Ku. Tennakoon et al., 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, Journal of Experimental Botany, 48(310), 1997, pp. 1047-1060
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.