Degradation of three kinds of bioplastics and their effects on microbial biomass and microbial diversity in soil environment were analyzed. The degradation rate of bioplastic in soil was closely related to the main components in the bioplastics. Poly (butylene succinate)-starch (PBS-starch) and poly (butylene succinate) (PBS) were degraded by 1% to 7% after 28 days in a soil with an initial bacterial biomass of 1.4 × 10 9 cells/g-soil, however poly lactic acid (PLA) was not degraded in the soil after 28 days. When the powdered-bioplastics were examined for the degradation in the soil, PBS-starch also showed the highest degradability (24.4% degradation after 28 days), and the similar results were obtained in the case of long-term degradation experiment (2 years). To investigate the effect of bacterial biomass in soil on biodegradability of bioplastics, PBS-starch was buried in three kinds of soils differing in bacterial biomass (7.5 × 10 6 , 7.5 × 10 7 , and 7.5 × 10 8 cells/gsoil). The rate of bioplastic degradation was enhanced accompanied with an increase of the bacterial biomass in soil. 16S rDNA PCR-DGGE analysis indicated that the bacterial diversity in the soil was not affected by the degradation of bioplastics. Moreover, the degradation of bioplastic did not affect the nitrogen circulation activity in the soil.
In plant species, when clonal growth produces a patchy structure and flowering ramets are clustered, the amount of pollen contributing to reproductive success is often regulated by pollinator efficiency and geitonogamy. The spatial population structure may influence reproductive success. We examined the clonal structure, the spatial ramet distribution, and their combined effects on fruit set in a natural population of the insect-pollinated, self-incompatible clonal herb, Convallaria keiskei, in northern Japan. The number of shoots, flowers, and fruits in 1-m 2 quadrats were counted at every 5 m grid point in an established 100 × 90-m study plot. From all the quadrats where shoots existed, leaf samples were collected for allozyme analysis. Using the two spatial parameters of flowering ramet densities and genotypes, we then constructed individual-based fruit-set models. A total of 236 quadrats contained shoots, and 135 contained flowering ramets, which indicated expanded distribution of this plant throughout the study plot, while shoots, flowers and fruits all showed clustering 3 distributions. Allozyme analysis of 282 samples revealed 94 multilocus genotypes. The largest clone extended to more than 40 m, whereas 56 genotypes were detected in only one sample. Several large clones and many small clones were distributed close to each other.Fine-scale spatial modelling revealed that the neighbouring flower numbers of different genotypes, compared with local genet or flower diversity, more influenced fruit set, in which the range of the neighbour was 14.5 m. These findings indicate that the compatible pollen dispersed by insect pollinators has a significant effect on sexual reproduction, in this C. keiskei population. Consequently, the spatial structure, which includes both genet distribution and clonal expansion by ramets, had a significant effect on pollination success.
Based on 13 years of monitoring, the fates of individuals and contributions of size and age to demography through the life-history from seedling to flower were investigated in a monocarpic perennial herb, Cardiocrinum cordatum (Thunb.) Makino var. glehnii (F. Schmidt) H. Hara. Of 6155 seedlings, 5264 (85.5%) and 852 (13.8%) plants died at the seedling and one-leaf stage during the 13 years, respectively. Twelve individuals (0.40%) at the three- to seven-leaf stage reproduced after vegetative growth for 7–11 years, and all of them always showed constant positive growth patterns. Significant differences of sizes were detected between surviving and non-surviving individuals in earlier years at the one- and two-leaf stages. Logistic regression models showed that the survival and stage-increase probabilities increased until 5-years-old but decreased over 6-years-old, suggesting the significance of aging effects. At the four-leaf stage, the flowering probability increased with size, while it increased with leaf-stage but not size at greater stages. Individual growth models then suggested that many plants grew moderately: not only slow-growing but also rapidly-growing individuals tended to die within 7 years. Our study clarified three aspects of the life-history of C. cordatum: longevity of about a decade, constantly positive growth to flowering, and aging effects on growth and survival.
Clonal growth occurring below the ground makes it difficult to identify individuals and demonstrate the demographic features of a focal plant species. In this study, genotypically identified ramets of a rhizomatous clonal herb, Convallaria keiskei Miq., were monitored for their growth, survival, and reproduction from 2003 to 2006. After the monitoring period, their subterranean organs were excavated to explore the underground connections of established ramets and the direction of clonal growth. We then combined data on the fate of the monitored ramets with the information of rhizome connections, clarifying reproductive demography at both the ramet and genet levels. Although each ramet initiated both sexual reproduction (via flowering) and clonal growth, clonal growth tended to precede sexual reproduction. In a surveyed genet, 51.0% of ramets produced flowers and 29.6% generated clonal offspring during the study period. Consequently, we clarified the reproductive demography of C. keiskei: clonal growth tended to precede flowering in a ramet, and a genet can keep reproducing every season at the genet level, despite a ramet not having inflorescence every year.
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