We investigated the patterns of soil nitrogen (N) and forest floor light availability, forest structure and tree species distribution along a topographic gradient on a 200‐m mountain slope in a cool‐temperate deciduous broad‐leaved forest in Japan. Rates of soil N mineralization and nitrification decreased from lower to upper slope positions, revealing that N availability decreased up the slope. Maximum tree height and above‐ground biomass were greater on the lower than the upper parts of the slope. Canopy openness, an index of light availability at the forest floor, increased up the slope. Tree species could be placed into three groups according to their distribution patterns on the slope. ‘Ridge’ and ‘valley’ species were distributed on the upper and lower parts of the slope, respectively, whereas ‘uniform’ species were distributed over the entire slope. Topography‐mediated resource gradients of soil N and light may be important determinants of species distribution patterns and forest regeneration, and the results of this study imply that the determinants of the regeneration process differ between the lower and upper parts of a slope. The former may be relatively light limited and the latter may be soil N limited. Valley species may have a greater ability to compete for light, whereas ridge species have a greater ability to compete for soil N. The broad distribution of uniform species probably reflects an ability to effectively compete for both light and soil N.

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The mechanisms underlying community composition and diversity of soil archaea are poorly understood. We compared both total archaea and ammonia oxidizing archaea (AOA) using 16S rRNA and amoA genes pyrosequencing respectively, in two different biomes: tropics (Malaysia), and temperate (Korea and Japan). Despite differences in characteristics of these biomes, we found that at the broad taxonomic level the dominant archaeal lineages are the same, except in certain instances (16S rRNA gene: group 1.1a Thaumarchaeota; amoA gene: Nitrososphaera and Nitrosotalea lineages). However, at the OTU level, both total archaea and AOA communities showed biome-specific patterns, indicating that at lower taxonomic levels biome differences are also important. In both biomes, total archaeal diversity showed a negative correlation with pH, but a hump-shaped curve for AOA diversity, peaking at ∼pH 6.0. Within each biome, pH also emerged as the delimiting factor determining variation in community composition of both total archaea and AOA. Communities from each biome clustered separately, even at analogous pH levels. At the OTU level, certain shared OTUs did occur at approximately the same pH range in both biomes. We found that closely related OTUs of both total archaea and AOA respectively tended to co-occur, suggesting that in evolutionary terms these closely related lineages have conserved very similar ecological requirements. This predictability also strongly suggests that soil archaeal community assembly has strongly deterministic aspect. Overall, our findings emphasize that soil archaeal communities are to large extent predictable and structured by both biome and by soil chemical environment, especially pH.

The amount and genetic composition of pollen grains that are transported to flowers influence the reproduction and fitness of plants. Despite the importance of insect-pollination systems, an understanding of those systems is still lacking due to the absence of a genetic analysis of pollen grains that are transported to flowers. We evaluated the pollination efficiencies of bumblebees (Apidae, Bombus spp.), flower beetles (Scarabaeidae, subfamily Cetoniinae, Protaetia and Eucetonia sp.), and small beetles (Lagriidae, Arthromacra sp.) that visited the flowers of Magnolia obovata (Magnoliaceae) using quantitative (flower visitation frequency, amount of adherent pollen per insect) and qualitative (origin and genetic diversity of adherent pollen per insect) criteria. Most of the pollen adhering to bumblebees and small beetles was self-pollen. This result suggests that visitation by these insects may cause geitonogamous pollen flow and negatively affect the reproduction of M. obovata, causing inbreeding depression. In contrast, flower beetles transported large amounts of genetically diverse outcross pollen. Our results suggest that certain beetle species contribute quantitatively and qualitatively to the pollination of M. obovata. Direct genetic analysis of pollen grains will advance our understanding of plant mating systems and may shed light on the mutualism and coevolution of plants and flower visitors.