长白山白桦山杨次生林细根形态特征和解剖结构对氮沉降的响应

根系作为植物与土壤物质交换和养分循环的桥梁,长期以来一直是生态学研究的热点。于2017年7月植物生长季,对长白山模拟11年氮(N)沉降控制试验样地的白桦(Betula platyphylla)山杨(Populus davidiana)天然次生林进行了根系采样,并利用根序法研究了根系形态特征和解剖结构对不同梯度N添加处理的响应,旨在探求两物种根系之间潜在生态联系。本试验共设置了三个N添加梯度,分别为对照(CK,0 g N m~(-2 )a~(-1))、低N处理(T_L,2.5 g N m~(-2 )a~(-1))和高N处理(T_H,5.0 g N m~(-2 )a~(-1))。研究结果如下:1)T_L显著抑制白桦和山杨前三级细根皮层厚度的生长。白桦通过增加皮层细胞直径(一级根增加了72.77%,二级根增加了53.22%,三级根增加了39.96%)但减少皮层层数来降低皮层厚度,而山杨主要通过皮层细胞直径的减少(一级根下降了40.80%,二级根下降了28.17%)来降低其皮层厚度。2)T_H显著抑制山杨前三级细根生长。主要通过增加皮层厚度(一级根增加了68.78%,二级根增加了50.81%,三级根增加了88.53%)以及降低导管横截面积来抑制吸收养分,从而达到影响生长的目的。3)白桦T_H相比于T_L细根直径呈抑制生长状态。其主要通过抑制中柱直径(一级根下降了17.61%,二级根下降了16.89%,三级根下降了20.62%)的生长来实现。以上结果表明,在同一立地条件下,白桦和山杨的细根对不同浓度N沉降的响应方式不同。

Response of fine root morphology and anatomical structure of Betula platyphylla and Populus davidiana natural secondary forest to nitrogen deposition in Changbai Mountains

As a bridge of material exchange and nutrient cycle between plant and soil, root system has been a research hot spot in ecology. The aim of this study was to explore the potential ecological relationship between the roots of two species. We carried out the research in the growing season in July 2017. The root system was collected in 11 years nitrogen (N) control simulation test sample of Betula platyphylla & Populus davidiana natural secondary forest in Changbai Mountains. The root sequence method was used to reveal responses of the root morphology and anatomical structure to different gradients of N addition. In the study, three N addition gradients were set, which were ambient environment (CK, 0.0 g N m^-2 a^-1), low nitrogen addition (T_L, 2.5 g N m^-2 a^-1), and high nitrogen addition (T_H, 5.0 g N m^-2 a^-1), respectively. The results were as follows. 1) The T_L significantly inhibited growth of the cortical thickness of the first three levels of roots of Betula platyphylla and Populus davidiana. Betula platyphylla reduced cortical thickness by increasing cortical cell diameter (the primary root increased by 72.77%, the secondary root increased by 53.22%, and the third level root increased by 39.96%). While Populus davidiana reduced cortical thickness mainly by decreasing cortical cell diameter (the primary root and the secondary root decreased by 40.80% and 28.17%, respectively). 2) The T_H significantly inhibited the growth of the first three levels of roots of Populus davidiana, which was inhibited mainly by increasing the thickness of the cortex (the primary root increased by 68.78%, the secondary root increased by 50.81%, and the third level root increased by 88.53%) and by decreasing the cross sectional area of the catheter so as to affect growth. 3) By comparing the T_H with the T_L, fine roots diameter of Betula platyphylla showed growth inhibition by inhibiting the growth of the stele diameter (the primary root decreased by 17.61%, the secondary root decreased by 16.89%, and the third level root decreased by 20.62%). The results indicate that the fine roots of Betula platyphylla and Populus davidiana respond differently to N deposition of different concentrations in the same site conditions.