Ku. Tennakoon et Js. Pate, HETEROTROPHIC GAIN OF CARBON FROM HOSTS BY THE XYLEM-TAPPING ROOT HEMIPARASITE OLAX-PHYLLANTHI (OLACACEAE), Oecologia, 105(3), 1996, pp. 369-376
Heterotrophic gains of carbon from various host species by the root he
miparasitic shrub Olax phyllanthi (Labill) R.Br. were assessed using t
echniques based on carbon isotope discrimination (delta(13)C) On C3 an
d C4 hosts and C:N ratios of xylem sap and dry matter of host and para
site. Heterotrophic benefits (H) to Olax based on delta(13)C values we
re 30% and 19% from two non-native C4 hosts (Portulaca oleracea and Am
aranthus caudatus respectively) compared with 13% and 15% from these h
osts when computed on the basis of C:N ratios of host xylem sap and C
and N increments of Olax dry matter. Nitrate was the source of N avail
able to pot cultures of the above species and estimates based on C:N r
atios assumed that all N accumulated by Olax: had come from nitrate ab
sorbed by the host. Equivalent estimates of H for Olax, grown in nitro
gen-free pot culture with the native N-2-fixing host Acacia littorea a
s its sole source of N, indicated 63% and 51% dependence on host carbo
n when assessed in terms of xylem sap composition of host and parasite
respectively. Comparisons of xylem sap solutes of Olax and a range of
partner hosts indicated marked selectivity in haustorial uptake and t
ransfer of nitrate, amino compounds, organic acids and sugars. Possibl
e implications of variations between hosts in absolute levels of C and
inorganic and organic forms of N in xylem are discussed in relation t
o evidence of much better growth performance of Olax on Acacia littore
a and other N-2-fixing legumes than on non-fixers.