Seasonal Color Variation And Physiological Distinction Of Fine Roots In Manchurian Ash Plantations

Fine roots are the most important components to absorb nutriets and water from soil, and have significant physiological and ecological functions in carbon and nutrients cycles of forest ecosystems. With the growth and senescence of root, pigmentation which influenced root morphology, physiology and mortality occured. Therefore, assessing the course of root color variation in pigmentation will help us understanding the life span of individual root. In this study, the first three branch order roots of Ash (Fraxinus mandshurica) with different color (white, yellow, brown and shrivel brown) were examined in root number population, morphology traits, anatomical structure and physiological functions. The results are as below.(1) In contrast with roots with the other colors, the number and biomass of yellow roots was the highest one. then the white roots, brown roots and shrivel brown roots. The total amount of roots reduced with decreasing soil depth. However, the proportion of root number and biomass in each color was similar. The amount of color roots had differed in seasonal patterns. In the first two order roots, yellow and brown roots had higher variations in root populations, contrasting with white roots. In the third order, all colors had a peak in summer, but lower in spring or autumn.(2) The diameter variation in different color roots was uncertaity, yet the coefficients of variation (CV) was significant within the branch orders. White indivadual roots were the longest in first three orders, the CV of root length declined from white to dark roots. The specific root length (SRL) of shrivel brown was the highest among the pigmentation roots in first-order, the second was brown roots, white and yellow roots was smaller. SRL of white and yellow roots were significant higher than that of brown and shrivel brown roots in 2- and 3-order roots. Root length density (RLD) of white and yellow roots was significantly greater than that of brown and shrivel roots across branch orders, the same partten was also observed for total root surface area.(3) With ascending root orders, the proportion of roots with diarch protoxylems reduced graduelly. In the first three order roots, the inner structure of white and yellow roots was integrity, but in dark roots of the first two orders, however, some cortical parenchyma cells disaggregated and pigmented, indicating senescense launched. Despite there was a few successived phellem layer and more dead cortical parenchyma cells occurred in 3-order dark roots, part of the parenchyma cells in phloem in these roots were still alive, and had ability to transport water and nutrition. It was indicated that dark roots of the first two orders differed from 3- order dark roots in physiological and ecological functions.(4) Total nitrogen concentrations decreased with ascending root orders among all pigmentation roots, but the pattern was not particular. Membrance permeability of white roots was lowest, and shrivel brown roots was the highest aross three orders. White and yellow roots had greater respiration rate, as well as higher root vigor (showed by TTC reduction), in contrasting with brown and shrived brown roots in the first order roots, which had higher N concentrations. This indicated that root respiration rate was not correlated with total N concentration in the first order roots, but denpanded on root vigor.