Effects Of Fertilization On Fine Root Dynamics In Manchurian Ash And Davurian Larch Plantations

Fine root is a major organ of trees in absorbing water and nutrition. The production and turnover of fine root in forest ecosystems play an important role in terrestrial carbon and nutrition cycles. By using Minirhizotron, the distribution, production, mortality and turnover of fine root among different soil depth and different diameter were investigated near two years in 18 years old pure Manchurian ash (Fraxinus mandshurica) and Davurian larch (Larix gmelinii) plantations, which were fertilized and located on the same stand conditions. At the same time, soil temperature, soil moisture and nitrogen availability were also measured in these plantations. The results were showed as follows:1. The results of studying on the distribution of fine root suggested: (1) As for two trees species in fertilized and controlled plots, the number of fine root and root length density were all decreased with soil depth increased, the number of fine root of Manchurian ash was more than that of Davurian larch, fine root length density of Manchurian ash was also higher than that of Davurian larch. Both of fine root number and root length density in fertilized plots were less than those in controlled plots. Most of Manchurian ash fine root occurred in spring and summer, but Davurian larch fine root mainly occurred in summer. For both of trees speices, the fine root length density was not significantly affected by fertilization, and was also no difference among diverse seasons;(2) Fertilization didn't significantly affect fine root diameter for Manchurian ash and Davurian larch fine root. Considering two trees species in fertilized and controlled plots, the mean root diameter of Manchurian ash was thinner than that of Davurian larch. Although the diameter of Manchurian ash fine root was significantly changed with different seasons, and became thicker in deep soil than in shallow soil, this status didn't exhibit for Davurian larch fine root.2. The experiment of fine root dynamics and soil environmental factors indicated: the production and mortality of fine root were not significantly influenced by fertilization in Manchurian ash and Davurian larch plantations. Analyzing two trees species in fertilized and controlled plots, the production and mortality of Manchurian ash fine root were all more than those of Davurian larch fine root. As for fine root production in fertilized and controlled plots, both of trees species had one peak value in early summer, respectively, and for Manchurian ash, about 44%~75% of annual fine root production happened in summer, then the production of Davurian larch fine root accounted for about 46%~60% in this season. The mortality of fine root was all evenly distributed with changed season for two trees species in fertilized and controlled plots, and occurred approximately 60% of annual fine root mortality in summer. Further analysis indicated the production of fine root may be controlled by the interactions ofendogenesis and exogenous factors for Manchurian ash and Davurian larch. However, the mortality of fine root was mainly impacted by integration of soil environmental factors for two trees species.3. The results of fine root dynamics among different soil depth showed: the influence of fertilization on fine root production and mortality was no significant at different soil depth in Manchurian ash and Davurian larch plantations, but in fertilized and controlled plots, fine root production and mortality decreased with depth soil increased, both of trees species are all the same. However, the production and mortality of Davurian larch fine root were all less than that of Manchurian ash fine root in every soil layer. As for the seasonal dynamics of fine root production, the difference between two trees species mainly occurred in 0~30cm depth soil in fertilized and controlled plots. Then the seasonal dynamics of mortality was all more evenly distributed over the growing season and no difference among different soil depths for Manchurian ash and Davurian larch in two treatments. In terms of the quantity of production and mortality, both of trees species were similar in fertilized and controlled plots, about 40% of annual fine root production and mortality was concentrated on the top soil. Synthesizing analysis demonstrated: besides soil environmental factors (soil temperature, soil moisture and nitrogen availability), inherent factors may be also influence on the production of fine root at different soil depth for Manchurian ash and Davurian larch. Furthermore, the mortality of fine root among different soil depth mainly influenced by exogenous environmental factors.4. The investigation of fine root dynamics among different diameter classes indicated: (1) In fertilized and controlled plots, for Manchurian ash, the distribution of fine root number and fine root length mostly located on 0.1~0.3mm diameter class, but for Davurian larch, mainly did on 0.3~0.5mm diameter class. (2) For different diameter fine root, effects of fertilization on production and mortality were insignificant for both of trees species. However, for Manchurian ash, the difference of fine root production and mortality was significant among different diameter classes in fertilized and controlled plots, but Davurian larch was not. The production and mortality of Manchurian ash fine root were more than those of Davurian larch fine root in different diameter classes. As for the seasonal dynamics of fine root production with different diameter, the distinctness between two trees species in two treatments mainly occurred in 0.1~0.3mm diameter class. Then, the dynamics of fine root mortality, both of trees species were similar in all different diameter classes. In fertilized and controlled plots, the quantity of fine root production and mortality, whose diameter is less than 0.5mm, was most in all diameter fine roots. For Manchurian ash, about 70% of annual fine root production and mortality mainly occurred in this diameter and approximately 60% for Davurian larch. Analyzing experiment date suggested the integration of soil environmental factors and other inherent factors, impacted the production of fine root in all different diameter classes forManchurian ash and Davurian larch. Then, exogenous factors significantly affected the mortality of fine root with distinct diameter for both of trees species.5. Estimating fine root turnover showed: the turnover of fine root with different diameter and different depth soil was significantly affected by fertilization. For both of trees speices in fertilized and controlled plots, the turnover of fine root was all decreased with soil depth and diameter increasing, but the rate of turnover in fertilized plots was higher than that in controlled plots. Moreover, the turnover of fine root had difference between Manchurian ash and Davurian larch, the turnover of Manchurian ash fine root was slower than that of Davurian larch fine root.By synthesizing all research, the results indicated: (1) the influence of fertilization on the distribution, production and mortality of fine root, was all insignificant in Manchurian ash and Davurian larch plantations, but the turnover of fine root was all increased by fertilization for Manchurian ash and Larch;(2) the characteristics of biology was different between Manchurian ash and Davurian larch, and experimental date suggested the interactions of endogenesis and exogenous factors may controlled fine root production for two trees species.