Physiological mechanism of invasion success of trees in the Bonin islands in Japan

小笠原群岛的植物群具有高度的特有性（70%的树种），特别是在土壤浅的山脊地区。在山脊处，一般都有万年青，其特征是大量树种共存。摘要研究了常绿矮生植物日照叶性状的种间变异。单位叶面积干重（LMA）与叶片寿命、木（茎）密度、单位叶质量氮、叶片厚度、δC呈显著正相关，与叶片渗透势、膨压含水量、基于叶质量的光合速率（Pn）、基于叶面积的Pn和基于叶氮的Pn呈显著负相关。δC值与LAM、木材（茎）密度和叶片厚度呈正相关。叶片脱落时氮重吸收率平均为50%，与叶片的任何特征都不相关。由于该物种的入侵经常被发现以下冠层间隙形成的岛屿，我们假设，B.爪哇有更大的驯化能力比本地树种林下光的波动。在阴转阳和阳转阴后，先锋树种的新叶产生率高，但老叶的适应能力低，而后期演替树种的新叶产生率低，但老叶的适应能力高。而B.javanica具有较高的新叶产生率和老叶驯化能力，生长速度最快。B.javanica幼苗在小笠原群岛遮荫林下有较高的存活率。我们认为，在资源条件下的高胁迫耐受性和在波动环境条件下的高资源利用是入侵成功的生理关键因素。

The flora of Bonin islands in Japan has a high degree of endemism (70% among tree species), especially in the ridge sites with shallow soils. The dwarf evergreen forests characterized by the co-existence of a magnitude of tree species are generally found at the ridge sites. The interspecific variability of sunlit leaf characteristics was investigated among the dwarf evergreens. LMA (dry mass per unit leaf area) was positively correlated to leaf lifespan, wood (stem) density, nitrogen per unit leaf mass, lamina thickness, δC, and negatively correlated to leaf osmotic potentials and water contents at full turgor, leaf-mass based photosynthetic rates (P_n), leaf area-based P_n, and leaf nitrogen-based P_n. The values of δC were positively correlated to LAM, wood (stem) density, and leaf thickness. Nitrogen re-absorption rates at leaf shedding were 50% in the average, and were not correlated to any leaf characteristics.Bishofia javanica is an alien tree species that has successfully invaded to the Bonin islands. Because the invasion of the species was frequently found following canopy-gap formation in the islands, we hypothesized that B.javanica has greater acclimation capacity than native tree species to fluctuations in understory light. Following the shade-to-sun and sun-to-shade transfers, pioneer tree species had high new-leaf production rates but low acclimation capacity of old leaves, whereas late-successional tree species had low new-leaf production rates but high acclimation capacity of old leaves. In contrast, B.javanica had high new-leaf production rates, high acclimation capacity of old leaves, and the highest growth rates among the tree species. B.javanica seedlings had relatively high survival rates under shaded understory in the Bonin islands. We conclude that high stress-tolerance under resource conditions and high resource-use under fluctuating environment conditions are a physiological key factor of invasion success.