Two-way nitrogen transfer between Dalbergia odorifera and its hemiparasite Santalum album is enhanced when the N2-fixing host effectively fixes nitrogen

Xinhua He1,2,3, Junkun Lu3, Lihua Kang3, Janet Sprent4, Daping Xu3

1 Centre of Excellence for Soil Biology, College of Resources and Environment, Southwest University, 2 Tiansheng Road, Beibei, Chongqing, China, 400715, http://zihuan.swu.edu.cn/viscms/zihuanidex/jiaoshou4231/20140901/278581.html and https://www.researchgate.net/profile/Xinhua_He3, 2School of Plant Biology, The University of Western Australia, 35 Stirling Highway, Crawley, Perth, WA, Australia, 6009; [email protected]

3 Research Institute of Tropical Forestry, Guangzhou, Guangdong, China, 510520

4 Division of Plant Sciences, University of Dundee at James Hutton Institute, Dundee, UK, DD2 5DA

Abstract

Understanding plant-parasite interactions between root hemiparasite Santalum album and its host trees has theoretical and practical significance in plantations of precious sandalwood as well as tree nutrition or fertilization management. Nutrient translocation from a host plant is vital to the growth and survival of its root parasitic plant, but few studies have investigated whether a parasitic plant is also able to transfer nutrients to its host. The role of N2-fixation in nitrogen (N) transfer between 7-month-old Dalbergia odorifera T. Chen nodulated with Bradyrhizobium elkanii DG and its hemiparasite Santalum album Linn. was examined by external 15N labelling in a pot study. Four paired treatments were used, with 15N given to either host or hemiparasite and the host either nodulated or grown on combined N. N2-fixation supplied 41–44% of total N in D. odorifera. Biomass, N and 15N contents were significantly greater in both nodulated D. odorifera and S. album grown with paired nodulated D. odorifera. Significantly higher total plant 15N recovery was in N-donor D. odorifera (68–72%) than in N-donor S. album (42–44%), regardless of the nodulation status in D. odorifera. Nitrogen transfer to S. album was significantly greater (27.8–67.8 mg plant−1) than to D. odorifera (2.0–8.9 mg plant−1) and 2.4–4.5 times greater in the nodulated pair than in the non-nodulated pair. Irrespective of the nodulation status, S. album was always the N-sink plant. The amount of two-way N transfer was increased by the presence of effective nodules, resulting in a greater net N transfer (22.6 mg plant−1) from host D. odorifera to hemiparasite S. album. Our results may provide better N management strategies for successfully mixed field plantation of S. album with D. odorifera, both are in great market demanding as preciously fragrant timbers, but have been globally over-exploited in the field.