树木不同着生位置1级根的形态、解剖结构和氮含量

Variations of morphology,anatomical structure and nitrogen content among first-order roots in different positions along branch orders in tree species

树木根系中1级根在养分和水分吸收方面发挥着重要作用。研究1级根的形态结构与功能的联系,对了解1级根的生理功能和寿命,以及森林生态系统碳和养分的循环具有重要的理论意义。但是,1级根在根系统中,因着生的位置不同,可能表现出不同的生理生态功能。该研究以胡桃楸(Juglans mandshurica)、黄波罗(Phellodendron amurense)和水曲柳(Fraxinus mandshurica)人工林根系的1级根为研究对象,研究了不同着生位置的1级根的形态、解剖结构和组织化学特征。将1级根按着生位置的不同分成3类:Ar类根为2级根上的1级根;Br类根为2级–4级根的根尖;Cr类根为3级–5级根上的1级根。结果表明:不同着生位置的1级根,形态、解剖结构和组织化学方面都具有高度的异质性。3类1级根中,Ar类根数量多、根长较短、直径细,N含量高,皮层比例高、维根比低,主要由二原型原生木质部的根组成;Br类和Cr类根数量较少、单根较长、直径粗,N含量低,皮层比例低、维根比高,主要由多原型原生木质部的根组成。研究结果对了解不同着生位置的1级根的吸收功能和寿命具有重要的理论意义。

Aims First-order roots play a key role in water and nutrient uptake from soil,and their positions along the branch orders may display differences in functions.However,few studies focused on the structure and functions of first-order roots with different positions in trees.Our objective was to explore the differences in morphological,anatomical and chemical properties among first-order roots with different branching positions and to understand the correlation between root structure and functions.Methods First-order root samples from plantations were separated into three categories,Ar（from 2nd-order roots）,Br（from 2nd–4th-order root tips） and Cr（from 3rd–5th-order roots）.We made paraffin slices stained by safranin and fast green to observe anatomical traits,including cortex proportion,development of stele and protoxylem type.We also examined morphology and tissue nitrogen concentrations among these roots.Important findings The first order roots in different branch positions showed differences in morphology and anatomy in three hardwood trees.Compared with root Br and root Cr,root Ar have larger root numbers,shorter length,lower stele/root diameter ratio,higher cortex proportion and N concentration,and more diarch roots.Root Br and Cr have smaller root numbers,longer length,higher stele/root diameter ratio,lower cortex proportion and N concentration,and more triarch-pentarch roots.These results suggest that the differences of the first-order roots in morphology,anatomy and tissue chemistry are related to root positions along branch orders,and are important in understanding root structures and functions in trees,particularly in revealing the roles of fine root longevity and turnover in forest ecosystems.