Concurrent carbon and nitrogen transfer between hemiparasite Santalum album and two N-2-fixing hosts in a sandalwood plantation

摘要

Root hemiparasites feed on host root xylem and prefer N-2-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 N-2-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 N-2-fixing Acacia confusa, N-2-fixing Dalbergia odorifera (rosewood) and non-N-2-fixing hemi-parasitic sandalwood by adding C-13-labeled and N-15-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. N-2 fixation by acacia and rosewood was quantified in the stand by N-15 natural abundance. Parasitic haustoria of sandalwood on roots and nodules of N-2-fixing acacia and rosewood were more frequent than on other non-N-2-fixing herbaceous plants, indicating strong host selectivity and preference. N-2 fixation supplied 19.7% and 52.3% of the total N in acacia and rosewood, respectively. During 14 days of labeling, more C-13 and N-15 was transferred from acacia or rosewood to sandalwood than from sandalwood to these two N-2 fixers. Net C and N transfer between tree pairs indicated that hemiparasite sandalwood was the C sink or N sink when associated with N-2-fixing acacia or rosewood, while N-2-fixing acacia was the C sink or N sink when associated with N-2-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 N-2-fixing plants via both direct and indirect transfers, suggesting a nutrient translocafion 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.