| Roots are the media of C, N transferred from plant to soil, which is the core aspects of the underground forest C,N cycle. There will be great significance to understand the physiological and ecological functions of the roots through the research of the C,N allocation and control mechanism. Thus, in this research, 1-year old Koelrenteria Paniculata seedlings was selected as the research objects to examin how root morphology, biomass, and chemistry to differ with root branch orders (1-6 with root tips classified as first order roots), how biomass, carbon and nitrogen distribution of 1-year old K Paniculata seedlings above and below ground responded to increased C sink strength (via N fertilization) and reduced carbon source strength (via stem girdling).Result shows that: fertilization affected root biomass significantly, in the early stages of fertilization treatment, root biomass increased, but decline in the later stages. Stem girdling reduced the root biomass ultimately. Sugar, starch, TNC concentration decreased after stem girdled in all the root branch orders, and when sugar, starch, TNC concentration of higher order roots decreased to their thresholds values at later stages after stem girdled, the TNC concentration in lower root orders began to drop, and it was most prominent in the higher root orders. Contrary to roots of the belowground part, TNC concentrations in aboveground organs (leaf and stem) were improved after stem girdled. In September, TNC concentration dropped to equal to CK in above ground because of absence accumulation. After fertilization, TNC concentration increased with root orders increasing, but N content decreased with root orders increasing. fertilization increased fine root N concentration and content in all six orders, while stem girdle decreased root N concentration.Form these researches; the following conclusions can be obtained:(1) The total nonstructural carbohydrate (TNC) concentration in 1-years old K Paniculata seedlings roots increased, but N content decreased with root orders increasing, and they kept the same ways in the all growth course as well.(2) Although coarse root has the highest TNC content, both the stem and leaves have a larger proportion of TNC storage due to larger biomass. Both leaves and fine roots have the highest N, stems and fine roots have lower N, as a result of biological differences between the various parts, so aboveground of a tree reserves the larger N content. In addition, K. Paniculata is a deciduous tree species, and 1-year old seedlings does not form branches, so coarse roots and stems are the main storage organs of carbohydrate and nitrogen when seedlings overwintering, but the TNC and N storage proportion is different in various organs.(3) Stem girdle will reduce TNC's content and reserves. The main reason may be when the transport of carbon to the root system blocked, TNC, which was stored in the root, was partially consumed during the respiration. After stem girdle, TNC in the higher root orders was firstly declined, which shows that TNC in the higher root orders can be transported to lower root orders in order to maintain their vitality when face to stress. Meanwhile, the biomass of the lower root orders reduced in order to decline the respiratory consumption of C.(4) Soil nitrogen fertilized not only increased the N concentration in the root, but also increased the N concentration in the aboveground part of the tree. With the increasing of N concentration in the lower root orders, which means the absorptive capacity of the root system was enhance. That is the key reason of an increase in productivity of seedlings response to fertilization. In addition, soil nitrogen fertilized did not increase fine root biomass, which indicating that fertilization may promote some of the photosynthate allocation to aboveground and then could lead the productivity of the aboveground parts were significantly higher than that of CK.(5) Fertilization did not have significant increase biomass and TNC content in fine root, and one-year-old seedlings were seldom death according to the change of TNC in K Paniculata seedlings root and biomass after soil fertilized. Consequently, we presumed that the carbon in fine roots will not have significant change, which supported the hypothesis of constant distribution proposed by Hendricks et al (1993). However, due to the lack of the experiment data of root respiration rate, it is unclear that whether fertilization can significantly improve the effect of carbon consumption by root respiration, more studies should also be carried out to determine the different effect of C distribution in fine roots. |
