Massoniana Seedlings Research Articles

Differential Sensitivity of Growth and Net Photosynthetic Rates in Five Tree Species Seedlings under Simulated Acid Rain Stress

This study investigated the effect of simulated acid rain (SAR) (heavy: pH 2.5; moderate: pH 4.0; and control: pH 5.6) stress on the growth and net photosynthetic rate (Pn) of five tree species, namely Castanopsis sclerophylla, Cinnamomum camphora, Manglietia fordiana, Pinus massoniana, and Elaeocarpus glabripetalus. Results showed variable responses to SAR with different pH values depending on the type of plants. P. massoniana seedlings exhibited significant growth reduction in response to all of the SAR treatments. The net photosynthetic rate of P. massoniana treated by SAR decreased by 20 and 34% under pH 4 and 2.5, suggesting that P. massoniana was susceptible when exposed to acid rain. These results indicate that P. massoniana was the highest sensitivity inhibitory type to SAR and should be protected. However, the growth, chlorophyll content, and Pn of three species (C. sclerophylla, C. camphora, M. fordiana) revealed the following result: moderate acid rain > control > heavy acid rain, suggesting that moderate acid rain promoted photosynthesis and growth to some extent. Among the five species, E. glabripetalus exhibited the highest extent of tolerance to acid rain. The sensitivity of growth and Pn of E. glabripetalus was significantly higher than that of the control, indicating that SAR promoted rather than inhibited its seedling, E. glabripetalus belonging to the promotional type. The stress tolerance of five species of trees to SAR was observed in the following order: E. glabripetalus > C. sclerophylla, C. camphora, M. fordiana > P. massoniana. But exposure to SAR at PH 2.5 to 5.6 did not affect the final mortality of five tree species.

Pathogenicity of Aseptic Bursaphelenchus xylophilus

Pine wilt is a disease of pine (Pinus spp.) caused by the pine wood nematode (PWN), Bursaphelenchus xylophilus. However, the pathogenic mechanism of pine wilt disease (PWD) remains unclear. Although the PWN was thought to be the only pathogenic agent associated with this disease, a potential role for bacterial symbionts in the disease process was recently proposed. Studies have indicated that aseptic PWNs do not cause PWD in aseptic pine trees, while PWNs associated with bacteria cause wilting symptoms. To investigate the pathogenicity of the PWN and its associated bacteria, 3-month-old microcuttings derived from certain clones of Pinus densiflora Siebold & Zucc. produced in vitro were inoculated under aseptic conditions with aseptic PWNs, non-aseptic PWNs and bacteria isolated from the nematodes. Six-month-old aseptic P. densiflora microcuttings and 7-month-old P. massoniana seedlings were also inoculated under aseptic conditions with aseptic PWNs and non-aseptic PWNs. The results showed that the aseptic microcuttings and seedlings inoculated with aseptic PWNs or non-aseptic PWNs wilted, while those inoculated with bacterial isolates did not wilt. Nematodes were recovered from wilted microcuttings and seedlings inoculated with aseptic PWNs and non-aseptic PWNs, and the asepsis of nematodes recovered from aseptic PWN-inoculated microcuttings and seedlings was reconfirmed by culturing them in NB liquid medium at 30°C for more than 7 days. Taken together, the results indicate that the asepsis of PWN did not cause the loss of pathogenicity.

Mycorrhizal associations in Pinus massoniana Lamb. and Pinus elliottii Engel. inoculated with Pisolithus tinctorius

Dichotomous mycorrhizas were induced in Pinus massoniana and Pinus elliottii seedlings inoculated with Pisolithus tinctorius growing under non-axenic conditions. Six months after inoculation, Pinus massoniana seedlings exhibited a higher degree of infection, bore more mycorrhizas and had developed more abundant extramatrical mycelium than seedlings of Pinus elliottii. Nevertheless, seedlings of Pinus massoniana were stunted and exhibited chorosis of the needles, indicating a possible nutrient deficiency. Histological examination of these pine mycorrhizas showed an ectomycorrhizal association typical of gymnosperms with an intercellular Harting net penetrating between several layers of cortical cells close to the endodermis. However, strong polyphenolic reactions, intracellular hyphae and wall modifications were occasionally observed, indicating that both host-tissue incompatibility and ectendomycorrhizal association can occur in pine species under stressed conditions.