Fine Root Turnover And Carbon Allocation In Manchurian Ash And Davurian Larch Plantations

Fine root turnover was the main topic of material cycling and energy flow in belowground ecosystem study, which determined the amounts of carbon (C) and nutrient flux to be transferred from the plant to the soil. Study of fine root turnover was the key to recognize the position of fine root in ecosystem C and nutrient circulation. The subject problem in fine root turnover study were: how to estimate fine root turnover rate accurately and which factors effect on fine root production and turnover. There were a lot of research on estimating fine root turnover in the past years, but the results were disunion because the defect of research method;The key factors control on fine root turnover were soil nitrogen (N) and C supply above-ground, but relevant research - especially study of C control on fine root turnover was seldom involved. For these reasons, this research regards Manchurian ash (Fraxinus mandshurica Rupr) and Davurian larch (Larix gmelinii Rupr) plantations as the research objects, different methods were used to estimate fine root turnover rate and study how N fertilization control on fine root turnover and C allocation;Stem girdling method control C allocation to belowground, study how C control on C and N allocation patterns in different root orders and aboveground organs, and discussion the mechanism of C control on fine root turnover.Fine root biomass, root length density (RLD) and specific root length (SRL) were higher in Manchurian ash than Davurian larch. Fine root turnover consumed about 18 percent and 10 percent of the net primary production (NPP) of Manchurian ash and Davurian larch respectively. A large amount of NPP was consumed because of the photosynthate allocated to the fine root constantly. Manchurian ash root consume more NPP than Davurian larch, which may be a reason why the productivity of Davurian larch higher than Manchurian ash. N fertilization reduced live fine root standing biomass of Manchurian ash significantly but dead fine root biomass have no prominent change. Live and dead root standing biomass of Davurian larch have not dropped or increased notably in fertilization plots. Fine root RLD of Manchurian ash declined in fertilized plots, but Davurian larch fine root root RLD have not changed notably within two years such as the standing biomass. In addition, fertilization reduced SRL of two species, SRL of Davurian larch fine root decreased prominently but not in Manchurian ash.Fine root standing biomass, RLD and SRL appear seasonal peak value in different month of Manchurian ash and Davurian larch plantations. Because of climatic various in two years in Maoershan area, fine root of the same species has variation seasonal pattern for 2003 and 2004. The living fine root standing biomass of Manchurian ash have a peak value in spring, and Davurian larch fine root standing biomass have two prominent peak in 2003 and 2004respectively. Dead fine root standing biomass of two species has a peak value in spring for 2003, two peak value appear in early spring and late autumn separately in 2004, the peak value in spring of dead fine root standing biomass was caused by the fact that the dead fine roots was accumulated in winter. Seasonal pattern of live fine root RLD and standing biomass were different because of the ratio of root order change seasonally. The peak value of RLD appear in June to August in two years of two species, but not all the trees appear in the same month year each. The maximum of fine root standing biomass, RLD and SRL in two species were not consistent means that fine root diameter relatively thin in summer, and relatively thick in autumn, which reflect that fine root in autumn have different structural compositions and physiological functions compare with what in spring and summer.Fine root of two species response diversely to fertilization, the mean value of fine root annual production and turnover rate of Manchurian ash in fertlized plots were less than unfertilized (CK), but the difference was not prominent. Fine root annual production and turnover rate of Davurian larch in fertilized plots were greater than CK plots significantly. The time of treatment influence on fine root production and turnover, in the first year, average production of two species were no significant difference between fertilized and CK plots, but the second year after fertilized, average amount of production and turnover rate of fertlized plots were greater than CK plots in Manchurian ash plantations, and fertilization reduced the production and turnover rate of Davurian larch notably. Two species were growth in the same site condition, difference responded to apply fertilizer of two species mainly decided by biological characteristics.Estimating fine root production and turnover rate of Manchurian ash and Davurian larch plantations with different research approaches and computing technology, results show that difference of root production and turnover rate can reach 10 times in the same ecosystem. Soil core method but computing technologies were different, production and turnover rate difference reaches about 3 times of two species. These results means that how to choose appropriate research approach or adopt many kinds of method were essential in evaluating the accuracy of result among fine root production and turnover research.Soluble sugar, starch and total nonstructural carbonhydrate (TNC) concentration in different root orders of Manchurian ash were higher than the same orders of Davurian larch, but this 3 kinds of material (soluble sugar, starch and TNC) concentration vary with root order and demonstrate the same trend in two species. The trend of soluble sugar concentration increased and than decreased with increasing root order, starch and TNC concentration increased systematically with root order, but the soluble sugar varies with the root order at the largest range, and the starch increase with root order was relatively low. Soluble sugar, starch and TNC concentration in different root orders of Manchurian ash and Davurian larchdemonstrate a decreased and then increased trend in a growing season. In the course of leaf expansion from May to June, soluble sugar, starch and TNC concentration drop notably in all root orders. After leaf fully unfold in June, new leaf can fixation carbohydrate and supplement to belowground again, soluble sugar, starch and TNC were accumulated progressively and reach a high-level in September in all root orders, most prominent in the higher root orders.Total N concentration in different root orders of Manchurian ash were higher than Davurian larch, total N concentration demonstrate decreased trend with increasing root order in two species, total N concentration in the lst-5th orders drop notably with order. Total N concentration in Manchurian ash and Davurian larch root orders demonstrate the decreased and then improved trend in a growing season. Though total N concentration in root orders of two species was in the ascendant trend from July to September, but the value in September was lower than May, total N concentration in lower root orders change at the largest range within a season.Soluble sugar, starch and TNC concentration decreased after stem girdled in all the root branch orders of two species, and decreased significantly in higher root order at first. In the later stage after girdled, when soluble sugar, starch and TNC concentration in higher root orders reach a certain threhold value, then the concentration in lower root orders begin to drop, and it was most prominent in the higher root orders. Soluble sugar in all the root orders of two species incline to keep certain a level at first after stem girdled, the higher root order drops notably until later stage and not prominent in the lower root orders. Starch concentration in root drop notably earlier than soluble sugar, starch concentration dropped and reach a prominent level finally in every root orders in the branch root system. Contrary to roots of the belowground part, TNC concentration of every organs aboveground were improved after girdled, it was more obviously in leaf and branch. In September, TNC concentration dropped to equal or lower than CK in above ground because of sbscence accumulation.Girdling have reduced the N concentration of roots in two species finally, but the degree of N concentration of two species respond to girdling were different. 30 days after girdled, N concentration were increased than CK in all root branch orders, and then dropped of every root order in later stage, but the degree of N concentration of Manchurian ash was relatively low, only a few root orders decreased significantly than CK. N concentration drops notably in every root ordes of Davurian larch in the later stage after girdled.