Heterotrophic carbon gain and mineral nutrition of the root hemi-parasite Santalum album L. in pot culture with different hosts

Summary

This paper examines heterotrophic gain of carbon and mineral composition of Santalum album partnered singly in pot culture with three beneficial woody N₂-fixing hosts and a non-beneficial eucalypt host. Based on dry matter gains of the parasite at 33 weeks, Sesbania formosa proved the best host followed by Acacia ampliceps and A. trachycarpa while no improvement in growth was seen with Eucalyptus camaldulensis as a host in comparison with Santalum grown without a host. Numbers of haustoria formed by Santalum on roots of different hosts were poorly correlated with host quality. A small proportion of haustoria on legume hosts were attached to root nodules. Santalum partnered with any host or grown alone exhibited self-parasitism where haustoria attached to its own root system.

Based on net C and N gains of Santalum and the C: N ratios of xylem solutes of Santalum, the heterotrophic gains of C from xylem of the three beneficial legume hosts over a nine week period were equivalent to 57.9% of total carbon (35.9 g C plant⁻¹) on A. ampliceps, 45.5% (12.7 g C plant⁻¹) on A. trachycarpa and 34.6% (29.9 g C plant⁻¹) on S. formosa.

Assays of leaf, stem, bark and root tissue of Santalum and its hosts and net increases in mineral contents of Santalum over the first nine weeks of the study showed that parasitism on beneficial hosts increased the mineral contents of the parasite, with evidence of net gains in certain elements (e.g. Ca, K, P, Na) being greatest when associated with hosts richest in the corresponding element. Foliage of Santalum was extraordinarily rich in Na and in some cases also in P and N in comparison with associated hosts. Net losses or only small gains of P, K, Ca and Na over the study interval in Santalum grown alone or associated with the eucalypt indicated poor ability for nutrient uptake through its own root system.

Regression analysis showed incremental gains of N, C and Na, leaf area, content of K, N and Na in foliage of the parasite and root: shoot ratio to be excellent predictors of growth benefit from different hosts. Examples of stepwise regression analysis are provided indicating how such data might be employed for monitoring growth and host benefit under future plantation cultures of the parasite.