RESUMO
This study aimed to examine the responses of persistent soil seed bank to future precipitation reduction of global climate change in the forest-steppe ecotone of Hulunbuir. Samples of soil seed bank were collected from 0-10 cm soil layer along a precipitation gradient. We examined the density, species composition, diversity of seed bank and their relationship with vegetation. Structural equation model was used to explore the direct impact of annual precipitation on soil seed bank and the indirect impact through vegetation, soil nitrogen, soil phosphorus, and soil pH. The results showed that seed bank density and species richness were negatively correlated with annual precipitation. The species diversity of soil seed banks in grasslands was higher than that in forests. The similarity between soil seed bank and vegetation was generally low. The results of structural equation model showed that the effects of annual precipitation on seed bank density and species richness were negative, with the standard path coefficients of -0.051 and -0.122, respectively. The direct effect of annual precipitation on seed bank density and species richness were positive. Precipitation had indirect and positive effect on seed bank density and species richness through soil nitrogen, a significantly indirect negative effect on seed bank species richness through soil pH and soil available phosphorus, and a significantly indirect negative effect on seed bank density through soil pH. The reduction of precipitation under furture climate change might alter the hedging strategies of plants. The persistent soil seed bank in the forest-steppeecotone had a potential buffering effect against future precipitation reduction.
Assuntos
Banco de Sementes , Solo , Ecossistema , Florestas , Nitrogênio , Fósforo , Sementes/fisiologia , Solo/químicaRESUMO
Seed traits (ST) influence seedling establishment, population dynamics, community composition and ecosystem function and reflect the adaptability of plants and the environmental conditions they experienced. There has been a historical and global accumulation of studies on ST, but with few pertaining to visual and quantitative analyses. To understand the trends in the field of ST research in the past 30 years, we conducted a bibliometric analysis based on the Science Citation Index-Expanded (SCI-E) database. The analysis provided annual publications, time trends for keywords, the most productive journals, authors, institutions and countries, and a comprehensive overview of the ST field. Our results showed that in the past 30 years, the number of publications in ST research has increased at an average annual growth rate of 9.1%, while the average number of citations per paper per year showed a rapid increase-slow increase-decrease trend. Keyword analysis showed that "germination" was the most popular research section. Crop Science ranked first among the top journals and Theoretical and Applied Genetics had greater influence in this area and more citations than other journals. The 10 most productive institutions were mostly located in the United States, China and Australia. Furthermore, the three countries also had the largest number of publications and citations. Our analysis showed that the research interests in ST have evolved from genetics and agricultural science to ecological research over the last thirty years; as more fields embrace ST research, there are opportunities for international and interdisciplinary collaborations, cooperative institutions and new advances in the field.
RESUMO
Polyetheretherketone (PEEK) has been widely investigated for improving its biological inert to enable it to achieve stronger osteogenic capability and to be a promising material in implant fields. The most important mechanism that makes a successful implantation is osteointegration. Surface modification is an appropriate method to maintain the excellent mechanical properties of PEEK and simultaneously endow PEEK certain biological characters. In this work, we attempted to shape the nano-topography of PEEK surface by nitrogen low-temperature plasma and polydopamine coating on the surface as a secondary reaction platform to bond the aminated poly (lactic-co-glycolic acid) (PLGA) microspheres encapsulating the BMP-2 gene for enhancing the biological activity. Scanning electron microscope, atomic force microscopy, X-ray photoelectron spectroscopy and water contact angle (CA) measurements were applied to characterize the surface of modified or untreated PEEK. Surface characterization showed that the modification was successfully performed on PEEK including a rougher and more hydrophilic surface with nanotopographic features. The influence on cell adhesion, proliferation and differentiation was evaluated by culturing of rat bone marrow mesenchymal stem cells on different modified PEEK substrates in vitro. The biological results indicated that the low-temperature plasma treatment and PDA-coating on PEEK significantly promoted cell adhesion and proliferation. And the osteogenic differentiation was effectively improved by BMP-2 gene releasing from PLGA-NH2 microspheres. The results showed that this novel biological surface modification endowed PEEK with outstanding bioactivity and osteogenic ability, providing a theoretical basis for application in the field of implantation.
