Root Identification And Variations In Architecture Of Fine Roots Of Subtropical Tree Species In Southern China

Fine roots (diameter≤2mm) with a complex branching system varied largely among different species in distribution, architecture and size. Studing the root architetures of different tree species and nutrient characteristics among different root orders played a significant role in understanding root architectures and variation patterns of chemical composition in different tree species, and their influences on belowground niche segregation, co-existence and the process of forest ecosystem.We have studied root architecture and functions of five subtropical tree species in Southern China. Our objectives were to:1) examine architecture among five subtropical tree species; 2) determine nutrient concentrations across different branch orders; and 3) know about the relationship between root architecture and nutrient exploration strategy.Intact fine root segments of 5 subtropical tree species (Cyclobalanopsis glauca, Liquidanbar formosana, Alniphyllum fortunei, Cunninghamia lanceolata and Pinus massoniana) were collected by using excavation method in Huitong County, Hunan Province, China. The sampled individual root was dissected according 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 higher order roots. Following the dissection, fine root samples were scanned by Win-RhIZO system to analyze specific root length, specific root area and diameter, tips and forks. The fine root samples were then oven-dried at 85℃to a constant weight to determine the weight. The concentrations of C and N in a given order were determined by applying the wet combustion method and the Semimicro-Kjeldahl method, respectively.The results showed that specific root length and specific root surface decreased, and root diameter increased from the first to third order roots for 5 selected subtropical tree species. Significant differences were also observed among different tree species:the highest specific root length(31.45 m·g-1)of the first order roots among 5 tree species was observed for L. formosana, the lowest SRL (16.34m·g-1) was observed for C. lanceolata. The highest specific root area were found in the first and the second order roots of P. massoniana, and the lowest SRL were found in the first order roots of C. lanceolata; the second and the third order roots of C. glauca had the lowest SRA, while the highest SRA were found in the third order roots of C. lanceolata. There were significant differences for fine root diameters among 5 tree species. The C. lanceolata had the largest fine root diameter, while A. fortunei showed the lowest diameter. No significant differences were found for the number of fine root tips among 5 tree species, in contrast, great differences was observed for the number of forks among tree species.Apart from C. lanceolata and L. formosana, C concentration in fine root has been significantly increased as root order increased. The C:N ratio was increased from low to high root order, but N concentration was decreased. C concentration in fine root of C. lanceolata was the highest one and that of A. fortunei was the lowest. No significant differences were found for other three tree species. Nitrogen concentration in fine root of A. fortunei was the highest while that of P. massoniana was the lowest. The C:N ratio of fine root was the highest for P. massoniana and the lowest for A. fortunei, respectively.Assessment of belowground interactions in mixed forests has been largely constrained by the ability of distinguish fine roots of different species. Here, we explored near infrared reflectance spectroscopy (NIRS) to predict the proportion of five fine roots of tree species in mixed samples. The results showed that there were aboundant information appeared in the range of 7100cm-1 to 4000cm-1 for roots of 5 tree species. The obvious absorptive peaks of roots of A. fortunei were 6895 cm-1,5196 cm-1,3992 cm-1; L. formosana were 6875 cm-1,5177 cm-1,3992 cm-1; C. lanceolata were6895 cm-1, 5196 cm-1,3992 cm-1; C.glauca were 6895 cm-1,5196 cm-1,3992 cm-1; P.massoniana were 6875cm-1,5196 cm-1,3992 cm-1. The best model to predict proportions of a particular species were based on retreatment by the second deviation and 17 smoothing points. With this models the proportion of each species in root mixtures was predicted accurately with low standard error of prediciton (RMSECV<5.92%) and high coefficient of determination (r2>0.96) for all fine root mixtures. P. massoniana tended to have a lower RMSECV (3.16), and higher r2 (0.988) than other tree species.The approach presented here is a promising alternative to hand sorting of fine roots, which may be influenced substantially by operator variation, and it will facilitate investigating belowground interations between tree species.