Toshizumi Miyamoto

Effects of bird ingestion on seed germination of Sorbus commixta

Abstract To determine the effects of ingestion by birds on seed germination, we performed germination experiments in the field and laboratory with Sorbus commixta. The germination of four groups of seeds was compared: ingested seeds, seeds defecated in feces after feeding of fruits to birds; extracted seeds, seeds deliberately extracted from the fruit pulp; juiced seeds, seeds plus the juice of the pulp after seeds had been deliberately extracted from the pulp; intact seeds, seeds in untreated intact fruits. In the laboratory, intact and juiced seeds hardly germinated, but ingested and extracted seeds germinated. Thus, the pulp and its juice appeared to inhibit germination, but seeds could germinate without ingestion by birds once the seeds had been manually extracted from the pulp. In the field, intact fruits did not germinate in the first spring, because the seed was still covered with pulp. The pulp of intact seeds decomposed during the first summer, and thus, the seeds had the potential to germinate during the second spring. In fact, most intact seeds do not germinate during the second spring either, since they lose their viability during the first summer. Thus, under natural conditions, most seeds of Sorbus commixta cannot germinate without bird ingestion.

Lignin-degrading ability of litter-decomposing basidiomycetes from Picea forests of Hokkaido

The frequency of occurrence of the litter-decomposing basidiomycetes ofPicea abies andP. glehnii forest floors in Hokkaido was investigated. In both theP. abies andP. glehnii forest plots (each 10 m×10 m), litter-decomposing basidiomycetes of the generaCollybia andMycena were frequently observed. Species composition, frequency of occurrence, and basidioma numbers of each species were different between the two forest plots, but several species were common to both. Seven species isolated from theP. glehnii forest plot (C. acervata, C. pinastris, Marasmius pallidocephalus, Ma. wettsteinii, My. aurantiidisca, My. clavicularis, Mycena sp. 1) and four species from theP. abies forest plot (C. pinastris, My. alphitophora (=My. osmundicola), Mycena sp. 1,My. vulgaris) were tested for their ability to degrade lignin by a simple plate test for extracellular phenoloxidases and by measuring Klason lignin loss from needle litter of spruce. All the strains of the litter-decomposing fungi tested showed positive reactions on the plate test. Lignin contained in the needle litter was degraded by all strains tested (onlyMy. alphitophora was not tested), and rates varied from 9% to 40% over a two-month period in vitro. Seven species with ligninolytic ability in theP. glehnii forest plot and four such species in theP. abies forest plot were found respectively in 77% and 60% of the 100 subplots in each plot. The results of this study suggest that lignin decomposition of needle litter by litter-decomposing basidiomycetes in the forest floor is a common event in the studiedPicea forests of Hokkaido and that the diversity of the ligninolytic activity among the species or strains may cause spatial heterogeneity of litter decomposition in thePicea forest floor.

Effects of bird ingestion on seed germination of two Prunus species with different fruit-ripening seasons

To evaluate the effects of ingestion by birds on seed germination under natural conditions, we carried out germination experiments in the field using seeds of two Prunus species that have different fruit-ripening seasons. Germination of seeds with the following three treatments was compared: ‘ingested seeds’, seeds excreted after feeding of fruits to birds; ‘extracted seeds’, seeds deliberately extracted from the fruit pulp; and ‘intact fruit’, seeds in untreated intact fruit. Many ingested and extracted seeds of both Prunus species germinated during the first spring, and the difference in germination percentage between ingested and extracted seeds was not significant. Many seeds in intact fruit of Prunus sargentii also germinated during the first spring, but those of Prunus ssiori did not germinate until the second spring. Pulp removal through bird ingestion enabled rapid germination for the autumn-fruiting P. ssiori, whose fruit pulp was not likely to be decomposed until the first spring. In contrast, the effects of ingestion were not striking for the summer-fruiting P. sargentii, whose fruit pulp is quickly decomposed.

Mycorrhizal associations in woody plant species at the Mt. Usu volcano, Japan

We investigated the association between ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) fungi and pioneer woody plant species in areas devastated by the eruption of Mt. Usu, Japan, in 2000. We observed eight woody plant species at the research site, most of which were associated with ECM and/or AM fungi. In particular, dominant woody plant species Populusmaximowiczii, Salixhultenii var. angustifolia and Salixsachalinensis were consistently associated with ECM fungi and erratically associated with AM fungi. We found one to six morphotypes in the roots of each ECM host and, on average, two in the roots of each seedling, indicating low ECM fungal diversity. ECM colonization ranged from 17 to 42% of root tips. Using morphotyping and molecular analyses, 15 ECM fungi were identified. ECM fungi differed greatly between hosts. However, Laccaria amethystea, Hebelomamesophaeum, Thelephoraterrestris and other Thelephoraceae had high relative colonization, constituting the majority of the ECM colonization in the roots of each plant species. These ECM fungi may be important for the establishment of pioneer woody plant species and further revegetation at Mt. Usu volcano.

Inhibition by Pulp Juice and Enhancement by Ingestion on Germination of Bird-dispersed Prunus Seeds

To evaluate what prevents seed germination and why ingestion by birds enhances germination, we carried out germination experiments using bird-dispersed seeds of twoPrunus species (Prunus sargentii andP. ssiori) in the laboratory. Germination of seeds with following four treatments was compared: “Ingested seeds” excreted after feeding of fruits to birds; “Extracted seeds” deliberately extracted from the fruit pulp; “Juiced seeds” which were supplemented with the juice of the pulp after seeds had been deliberately extracted from the pulp; and “Intact seeds” in untreated whole fruits. Many ingested (27%, 23% inP. sargentii, 18% inP. ssiori) and extracted seeds (24% inP. sargentii, 17% inP. ssiori) germinated, and difference in germination percentages between ingested and extracted seeds were not significant, for eitherPrunus species. The Juiced seeds rarely germinated (2% inP. sargentii, 6% inP. ssiori), and seeds within intact fruits did not germinate. These results suggest that the fruit pulp and the juice of the pulp inhibit germination and the seeds could germinate without ingestion by birds once they had been manually extracted from pulp. Therefore, it is considered that bird ingestion enahnces germination by removing pulp, especially juice of the pulp, in these twoPrunus species.

Decomposition and nitrogen release from the foliage litter of fir (Abies sachalinensis) and oak (Quercus crispula) under different forest canopies in Hokkaido, Japan

When two tree species co-occur, decomposition and nitrogen (N) release from the foliage litter depend on two factors: the forest floor conditions under each canopy type and the species composition of the litter. We conducted an experiment using fir and oak to answer several questions regarding decomposition beneath canopies of the two species and the effects of litter species composition on decomposition. We compared the rates of decomposition and N release from three different litters (fir needle, oak leaf, and a mixture of the two) in 1-mm-mesh litterbags on the forest floor under three different canopies (a 40-year-old fir plantation, large oak trees, and mixed fir and oak trees) in Hokkaido, Japan, over a 2-year period. Beneath each of these canopy types, the litter decomposition rate and percentage of N remaining in the litterbags containing a mixture of fir and oak litter were not significantly different from the expected values calculated for litterbags containing litter from a single tree species. Oak leaf litter decomposed significantly faster than fir needle litter beneath each canopy type. The litter decomposition rate was significantly higher beneath the fir canopy than under the oak canopy, and was intermediate under the mixed canopy of fir and oak. No net N release, that is, a decrease in the total N compared to the original amount, was detected from fir litter under each canopy type or from oak leaf litter beneath the oak canopy. N increased over the original amount in the fir litter beneath the oak canopy and the mixed canopy of fir and oak, but N was released from the oak litter under the fir canopy and the mixed canopy of fir and oak. These results suggest that oak leaf litter blown onto fir forest floor enhances nutrient cycling, and this might be a positive effect of a mixed stand of conifer and broad-leaved trees.

Mycorrhizal colonization status of plant species established in an exposed area following the 2000 eruption of Mt. Usu, Hokkaido, Japan

We investigated the ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) colonization status of plant seedlings that established in areas devastated by the eruption in March 2000 of Mt. Usu, Hokkaido, Japan. In 2005, we estimated the mycorrhizal colonization ratios and frequencies in seedlings of twelve herbaceous and seven woody plant species. Although arbuscular mycorrhizas were found to colonize Equisetum arvense and Polygonum sachalinense, they were presented at very low frequencies and colonization ratios. Other herbaceous plants exhibited higher frequencies of AM associations and either AM and/or ECM fungal associations were observed in all of the woody plant seedlings investigated. The dominant woody plant species (Populus maximowiczii, Salix sachalinensis and Salix hultenii var. angustifolia) associated mainly with ECM fungi and exhibited variable associations with AM fungi. Mycorrhizal associations were common and significant events for plant establishment, even in the early stages of the revegetation process.

Spatial distribution of Collybia pinastris sporophores in a Picea abies forest floor over a 5-year period

Collybia pinastris is a relatively common litter-decomposing basidiomycete in spruce forests in Hokkaido, Japan. The spatial distribution of sporophores of C. pinastris was investigated for 5 years within a plot of 3 m × 10 m in size (subdivided into 0.5 m × 0.5 m subplots) in a pure stand of Picea abies. There were significant differences in the total numbers of sporophores during the sampling years. The total number of subplots in which sporophores occurred were also significantly different during the sampling years. However, the spatial distribution of the subplots with sporophores showed agreement with the distributions in subsequent years. There was no significant correlation between the number of sporophores and the thickness of the litter layer in the subplots, whereas the litter layers in the subplots with sporophores were significantly thinner than those without sporophores. These results suggested that perennial or renewable mycelia of C. pinastris occupied the same or close locations year to year for at least 5 years and that the spatial distribution in this plot was restricted not by a shortage of substrates but by other factors.

Morphological and genetic characteristics of the entomopathogenic fungus Ophiocordyceps nutans and its host insects

We examined the morphology, genetic variation, and insect host species of the fungus Ophiocordyceps nutans. Fifty-two fruit bodies collected in Hokkaido, Japan, were grouped by host species, and 19 samples were analysed. The ranges of the lengths and breadths of all fruit body parts were similar among host groups. In the genetic analysis, the 5.8S rDNA region showed completely identical sequences, although differences of up to six nucleotides were recognized in the ITS regions. The distance values between our samples using the Kimura two-parameter model were lower than 0.007. Thus, the O. nutans examined here were concluded to form a closely related group with little detectable variability that parasitized nine hemipteran species.