三倍体毛白杨叶片营养年变化规律初探

研究了三倍体毛白杨Populus tomentosa 11个无性系（无性系号分别为S1，S2，S3，S4，S5，S6，S7，S8，S9，S11，S12）叶片中营养元素氮、磷、钾、钙和镁年变化规律，并以二倍体毛白杨（无性系号为S10）为对照。研究结果表明：①同一营养元素在三倍体毛白杨叶片中表现出大体相似的季节性动态变化趋势，其中氮、磷、钾在整个生长期呈现出明显下降的年变化趋势，而不同无性系叶片中钙的年变化趋势为逐渐上升，镁为先上升后下降；②毛白杨不同无性系叶片中仅磷全年差异达到了显著水平（P〈0．01，n=36），12个无性系中S5磷质量分数最高，全年平均为1．85g·kg^-1；③在整个生长季节中，与对照二倍体毛白杨S10比较，三倍体毛白杨无性系S5，S6，S3，S12，S7，S1，S4叶片磷质量分数均有所提高：④毛白杨不同无性系在生长季节内，叶片中积累大量元素的规律相似，平均质量分数由大到小的顺序均为氮〉钾〉钙〉镁〉磷，分别为24．31，17．23，4.36，1．94，1．56g·kg^-1。

Annual changes of N, P, K, Ca, and Mg leaf nutrients in triploid Populus tomentosa

Populus tornentosa is the main tree species for afforestation in north China. To maintain its productivity, annual changes in leaf nutrient concentrations of N, P, K, Ca, and Mg with 11 clones of triploid P. tomentosa （S1 through S9, S11, and S12） were studied with diploid P. tomentosa （S10） as a control. The one-year-old seedlings were afforested in 2005, in Pinggu of Beijing, and leaves were gathered respectively in April, July and October of 2006 by representative sampling method with three replications, for determining N, P, K, Ca, and Mg concentrations in leaves. Results showed that （1） for a given nutrient, triploid P. tomentosa leaves had similar seasonal variations, N, P, and K, levels declined during the whole growth period; Ca gradually increased, while Mg increased and then decreased. Also, （2） greater P concentrations in leaves of different clones were highly significant （P 〈 0.01, n = 36） with the greatest being 1.85 g·kg^-1 in S5. Additionally, （3） compared to diploid P. tomentosa, throughout the growing season, P concentrations in leaves of triploid P. tomentosa increased for clones S1, S3 through S7, and S12. Finally, （4） during the growing season, for the different clones of P. tomentosa, concentrations of these macro elements were similar with the order and average content （in g·kg^-1） of the five nutrients as： N （24.31）〉K（17.23）〉Ca（4.36）〉Mg（1.94）〉P（1.56）.