Regeneration Limitation In The Natural Populations Of Endangered Metasequoia Glyptostroboides

The recruitment limitation of plants is a hot topic both in biological conservation,diversity,and dynamics of plant communities.Knowing the natural regeneration mechanisms has important significance for biological conservation,particularly for endangered species.Conditions that mediate seed germination and seedling survival,can be generally partitioned into seed production(i.e.source limitation),seed dispersal(i.e.dispersal limitation),and those that limit seedling establishment(i.e.germination limitation and survival limitation).Seed augmentation into existing populations or seed introduction into unoccupied habitats,are the best available evidence for the different types of limitations.To determine the range of seed-addition levels used in the experiment,we measured local seed rain and soil seed bank.This study focuses on the seed rain,soil seed bank and recruitment mechanisms of Metasequoia glyptostroboides(Taxodiaceae),a famous living fossil.Commonly,the mother tree of dawn redwood is distributed mainly in the Lichuan of Hubei Province.We conducted seed augmentation experiment in inside existing mother tree(occupied)and seed introduction into upside,hillside(unoccupied).At each site,we applied artificial treatments(mowing,removing-litters and seed protection),added seeds at different densities(50,200),and monitored the seed germination and the survival of seedlings over two consecutive years.Observations on seedling survival and growth of transplanted seedlings had been used to test germination limitation and survival limitation.There results indicate that:(1)The fall of seed rain lasted about 5 months and the peak seed density lasted about one month from late November to late December.Most seed of dawn redwood were dispersed within 20m from the source tree.Most seed were dispersed in leaf litter.Soil seed bank was transient because seed density was decreased from January to April.The number of seed bank in upside and hillside were found to be significantly lower than those in inside.(2)In summary,the natural population of M.glyptostroboides was found to be limited by seed because the germination is higher after seed-addition than control.Source limitation was supported by the increasing germination of seed at the level of 50 and 200 in occupied habitat.M.glyptostroboides appeared to be strongly dispersal limitation and habitat limitation because seed addition to unoccupied habitats resulted in successful germination in upside and hillside.(3)There was habitat limitation in the natural population of M.glyptostroboides because that the germination in inside was significantly higher than upside and hillside.Microsite limitation was evident in inside and germination limitation was evident in upside and hillside because germination at the same level was significantly enhanced under the artificial treatments counter to our expectation.There were no differences in survival and growth transplanted seedlings,between three types of habitats suggest that survival limitation did not exist.The recruitment limitation of M.glyptostroboides in occupied habitat was because of source limitation and microsite limitation.There was not seedling in unoccupied because of dispersal limitation,habitat limitation and germination limitation.There was not survival limitation once seedling established in habitat.