不同年龄巴山木竹种群克隆结构

很多竹类植物是典型的克隆植物,也是大熊猫的食物。研究典型竹子种群克隆结构的形成和发展对竹林的生产和抚育具有理论和实践意义,可为预测该竹林群落的演替趋势和大熊猫保护提供科学依据。利用SSR标记研究不同年龄A(7龄)、B(30龄)和C(60龄)巴山木竹种群的克隆结构和多样性,探讨小尺度范围内不同年龄巴山木竹种群的克隆结构及斑块的建立和发展。8对SSR引物共扩增出了118个位点,3个种群样地的256个样本共检测到了49个克隆(基因型),A、B和C种群分别检测出31、10个和8个克隆。随着种群年龄的增长,巴山木竹克隆面积增加,克隆数量减少;A和B样地各克隆分布格局为团块状,而C样地克隆既有团块状又有离散状。这一结果显示出在幼苗定居的初期,基株可能以短距离的克隆延伸为主从而呈现出团块状;而随着年龄的增长,克隆面积不断扩大,当复轴混生型的巴山木竹克隆受到强大的压迫时,基株可能会进行较多的单轴和长距离克隆延伸,呈现出离散状。Mantel检测和空间自相关分析都支持3个样地在小尺度范围内存在明显的克隆空间遗传结构。3个样地在10 m等级下显著的正相关空间遗传结构距离为3.1、28、48 m,X-轴截距为9.051、30.698和50.536,空间自相关系数的范围分别为0.1—0.167、0.008—0.703和0.006—0.735。由此可推断,随着年龄的增长,巴山木竹克隆斑块的规模在不断地扩大,同一克隆的分株数量增加,在均匀取样情况下,正相关空间遗传结构距离范围内取到具有相同基因型的可能性越大。A、B和C 3样地的基因型比率(G/N)为1、0.14和0.055,Simpson多样性指数(D)分别为1、0.876和0.744。这说明巴山木竹幼苗期基因型比例远远高于成年的竹林,随着年龄的增长巴山木竹克隆多样性虽有所降低,但由于有性繁殖的作用仍然保持了较高的多样性。聚类和主坐标分析均表明总体上各样地的克隆被聚为一类,但不同样地少数克隆的基因型有重叠和聚集,可推断出不同巴山木竹种群之间可能存在着基因流动和近似的克隆起源。

Clonal structure of Bashania fargesii populations at different ages

Bamboos are typical clonal plants commonly used as food for giant pandas. Studies of the clonal structure of typical bamboo populations are of both theoretical and practical importance for bamboo forest production and tending. Studies have attempted to predict its population succession for the protection of giant pandas. In this study, simple sequence repeat fingerprints were used to reveal the clonal structure and diversity of Bashania fargersii populations at three different genet ages (A 7 years, B > 30 years and C > 60 years). We described how the clonal structure of B. fargersii populations at different genet ages established and developed at the small scale. We amplified 118 microsatellite locus using 8 selective primer pairs. A total of 49 clones were identified from 256 leaf samples collected from three populations, among which 31 clones were detected in plot A, 10 clones in plot B, and 8 clones in plot C. The size of clones in the three plots increased and the number of clones decreased with population aging. The spatial distribution pattern of clones in plots A and B exhibited a clumped distribution, while plot C showed two different patterns with simultaneously clumped and discrete distributions. The results showed that the genet generally formed a clumped distribution pattern during the seeding stage. The clones may expand into either the more sympodial type of ramets or short-distance clones, indicating that clonal propagation restricts dense seedling growth. However, with increasing clone size and genet age, compound axis mixed B. fargesii may expand into either the more monopodial type of ramets or long-distance clones representing a discrete distribution pattern when the genet are pressured by other strong clones. In addition, in our study, both the Mantel test and spatial autocorrelation analysis supported the significant presence of positive spatial clonal structures in three plots at the small-scale level. Spatial autocorrelation analysis also showed that the positive spatial genetic structure distance of the three plots in the 10 m distance class were 3.1, 28, 48 m, X-intercepts were 9.051, 30.698, and 50.536, and scope of spatial autocorrelation coefficients r were 0.1-0.167, 0.008-0.703, and 0.006-0.735, respectively. Our results showed that the size and scale of clones increased with genetic aging. Additionally, the number of ramets in the same clone increased under uniform sampling conditions, indicating that more samples with the same genotype can be collected with a positive spatial genetic structure distance. In our study, the distinguishable genotypes (G/N) from populations A, B, and C were 1, 0.14, and 0.055 and the Simpson''s indices of diversity (D) were 1, 0.876, and 0.744, respectively. This result revealed that the distinguishable genotypes at the seeding stage (A 7 years) was much greater than that at the adult stage (B 30 years and C 60 years). Although the genotypic diversity of clonal populations reduced with genet aging, because of initial seedling recruitment, the value remained high. The unweighted pair-group method and principal component analysis demonstrated that clones in the same plot were always classified into the same clade. However, a few clones from different plots exhibited aggregation and overlap during analysis. In conclusion, we demonstrated that gene flow and an approximate clone origin might exist in different populations.