Effect of Plant Diversity on the Occurrence of Diplodia Tip Blight in Natural Secondary Japanese Red Pine Forests

Diplodia tip blight caused by Sphaeropsis sapinea (Fr.) Dyko and B. Sutton is a serious threat to the health of natural secondary Japanese red pine (Pinus densiflora Sieb. et Zucc.) forests. To explore the effect of plant diversity on Diplodia tip blight disease occurrence, the correlation between Diplodia tip blight in P. densiflora and plant diversity in various stand types and vertical structure layers were analyzed by Pearson correlation coefficients and generalized linear model while keeping environmental factors relatively consistent. Disease index of Diplodia tip blight in P. densiflora was positively correlated with the plant diversity indices in the tree layers of P. densiflora–conifer mixed forest. In contrast, it was negatively correlated with the plant diversity indices in the tree layers of P. densiflora–hardwood mixed forest and P. densiflora pure forest. In shrub–herb layers of all stands except the P. densiflora pure forest herb layer, the disease index was positively correlated with the plant diversity indices. The prediction models for the disease index of Diplodia tip blight in the P. densiflora–hardwood mixed forest, P. densiflora–conifer mixed forest, and P. densiflora pure forest were also established. The foregoing results suggest that in the Kunyu Mountains of China, the differences in plant diversity among various stand types and vertical structure layers have different effects on the occurrence of Diplodia tip blight in P. densiflora. Plant diversity largely reflects the occurrence of Diplodia tip blight disease. However, if the effect of plant diversity on Diplodia tip blight is fully reflected, the plant species characteristics, especially tree genetic relationships, should be considered. In this way, plant species diversity structure in natural secondary Japanese red pine forests may be modified through forest management to lower the incidence of Diplodia tip blight.

Cytogenetic effects in the needles intercalar meristem of Japanese red pine in the remote period after the Fukushima NPP accident

Background. The study of the long-term effects of chronic radiation exposure on plants and animals, which are still the subject of scientific discussion, is necessary to understand the consequences of radiation accidents. After the Fukushima nuclear power plant accident, some of the young pines and spruces showed an increased frequency of apical dominance cancelling. The most probable cause of the observed morphoses is associated with damage to the apical meristem of coniferous plants by radiation in the first year of the accident, when they received the highest absorbed doses. If this hypothesis is true, then even 8 years after the accident it will be possible with high degree of probability to detect an increased level of cytogenetic abnormalities in the intercalary meristem of needles of plants from these populations. The aim of this work was to verify this hypothesis. Materials and methods. Five populations of Japanese red pine from territories contaminated with radionuclides as a result of the accident at the Fukushima nuclear power plant were investigated. The frequency and spectrum of cytogenetic abnormalities in the intercalary meristem of needles were determined by the ana-telophase analysis. Results. The frequency of aberrant cells in the needles intercalary meristem of Japanese red pine from the contaminated with radionuclides territory statistically significantly exceeds the control level in all impact sites and increases along with the dose rate. Although there is no correlation between the frequency of cytogenetic abnormalities in needles and the presence of cancellation of apical dominance in plants, all pine populations from radioactively contaminated territories are characterized by an increased frequency of both cytogenetic abnormalities and morphoses associated with the cancellation of apical dominance. Conclusion. Radiation damage to the apical meristems of conifers in the first year of the accident, when they received the highest absorbed doses, is the most likely cause of the increased frequency of cancellation of apical dominance in the studied populations of Japanese red pine from the zone affected by the accident at the Fukushima nuclear power plant.

Stand Characteristics and Soil Properties Affecting the Occurrence of Kunyushan Web-Spinning Sawfly (Cephalcia kunyushanica Xiao) in Japanese Red Pine (Pinus densiflora) Pure Forests in the Kunyushan Mountains, China

: The Kunyushan web-spinning sawfly (Cephalcia kunyushanica) is a major pest in the Japanese red pine (JRP, Pinus densiflora) pure forests in the Kunyushan Mountains of China. In this study, four stand types (ST1–4) were identified in plots of JRP pure forests, based on the pest severity index (PSI; ranging from 0–100). The order of infestation ratio in the four type stands was as follows: ST4 > ST3 > ST2 > ST1. We investigated the correlation of C. kunyushanica occurrence with stand characteristics and soil physicochemical properties in the four stand types. The results showed that all stand characteristics were different among the four stand types. Compared with infested plots, healthy (ST1) plots had a higher soil bulk density, and the differences among the groups were significant. Differences in soil water content, non-capillary porosity, and total porosity were significant among the four ST groups. The average organic matter content, total nitrogen (N), and available N were lower in ST1 plots, whereas total potassium (K) was higher compared with other ST groups. In addition, a redundancy analysis suggested that seven (total N, diameter at breast height (DBH), soil water content, bulk density, available K, zinc ion (Zn2+), and stem density) of 24 environmental variables were significantly correlated with the ordinations of C. kunyushanica occurrence. The results provide theoretical guidance for the ecological control of C. kunyushanica, and are also useful for the management of forests in areas where C. kunyushanica is a major pest and where site and stand conditions are similar.