA MIQ

Budgets for utilization of dry matter, nitrogen and a range of mineral elements were constructed for the reproductive season (September 1988-May 1989) of plants of the mistletoe Amyema linophyllum (Loranthaceae) parasitizing the swamp she oak (Casuarina obesa Miq.) at Gingin, W. Australia. Shed buds comprised 55% of the allotment of dry matter to reproduction, shed flowers 7%, abscised perianths and styles 15%, prematurely shed fruits 15%, and successfully ripened fruits a mere 12%. Commitment to reproductive biomass peaked sharply in October, while the generally higher rate of allocation to vegetative biomass declined from beginning to end of the 9.5 month reproductive cycle. Investments of dry matter in new leaves and secondary thickening of previous season's stems were several-fold greater budget items than production of new stems and shedding of leaves. There was no evidence of pre-senescence retrieval of N, P, and K from leaves, and concentrations of Ca, Mg, Na, and Cl increased steadily in dry matter with leaf age. Values for reproductive effort (RE) for dry matter and specific mineral elements were calculated as commitment to reproduction divided by commitment to reproduction plus vegetative biomass (x 100). Due to highly differential partitioning of certain elements between reproductive and vegetative parts, RE values for minerals for the reproductive season ranged widely, viz. 7% for Ca, 10% for Mn, 15% for Mg, 17% for N, 25% for K and Zn, 26% for Cu, and 35% for P. The comparable RE for dry matter was 29%. The weight ratio for net intake of nutrient elements from the host by A. linophyllum for the reproductive season was 21.5:20.2:6.6:1.6:1 (N:K:Ca:Mg:P), while the mean weight ratio for the concentrations of these elements in xylem (tracheal) sap of the Casuarina host was 13.9:15.6:4.1:3.0:1, respectively. The data are discussed in relation to the demonstration of a direct lumen-to-lumen tracheary continuity between host and mistletoe in mature regions of the haustorial interface.