| Camellia flavida, one of golden Camellia with yellowy petals, is a shade-tolerant shrub with narrow and fragmented distribution and suffers a certain degree of human destruction, recognized as precious germplasm resources with ornamental and economic value. There is typical karst seasonal tropical rain forest with varied vegetation types, abundance of endemic species and high habitat heterogeneity in Nonggang national natural reserve, Guangxi. However, there are few studies how the high karst habitat heterogeneity influences fine-scale spatial genetic structure (SGS), gene flow and genetic differentiation over small scale of shade-tolerant shrub. In this research, the typical shade-tolerant shrub of karst, C. flavida, was selected as the research object to solve above the problem based on 15 ha (300 m × 500 m) plot and 1 ha (100 m × 100 m) plot of northern tropical karst seasonal rainforest permenant monitoring plots in Nonggang National Nature Reserve and five populations over small scale (radium about 1 km) using 13 microsatellites. The main results were as follows:1) The point pattern analysis (g function) indicated that C. flavida showed a significantly aggregated distribution pattern within 25 m in 15 plot and and 35 m 1 ha plot, respectively. However, the degree of spatial aggregation of the former was 4 times as much the latter, which may be due to topography.2) The age structure of C. flavida in 15 ha plot was an approximately normal distribution, indicating a stable age structure. However, the age structe of C. flavida in 1 ha plot was the inverted "J" type, indicating an increasing age structure.This showed that the age structure in different habitat was diverse.3) 13 microsatellites with highly polymorphism and clearly amplified bands were applied in this research. The number alleles(At), average number of alleles (A), effective number of alleles (AE), observed heterozygosity (Ho), expected heterozygosity (HE) and fixed index (Fis) of C. flavida in 15 ha plot (144 individuals) and 1 ha plot (219 individuals) were 94,7.23,3.95,0.748,0.729,-0.027 and 89,6.85,3.57,0.710,0.700,-0.016, respectively. This indicated that C. flavida in two plots showed comparatively high genetic diversity, of which 15 ha plot was slightly higher than 1 ha plot.4) There was significant SGS of C.flavida wthin 50 m in 15 ha plot, which F1 was 0.0521 and intensity of SGS (Sp) was 0.0248 in first distance class (10 m). However, there was significant SGS wthin 20 m in 1 ha plot, which F1 was 0.0282 and intensity of SGS (Sp) was 0.0136 in first distance class (10 m). This indicated that there was a stronger SGS in 15 ha plot than 1 ha plot, which the former Sp was 1.8 times as much the latter. The Sp of C.flavida was moderate comparing other shrubs or gravity-dispersed species.5) Analysis of SGS of seedlings and adults in 1 ha plot found that they were both significant SGS within 20 m, but Sp of adults was obvious stronger than seedlings, which the former was 1.64 times as much as the latter. This may be due to overlapping generations of adults, a high mortality rate of seedlings and so on, but it was irrelevant to the life form (light-depend or shade-tolerant) and the degree of spatial aggregation.6) The sample scale was of great influence to SGS, which was not only caused by samples although the reason was not clear.7) Parentage analysis of seedling of C. flavida in 15 ha plot showed that the seed dispersal distance was 0.65～51.05 (mean 12.88) m and pollen dispersal distance was 3.06-194.93 (mean 34.84) m.72.2% of seed dispersal and 85.7% of pollen dispersal were found within 20 m, demonstrating that the pollen and seed mainly spread in vary short distance and the result was inconsistent with long pollen dispersal distance of tropical rainforest.8) There was a significant genetic differentiation (Fst= 0.079, P<0.05) between the two patches of C. flavida with the distance about 100-200 m separated by depression, so were the two populations with only distance of 38 m isolated by peak-cluster (Fst= 0.112, P <0.05) and five populations over small scale (a radius of about 1 km) (Fst= 0.104～0.160, P< 0.05). This suggested that there was genetic differentiation over small scale and FST was positively correlated with geographic distance, which increased from a single peak-cluster depression (average 0.096), small scale (average 0.133), to large scale (average 0.276).The above studies revealed that the basic characteristics of shade-tolerant shrub C. fladida in karst were fragmented distribution, short gene flow, moderate level of SGS and genetic differentiation over small scale. And these characteristics are closely linked. The habitat preferences of C. fladida and habitat heterogeneity of karst led to fragmented distribution and then hindered the gene flow together with habitat heterogeneity, resulting comparatively strong SGS and genetic differentiation over small scale. This provided implications to understand how the shade-tolerant shrubs adapt to karst lanform and also theoretical basis for management of C. fladida. |
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