Ma Zhong, Shi Jisen, Wang Guang, He Zhenxiang
Department of Biology, University of Louisiana at Lafayette, LA 70503, USA.
Genetica. 2006 Mar;126(3):343-51. doi: 10.1007/s10709-005-1358-y.
Growth within tree populations varies among individuals due to changes in biotic and abiotic factors. The degree of such variation, defined as growth inequality, serves as a useful indicator of the uniformity of growth within a population in response to the prevalent environmental conditions. By application of the Gini coefficient (G), an index for inequality, we characterized the early growth inequality of ninety crosses of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) and their open-pollinated parental lines. Tree cumulative height was measured annually for 8 consecutive years. Both the crosses and parental lines exhibited temporal changes in growth inequality. The inequality of total height among the crosses decreased logarithmically with age by nearly 3-fold after 13 growing seasons, suggesting that tree height became less variable among the crosses as trees grew larger. Interestingly, the Lorenz asymmetry, an index reflecting the shape of the Lorenze curve from which G is derived, revealed that the inequality of annual height increment among the crosses resulted from an alternate contribution of the fast-growing and slow-growing trees. Among parental lines, two provenances with the smallest and the largest overall inequality in total height showed a similar pattern of changes in annual growth inequality, and the provenance differences were consistent over time. Compared to the other provinces, a local provenance exhibited less variation in total height among individual trees as reflected by a smaller value of inequality, and was better adapted to the field conditions. Our results demonstrated the sensitivity and usefulness of the Gini coefficient and Lorenz asymmetry for the analysis of growth inequality in non-natural populations. Growth inequality is a potentially useful evaluation criterion for early selection. Given comparable initial growth, provenances/families with lower growth inequality values would likely outperform those with higher growth inequality, and eventually tree size of the latter would be more variable due to greater variations among individual trees. Assessment of growth inequality at early ages will advance our understanding of variability of tree growth within a population, facilitate forest genetics improvement programs, and enhance the efficiency of tree breeding.
由于生物和非生物因素的变化，树木种群内个体间的生长存在差异。这种差异程度，即生长不平等，是种群内生长对普遍环境条件响应均匀性的一个有用指标。通过应用不平等指数基尼系数（G），我们对90个杉木（Cunninghamia lanceolata (Lamb.) Hook.）杂交组合及其自由授粉亲本系的早期生长不平等进行了特征描述。连续8年每年测量树木的累积高度。杂交组合和亲本系在生长不平等方面均表现出时间变化。杂交组合间总高度的不平等在13个生长季节后随年龄呈对数下降近3倍，这表明随着树木长大，杂交组合间树高的变异性降低。有趣的是，洛伦兹不对称性（一个反映导出G的洛伦兹曲线形状的指数）表明，杂交组合间年高度增量的不平等是由快速生长和缓慢生长树木的交替贡献导致的。在亲本系中，总高度总体不平等最小和最大的两个种源在年生长不平等方面表现出相似的变化模式，且种源差异随时间保持一致。与其他省份相比，一个本地种源个体树木间总高度的变异较小，不平等值较小，表明其更适应田间条件。我们的结果证明了基尼系数和洛伦兹不对称性在分析非自然种群生长不平等方面的敏感性和实用性。生长不平等是早期选择的一个潜在有用评估标准。在初始生长相当的情况下，生长不平等值较低的种源/家系可能比生长不平等值较高的表现更好，最终后者的树木大小由于个体间差异更大而变异性更高。早期评估生长不平等将增进我们对种群内树木生长变异性的理解，促进森林遗传改良计划，并提高树木育种效率。
