栓皮栎根系解剖结构、水力特性及碳、氮含量研究

Anatomical structure, hydraulic traits and carbon-nitrogen contents of Quercus variabilis roots

关键词:  细根, 木质部, 比导水率, 栓塞脆弱性,碳氮比

Key words:  fine roots, xylem, specific hydraulic conductivity, embolism vulnerability, caron/nitrogen ratio

摘要:

为阐明栓皮栎根系随径级的变化规律,探究其细根的合理划分标准。以1年生栓皮栎幼苗为研究对象,将其根系分为1、1～2、2～3、3～4 mm四个径级,分别制作石蜡切片观察解剖结构,比较木质部水力特性,测定碳氮含量及其比值,并采用主成分法对根系进行分类。结果表明:(1)随着径级增加,栓皮栎根系周皮、韧皮部和形成层组织厚度增加而占径比降低,木质部直径及其占径比均增加。(2)直径2 mm以上的栓皮栎根系木质部平均最大和最小导管直径、根比导水率和栓塞脆弱性指数增加显著; 而导管密度显著下降,导管面积与木质部面积之比变化不显著。(3)直径2 mm以上栓皮栎根系碳含量表现出显著增加,随着径级增加,根系氮含量下降、碳氮比升高。(4)主成分分析表明,13项根系结构和元素含量指标降维后,前2个主分量方差贡献率达62%,PCA双序轴显示栓皮栎根系可划分为2 mm以下的吸收根群和2 mm以上的运输根群。综上认为,以2 mm作为栓皮栎细根划分的标准兼顾了形态和功能的特点,更具有准确性。

Abstract:

To explore the dynamic of internal structure of Quercus variabilis roots with increasing diameter and detect the rational criteria for the division of its roots, the roots of one-year-old Q. variabilis seedlings were divided into four diameter classes: 1 mm, 1-2 mm, 2-3 mm and 3-4 mm. These roots were made paraffin sections separately to observe anatomical structure and determine hydraulic traits of xylem. The carbon and nitrogen content were detected with carbon/nitrogen ratios. These roots were divided by principal component method. The results were as follows:(1)The thickness of periderm, phloem and cambium of Q. variabilis roots increased with the increase of diameter class, while their percentage decreased. The diameter and percentage of xylem showed the increasing trend.(2)The mean maximum and minimum vessel diameters, root specific hydraulic conductivity and embolism vulnerability index of xylem increased significantly in the roots with the diameter above 2 mm. The vessel density decreased and the percentage of vessel area to xylem area altered without significance.(3)The carbon content in the roots with the diameter above 2 mm increased significantly. With the increase of diameter class, the root nitrogen content decreased and the carbon/nitrogen ratio increased.(4)The principal component analysis showed that the variance contribution of the first two principal components reached 62% after dimensionality reduction of 13 root structure and element content indexes. PCA biplot indicated that the roots of Q. variabilis were divided into two groups: absorbing root group in diameter below 2 mm and transporting root group above 2 mm. It is concluded that 2 mm is the criterion for fine root classification of Q. variabilis, which is more accurate with both morphological and functional characteristics.