青海黄土高寒区4种典型人工林树木叶片碳氮磷含量及化学计量特征

Content and Stoichiometric Characteristics of Carbon,Nitrogen,and Phosphorus in Leaves of Four Typical Plantation Species in the Alpine Zone of the Loess Plateau in Qinghai

【目的】探究青海黄土高寒区4种典型人工林树木(针叶和阔叶2种生活型)叶片的有机碳(OC)、全氮(TN)、全磷(TP)含量和化学计量特征,及其随生长季阶段(Ⅰ:5月15日—6月15日;Ⅱ:6月15日—7月15日;Ⅲ:7月15日—8月15日)和坡位的变化,为指导青海高寒森林的经营管理提供科学依据。【方法】野外采集华北落叶松、青海云杉、白桦和青杨4种树木叶片样品,室内测定叶片的OC、TN和TP含量,通过正态性检验、单因素方差分析、邓肯多重比较、相关性分析、除趋势对应分析、冗余分析和蒙特卡洛置换检验,探究叶片养分含量及化学计量特征。【结果】4种树木叶片的OC、TN和TP含量平均值(变化范围)分别为591.84(571.19~605.67)、17.76(7.14~27.62)和1.47(0.81~2.65)g·kg^(-1),变异系数表现为TP>TN>OC;阔叶树叶片TN含量高于针叶树,阔叶树叶片TN和TP含量受生长季阶段的影响大于针叶树;4种树木叶片的C∶N(OC∶TN)、C∶P(OC∶TP)和N∶P(TN∶TP)平均值(变化范围)为38.87(26.04~97.73)、1042.97(667.53~1971.00)和28.32(18.87~51.50),变异系数表现为C∶N<N∶P<C∶P;阔叶树叶片C∶N和C∶P受生长季阶段的影响大于针叶树;除青海云杉外,其他3种树木叶片的TN和TP含量极显著正相关(P<0.01);生长季阶段和生活型均极显著影响树木叶片OC、TN和TP含量及化学计量比(P<0.01),而坡位影响不显著(P>0.05)。【结论】青海黄土高寒区青海云杉叶片C∶N和C∶P较高,N∶P较低,说明其生长较慢且更多受TN限制,要注意TN养分的补给。生长季阶段和针叶、阔叶生活型是影响青海黄土高寒区4种树木叶片养分含量和化学计量比的显著因素(P<0.01),养分管理要关注树木所属的生活型和所处的生长季阶段。

【Objective】The purpose of this study was to investigate the contents of organic carbon(OC),total nitrogen(TN),and total phosphorus(TP)and their stoichiometric characteristics in leaves of four typical plantation species(coniferous and broad-leaved life forms)in the alpine zone of the Loess Plateau in Qinghai,and their changes with the stages of the growing season(Ⅰ:May 15 to June 15;Ⅱ:June 15 to July 15;Ⅲ:July 15 to August 15)and the slope positions,and to provide a scientific basis for the management of forest in Qinghai.【Method】The OC,TN,and TP in leaf samples of four typical plantation species(Larix principis-rupprechtii,Picea crassifolia,Betula platyphylla,and Populus cathayana)were measured by field manual sampling and indoor experimental analysis.The nutrient contents and stoichiometric characteristics were analyzed by normality test,one-way analysis of variance,Duncan multiple comparison,correlation analysis,detrended correspondence analysis,redundancy analysis,and Monte Carlo permutation test.【Result】The mean values and variation range of the OC,TN,and TP contents in leaves of the four typical plantation species in the alpine zone of the Loess Plateau in Qinghai were 591.84(571.19-605.67),17.76(7.14-27.62),and 1.47(0.81-2.65)g·kg^(-1),respectively.The coefficients of variation were ranked TP>TN>OC.The leaf TN content of the broad-leaved trees was higher than that of the coniferous trees.The leaf TN content and TP content of the broad-leaved trees were more affected by the stages of the growing season than that of the coniferous trees.The mean values and variation range of leaf C∶N(OC∶TN),C∶P(OC∶TP),and N∶P(TN∶TP)were 38.87(26.04-97.73),1042.97(667.53-1971.00),and 28.32(18.87-51.50),respectively.The coefficients of variation were ranked C∶N<N∶P<C∶P.The leaf C∶N and C∶P of the broad-leaved trees were more affected by the stages of the growing season than that of the coniferous trees.Except for P.crassifolia,the contents of TN and TP in leaves of the other three tree species showed a very significant positive correlation(P<0.01).The effects of stages of the growing season and life forms on leaf OC,TN,and TP contents and stoichiometric ratios of the four typical plantation species reached extreme levels of significance(P<0.01),while the effect of slope positions was not significant(P>0.05).【Conclusion】In the alpine zone of the Loess Plateau in Qinghai,the mean values of C∶N and C∶P in leaves of P.crassifolia were at a high level,while N∶P was at a low level,indicating that the growth rate of P.crassifolia was relatively slow and the major reason was probably the limitation of TN.Attention should be paid to the supply of TN nutrient.Since the stages of growing season and the life form were two significant factors affecting leaf nutrient contents and stoichiometric ratios of the four typical plantation species(P<0.01),both of them should be concerned carefully in the nutrient management in the alpine zone of the Loess Plateau in Qinghai.