| Chinese Fir is one of the most important fast-growing timber tree species in China.It is widely distributed in the south of Yangtze River Valley and south of Qinling Mountains,and has been cultivated for thousands of years.The eighth national forest resources inventory results showed that Chinese fir plantation area and volume accounted for 6.66%of the whole tree inventory area,4.91%of the total volume,ranking the main afforestation tree species in China in the first place,therefore it plays an important position and role in the forestry production and ecological construction.In forest ecosystem,as the bridge which connects the ground and underground parts,litter plays a very important role in maintaining soil fertility and promoting nutrient cycling in forest ecosystem,so the litter is an ideal approach to explore the relationship between different plant communities and soil ecological function.As the main decomposer of litter,soil microorganism play a decisive role in soil biogeochemical cycles,they not only decompose and utilize the soil organic matter but also drive the soil nutrient cycling and renewal and provide nutrients and energy for plant growth.Mixed litter affects the decomposition rate and nutrient release law through changing the nutrient composition of litter,thus affecting the diversity and activity of soil microorganisms.Therefore,the decomposition of soil microbes and litter is a process of mutual influence.In this study,different proportions of litter were used to simulate different proportions of Chinese fir and broad-leaved mixed forest.The field control experiments were conducted to reveal the effects of mixed decomposition of different Chinese fir and board leaf litter on soil nutrient,carbon and nitrogen forms,enzyme activities and soil microbial diversity.The test is divided into two parts,respectively,different proportion of Cunninghamia lanceolata and Michelia macclurei mixed leaf litters decomposition and Manglietia hybrid decomposition.During the decomposition process of litter decomposition in one year,there were different dynamic changes of soil related indexes under different proportions of litters.(1)The soil pH on the whole showed a downward trend on the whole.After one year of litter decomposition,the order of soil pH size was "S">"SH1:3">"SH1:1”>"H">"SH3:1"?"SR1:1”>"SR1:3”>"S">"R">"SR3:1"?(2)After one year of decomposition,there were no significant increase of total phosphorus and total potassium content.However,available potassium content increased significantly,and "S" was the smallest.available potassium in soil increased with the increase of broad-leaved tree proportion.(3)With the decomposition of litter,the total carbon total nitrogen content of different treatments decreased gradually.The total carbon and nitrogen content of soil treated by different proportion of fir litter were higher than that of pure fir litter decomposition,and the effect of "SR1.1"was the best.The total carbon and nitrogen of soil increased with the increase of the proportion of Phoebe,but only the effect of "SH1:3" was better than "S" in the treatment of different proportion of litters.(4)Compared adding litter of Michelia macclurei,the mixed decomposition of litters are more beneficial to increase the DOC content of soil.After one year of litter decomposition,the "S" soil DON is far higher than the different proportion of Chinese fir and broad-leaved litters mixed treatment.(5)The content of ammonium nitrogen and nitrate nitrogen in soil under the mixed decomposition of litters and deciduous leaves was higher than that of "S".In the early stage of decomposition,the soil nitrate nitrogen in different proportion of fir and broad-leaved litters were much higher than other treatments.After one year,the soil nitrate nitrogen content of "SH1:3" "SR1:3" was much larger than that of Chinese fir,while "SH1:3" and "SR1:1" were more helpful to increase nitrate nitrogen in soil.(6)SH1:1 and SR1:1 decreased the MBC content in the soil after four months of decomposition.Except for "SH1:1" and "SR3:1",the contents of MBN in the mixed decomposition of Chinese fir and broad-leaved litters were all less than "S".After one year,the MBC content of soil treated with different proportion of Chinese fir and broad-leaved litters was higher than that of "S",and the order of MBN size was "H">"SH1:3”>"S">"SH3:1”>"SH1:1" ? "SR3:1”>"S">"SR1:1”>"R">"SR1:3".(7)During the process of decomposition,different proportion of Chinese fir and broad-leaved litters reduced soil urease and acid phosphatase activity,soil invertase activity increased gradually and in"SH1:3" soil invertase activity was the largest,there was no significant difference between "S" and the mixed litter decomposition of Chinese fir and Michelia macclurei.At the early stage of decomposition,the invertase activities in soil of different proportions Chinese fir and Manglietia yuyuanensis Law litters increased significantly,higher than that of "S".Soil cellulase activity increased with time and soil acid phosphatase decreased.In addition to soil sucrase,the activity of invertase,cellulase and acid phosphatase in"SR3:1" soil was higher than that of "S" after one year of litter decomposition.(8)The order of bacterial OTUs in different proportions of Chinese fir and broad-leaved litters was "R">"H">"SH1:3">"SR3:1">"S">"SR1:3">"SH3:1">"SR1:1">"SH1:1" Chao1 and ACE all indicate the corresponding bacterial abundance index.Compared with "S",except"R","H","SH1:3" and "SR3:1","R""H""SH1:3""SR3:1" all increased the soil bacterial richness.The number of soil fungi OTUs was S"SR1:1">"R">“SR1:3">"SH3:1">"SH1:3">"SH1:1”>"H">"SR3:1”>"S".The soil fungal richness under the mixed decomposition of single broad-leaved tree litter and the mixed decomposition of litters and were allgreater than "S".(9)After one year of decomposition,the dominant soil bacteria categories at Phylum level under the mixed decomposition of different proportion of Chinese fir and broad-leaved leaves wre Proteobacteria,Chloroflexi,Actinobacteria,Acidobacteria,Firmicutes,Planctomycetes.The abundance of soil bacteria in different treatments were significant different:such as the abundance of Proteobacteria,Actinobacteria,Firmicutes in "SH1:1" "SH1:3" "SH3:1" "SR1:1" "SR3:1" were significantly less than the "S",but "S" improved the abundance of Firmicutes.Ascomycota,Basidiomycota,and Streptophyta,Chlorophyta,unidentified_Fungi were the dominant fungi categories in soil.In"SH1:3" "SR1:1" "SR1:3" "SR3:1",the abundance of Ascomycota,Basidiomycota were significantly less than the "S",and in "S",Streptophyta and Chytridiomycota were less than other treatments.(10)Compared with "S","SH1:1" decreased significantly the number of soil bacteria and fungi at the level of order,family and genus.The rest of mixed decomposition of different proportion of Chinese fir and broad-leaved leaves increased the diversity of soil bacteria and fungi at different classification levels.(11)PCoA indicated that the first two main functions revealed 60.79%bacterial diversity information on the phylum level,the first and second spindles summarized 49.03%and 11.76%information of bacterial diversity respectively."SR1:3" "S" and "R" were similar in bacterial community structure,while the similarity of "SH1:3" and "SH1:1"bacteria communities was higher.The first spindle can generalize 29.88%soil fungal diversity information,and the second spindle can generalize 17.66%fungal diversity information.The first two main spindle can explain 47.54%of the soil fungal diversity information.The soil fungal species composition and structure of "SH1:3”and“SR3:1”showed high similarity,and the<"SH1:1 "soil fungal community structure was far different from the rest treatments.(12)The results RDA indicated that 4 environmental factors had a good explanatory power on the diversity of soil bacteria at the phylum level.The influencing factors ranged from large to small,followed by total carbon(0.4455),ammonium nitrogen(0.2378),total nitrogen(0.0608)and nitrate nitrogen(0.0428).Total carbon mainly explained the diversity information of Cyanobacteria and Proteobacteria,and ammonium nitrogen mainly explained the diversity information of Thaumarchaeota and Chloroflexi.Total carbon(0.5688),nitrate nitrogen(0.5157)and ammonium nitrogen(0.4821)can explain the diversity of soil fungi at the phylum level,the richness of Rotifera and Streptophyta are related to total carbon,ammonium nitrogen and nitrate nitrogen can mainly explain the diversity of Chytridiomycota.(13)Compared with Chinese fir litter,mixed decomposition of different proportional Chinese Fir and broad-leaved litters increased soil ecological function.The effect of mixed decomposition of Chinese fir and Manglietia fordiana Oliver litters was better than that of Chinese fir and Michelia macelurei Dandy litters,and the ecological function of soil increased with the increase of the proportion of Manglietia fordiana Oliver litters. |
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