| Soil carbon pool is a large volume and low activity carbon pool on substanceflowing in terrestrial ecosystems, which has great potential and good effectiveness toremove atmospheric CO2. Litter decomposition and fine root turnover are two mainways of soil carbon inputs which have the irreplaceable role and status to maintainingsoil carbon reserves. Nitrogen fertilization treatments or nitrogen deposition influence,directly or indirectly, litter and fine root decomposition by changing litter quality orsite environment factors.In this paper, we conducted controlled experiments and nitrogen fertilizationtreatments for the litter and fine root decomposing process of alpine Sibiraeaangustata shrub to quantitative study soil carbon inputs of litter decomposition andfine root decomposition pathways and its response to nitrogen fertilization treatmentsusing the litterbag method. The objectives were to assess the soil current and potentialsituation of carbon sequestration in alpine terrestrial ecosystems under global change.The main results are shown as follows.1.After six months of litter and fine root decomposition, when the initial masswas5g, the litter residual mass was4.25±0.33g; the litter mass loss rate was15.00±6.56%; and when the initial mass was2g, the fine root residual mass was1.71±0.11g; the fine root mass loss rate was14.30±5.40%. After one year of litter andfine root decomposition, the litter residual mass was2.33±0.43g; the litter mass lossrate was53.50±8.63%; and the fine root residual mass was1.30±0.09g; the fineroot mass loss rate was34.98±4.26%. The results showed that litter and fine rootdecomposition have a close rate in the first half year of test, but litter decompositionwas faster than fine root decomposition in the second half year of test.2.With exponential decay model, the relations between litter residual rate and time and between fine root residual rate and time have been fitted. Get the averagedecomposition coefficients of litter and fine root were-0.60t-1+1.45,-0.06t-1+0.52in the test period, respectively. The coefficients were variables over time so theaverage decomposition coefficients of litter and fine root were0.85,0.46in the firstyear of test, respectively. From the (same decomposition time) decompositioncoefficients can be seen that litter decomposition was faster than fine rootdecomposition.3.After one year of litter and fine root decomposition, the litter mass loss rateswere53.50%,53.83%,63.00%and69.02%under N0, N2, N5, N10treatments,respectively. There were no significant differences between the different treatments.The fine root mass loss rates were34.98%,35.87%,37.98%and39.02%under N0,N2, N5, N10treatments, respectively. There were also no significant differencesbetween the different treatments. The average decomposition coefficients of litterwere0.85,0.75,0.94and1.08, and the time required to decompose50%of the initialmasses were326days,346days,308days and291days, and the time required todecompose95%of the initial masses were906days,1117days,843days and729days under N0, N2, N5, N10treatments in the first year of test, respectively. Theaverage decomposition coefficients of fine root were0.46,0.41,0.49and0.50, andthe time required to decompose50%of the initial masses were529days,576days,502days and489days, and the time required to decompose95%of the initial masseswere2145days,2291days,2059days and1963days under N0, N2, N5, N10treatments in the first year of test, respectively. The results showed that litterdecompositions and fine root decompositions have the positive effects under N5andN10treatments and the negative effects under N2treatment. But there were nosignificant differences between the different treatments.4.After the test conducted six months, the soil carbon inputs unit mass of litterwere0.05±0.02g·g-1,0.07±0.02g·g-1,0.06±0.02g·g-1and0.05±0.02g·g-1, andthe soil carbon inputs unit mass of fine root were0.08±0.03g·g-1,0.11±0.03g·g-1,0.10±0.05g·g-1and0.08±0.03g·g-1under N0, N2, N5, N10treatments, respectively.After the test conducted one year, the soil carbon inputs unit mass of litter were0.18±0.03g·g-1,0.18±0.03g·g-1,0.21±0.05g·g-1and0.23±0.06g·g-1, and the soilcarbon inputs unit mass of fine root were0.20±0.02g·g-1,0.21±0.04g·g-1,0.22±0.02g·g-1,0.23±0.04g·g-1under N0, N2, N5, N10treatments, respectively. Theresults showed that the soil carbon inputs unit mass of litter were less than the soilcarbon inputs unit mass of fine root in the first half year of test and the soil carbon inputs unit mass of litter and fine root have the close amounts in the test period.The comprehensive results showed that the decomposition of litter and fine rootwere slowness by low temperature affects in the non-growing season, while with thetemperature rising, the rate of decomposition was increasing in the growing season.Because litter containing more water soluble substances and easy decompositioncarbohydrates and less lignin, cellulose and other difficult decomposition substancesthan fine root, the time required to decompose50%and95%of the intial masses oflitter were shorter than the time required to decompose50%and95%of the intialmasses of fine root. To some degree, litter and fine root decomposition were promotedunder N5, N10and inhibited under N2. But there were no significant differencesbetween the different treatments so as to think that nitrogen fertilizations (simulatednitrogen deposition) have no direct influences on litter and fine root decomposition. |
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