Characteristics Of Enzyme Activities In The Decomposition Of Mixed Leaf Litter From Pinus Massoniana And Broad-leaved Tree Species

Litter decomposition is the key to maintain nutrient balance and long-term productivity of plantation.The enzymes associated with carbon,nitrogen and phosphorus cycling play an important role in driving litter decomposition and ultimately releasing nutrients.It is considered to be one of the effective measures to accelerate litter decomposition,promote nutrient cycling and improve soil fertility decline of pure coniferous forest.Therefor,to investigate on the variation of enzyme activities in the process of mixed litter decomposition under different tree species richness,different tree combinations and their mixing ratios,three broad-leaved tree species including Cinnamomum camphora,Sassafras tsumu and Toona sinensis were mixed with Pinus massoniana by foliar litter to form mixed litters in this study,respectively,and to further provide some theoretical basis for the selection of suitable associated tree species and the determination of appropriate mixing proportion for the transformation of pure Pinus massoniana to mixed forest.(1)Overall,there was a extremely significant quadratic fuction relationship between the cumulative mass loss of foliar litter and cellobiohydrolase,?-glucosidase,polyphenol oxidase,?-N-acetylglucosaminidase,acid phosphatase or dehydrogenase activity(P< 0.001),among which ?-N-acetyl glucosaminidase activity had the highest explanation for the cumulative mass loss of foliar litter,followed by cellobiohydrolase,?-glucosidase and acid phosphatase,polyphenol oxidase and dehydrogenase activity which were the lowest.(2)The increase in richness of broad-leaved tree species can improve the decomposition of single Pinus massoniana in varying degrees,and the higher the richness of tree species,the more likely it will be beneficial to the rapid fusion of different leaves and the relationship between nutrients and microbes,thus improving the activity of the enzymes and accelerating the decomposition.(3)The enzyme activity varies with the broad-leaved tree species mixed with Pinus massoniana,and the effect of the composition of tree species on the enzyme activity is greater than that of richness.Whether the combination of Pinus massoniana and Pinus massoniana,Pinus massoniana + Cinnamomum camphor + Toona sinensis,Pinus massoniana + Sassafras tsumu + Toona sinensis or Pinus massoniana + Sassafras tsumu+ Cinnamomum camphor + Toona sinensis,each combination of them could help to improve the enzyme activity to a certain extent,thus promoting the decomposition of litters.The effect of three broad-leaved tree species on enzyme activity can be arranged as Toona sinensis > Cinnamomum camphora > Sassafras sassafras.(4)Compared with Pinus massoniana,Pinus massoniana + Cinnamomum camphor and Pinus massoniana + Sassafras tsumu mixed with 8: 2: 7: 3: and 6: 4 were inhibited first and then promoted during the whole experiment period.The mixture of Pinus massoniana + Toona sinensis at 6:4 had a certain promoting effect on the enzyme activity of carbon and nitrogen cycling.The combination of Pinus massoniana + Sassafras tsumu + Cinnamomumamphor,Pinus massoniana + Cinnamomum camphor + Toona sinensis and Pinus massoniana + Sassafras tsumu + Toona sinensis mixed with 6: 2: 2,6: 3: 1 and 6:1:3 can help improve the enzyme activity to a certain extent,especially Pinus massoniana + Cinnamomum camphor + Toona sinensis and Pinus massoniana + Sassafras tsumu + Toona sinensis could promote the activity of carbon and nitrogen cycling hydrolase in the early stage.Pinus massoniana + Sassafras tsumu+ Cinnamomum camphor + Toona sinensis mixed with 7: 1: 1: 1,6: 1: 2: 1 could promote the activity of carbon and nitrogen cycling hydrolase.(5)In early stage of leaf litter decomposition,the activities of hydrolytic enzymes related to carbon and nitrogen cycle were significantly positively correlated with C,N,P and N/P,while negatively correlated with C/N,lignin and lignin/N(P < 0.01).With the decomposition of the litter leaves,the substrate mass changed continuously,and the correlation between the initial mass and the enzyme activities changed gradually.On the whole,hydrolase activities related to nutrition cycling were negatively correlated with pH,and all enzyme activities were positively correlated with water content,which showed a very significant primary function relationship(P < 0.01).In conclusion,the combination of Pinus massoniana + Toona sinensis mixed with 6: 4,Pinus massoniana + Cinnamomum camphor + Toona sinensis,Pinus massoniana + Sassafras tsumu + Toona sinensis mixed with 6: 2: 2,6: 3: 1 and 6: 1: 3,Pinus massoniana + Sassafras tsumu+ Cinnamomum camphor + Toona sinensis mixed with 7: 1: 1: 1 and 6: 1: 2: 1,which can help to increase the activity of carbon and nitrogen cycling hydrolases rapidly in the early stages.And the nutrient cycling of Pinus massoniana forest can be improved to some extent.