滇中喀斯特森林土壤种子库的种-面积关系

SPECIES-AREA RELATIONSHIPS OF SOIL SEED BANK IN KARST FOREST IN CENTRAL YUNNAN, CHINA

土壤中的种子是植物群落更新与再恢复的种源基础。国内对土壤种子库的取样面积与种子检出之间的关系还很少涉及。在采用萌发方法对采集自滇中喀斯特山地的100个10cm×10cm×10cm土样的物种数进行研究后，分析了土壤种子库的种-面积关系。面积与总物种和乔、灌、草本物种数之间的关系与二次方程和对数方程之间的拟合关系都较好。总物种数和草本物种数的基数较大且随面积增长较明显，而乔木和灌木的基数相对较小，增长较慢。总物种数的增加在面积位于0．15～0．2m^2，也即15～20个10cm×10cm×10cm土样之间时逐渐趋缓，可将这一面积和取样数量作为同类地区种子库取样的参考。

Aims Seeds stored in soil are important for plant regeneration and ecological restoration. Seeds are dispersed from parent plants stochastically, and this results in a non-uniform distribution of seeds across the litter and soil. Soil samples must be collected to overcome this variation and to obtain a reasonable richness and density of seeds. However, extracting seeds from soil is time-consuming and studying the germination of seeds from soil samples requites much space. Therefore, it is important to determine a reasonable sample size for soil seed bank studies. However, the relationship between soil sampling area and seeds has rarely been explored in China. Methods We collected 100 soil samples of 10 cm×10 cm ×10 cm in a Karst forest in central Yunnan. Species and seed density were determined with the seedling emergence method after washing soil samples through 4 and 0.21 mm mesh sieves to eliminate coarse and fine materials, respectively. Soil samples were treated as quadrats and arrayed in a regular but non-contiguous grid to establish a species-area relationship. Important findings A total of 2 536 seedlings from 69 species （7 trees, 6 shrubs and 56 herbs） emerged from the samples. There were 3 - 67 seeds from 1 - 14 species in a soil sample, with an average of 23.4 seeds and 7.1 species. The percentage of samples in which a species germinated ranged from 1% to 90%. The number of total, tree, shrub and herb species had significant quadratic and logarithmic relationships with area. The bases of total species and herb species were large and the slopes of their species-area curves were steep. In contrast, the bases for tree species and shrub species were small and showed little increase. The increase of total species leveled out at 0.15 -0.2 m^2, i.e., 15 -20 samples （10 cm×10 cm×10 cm）. This study indicates that 15 -20 samples with total surface area of 0.15 -0.2 m^2 can serve as a reference for soil seed bank studies in areas similar to this study. However, the seedling emergence method, even with the total sample area in this study, needs to be improved or replaced to determine the sampling requirement for tree and shrub species.