Ecological Response Of Alternanthera Philoxeroides To The Local Parasitic Cuscuta Australis

In order to explore the feasility of the biological control of Alternanthera philoxeroides by the parasitization of local parasitic Cuscuta australis, we analyzed the effect of different levels of parasitization by Cuscuta australis on the photosynthetic, growth, the stem structure and the primary and secondary metabolites of A. philoxeroides in order to elucidate the response of invasive A. philoxeroides to the local parasitic Cuscuta australis. In addition, we selected the resistant, tolerable and no resistanct and tolerable A. philoxeroides according to the growth, stem structure and the content of metabolites and analyzed the change of the growth, stem structure and the contenet of metabolites after the reprasitized by C. australis to evaluate the adapatative response of invasive A. philoxeroides to local parasitic C. australis. The results were shown as the followings.1. Pn、Pmax and Ci、 Gs of A. philoxeroides at different parasitization levels were all lower than those of A. philoxeroides without parasitization, indicating that the parasitism of C. australis could decrease the photosynthetic ability of invasive A. philoxeroides. The parasitization of A. philoxeroides by C. australis at different levels affect differently on the photosynthetic ability of A. philoxeroides. The effect increased with the increasing of the levels. The Pn、 Pmax and Ci、 Gs of A. philoxeroids lightly parasitzed by C. australis were significantly higher than those of A. philoxeroids moderately and heavily parasitized by the C. australis. The photosynthetic ability of A. philoxeroids heavily parasitzed by C. australiswas the least. The light saturation point (LSP) and apparent quantum efficiency (AQE), Carboxylation efficieicny (Vc), the largest electronic transfer efficiency and the maximum use sugar phosphate of A. philoxeroides at different parasitization levels were all lower than those of A. philoxeroides without parasitization. Theere was significant differences of Vc among different parasitization levels with the largest after the light parasitization. The content of chlorophyll of A. philoxeroides at different parasitization levels were all lower than those of A. philoxeroides without parasitization, with the largest at the heavy parasitization treatment. The Fv/Fm of A. philoxeroides without parasitization was significantly higher than that of moderate and heavy parasitization treatments.2. The growth of of A. philoxeroides at different parasitization levels were lower than those of A. philoxeroides with parasitization, but there was no significant differences among treatments with different levels. Parasism signicantly affect the stem structure of A. philoxeroides, but there was no significant difference among treatments with different levels. Parasism signicantly affect the soluble protein content, the cellulose, hemicellulose, lignin, tannin, phenol and the total saponins content. The different parasitization levels had different effect on the content of metabolites of A. philoxeroide with the least at the light parasitization level and the highest at the heavy parasitization level. The results indicated that the parasitism of C. australis had significant effect on the growth and the metabolites content of A. philoxeroide, especially the content of metabolites.3. According to the field investigation of the growth related parameters, the stem length, branches number, leaves number and the biomass of tolerable A. philoxeroide were significantly higher than those of resistant A. philoxeroide, which were significantly higher than those of control. The stem length, stem vascular cylinder diameter and the medullary cavity diameter of tolerable A. philoxeroide were significantly higher than those of resistant A. philoxeroide and control, while those of resistanct A. philoxeroide were also significantly higher than those of control. The content of soluble protein and the secondary metabolites of resistant A. philoxeroide were significantly higher than those of tolerable A. philoxeroide and control, while those of tolerable A. philoxeroide were significantly higher than those of control. The results indicated that the invasive A. philoxeroide could be resistant or tolerant to parasitic C. australis with the adaptation to parasitic C. australis. Therefore, the feasibilyt of the prevention and control of plants A. philoxeroide by using parasitic C. asutralis need to be further studied.