| 4,15 and 32 year-old Cunninghamia lanceolata plantations in Shaowu city of Fujian province in typical acid rain areas were acted as the testing forests,the changes of soil nutrient and microbial diversity of surface soil after 360 days of decomposition were analyzed under the treatments of different ratio of Cunninghamia lanceolata-Michelia macclurei(C&M)litter.The results were as follows:(1)The effects of different litter treatments on soil pH value varied in different forests,and the effect of mixed litters on soil pH mainly concentrated in the late stage of decomposition of litter,C1M1 in young(4 years old)and mature forest(32 years old)can be better to improve soil pH.Changes of the total carbon content of different litter treatments in three stands mainly concentrated in the late stage of decomposition,the middle-age forest had higher rapid growth,while the other two stands declined;At the same time,the total carbon content of C1M1 was relatively higher than other treatments in the young forest and mature forest,but C2M1 was higher in the middle-age forest.The total nitrogen content of different litter treatments in three stands had increased significantly in the late stage of decomposition,and the improvement of middle-age forest was the most,while the soil total nitrogen of C2M1 in three ages were the highest.Soil available phosphorus and available potassium of the mixed litter treatment was higher than that of the single treatment,but in the mature forest,the available potassium of C2M1 was higher than the other two mixed treatment,and the differences among them were not significant;At the same time,it also showed a downward trend in the overall change of the whole cycle decomposition of available phosphorus and available potassium.In this three stands,the content of exchangeable calcium and magnesium in middle-age forest was higher than that of the other two kinds of forests;In addition,the exchangeable calcium and magnesium of the mixed litter treatments were higher than that of Chinese fir single treatment,but there was no significant differences among three kinds of mixed treatments.(2)The content of soil microbial biomass carbon under C2M1,C1M1 treatment relatively in young and middle-age Chinese fir plantation was highest than others,while their differences were not obvious in mature stands.The content of soil microbial biomass nitrogen under C1M1 treatment relatively in young and middle-age Chinese fir plantation was highest than others,while their differences were not obvious in mature stands.The soil temperature and moisture content had a significant effect on the soil microbial biomass carbon and nitrogen in the young and middle-age forest,but not in the mature forest.Under natural acid rain,Soil microbial biomass carbon and nitrogen contents were significantly correlated with soil pH.On the multiple effects of the different ages,ratio and decomposition times of Chinese Fir and Michelia macclurei litter,the soil microbial biomass C and N content showed a wavy change during the whole period of decomposition,the peak value of MBC appeared at 60 days and 240 days after treatment,but that of MBN appeared at 120days and 240 days after treatment.(3)The results showed that the total soil microbial metabolic activity increased with the age of forests.The difference of Shannon and Simpson under different litter treatment was not significant,and the effect of C1M2(P=0.001)on McIntosh of soil microbial is very significant.The main types of carbon source utilization in those plantations were carbohydrate,polymer and amino acid,which was under C2M1 and C treatments in three stands were both clustered into one group,but under C1M2,C1M1 and M treatments in the middle-age and mature forests are clustered into other one group.(4)Blank treament and C,M,C1M1 this three kind of litter treatments were selected respectively in the young and muture stands,in order to analyze the diversity of their bacteria.we found that three kinds of litter treatments in young and mature forest could improve the diversity of soil bacterial species.M,C1M1 treatment of soil bacterial species richness increase was significantly higher than that of C in young forest,but in the mature forest,the enhancement of C1M1 species richness was significantly lower than that of C.The soil bacteria of two age of Chinese Fir Plantation at the phylum level which was in the higher advantage position was Acidobacteria,Proteobacteria,their relative abundance changed with time.The relative stability of soil bacterial community under the mixed treatment was higher,and the decomposition of mixed litter could provide the suitable conditions for the soil nutrient cycle and ecological function.In the genus level,after 360 days of decomposition,the change of dominant bacterial genus under different litter treatments in young forest showed the change in relative abundance,the relative abundance of two dominant bacterial genus {Koribacter Candidatus and Rhodoplanes)which was treated by C1M1,tended to be consistent;after 360 days of decomposition,the categories of dominant bacterial genus under different litter treatments in mature forest changed from the initial Rhodospirillaceae,Syntrophobacteraceae to Candidatus and Koribacter Rhodoplanes,and their relative abundance under C1M1 tended to be consistent.The contribution rates of seven environmental factors for whole environmental factors(12)were soil temperature(60.6%),available phosphorus(9.8%),soil pH(4%),soil microbial biomass carbon(2.6%),exchangeable calcium(2.6%),forest temperature(3.5%),exchangeable magnesium(1.1%).The soil microbial biomass carbon mainly explains the diversity information of Acidobacteria,Verrucomicrobia,Crenarchaeota,Gemmatimonadetes,Elusimicrobia at the gate level,and other can explain that of Actinobacteria,Chloroflexi,Nitrospirae,Firmicutes,Bacteroidetes,Synergistetes.In a word,Mixed litter treatment was to improve the soil bacteria community ecological relative balance,to ensure the rational and orderly operation of bacterial community system.At the same time,litter treatment in the young forest could be better to play its ability to improve the ecological balance of microbial communities,but it was difficult to produce a timely response for the addition of short-term litter due to the ecological decline in the mature forest. |
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