| Summary: | 碩士 === 國立臺灣大學 === 生態學與演化生物學研究所 === 105 === Holoparasitic plants lack chlorophylls and gain all the nutrients only from host plants. The absorption mechanism and nutrient status of the holoparasitic plants in Taiwan have not been studied. This research investigated the nutrient relationship between five holoparasites (Aeginetia indica, Balanophora laxiflora, Mitrastemon kanehirai, Mitrastemon kawasasakii, Cuscuta campestris) and their hosts. These studied parasitic plants differ in degree of host-specificity, parasitic location on host (root or stem/leaf) and parasitic forms (endoparasite or ectoparasite).
Tissue sections were made and investigated to confirm whether there are connecting tissues between holoparasites and their hosts. Subsequently, carbon (C), nitrogen (N), phosphorus (P), calcium (Ca), magnesium (Mg), potassium (K), sodium (Na) contents and carbon (δ13C), nitrogen (δ15N) stable isotopes of the parasitic plants and their hosts were analyzed. The following objectives were studied: 1) to investigate the nutrient contents of holoparasites, and to compare whether the holoparasites of different degree of host-specificity are different in nutrient contents; 2) to investigate whether the holoparasites and their hosts have identical δ13C and δ15N values, and to evaluate the possibility of using the stable isotope ratio for tracing the hosts of holoparasites.
The structures of haustoria of A. indica and C. campestris revealed that these two parasitic plants invaded hosts by the parenchyma cells and had xylem connection with their hosts. In the tuber of B. laxiflora, there were composite bundle consisting both the holoparasite and the host tissues and the transfer cells were found in the center. The two Mitrastemon spp., belonging to endoparasite, formed large masses between cortex and phloem of host roots.
The results showed that the studied holoparasites had significantly higher C, P, K, lower Ca contents and higher K/Ca ratio than their hosts. Accordingly, by accumulation of K for lowering the osmatic and water potential, the holoparasites might gain water and solute from their hosts. Besides, the high K/Ca ratio indicated that these holoparasites obtained nutrient mainly from host phloem. The two Mitrastemon spp. had significantly higher C but lower K contents than other three holoparasites which might be related to their high degree of host-specificity and being endoparasitic.
The holoparasites had significantly higher δ13C and δ15N values than their hosts. In addition, there were positive correlations in δ13C and δ15N values between holoparasites and their hosts. Thus, it is possible to use the ratio of carbon and nitrogen stable isotopes ratio as an indicator for tracing the hosts of the holoparasites.
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