【目的】碳(C)、氮(N)和磷(P)在林木的生长发育中有着重要作用,三者的含量变化和元素比值控制着林木的营养和生长状况。本研究主要分析了秦岭山区同一树种不同林龄叶片的C、N、P含量及化学计量比随季节变化的规律,为林木施肥管理提供依据。【方法】在林木生长季的不同月份(2012年5月到10月每月中旬),对秦岭5年生(5 a)、10年生(10 a)、20年生(20 a)3种林龄的华北落叶松针叶进行定期采集,并测定不同月份各林龄针叶的C、N、P含量和化学计量比值,对不同林龄不同生长季华北落叶松针叶的C、N、P及C ∶N、C ∶P、N ∶P的动态变化进行分析,并对其C ∶N与氮含量、C ∶P与磷含量进行相关性分析。【结果】1)3种林龄针叶的碳含量从生长初期(56月)到生长旺盛期(78月)逐渐增加,生长末期(89月)逐渐降低,但到落叶期(10月)又小幅回升。2)3种林龄华北落叶松针叶的氮含量在整个生长季内(510月)均呈现先降低后升高再降低的趋势,各林龄针叶氮含量升高和降低的时间存在差异,5 a和20 a林龄的针叶N含量从6月到生长旺盛期(7月、8月)基本上保持上升趋势,而10 a林龄针叶的氮含量67月份先逐渐降低,79月份急剧升高,落叶前期到落叶(910月)这段时间3种林龄针叶的N含量均急剧下降为最低值。3)3种林龄针叶磷含量在整个生长季节内的变化趋势基本一致,均先降低后升高再降低最终维持稳定。4)5 a、10 a和20 a林龄的华北落叶松在生长季节内针叶的C ∶N变化范围分别为21．8356．42、18．4358．49和22．5487．83,变异系数分别达到了37．74%、42．05%和68．42%,随着树龄的增长其变异系数逐渐增大。5)5 a、10 a、20 a林龄的华北落叶松在生长季节内针叶C ∶P的变化范围分别为169．17402．85、180．54395．01和213．02398．75,变异系数依次为31．35%、31．43%和22．88%。6)针叶的N ∶P,5 a、10 a、20 a在生长季节内的变化范围分别为6．7715．42、6．3820．13和4．4414．45,变异系数分别为39．65%、50．86%和33．03%。7)各林龄针叶的C、N、P平均含量以及各比值之间的差异均不显著( P>0．05)。【结论】3种林龄的华北落叶松针叶的C ∶N、C ∶P均与相应的N、P含量呈显著负相关(P<0．05),随着N、P含量的变化以对数方程的形式减小。同时发现,氮是秦岭地区幼、中林龄华北落叶松生长的主要限制性因子,土壤中的氮养分不足会制约林木的生长,因此对本研究区的土壤应及时补充氮肥以满足华北落叶松正常生长的营养需求。%[Objectives]Carbon (C), nitrogen (N) and phosphorus (P) play an important role in forests growth. The contents and ratios of C, N and P element reflect the nutritional status and healthy growth of forests. The objective of this research was to explore the seasonal variations of C, N, P contents in the leaves in different ages, so to provide a basis for the academic mamgement of the artificial forests. [Methods]Three different ages, namely 5 years old (5 a) , 10 years old (10 a) and 20 years old (20 a) of Larix principis-rupprechtii in Qinling Mountains were chosen as experimental materials. Leaf samples were collected in different growth phases in the middle of a month from May to October in 2012. The C, N, P contents and stoichiometry were monitored. Seasonal dynamics of leaf C, N, P contents and C ∶N, C ∶P, N ∶P mass ratios in different ages of Larix principis-rupprechtii were analyzed. Data were also analyzed by correlation analysis between N content and C ∶N and P content and C ∶P .[Results] 1 ) C content of these three ages increased gradually from growth stage ( May to June ) to the vigorous growth period ( July to August) ,then decreased at growth anaphase ( August to September) , but there had been a slight pick-up in the defoliation (October). 2) The N content of three ages increased first, then decreased and went up again throughout the growing season ( May to October) . The increasing or reducing time among three ages was different. 5 a and 20 a maintained the upward trend basically from June to vigorous growth period, while the N content of 10 a decreased first from June to July, and then increased sharply from July to September. The N content of three ages decreased sharply to the lowest value from early defoliation to defoliation. 3) The P content of three ages kept the same trend throughout the growing season. They all decreased first, then increased and decreased again, finally they kept stable. 4) Seasonal dynamics of leaf C ∶N mass ratios in three ages were different. C ∶N mass ratios in 5 a, 10 a and 20 a varied in the range of 21. 83-56. 42, 18. 43-58. 49 and 22. 54-87. 83, respectively. The values of coefficient of variation ( CV) were 37. 74%, 42. 05% and 68. 42%, respectively. The value of CV increased gradually along with increasing age. 5) C ∶P mass ratios of needles in 5 a, 10 a and 20 a varied in the range of 169. 17-402. 85, 180. 54-395. 01 and 213. 02-398. 75, respectively. The values of CV were 31. 35%, 31. 43% and 22. 88%, respectively. 6) N ∶P mass ratios of leaf in 5 a, 10 a and 20 a varied in the range of 6. 77-15. 42, 6. 38-20. 13 and 4. 44-14. 45, respectively. The values of CV were 39. 65%, 50. 86% and 33. 03%, respectively. 7 ) C, N, P content and stoichiometry had relationships with the age of Larix principis-rupprechtii, but the differences among the ages in average C, N, P content and their ratios were not significant( P>0. 05 ) .[Conclusions] Correlation analysis indicated that C ∶N mass ratio and C ∶P mass ratio were negatively correlated with corresponding N, P content in different ages of Larix principis-rupprechtii. Furthermore, N is a restrictive factor for young and middle-aged Larix principis-rupprechtii of Qinling Mountains during its growth and development. The growth of trees was restricted by the shortage of soil nitrogen. N fertilizer should be timely supplied in this place to meet the nutritional needs of the normal growth of Larix principis rupprechtii.
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