亚热带6种树种细根序级结构和形态特征

Fine root architecture and morphology among different branch orders of six subtropical tree species

以福建省建瓯市万木林自然保护区内占优势的6种天然林树种(沉水樟Cinnamomum micranthum,CIM;观光木Tsoongiodendron odorum Chun,TOC;浙江桂Cinnamomum chekiangense,CIC;罗浮栲Castanopsis fabri,CAF;细柄阿丁枫Altingiagracilipes,ALG;米槠Castanopsis carlesii,CAC)为研究对象,对其1—5级细根的结构,形态特征及生物量进行了分析。结果表明:沉水樟,细柄阿丁枫和米槠细根分支比表现出在1,2级(4倍以上)明显大于其它序级(3倍左右);其余3种树种则是在3,4级的细根分支比最大,其中浙江桂达到8.65倍,其它序级则大致为3倍左右。6种树种1,2级细根数量占到总数的70%—90%。6种树种细根直径,根长,组织密度随序级升高逐渐增大,比根长减小,生物量未表现出一致的变化规律,6种树种生物量主要集中在高级根部分。方差分析表明,树种对细根分支比例有显著影响(P<0.05),浙江桂和米槠细根分支水平对分支比例有极显著影响(P<0.01),其余4种树种分支水平对分支比例有显著影响(P<0.05),树种和分支水平的交互作用对6种树种细根分支比均有极显著的影响(P<0.01);树种对细根根长,直径以及生物量均有极显著影响(P<0.01),对比根长有显著影响(P<0.05),而对组织密度的影响则不显著(P>0.05);树种和序级的交互作用对细根根长,直径以及生物量均有极显著影响(P<0.01),对组织密度有显著影响(P<0.05),对比根长影响不显著(P>0.05)。序级对6种树种细根根长,直径,比根长以及生物量的影响并未达到一致,对6种树种细根组织密度有极显著影响(P<0.01)。树种间1—4级根的比根长变异主要由组织密度引起,而5级根的比根长变异则由直径引起,同时在1级根中组织密度与直径呈现出权衡的关系。6种树种细根数量,直径,根长,比根长,组织密度以及生物量与序级之间回归分析发现它们与序级之间具有指数函数,线性函数,二次函数,三次函数或者幂函数关系。

Fine roots play an important role in the function of individual plants. Recent studies indicated large heterogeneity in architecture, morphology, anatomy, physiology, and longevity within the fine root pool which can be systematically described by branching order. To date, while it is remarkable how little we know about the architecture and morphology in fine roots of subtropical evergreen broadleaf forest. So in this study intact fine root segments of six dominant tree species （ Cinnamomum micranthum, CIM ; Tsoongiodendron odorum Chun, TOC ; Cinnamomum chekiangense, CIC ; Castanopsis fabri, CAF; Altingia gracilipes, ALG; and Castanopsis carlesli, CAC ） were collected by excavation in an evergreen broadleaved forest located at the Wanmulin Nature Reserve. Jian＇ ou. Fuiian province. Individual roots were dissectedaccording to the branching order, starting from the distal end of the root system that was numbered as the first order and then increasing sequentially with each branch from the first order to fifth order roots. Then, fine root samples were scanned by the Espon scanner, used WinRHIZO system to analyze root architecture and morphology. We attempted to address the following questions ： （ 1 ） the effect of root order and tree species on fine root architecture and morphology ; and （ 2 ） the relationship between specific root length, tissue density and diameter across root order and tree species. The result showed that： for CIM, ALG and CAC, the branching ratios （Rb） was higher between the first two root orders （over 4） than between the other orders （ about 3） ; while for TOC, CIC and CAF, Rb were higher between the third and forth orders than between the other orders （ about 3 ）, with the highest Rb value of 8.65 between the third and forth orders of CIC. For all species, 70% to 90% of total root number comprised the first two orders. Root diameter, length, and tissue density increased and specific root length （SRL） decreased with increase in order for all species. Though there was no consistent changed with root order, root biomass was mainly concentrated in the higher root orders. The ANOVA demonstrated that both tree species （P〈0.05 for all cases） and tree species branching level （P〈0.01 for all cases） had significant effect on Rb. The branching level had significant effect on Rb for CIC and CAC （ P〈0.01 ） and for the other four species （ P〈 0. 05 ）. Tree species had significant effect on root length, diameter, biomass （P〈0.01） and SRL （P〈O. 05）, but had no significant effect on tissue density （P〉0.05）. The tree species root order interaction had significant effect on root length, diameter, biomass （P〈0.01） and tissue density （P〈0.05）, but had no significant effect on SRL （P〈0.01）. Though root order had no consistent effect on root length, diameter, SRL and biomass, it had significant effect on tissue density for all species （P〈0.01）. The variations in SRL of the first to the forth orders among species were mainly caused by tissue density, while those of the fifth order caused by root diameter. A tradeoff between root diameter and tissue density occured in the first order. For individual species, changes in root number, diameter, length, SRL, tissue density and biomass with root order can be represented by exponential, linear, quadratic, cubic or power functions.