不同林龄华北落叶松人工林生态化学计量特征

Ecological stoichiometry characteristics of Larix principis-rupprechtii plantations at different ages

【目的】探究C、N、P含量及化学计量特征随时间的变化以揭示人工林的养分循环规律,为人工林的高效经营提供参考。【方法】以塞罕坝机械林场幼龄林(14年生)、中龄林(20年生)、近熟林(37年生)的华北落叶松(Larix principis-rupprechtii)人工林为研究对象,采用方差和回归分析的方法,分析针叶和土壤C、N、P含量及化学计量比随林龄的变化规律。【结果】①不同林龄同一土层土壤P含量差异显著(P<0.05),华北落叶松近熟林土壤P含量显著低于幼龄林和中龄林土壤P含量,C、N含量差异不显著(P>0.05);同一林龄不同土层土壤C、N含量随土层厚度增加呈下降趋势,P含量变化趋势不明显;随着林龄增长和土层厚度的加深,土壤C/N、C/P和N/P(碳氮比、碳磷比和氮磷比)均呈先下降后上升趋势。②不同林龄针叶C和P含量差异不显著(P>0.05),N含量差异显著(P<0.05),华北落叶松中龄林针叶N含量显著低于幼龄林和近熟林针叶N含量;不同林龄针叶C/N、C/P和N/P差异显著(P<0.05),中龄林针叶C/N最高,而近熟林针叶C/P和N/P最高。③不同林龄落叶松林P含量和C/P在针叶与土壤之间呈显著正相关(P<0.05),而C/N在针叶与土壤之间呈显著负相关(P<0.05)。【结论】华北落叶松中龄林生长受土壤N含量限制,而近熟林生长受P含量限制,幼龄林生长尚未表现出土壤养分亏缺。在不同生长阶段进行合理施肥有利于华北落叶松的生长。

【Objective】Exploring changes in carbon(C),nitrogen(N)and phosphorus(P)contents and stoichiometric patterns over time is important examine nutrient cycles in plantations and may provide reference values for efficient plantation management.Larix principis-rupprechtii has become the predominant species of shelter and timber forests in China due to its high survival rate,fast growth,high yield and resistance to cold climate.This species is also the dominant tree in forest plantations in Saihanba area,Hebei Province,China.In recent years,research on Larix principis-rupprechtii focused on forest soil fertility changes,biomass and carbon storage,or stand growth models.In the current study,the main nutrients C,N and P in Larix principis-rupprechtii trees and in soil were examined separately.Considering the variable ages of the plantations in question,trees and soil were analyzed using eco-chemometrics.The content of C,N and P in forests changes over time;however,this method has so-far not been applied in studies on Larix principis-ruppre-chtii plantations in Saihanba area.【Method】Variance and regression analysis were used to analyze changes in C,N and P content and to assess stoichiometric characteristics of soil and leaves in Larix principis-rupprechtii plantations of different ages,including young stands(14 years),middle-aged stands(20 years)and near-mature stands(37 years)at the Saihanba Mechanized Forest Farm.【Result】①Soil P content within the same soil layer showed significant differences among the differently-aged L.principis-rupprechtii stands(P<0.05),with significantly lower concentrations in near-mature than in other stands;however,no significant differences in C and N content were observed among stands(P>0.05);soil C and N content in stands of the same age decreased with increasing soil depth,while P content remained stable;soil C/N,C/P and N/P ratios first decreased and then increased with increasing forest age and soil depth;②tree N content differed significantly among the differently-aged forest stands(P<0.05),whereas no significant differences in leaf C and P contents were observed among stand of different ages(P>0.05).Tree N content was significantly lower in20-year-old than in 14-and 37-year-old stands.Tree C/N,C/P and N/P ratios differed significantly among stands of different ages(P<0.05);C/N ratios were highest in 20-year-old stands,and C/P and N/P ratios were highest in 37-yearold stands;③P content and C/P ratio of the trees showed significant positive correlations with those of soils in differently-aged stands(P<0.05),while C/N ratios of leaves produced negative correlations with those of soil(P<0.05).【Conclusion】Soil N availability was the predominant factor limiting growth of L.principis-rupprechtii in the 20-year-old stands.In the 37-year-old stands,tree growth was mostly limited by P availability.However,neither N nor P were not major growth-limiting factors in the 14-year-old stands.Fertilization may thus help promote growth of L.principis-rupprechtii at different growth stages.