| Litter decomposition plays an important role in biogeochemical cycling. The nutrients it released is an important nutrient resources for trees'growth and would provide 69%-87% nutrients needed by forest growth. Tsuga longibracteata, Tsuga Tchekiangensis, Taxus chinensis var. mairei,Cephalotaxus fortunei, Cryptomeria fortunei Hooibrenk ex Otto et Dietr, Metasequoia glyptostroboides Hu et Cheng, Fokienia hodginsii(Dunn)Henry et Thomas are ancient relic plants which are precious rare endemic national protected species and have important values on economic and research. Due to their special habitats, once the species destroyed, they were hard to restored and would be in endangered. The hard decomposition of litter fall was one of the important limiting reason for seeds germination and seedling growth to a certain extent, which means that the conifer leaves played important roles in ecological nutrients cycling and their natural regeneration. Therefore, it is very important to study their leaves decomposition and establish a fast decomposition mechanism in order to promote nutrients recycling use. But up to now, there were hardly any report about the decomposition of the 7 conifer leaves except a few papers on Cryptomeria fortunei Hooibrenk ex Otto et Dietr, Metasequoia glyptostroboides Hu et Cheng and Fokienia hodginsii(Dunn)Henry et Thomas leaves, and there is no report to study the 7 conifer leaves decomposition in the view of endogenous and exogenous substances.The effects of exogenous substance on precious conifer leaves decomposition were studied by nylon bags method with 5 different treatments: CK(contrast), N1(2.5g nitrogen fertilizer),N2(5.0g nitrogen fertilizer), JG1(10g tobacco straw), JG2 (20g tobacco straw). Ammoniation and alkalization concepts were first put forward to promote decomposition of the precious conifer leaves and to study the effects of exogenous substances (nitrogen fertilizer, tobacco straw) on endogenous substances (lignin, nitrogen and ect ),which would thereby affect conifer leaves decomposition, and to establish conifer leaves fast decomposition mechanism. Tobacco straw was firstly added to forest litter to promote litter decomposition which explored a new way for tobacco straw comprehensive utilization. And in this paper, wave-type time series model was firstly applied to simulate the dynamic nutrient contents of conifer leaves. The conifer leaves decomposition ratios were simulated and predicted by applying neural network method and support vector machine method to analyse the relationship between conifer leaves decomposition ratios and substrate qualities for the first time. Cobb-Douglas production function was also firstly applied to establish the conifer leaves decomposition mechanism by analysing the effects of exogenous substance on conifer leaves decomposition, and the sensitivity was analyzed basing on the decomposition mechanism. The results showed that the simulated and predicted effects of those model were acceptable. In this paper, the weight loss regularity, nutrient dynamics and the relationships between the conifer leaves decomposition and their substrate qualities were mainly discussed for 7 conifer leaves with 5 different treatments under 13-month decomposing, the results and conclusions were as follows:1.Adding exogenous substances promoted the conifer leaves decomposition to different degrees.After 13-month decomposing, the weight loss ratios order of Tsuga longibracteata leaves was: JG2>JG1>N2>N1>CK; the weight loss ratios order of Tsuga Tchekiangensis leaves was: JG2>CK>N1>JG1>N2;the weight loss ratios order of Taxus chinensis var. mairei leaves was: JG2>CK>JG1>N2>N1;the weight loss ratios order of Cephalotaxus fortunei leaves was: CK>JG2>N1>JG1>N2;the weight loss ratios order of Metasequoia glyptostroboides Hu et Cheng leaves was:JG2>N2>JG1>CK>N1; the weight loss ratios order of Cryptomeria fortunei Hooibrenk ex Otto et Dietr leaves was: JG1>JG2>N2>CK>N1;the weight loss ratios order of Fokienia hodginsii(Dunn)Henry et Thomas leaves was: JG2>JG1>CK>N1>N2.As a whole, compared to CK treatment, the tobacco straw treatments had more influence on conifer leaves'decomposition than nitrogen fertilizer treatments did basically, however, nitrogen fertilizer treatments greatly promoted leaves decomposition in the early stage. The possible reason was that adding nitrogen fertilizer would cause changes of substrate qualities such as C/N ratios which would affect microbial activities and mineralization and nitrification rate of nitrogen, and ect, and therefore affected the conifer leaves decomposition in the early stage. But in later stage, lignin nitrogen ratios had more influence on conifer leaves decomposition, and adding tobacco straw to conifer leaves would generate alkalinization effect, therefore promoted conifer leaves decomposition.2.Various conifer leaves had different substrate qualities which were the main causes of different decomposition ratios of conifer leaves under the same treatment.After 13-month decomposing, the decomposition ratios order of conifer leaves under CK treatment was: Cephalotaxus fortunei>Tsuga Tchekiangensis>Cryptomeria fortunei Hooibrenk ex Otto et Dietr>Metasequoia glyptostroboides Hu et Cheng>Taxus chinensis var. mairei>Fokienia hodginsii(Dunn)Henry et Thomas > Tsuga longibracteata; the decomposition ratiosorder under N1 treatment was: Cephalotaxus fortunei>Cryptomeria fortunei Hooibrenk ex Otto et Dietr>Tsuga Tchekiangensis>Metasequoia glyptostroboides Hu et Cheng>Fokienia hodginsii(Dunn)Henry et Thomas>Taxus chinensis var. mairei>Tsuga longibracteata; the decomposition ratios order under N2 treatment was: Metasequoia glyptostroboides Hu et Cheng> Cryptomeria fortunei Hooibrenk ex Otto et Dietr > Cephalotaxus fortunei > Tsuga Tchekiangensis > Tsuga longibracteata > Taxus chinensis var. mairei > Fokienia hodginsii(Dunn)Henry et Thomas; the decomposition ratios order under JG1 treatment was: Cryptomeria fortunei Hooibrenk ex Otto et Dietr>Metasequoia glyptostroboides Hu et Cheng>Cephalotaxus fortunei>Tsuga Tchekiangensis>Fokienia hodginsii(Dunn)Henry et Thomas>Taxus chinensis var. mairei>Tsuga longibracteata; the decomposition ratios order under JG2 treatment was: Metasequoia glyptostroboides Hu et Cheng>Tsuga Tchekiangensis>Fokienia hodginsii(Dunn)Henry et Thomas > Cephalotaxus fortunei > Taxus chinensis var. mairei > Cryptomeria fortunei Hooibrenk ex Otto et Dietr>Tsuga longibracteata. The results showed that different conifer leaves had different decomposition ratios which had much to do with their substrate qualities. Different exogenous substances had different influences on the conifer leaves decomposition ratios, but the results showed that Tsuga longibracteata leaves had the lowest decomposition ratios under each treatment which had much to do with its texture.3.Beside environmental conditions such as water and heat, other factors also played important roles in conifer leaves decomposition.By analysing monthly weight loss ratio, the results showed that peak values of weight loss ratio appeared in every month(Jan-Dec 2008) either in different leaves or under different treatments. But for most conifer leaves and treatments, May-Nov emerged more peak values than other periods when it was hot and rainy, which indicated that environmental conditions, such as water and heat had great influences on decomposition. But the lowest decomposition ratios values also appeared in every month among different conifer leaves or treatments which indicated that beside the water and heat, other factors also had great influences on conifer leaves decomposition. Beside, angleworms and ants were found in the nylon bags among May-Aug,2008, which indicated that soil animals and microorganism also played important roles in leaves decomposition.4.Conifer leaves decomposition ratios were significant different among various treatments and different conifer leaves during decomposing process.The results of ANOVA of dynamic decomposition ratios of 7 precious conifer leaves under various treatments showed significant differences among different conifer leaves, various treatments, periods. And the differences also emerged between specie and treatment, specie and period, treatment and period which indicated that different species had different decomposition ratios, various treatments had different effects on conifer leaves decomposition and the results were distinct, decomposition ratios changed by the time, and interactions between species and treatments, species and periods, treatments and periods had great influences on conifer leaves decomposition. The results also indicated that it was practically viable to use exogenous nitrogen fertilizer and tobacco straw to accelerate conifer leaves decomposition, which had practical significances on nutrients cycling and reusing, precious rare trees'long-term productivity maintaining and tobacco straw's utilization.5. During decomposing process, different nutrient contents had different change regularities, the change regularities of the same nutrient content were different among different conifer leaves and treatmentsBy analyzing the carbon, nitrogen, phosphorus, kalium, natrium, calcium, magnesium, zinc, manganese and lignin of 7 conifer leaves under 5 treatments, the results showed that the change tendencies of nutrient content, release, net release, remaining ratio and net releasing ratio were in fluctuant styles. After 13-month decomposing, the contents of nitrogen and manganese were higher than initial contents which were in enrichment state, kalium and natrium contents decreased continuously, other nutrients were either in release state or in enrichment state to various degrees during decomposing process.After 13-month decomposing, except Tsuga longibracteata and Tsuga Tchekiangensis leaves, the carbon contents of other 5 conifer leaves decreased in various treatments. The phosphorus contents decreased in Tsuga longibracteata leaves, Taxus chinensis var. mairei leaves, Metasequoia glyptostroboides Hu et Cheng leaves and Fokienia hodginsii (Dunn) Henry et Thomas leaves under various treatments during decomposing process. The calcium contents were in enrichment state in Tsuga longibracteata leaves, Tsuga Tchekiangensis leaves and Metasequoia glyptostroboides Hu et Cheng leaves after 13-month decomposing. The magnesium contents were in enrichment state in Tsuga longibracteata leaves and Tsuga Tchekiangensis leaves after 13-month decomposing, but were in releasing state in Metasequoia glyptostroboides Hu et Cheng leaves. The zinc contents were all in enrichment state except Fokienia hodginsii (Dunn) Henry et Thomas leaves.After 13-month decomposing, in Tsuga longibracteata leaves, Tsuga Tchekiangensis leaves and Cephalotaxus fortunei leaves, the carbon contents were higher in exogenous substances treated leaves than CK treated leaves, and except Cephalotaxus fortunei leaves, the carbon contents were higher in nitrogen fertilizer treated leaves than in tobacco straw treated leaves, the carbon contents order of Taxus chinensis var. mairei leaves was: tobacco straw treatments > CK treatment > nitrogen fertilizer treatments, in Metasequoia glyptostroboides Hu et Cheng leaves, Cryptomeria fortunei Hooibrenk ex Otto et Dietr leaves and Fokienia hodginsii(Dunn)Henry et Thomas leaves, the carbon contents were higher in CK treated leaves than in exogenous substances treated leaves, the carbon contents were higher in tobacco straw treated leaves than in nitrogen fertilizer treated leaves. In Tsuga longibracteata leaves, Tsuga Tchekiangensis leaves, Cephalotaxus fortunei leaves and Metasequoia glyptostroboides Hu et Cheng leaves, the nitrogen contents were higher in exogenous substances treated leaves than CK treated leaves, except Tsuga longibracteata leaves, the nitrogen contents were higher in nitrogen fertilizer treated leaves than in tobacco straw treated leaves, in Taxus chinensis var. mairei leaves and Fokienia hodginsii(Dunn)Henry et Thomas leaves, the nitrogen contents were higher in CK treated leaves than in exogenous substances treated leaves, the nitrogen contents order of Cryptomeria fortunei Hooibrenk ex Otto et Dietr leaves was: nitrogen fertilizer treatments > CK treatment > tobacco straw treatments. For 7 conifer leaves, the phosphorus contents were higher in CK treated leaves than in exogenous substances treated leaves, and in Tsuga longibracteata leaves,Tsuga Tchekiangensis leaves,Metasequoia glyptostroboides Hu et Cheng leaves and Cryptomeria fortunei Hooibrenk ex Otto et Dietr leaves, the phosphorus contents were higher in nitrogen fertilizer treated leaves than in tobacco straw treated leaves.After 13-month decomposing, except in Cephalotaxus fortunei leaves,the kalium contents order was: tobacco straw treatments > CK treatment > nitrogen fertilizer treatments, in other conifer leaves, the kalium contents were higher in CK treated leaves than in exogenous substances treated leaves. For natrium contents, the contents were higher in nitrogen fertilizer treated leaves than in tobacco straw treated leaves, the contents were higher in CK treated leaves than in tobacco straw treated leaves. For calcium contents, the contents were higher in tobacco straw treated leaves than in nitrogen fertilizer treated leaves, the contents of CK treated leaves were in the middle of them. In Tsuga longibracteata leaves, Tsuga Tchekiangensis leaves and Cryptomeria fortunei Hooibrenk ex Otto et Dietr leaves, the magnesium contents were higher in CK treated leaves than in exogenous substances treated leaves, but for other leaves, the magnesium contents of CK treated leaves were in second place, and basically, the magnesium contents were higher in tobacco straw treated leaves than in nitrogen fertilizer treated leaves.After 13-month decomposing, basically, in Tsuga longibracteata leaves, Tsuga Tchekiangensis leaves, Taxus chinensis var. mairei leaves and Cryptomeria fortunei Hooibrenk ex Otto et Dietr leaves, the zinc contents were higher in CK treated leaves than in exogenous substances treated leaves, in Cephalotaxus fortunei leaves, the contents of CK treated leaves were between tobacco straw treated leaves and nitrogen fertilizer treated leaves, and basically, the contents were higher in nitrogen fertilizer treated leaves than in tobacco straw treated leaves, in Metasequoia glyptostroboides Hu et Cheng leaves and Fokienia hodginsii(Dunn)Henry et Thomas leaves, the contents were higher in CK treated leaves than in exogenous substances treated leaves, and the contents were higher in tobacco straw treated leaves than in nitrogen fertilizer treated leaves. For manganese contents, the contents were higher in exogenous substances treated leaves than in CK treated leaves in Tsuga longibracteata leaves,Cephalotaxus fortunei leaves and Fokienia hodginsii(Dunn)Henry et Thomas leaves, in Tsuga Tchekiangensis leaves, Taxus chinensis var. mairei leaves and Cryptomeria fortunei Hooibrenk ex Otto et Dietr leaves, the contents were higher in CK treated leaves than in exogenous substances treated leaves, in Metasequoia glyptostroboides Hu et Cheng leaves, the contents of CK treated leaves were between tobacco straw treated leaves and nitrogen fertilizer treated leaves, except Tsuga Tchekiangensis leaves and Cryptomeria fortunei Hooibrenk ex Otto et Dietr leaves, the contents were higher in tobacco straw treated leaves than in nitrogen fertilizer treated leaves basically.After 13-month decomposing, basically, in Tsuga longibracteata leaves and Taxus chinensis var. mairei leaves, the lignin contents were higher in CK treated leaves than in exogenous substances treated leaves, but in other conifer leaves, the lignin contents were higher in exogenous substances treated leaves than in CK treated leaves, and in Taxus chinensis var. mairei leaves, Cephalotaxus fortunei leaves and Fokienia hodginsii(Dunn)Henry et Thomas leaves, the contents were higher in tobacco straw treated leaves than in nitrogen fertilizer treated leaves. The result showed that adding exogenous substances had different impacts on the nutrient contents of different conifer leaves and different nutrients.6.Different conifer leaves decomposition ratios had different relationships with different substrate qualities, but basically had positive linear correlativity with nitrogen content, and had negative linear correlativity with carbon nitrogen ratio and lignin nitrogen ratio The decomposition ratios of Tsuga longibracteata leaves had positive linear correlativity with nitrogen contents, carbon phosphorus ratios and calcium contents, and had negative linear correlativity with phosphorus contents, carbon nitrogen ratios and lignin nitrogen ratios. Tsuga Tchekiangensis leaves decomposition ratios had positive linear correlativity with nitrogen content s and phosphorus contents, and had negative linear correlativity with carbon nitrogen ratios, carbon phosphorus ratios, lignin contents and calcium contents. Taxus chinensis var. mairei leavesdecomposition ratios had positive linear correlativity with nitrogen contents, carbon phosphorus ratios, lignin contents and calcium contents, and had negative linear correlativity with carbon nitrogen ratios phosphorus contents and lignin nitrogen ratios. Cephalotaxus fortunei leaves decomposition ratios had positive linear correlativity with nitrogen contents and lignin contents, and had negative linear correlativity with carbon nitrogen ratios and lignin nitrogen ratios Metasequoia glyptostroboides Hu et Cheng leaves decomposition ratios had positive linear correlativity with nitrogen contents and calcium contents, and had negative linear correlativity with carbon nitrogen ratios, phosphorus contents and lignin nitrogen ratios. Cryptomeria fortunei Hooibrenk ex Otto et Dietr leaves decomposition ratios had a distinctly positive linear correlativity with nitrogen contents, and had a distinctly negative linear correlativity with carbon nitrogen ratios, and had a distinctly positive linear correlativity with phosphorus contents in N1 treated leaves, and had a distinctly negative linear correlativity with phosphorus contents in JG1 treated leaves; had a distinctly negative linear correlativity with carbon phosphorus ratios in JG1 treated leaves; had positive linear correlativity with lignin contents; had negative linear correlativity with lignin carbon ratios. Fokienia hodginsii(Dunn)Henry et Thomas leaves decomposition ratios had positive linear correlativity with nitrogen contents, carbon phosphorus ratios and calcium contents, and had negative linear correlativity with carbon nitrogen ratios, phosphorus contents and lignin nitrogen ratios.The result of multilinear regression analysis about 7 precious conifer leaves decomposition ratios and substrate qualities(carbon content ,nitrogen content, phosphorus content, lignin content and calcium content ) showed that, whether analyzing every single treatment or as a whole, the multilinear regression models were satisfactory, and correlative coefficients were high and the linear relationships were very distinct. 7 precious conifer leaves decomposition ratios had negative linear correlativity with carbon contents and phosphorus contents, and had positive linear correlativity with nitrogen contents, lignin contents and calcium contents.In CK treatment, 7 precious conifer leaves decay constants (k) had positive correlativity with initial carbon contents, nitrogen contents, phosphorus contents, kalium contents, natrium contents , calcium contents and magnesium contents, and had negative linear correlativity with initial zinc contents, manganese contents, lignin contents, lignin nitrogen ratios, carbon nitrogen ratios and carbon phosphorus ratios. Among them, decay constant (k) had a distinctly negative correlativity with initial lignin contents, and had a very distinctly negative correlativity with initial lignin nitrogen ratios.7.Conifer leaves decomposition promoting mechanism established by analyzing the effect of exogenous substances on conifer leaves decomposition showed that reducing exogenous nitrogen fertilizer or increasing exogenous tobacco straw would accelerate conifer leaves decomposition The relationship of decay constant and exogenous substances was established by multilinear regression model and Cobb-Douglas production function treating 7 conifer leaves as a whole, which indicated that decay constant had a very distinctly negative correlativity with exogenous nitrogen fertilizer treatments, and had a very distinctly positive correlativity with exogenous tobacco straw treatments, namely, reducing exogenous nitrogen fertilizer or increasing exogenous tobacco straw would accelerate conifer leaves decomposition. The result matched with the decomposition ratios of different species under various treatments. Marginal analysis of Cobb-Douglas production function showed that ,on current conditions, other conditions being equal, decay constant would decrease 0.0034 by adding 1g nitrogen fertilizer and increase 0.0025 by adding 1g tobacco straw. However, the analysis of conifer leaves decomposition during the decomposing process showed that adding nitrogen fertilizer to conifer leaves had accelerated the decomposition in early stage. |
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