Abstract:

Objective: Castanopsis hystrix is a rare broadleaved tree species under the second grade national protection in China, and it is difficult to regenerate in nature. Our study aims to examine whether population regeneraion is limited by seedling recruitment. We investigated dynamics of seed rain, soil seed bank and seedling regeneration of C. hystrix. Methods: The line transect method was used to collect the seed rain and fallen leaves of C. hystrix in 2017 and 2018. Seed rain density, quality, total of seed rain and weight of fallen leaves in different seed dispersal stages were analyzed. At the same time, small plots were also set under the seed trees for collecting samples in litter layer, 0-5 cm humus layer and 5-10 cm soil layer. The soil seed bank density and the number of full seeds were calculated then, and the germination capacity and the weight of thousand seeds were measured in laboratory. In May 2018, small plots were set around each of sampling seed trees to investigate the seedlings regeneration. Results: 1) Seed rain of C. hystrix lasted from the middle of September to the late of December, and its concentrated scatter period was from October to November. In 2017, it was a big year for producing seeds of C. hystrix, and the seed rain density was (480.97±11.61) seeds The seed quality was good, the number of full seeds was (433.86 ±12.65) seeds·m^-2, accounting for 90.20%±1.09% of the total seed rain. In 2018, it was a small year for seed production, both seed production and full seeds proportion were lower than those in 2017. The seed rain density was (126.37±12.04) seeds·m^-2, and the full seeds accounted for 36.04%±0.95% of the total seed rain. 2) The soil seed bank in April 2018 was mainly from the seed rain in 2017, and the average density of soil seed bank was (360.09±10.43) seeds·m^-2, of which full seeds accounted for 59.74%±8.56%. By indoor germination test in 2018, the average germination rate of full seeds was 28.53%±7.50% in seed bank. There were about (61.38±18.57) seeds·m^-2 having germination potential before natural regeneration. However, when the seeds were buried into the forest soil till April in 2019, the germination rate decreased to 2.85%±0.86%, and only about (8.59±1.90) seeds·m^-2 had germination capacity in seed bank. Approximate 63.79%±3.55% of seeds in the bank were mainly distributed in litter layer. 3) The average renewal frequency of seedlings of C. hystrix was 16%, and only 11 of the 78 regenerated seedlings were survived. Conclusion: The dynamics of seed rain diffusion is consistent with that of fallen leaves of C. hystrix. The vertical spatial distribution of soil seed bank is significantly different, and the most of the seeds fall into litter layer. The germination rate and survival rate of seedlings are low, it is still difficult for seedling recruitment even if after a big year of C. hystrix. Thus, low seed germination rate and litter barrier are the main influencing factors leading to the poor regeneration of C. hystrix.

Key words: Castanopsis hystrix, seed rain, soil seed bank, seed tree, seedling regeneration