Concurrent carbon and nitrogen transfer between hemiparasite Santalum album and two N2-fixing hosts in a sandalwood plantation

Abstract Root hemiparasites feed on host root xylem and prefer N2-fixing hosts. Carbon (C) and nitrogen (N) translocation from hosts to hemiparasites affect growth and development, but detailed C and N economies between hemiparasites and N2-fixing hosts are unknown. In a 6-year-old Santalum album (sandalwood) plantation, concurrent movement of C and N between plants over 14 days were traced among N2-fixing Acacia confusa, N2-fixing Dalbergia odorifera (rosewood) and non-N2-fixing hemi-parasitic sandalwood by adding 13C-labeled and 15N-labeled urea to leaves of one species (donor) and tracing the label into other two species (receivers) within three triple-tree combinations. Haustorial connections and host selectivity were also examined on roots and nodules within adjacent plants. N2 fixation by acacia and rosewood was quantified in the stand by 15N natural abundance. Parasitic haustoria of sandalwood on roots and nodules of N2-fixing acacia and rosewood were more frequent than on other non-N2-fixing herbaceous plants, indicating strong host selectivity and preference. N2 fixation supplied 19.7% and 52.3% of the total N in acacia and rosewood, respectively. During 14 days of labeling, more 13C and 15N was transferred from acacia or rosewood to sandalwood than from sandalwood to these two N2 fixers. Net C and N transfer between tree pairs indicated that hemiparasite sandalwood was the C sink or N sink when associated with N2-fixing acacia or rosewood, while N2-fixing acacia was the C sink or N sink when associated with N2-fixing rosewood. This study indicated that mixed plantations had high rates of interplant nutrient transfer. Our results also showed that the herbaceous plants might acquire some C and N from sandalwood and two N2-fixing plants via both direct and indirect transfers, suggesting a nutrient translocation between plants within this community. This mixed plantation of acacia/rosewood/sandalwood could replace low-valued single species or mixed plantations for growing both high-value sandalwood and rosewood heartwoods. Our study quantified nutrient transfer among plants in a sandalwood plantation. These results have improved our understanding of the physiological interactions in resource acquisition between host species and parasitic plants and provided insights into promising mixed-plantation patterns for valuable tropical trees in south China and globally.