Intermediate host influences on the root hemi-parasite Santalum album L. biomass partitioning

Abstract

Santalum album L. seedlings parasitised on the N 2-fixing woody hosts Sesbania formosa (F. Muell.) N. Burb., Acacia trachycarpa E. Pritzel and A. ampliceps Maslin and the non-N 2-fixing woody host Eucalyptus camaldulensis Dehnh. were grown for 38 weeks in 25 l nursery containers. S. album growth was greater and root : shoot ratio lower for S. album seedlings grown with N 2-fixing hosts compared with seedlings grown with E. camaldulensis or with no host. Seedlings grown with S. formosa had a greater stem diameter, height, leaf area, root and shoot dry weight (DW) than all other treatments. S. album grown with S. formosa and A. ampliceps had a lower root : shoot ratio than all other treatments at all assessments. The root : shoot ratio of unattached S. album increased exponentially over the 38 week period. Seedling growth declined for all treatments between the 33 and 38 week harvests, except for those seedlings attached to A. trachycarpa. A strong positive linear relationship was shown between S. album leaf area and shoot DW irrespective of host species. No relationship was found between S. album shoot DW and root : shoot ratio with host shoot DW. The combined E. camaldulensis and S. album root system supported a smaller S. album shoot biomass compared with the S. album shoot biomass supported by the combined root systems of the N 2-fixing hosts and S. album. Compared with all other host species the A. trachycarpa root system was more efficient in supporting its own shoot biomass and the total biomass of S. album. Host use efficiency ( S. album shoot DW/host shoot DW) values of S. formosa and A. trachycarpa were greater than the host use efficiency values of A. ampliceps and E. camaldulensis. Values for unparasitised S. formosa leaf area, shoot and root DW and root : shoot ratio were greater than those for parasitised plants.