氮添加对华北落叶松叶片化学计量与养分重吸收效率的影响

为了解华北落叶松林叶片化学计量特征和养分重吸收效率与N素供应的关系,以24年生华北落叶松人工林为研究对象,设置3个水平(0,8,15 g/(m~2·a))连续6年的野外氮添加控制试验,测定氮添加后华北落叶松成熟叶片、凋落叶片和林分土壤养分含量的变化。结果表明:成熟叶片C含量在年际间差异显著(P0.05),氮添加显著增加成熟叶2016—2018年的C、N含量,降低2018年的P含量,导致2018年N/P在轻度氮添加下比对照增加20.20%,重度氮添加下增加34.43%,2018年N/P在重度氮添加下出现峰值20.50,表明氮添加在一定程度上驱动该林分生长的P养分限制;凋落叶中的C、N、P含量及化学计量在年际间和氮添加处理下均呈显著差异(P0.05),氮添加显著增加凋落叶2016—2018年的C含量、C/P和N/P,显著降低2016—2018年的P含量;2016—2018年,轻度氮添加下NRE(氮重吸收效率)和NRE/PRE(氮重吸收效率/磷重吸收效率)显著降低,氮添加下PRE(磷重吸收效率)显著增加;相关分析表明,NRE与凋落叶N含量,PRE与凋落叶P含量呈显著负相关,相关系数分别为-0.860和-0.772;氮添加显著增加土壤有效氮的含量,降低土壤pH(除2016年)和速效磷含量。氮添加导致华北山地针叶林树木生长受不同程度的P养分限制,推测氮添加驱动的林分受P限制可能与该区土壤养分初始状况有关,为全球气候变化下森林的养分管理提供参考依据。

Effects of Nitrogen Addition on Leaf Stoichiometry and Nutrients Reabsorption Efficiency of Larix principis-rupprechtii

Our objective was to understand the relationship between leaf stoichiometric characteristics, nutrients reabsorption efficiency and nitrogen (N) supply of Larix principis-rupprechtii. We selected 24-year-old Larix principis-rupprechtii plantation as study object, and set up a 3-level (0, 8 and 15 g/(m²·a)) field experiment of N addition for 6 years to explore the change of mature leaves, leaves litter and soil nutrients contents. The results showed that the content of C in mature leaves was significantly different among years. The N addition significantly increased the C and N contents of mature leaves in 2016-2018, and decreased the P content in 2018, resulting in an increase of 20.20% in N/P ratio under light nitrogen addition and 34.43% under heavy nitrogen addition in 2018, and a peak of 20.50 in N/P ratio under heavy N addition in 2018, which indicated that N addition could drive the P nutrient limitation of the stand growth to a certain extent. The contents and stoichiometry of C, N and P in leaves litter were significantly different between years and different N addition. The N addition significantly increased the C content, C/P and N/P of leaves litter in 2016-2018, and significantly decreased the P content in 2016-2018. NRE and NRE/PRE decreased significantly under light N addition, while PRE increased significantly under N addition in 2016-2018. Correlation analysis showed that there were significant negative correlations between NRE and leaf N contents, and between PRE and leaf P contents, with the correlation coefficients of -0.860 and -0.772 respectively. The N addition significantly increased the content of soil available N, decreased soil pH (except 2016) and available P content. The results indicated that the growth of coniferous forests in North China was limited by P in different degrees due to N addition. It was speculated that the P nutrient limitation of the forests driven by N addition might be related to the initial soil nutrient status in this region, which provided reference for forest nutrient management under global climate change.