The Study Of Heterogeneity In Fine Root Structure And Function Of Six Subtropical Evergreen Broadleaved Forest Tree Species

In this study intact fine root segments of six dominant tree species (Cinnamomum micranthus, CIM; Tsoongiodendron odorum Chun, TOC; Cinnamomum chekiangense, CIC; Castsanopsis fabri, CAP; Altingia gralilipes, ALG; and Castanopsis carlesii, CAC) were collected by excavation in an evergreen broadleaved forest located at the Wanmulin Nature Reserve, Jian’ou, Fujian province. We investigated fine root structure (fine root number、the branching ratios) and morphology(fine root diameter、length、specific root length、tissue density、specific root surface area、biomass)) of the first five orders, and measured for fine root order respiration rate by an Li-6400portable photosynthesis system, then measured the nutrient concentrations (C、N、P) of different root order. We mainly attempted to investigated the following questions:the effect of root order and tree species on fine root structure, morphology, respiration, nutrient content; the relationship between fine root morphology, respiration and nutrient content. Meanwhile leaves of six dominant tree species were sampled, and measured the nutrient congtent (C、N、P), then investigated the correlation of chemical traits between the chemical and fine root and leaf. The results showed that:(1) For CIM, ALG and CAC, the branching ratios (Rb) was higher between the first two root orders (over4) than between the other orders (about3); while for TOC, CIC and CAF, Rb were higher between the third and forth order than between the other orders (about3), with the highest Rb value of8.65between the third and forth orders of CIC. For all species,70%to90%of total root number comprised in the first two orders; for individual species, changes in root number with root order can be represented by exponential functions.The ANOVA demonstrated that:both tree species (P<0.05for all cases) and tree species xbranching level (P<0.01for all cases) had significant effected on Rb. The branching level had significant effected on Rb for CIC and CAC(P<0.01)and for the other four species (P<0.05)(2) Fine root diameter, length, and tissue density increased and specific root length (SRL) decreased with increased in order for all species. Though fine root biomass not consistent changed with root order, fine root biomass was mainly concentrated in the higher root orders. For individual species, changes in root diameter, length, SRL, tissue density, SRA and biomass with root order can be represented by exponential, linear, quadratic, cubic or power functions. The correlation analysis indicated that:there were significant related among fine root morphology; 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 trade-off between root diameter and tissue density occured in the first order. Tree species had significant effected on root length, diameter, SRA, biomass (P<0.01) and SRL (P<0.05), but had no significant effected on tissue density (P>0.05). The tree species×root order interaction had significant or marked effected on root length, diameter, biomass (P<0.01) and tissue density (P<0.05), but had no significant effected on SRL and SRA (P>0.05). Though root order had no consistent effected on root length, diameter, SRL, SRA and biomass, it had significant effected on tissue density for all species (P<0.01)(3)For CIM, C content increased as root order increased, while there was no distinct trend for the other five species. There was a negative relationship between root branch order and N and P concentration, and a positive relationship between root branch order and C/N ratios for the six tree species, while the N/P ratios had no distinct pattern with branch order. For individual species, changes in root N、P content and C/N with root order can be represented by exponential, linear, cubic functions; for CIM, TOC and CAC, fine root C content with root order can be represented by cubic functions, while the fine root C content can not be represented by regression model for the other five species.The correlation analysis indicated that:there had no significant correlation between C content and morpholory, and good relation between N、P content、N/P and morphology;the one-way ANOVA demonstrated that tree species had significant effected onC、N、P concentration, C/N ratio, and N/P ratio (P<0.01). Though root order had significant or marked effected on N、P concentration and C/N ratio (P<0.01, P<0.05), it had no significant effected on C concentration and N/P ratio(P>0.05)for the six tree species. The two-way ANOVA showed that:tree species xroot order interaction had significant or marked effected onC、N、P concentration and C/N ratio (P<0.01, P<0.05), while it had no effected on N/P ratio (P>0.05) (4) SRR significantly declined with increasing root order, which was consistent for the six tree species (P<0.01). This decline, however, differed among species, with SRR decreased most sharply for CIC. The regression analysis showed that:SRR changed systematically with root order, which could be represented by quadratic, cubic, exponential or power functions. The correlation analysis indicated that:there were significant or very significant correlation between SRR with fine root morphology and nutrient in the same tree species but different root order, while there were not significant correlation in the same root order but different tree species. The analysis of covariance demonstrated that:tree species had significant effected on (P<0.01) the slope of the regression straight line which between SRR and SRL, but root order had no significant effected on slope and intercept of the regression straight line, these means the correlation between SRR and SRL was significantly affected by tree species but not by root orders, and the correlation between SRR and nitrogen concentration was significantly affected both by tree species and root orders. It is concluded that there existed evident functional heterogeneity among fine roots of different branch orders, and SRL could reflect this heterogeneity only in specific tree species.The one-way and two-way ANOVA revealed that:tree species, root order and tree species×root order all had significant effected on SRR (P<0.01for all cases)...