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The introgression from genetically modified soybean (Glycine max (L)) to wild soybean (Glycine soja Sieb. et Zucc.) could be threat the genetic diversity of wild soybean. Flowering synchrony is essential to the occurrence of outcrossing, but the flowering phenology of wild soybean is less well researched than that of cultivated soybean. We developed models to predict flowering initiation of wild soybean, based on the flowering initiation dates of wild soybean five accessions from different latitudes (31.4°N to 42.6°N) in growth chambers in which temperature and day length varied. Our proposed models predicted the flowering initiation date of wild soybean in the natural habitat well; the averaged difference from observed date in 5 areas was -1.8 days (-8 to +5). In the long day condition, there was a clear latitudinal cline of photoperiodic sensitivity throughout Japan. Accessions in southern part of Japan archipelago required higher temperature even under the short-day conditions and northern accessions were less-sensitive to long-day conditions. Our result showed the possibility of predicting the flowering initiation of wild soybean, corresponding to latitudes.

Faunal assemblage alterations due to anthropogenic impacts have changed herbivore–vegetation relationships in various ecosystems, but the influences of small vertebrates on revegetation processes remain unclear. In a peri-urban agricultural landscape in eastern Japan that lacks large ungulates but supports small generalist herbivores, fewer native seedlings have become established in thickets dominated by native dwarf bamboo, Pleioblastus chino (Franch. et Sav.) Makino. The mechanisms limiting tree seedling establishment are unknown. Our aim here was to evaluate the influence of interactions among the dwarf bamboo, its litter cover and small vertebrate herbivores on the microsite conditions governing the establishment of native tree seedlings from different successional stages in an old field in temperate Japan. First, seedling emergence and survival of seeded Pinus densiflora Siebold et Zucc., Celtis sinensis Pers., Aphananthe aspera (Thunb.) Planch., Quercus serrata Murray, Quercus myrsinifolia Blume and Castanopsis sieboldii (Makino) Hatus. ex T. Yamaz. et Mashiba were observed in a factorial design that accounted for the presence or absence of dwarf bamboo and its litter cover, as well as the exclusion or access of small vertebrate fauna, in 2009 and 2010. To identify small vertebrate herbivores that reduced the emergence or survival of tree seedlings in the first experiment, reseeding experiments using P. densiflora, C. sinensis, A. aspera and Q. myrsinifolia were conducted by video trapping in 2011 and video and still-camera trapping in 2012. The abiotic conditions under the dwarf bamboo were lethal to early- to mid-successional P. densiflora, C. sinensis, A. aspera and Q. serrata but led to better survival—although spindly growth—of late-successional Q. myrsinifolia and C. sieboldii. The main consumers and the plants they found palatable differed between the bamboo thickets and the intervening gaps. Predation by mice appeared to have severely limited the emergence of all species, particularly in the bamboo thickets but occasionally in the gaps, whereas litter cover slightly mitigated this limitation. However, bamboo litter cover reduced the emergence of P. densiflora in the gaps. Chinese bamboo partridge (Bambusicola thoracicus Temminck), an introduced game bird, selectively and severely fed on the cotyledons—and probably seeds—of A. aspera and moderately preyed upon those of P. densiflora in the gaps. Apparent consumption of seedlings in the gaps by the Japanese hare (Lepus brachyurus Temminck) suppressed the growth of all species but apparently did not severely affect emergence and survival. Thus, the net balance of positive and negative interactions at the bamboo thicket scale (i.e. the presence of dominant dwarf bamboo cover or intervening gaps and the herbivore behaviours in these two environments) and at the microsite level (i.e. litter cover) shapes the early establishment patterns of native tree seedlings, and this balance differs among tree seedling species.

In the subalpine zone on Mt. Hakusan, Japan, Plantago asiatica, an alien plant, and Plantago hakusanensis, a native alpine species, grow sympatrically along with their putative hybrids. Here, their flowering behavior, which affects the frequency of hybridization and the colonizing ability of P. asiatica and its hybrids, is described. The flowering behavior of each species and of two F1 hybrids from different seed parents was determined based on the position of the flower in the inflorescence by using a generalized linear mixed model. The percentage fruit set of individually bagged inflorescences was calculated to corroborate the assumptions of the opportunities for self-pollination. All the flowers were protogynous; however, many P. asiatica anthers dehisced before browning of the stigma in the flower and the sex presentations in the inflorescence were asynchronous. The percentage of fruit set was high. Consequently, P. asiatica has the opportunity for self-pollination within the flower and in the inflorescence. In contrast, the P. hakusanensis anthers dehisced after browning of the stigma in the flower; their sex presentation was synchronous in the inflorescence, showing negligible opportunities for self-pollination, and the fruit set was low. Accordingly, in the field, P. hakusanensis might require pollination among the inflorescences for seed production and be actively outcrossed, while P. asiatica is able to outcross in the early flowering phase. Therefore, P. asiatica and P. hakusanensis have opportunities for hybridization. The F1 hybrids exhibited intermediate flowering behavior and produced fruits, demonstrating the potential to reproduce by selfing.

Natural forest recovery on abandoned farmland is hindered by a variety of factors and active restoration plays an important role when quick afforestation is desired. We investigated seedling survival of four transplanted native tree species (Quercus myrsinifolia, Quercus serrata, Aphananthe aspera, and Rhus sylvestris) by experimentally manipulating the vegetation cover, which was mainly dominated by dwarf bamboo (Pleioblastus chino), and herbivore access to the planting sites on farmland that had been abandoned for 15 years at the start of the study. Few transplanted seedlings of any species survived under intact vegetation cover, irrespective of herbivore presence. In gaps in the vegetation cover, winter browsing by Japanese hare (Lepus brachyurus) damaged all species. However, lower browsing frequency and higher resprouting ability after grazing of the seedlings enabled both Quercus species to survive better than the other species. These results indicate that dwarf bamboo and the hare jointly limit the establishment of native trees in old fields. If active afforestation by transplanting seedlings at sites dominated by dwarf bamboo is planned, a combination of vegetation removal, selection of suitable species, and temporary seedling protection will be most effective.

Restoring natural forests after field abandonment is a land management objective that fosters the recovery of forest biodiversity. We performed seeding and transplanting of native tree species 40 years after the abandonment of an arable field that became dominated by a dwarf bamboo (Pleioblastus chino (Franch. et Sav.) Makino) and by kudzu (Pueraria lobata (Willd.) Ohwi). By permutation tests, the removal of competing vegetation (gap creation) significantly increased the survival of three seeded species of Fagaceae and of eight transplanted species. In contrast, intact vegetation prevented most individuals of all species from surviving for 1 year after planting. The lack of natural recruitment of Fagaceae in the nonseeded subplots indicated that seed limitation was a cause of the slow afforestation. Although litter accumulation in gaps at the time of seeding slightly increased survival for late-germinating Quercus myrsinifolia Blume and Castanopsis sieboldii (Makino) Hatus. ex T. Yamaz. et Mashiba, the effect was not consistent among plots and was not statistically significant. Our results suggest that for successful afforestation using native trees in abandoned fields, it will be necessary to remove competitive native species to avoid severe limitations on microsite availability and that simultaneous tree establishment by seeding or transplanting should be implemented to accelerate the establishment of native tree species.

We simultaneously examined the bacteria, fungi and nematode communities in Andosols from four agro-geographical sites in Japan using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and statistical analyses to test the effects of environmental factors including soil properties on these communities depending on geographical sites. Statistical analyses such as Principal component analysis (PCA) and Redundancy analysis (RDA) revealed that the compositions of the three soil biota communities were strongly affected by geographical sites, which were in turn strongly associated with soil characteristics such as total C (TC), total N (TN), C/N ratio and annual mean soil temperature (ST). In particular, the TC, TN and C/N ratio had stronger effects on bacterial and fungal communities than on the nematode community. Additionally, two-way cluster analysis using the combined DGGE profile also indicated that all soil samples were classified into four clusters corresponding to the four sites, showing high site specificity of soil samples, and all DNA bands were classified into four clusters, showing the coexistence of specific DGGE bands of bacteria, fungi and nematodes in Andosol fields. The results of this study suggest that geography relative to soil properties has a simultaneous impact on soil microbial and nematode community compositions. This is the first combined profile analysis of bacteria, fungi and nematodes at different sites with agricultural Andosols.

Field abandonment has increased over several decades under a long-term recession in Japanese agriculture. To support effective farmland management or reforestation, the patterns of tree recruitment in abandoned fields, which influence management costs, need to be clarified. We investigated tree seedling establishment and microsite variables along forest–field transects in 11 abandoned fields adjacent to secondary broad-leaved forests in the eastern Kanto region of Japan. Generalized linear mixed model analysis indicated that tree seedling establishment in abandoned fields was not correlated with the period of abandonment. Instead, it was positively correlated with vegetation openness. The dominance of a woody vine (Pueraria lobata), an annual liana (Humulus japonicus), and a dwarf bamboo (Pleioblastus chino) mainly explained low vegetation openness within the fields. In addition, the establishment of evergreen tree seedlings and tree seedlings dispersed by hoarding was negatively correlated with the distance from the forest edge. In the forest interior, taller understory vegetation at the edge correlated with lower seedling establishment. These results suggest that seedling establishment across forest–field ecotones is restricted by the dominance of competitive natives within abandoned fields and distance-dependent limitations in both abandoned fields and adjacent forest.

Accumulation of information about natural hybridization between GM soybean (Glycine max) and wild soybean (Glycine soja) is required for risk assessment evaluation and to establish biosafety regulations in Japan. This is particularly important in areas where wild relatives of cultivated soybean are grown (i.e. East Asia including Japan). To collect information on temporal and spatial factors affecting variation in hybridization between wild and GM soybean, a two year hybridization experiment was established that included one wild soybean and five GM soybean cultivars with different maturity dates. Hybridization frequencies ranged from 0 to 0.097%. The maximum hybridization frequency (0.097%) was obtained from wild soybean crossed with GM soybean cv. AG6702RR, which were adjacently cultivated with wild soybean, with 25 hybrids out of 25 741 seedlings tested. Cultivar AG6702RR had the most synchronous flowering period with wild soybean. Ten hybrids out of 25 741 were produced by crossing with cv. AG5905RR, which had the second most synchronous flowering period with wild soybean. Most hybrids were found where GM and wild soybeans were adjacently cultivated, whereas only one hybrid was detected from wild soybean plants at 2 m, 4 m and 6 m from a pollen source (GM soybean). Differences in flowering phenology, isolation distance and presence of buffer plants accounted for half of the variation in hybridization frequency in this study. Temporal and spatial isolation will be effective strategies to minimize hybridization between GM and wild soybean.