Studies On Seedling Recruitment And Growth Performance Of Common Herbaceous Species In Alpine Meadow Community Of The Eastern Qinghai-Tibetan Plateau

Seedling period is the crucial stage during the whole plant life-history. Plants mainly make population extended, distributed and continued by seedling recruitment. The recruitment process from seed germination to seedling establishment is nearly related to species distribution, abundance and community succession in plant communities. Especially for alpine meadows which belong to perennial plant community, seeds of component species as potential dynamical of vegetation recruitment have significant contribution to vegetation recruitment and succession, because offspring recruitment may influence general patterns of succession and maintenance of diversity within communities and plant species richness and density in an area depends on a combination of patterns of arrival and survival of seeds, seedling emergence, and seedling survival. Fitting habitats were the extrinsic conditions for successful seedling recruitment in plant community. There are many different microsites in alpine meadow communities which were caused by different grassland management measures, e.g. overgrazing and fertilization. But. up to now. there is little systemic research on seed germination, seedling growth and establishment of component species in alpine meadow communities under different microsites were reported. So. we conducted this study on seedling recruitment process and growth performance of some familiar forbs component species under different microsites (light and nutrient availability), which were made by a simulative artificially method, in alpine meadow communities of the eastern Qinghai-Tibetan Plateau. Our objective was to study the seedling recruitment mechanism and process of familiar forbs component species in alpine meadow communities, and offer a theoretical foundation for understanding on grassland degradation and restoration process. Main results were following:1) Seed germination characteristics were significantly affected by light availability and seed mass for these forbs component species in alpine meadow communities. Among twenty species for this study, the smaller-seeded species had a bigger light requirement for germination than the larger-seeded species. Most of the studied species presented a lesser or neutral light dependence and the optimum light microsites were the middle and low light availability. For these species, they mostly adopt short-term and concentrative germination strategy and presented a higher germination percent, but several species adopt long time, scattered and stochastic germination strategy with a lower germination percent.2) Light availability and seed mass also affected significantly seedling emergence rate, seedling survival rate and overwinter survival rate. They all presented a significant positive correlation with light availability. The relationships between seed mass and seedling emergence rate, seedling survival rate and overwinter survival rate were altered by the microsites change. For studied species, the maximum seedling emergence rate, survival rate and overwinter survival rate mostly appeared in middle and higher light conditions. Higher nutrient availability could significantly advanced seedling survival rate and overwinter survival rate for some species, but no significant effect on seedling emergence rate.3) Middle light and higher nutrient microsite can significantly advanced seedling recruitment probability for these species. For studied species, seedling recruitment rate was significant positively related to light availability, and nutrient difference also significantly affected seedling recruitment rate within species. For studied twenty species in ten microsites, the mean seedling recruitment percent (from seed to seedling overwinter survival) were about 10% to 30%.4) Microsite and seed mass both significantly affected seedling growth rate and biomass allocation characteristics. Seedling relative growth rate, biomass accumulation, root allocation, root to shoot ratio on biomass and on length all were significant positively related to light availability, but leaf allocation, stem allocation, specific leaf area and leaf area ratio were significant negatively related to light availability. Seed mass presented significant positive relationships with initial seedling size, seedling biomass at 80d and stem allocation, but negative relationships with relative growth rate, leaf allocation and root to shoot ratio on length under shade. The maximum seedling relative growth rate and biomass mostly appeared in microsites with higher nutrient and higher or middle light availability. 5) The smaller-seeded species presented larger recruitment and growth plasticity than the larger-seeded species in this study. Microsites differences brought the larger influences on seedling growth and recruitment for the smaller-seeded species, but the lesser influences for the larger-seeded species.6) Seedling advanced their recruitment probability by their morphological performance plasticity in heterogeneous microsites. Species with lesser growth plasticity showed a higher seedling survival rate under different micorsites. Meanwhile, species with larger plasticity in biomass and height, and mean plasticity index presented higher seedling overwinter survival rate. Additionally, species with larger plasticity in biomass allocation and relative growth rate also showed higher seedling survival rate.7) All these suggested that higher light availability in grazed disturbed meadow community favor seedling recruitment for these familiar forbs component species, but bottom shade in fertilized meadow community restrain seedling recruitment for these species. Species with different seed mass show different seedling recruitment characteristics under variational microsites. Seedlings advance their fitness in emergence, survival. overwinter survival and successful recruitment by their morphological performance plasticity under variational microsites.