| In this essay, the31year-old Cryptomeria fortunei plantations of different density were studied in southeastern Guangxi. The biomass, productivity and allocation pattern of carbon and nitrogen storage of Cryptomeria fortunei plantations in tropical regions of South Asia is researched.Monsic layered cut method, whole root excavation and quadrant harvest method were adopted for the determination of biomasses of various forest stand-level in different density plots. The correlate data of sample trees were used to establish the regression model of different organs, and the total biomass of arbor layer. Elemental analyzer was used to determine the carbon and nitrogen content of vegetation and soil, as well as to calculate the total carbon, nitrogen reserves of forest stand. Indoor analog nitrogen source addition was applied to determine the respond of forest stand soil respiration to atmospheric nitrogen deposition.The result showed that: (1) By using correlate data of sample trees and linear and nonlinear regression analysis of software, the Optimal equation of Cryptomeria fortunei plantation biomass is W=a×Db×Hc, among which the goodness of fit of regression model of the root stump and whole plant are the best, whereas the goodness of fit of regression model of the leaf is relatively poor.(2) The biomass in the low density, medium density and high density of Cryptomeria fortunei plantation were180.78t·hm-2,193.28t·hm-2, and207.59t·hm-2respectively, which presented as the orders of low density> medium density> high density; arbor layer> litter layer> shrub and herbage layer; trunk> stump roots> leaves> branches> bark> fine roots> coarse roots> root. The net biomass accumulation in the high density, medium density and low density of Cryptomeria fortunei plantation were5.66t·hm-2·a-1,6.04t·hm-2·a-1, and6.55t·hm-2·a-1respectively.(3) The average carbon contents in three densities of Cryptomeria fortunei plantation arbor layer were:high density between499.8and532.7g·kg-1; medium density between500.0and531.9g·kg-1; low density between476.9and519.6g·kg-1. The average nitrogen contents were:high density between0.83and13.87g·kg-1, medium density between0.76and13.28g·kg-1, low density between0.96and15.34g·kg-1. The carbon and nitrogen content among different organs and different densities were of significantly differences (P<0.01), through ANOVA test.(4) Estimation of ecosystem carbon stocks in the high density, medium density and low density of Cryptomeria fortunei plantation were:371.55t·hm-2,414.96t·hm-2, and332.40t·hm-2respectively; nitrogen reserves were:19.95t·hm-2,22.11t·hm-2, and17.67t·hm-2respectively, which presented as the orders of medium density> high density> low density. Carbon and nitrogen reserves in0-100cm depth soil layer accounted for a major part of the entire ecosystem, among which soil carbon storage accounted for68.59to75.96percent, and soil nitrogen reserves accounted for95.41to97.08percent.(5) The experimental data showed that:for soil with different moisture content, at the beginning of the experiment, when the amount of the nitrogen source added reached a certain value, the inhibition effect on soil respiration is gradually increased as the increase of nitrogen addition amount. Nevertheless, as time went by, nitrogen’s inhibition effect on soil respiration changed into acceleration effect, and at last, soil respiration gradually became consistent with the blank value. Conclusion can be made that the influence of nitrogen addition on soil respiration is related to the nitrogen addition amount and the time. |
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