Teruo Arase

Ecological significance of root tip rotation for seedling establishment of Oryza sativa L

How plant seeds secure root penetration into soil to obtain good seedling establishment is one of the basic ecological problems. In this study, seminal root growth was investigated to clarify the cause of varietal difference of seedling establishment in direct seeding of rice in flooded paddy fields, with special reference to root tip rotation. In a field experiment, seedling establishment percentage had a weak correlation with seminal root elongation rate but was not correlated with apparent seedling weight in water, which has been reported to be the cause of floating seedlings resulting in poor seedling establishment. Root tip rotation was analyzed for indoor-grown seedlings using spectrum analysis: the maximum entropy method (MEM) was used. Maximum entropy method power spectrum analysis clarified that maximum MEM power density (practically corresponds to spiral angle) detected in the frequency range above 0.1 cycles mm-1 was highly and positively correlated to seedling establishment percentage in the field experiment. Maximum MEM power density in high correlation with seedling establishment was mostly found around frequencies of 0.2 cycles mm–1, which corresponded to 2.0–3.4 cycles of root tip rotation per day. From these results, root tip rotation (circumnutation) with a larger spiral angle was suggested to play an important role in the establishment of rice seedlings on flooded and very soft soil. A possible explanation for why a larger spiral angle was advantageous for seedling establishment is that if buoyancy and seedling weight are constant, a larger pushing force of the seminal root is available without causing floating of a seedling, due to the upward force being a reaction of the seminal root pushing force.

INFLUENCE OF FERTILIZATION ON NATIVE PLANTS AND EXOTIC PASTURE GRASSES ON THE FASCINED LANDSLIDE SLOPES IN MIKURA-JIMA ISLAND, JAPAN

Typhoon 9512 hit Mikura-jima Island, Izu Islands, Japan in 1995, producing many landslide slopes. Torino-o No.3 landslide slope was fascined with fallen trees and planted with seedlings of native species (Alnus sieboldiana tree and Miscanthus condensatus grass) as part of vegetation recovery efforts, and was subsequently seeded by helicopter in 2002 with exotic pasture grasses. To elucidate the influence of fertilization on the growth of transplanted seedlings of native species, exotic pasture grasses and newly invading trees and herbs, we designated seven plots in 2004, and surveyed vegetation every summer until 2013: four fertilized plots (fowl manure applied at 0.2 g/m 2 ) and three non-fertilized plots. The native species seedlings grew steadily irrespective of fertilization, but with self-thinning in A. sieboldiana. Exotic pasture grasses decreased gradually and almost disappeared in 2013. Fertilizing temporarily enhanced the growth of some species, but seemed to induce species competition, judging from the delay of invading of native trees and the increase of climbing plants in herbaceous layer in fertilized plots.

THE RELATION BETWEEN ROAD CRACK VEGETATION AND PLANT BIODIVERSITY IN URBAN LANDSCAPE

The objective of this study is to collect basic information on vegetation in road crack, especially in curbside crack of road, for evaluating plant biodiversity in urban landscape. A curbside crack in this study was defined as a linear space (under 20 mm in width) between the asphalt pavement and curbstone. The species composition of plants invading curbside cracks was surveyed in 38 plots along the serial National Route, over a total length of 36.5 km, in Fukuoka City in southern Japan. In total, 113 species including native plants (83 species, 73.5%), perennial herbs (57 species, 50.4%) and woody plants (13 species, 11.5%) were recorded in curbside cracks. Buried seeds were also obtained from soil in curbside cracks, which means the cracks would possess a potential as seed bank. Incidentally, no significant differences were found in the vegetation characteristics of curbside cracks among land-use types (Kolmogorov-Smirnov Test, P > 0.05). From these results, curbside cracks would be likely to play an important role in offering habitat for plants in urban area.

COLONIZATION AND MORPHOLOGICAL CHANGES OF A SEDGE RESTRICTING REGENERATION AFTER WIND DAMAGE IN A NATURAL FOREST

Many old trees were blown down by typhoons in 1959 and 1961 in a natural coniferous forest deep in the mountains of Kiso District, Central Japan, and dense dwarf bamboo subsequently delayed the growth of tree seedlings. Forest engineers have tried to suppress dwarf bamboo to promote the regeneration of arboreal vegetation. However, after suppression of dwarf bamboo, an unknown grass unexpectedly colonized the area and replaced them. Afterward, almost no tree seedlings could be observed in the newly formed community, which seemed to worsen the extent of regeneration. It has been identified that the grass as Carex oxyandra, a native sedge species indigenous to Kiso District. Commonly, Carex oxyandra grows as short as about 10 cm like lawn grass, but it seems to have exceedingly enlarged the size in the community. Thus, investigation on the morphological variation of this sedge in Miure Experimental Forest within the Kiso National Forest was carried out. Leaf blade length, basal tiller length, and number of leaves per tiller were measured in upper and lower stands on three slopes in 2009. Results revealed that leaf blade length and basal tiller length in lower stands were approximately twice as large as those in upper stands on each slope, whereas the number of leaves per tiller was almost the same (8.8-9.4 leaves). Consequently, tussocks of this sedge became large in lower stands on a slope, which made the community overcrowded and damp, restricting tree regeneration.

VEGETATION RECOVERY PROCESS ON LANDSLIDE STEEP SLOPE AFTER Alnus sieboldiana AND Miscanthus condensatus PLANTING WITH SIMPLE TERRACING WORK IN MIKURA-JIMA ISLAND, JAPAN

Typhoon 9512 hit the island of Mikura-jima in 1995, causing many landslides and destruction of forest vegetation. For long-term observation of vegetation change, a research plot was established on a landslide slope in 2003. A simple terrace was built on this slope, which was planted with native species (Alnus sieboldiana and Miscanthus condensatus) in 2000 to accelerate vegetation recovery. From 2003 to 2012, a vegetation survey of the plot was conducted to elucidate the vegetation recovery process at an early stage. A. sieboldiana grew steadily and its density of individuals decreased. The number of species gradually increased due to invasion of new seedlings from adjacent forests, i.e. Castanopsis cuspidata, Persea thunbergii. We found some differences in vegetation recovery from another research site, which is a landslide slope seeded with exotic pasture grasses by helicopter in 2002. Seeding of exotic pasture gasses prevented the establishment of trees and reduces successional velocity.

DEVELOPMENT OF FLORA IN RELATION TO WATER MANAGEMENT IN OBASUTE-OIKE IRRIGATION POND, JAPAN

In order to clarify the factors affecting the species diversity of plant communities around an irrigation pond, we surveyed Obaste-oike Irrigation Pond in Nagano Prefecture, Japan. The pond is comprised of three subdivided ponds, Kami-ike, Naka-ike, and Shimo-ike. Despite being adjacent to each other and connected by streams, the water levels in the three ponds differ. Five plant communities were studied, and one or two survey plots were selected in each community along each subdivided pond. A 32-m 2 quadrat was established in each plot of grassland, and a 400-m 2 quadrat was established in each plot of forest. The results of the distribution of species revealed that approximately 40% of the species were endemic to each subdivided pond in the terrestrial communities, whereas over 60% were endemic in the hydrophytic communities. To increase species diversity in irrigation ponds, especially in hyrdophytic communities, we suggest that dividing the ponds into several zones with distinct water levels and managing them in a sustainable manner is important.