Effects Of Planting Mixed Forests After Clear Cutting Of Eucalyptus Grandis Pure Forests On Soil Ecological Enzyme Activities And Stoichiometry In The Early Stage Of Afforestation

Soil ecological enzymes play important roles in regulating the degradation of soil organic matter and nutrient cycling,and their stoichiometry can be used to measure the nutrient limitation of soil microorganisms.The transforming artificial pure forests into mixed forests is an important means to maintain the sustainable development of forest ecosystem.However,the impacts of the transforming artificial pure forests into mixed forests on soil ecological enzyme activities and stoichiometric characteristics are still unclear.To study the effects of planting mixed forests after clear cutting of Eucalyptus Grandis pure forests on soil physicochemical properties,microbial biomass and ecological enzymes,we choosed four built forests at the demonstration site of Eucalyptus grandis pure forest replacement and transformation in Shawan District,Sichuan Province.The four different types of forests were mixed forests of Cinnamomum camphora × Metasequoia glyptostroboides(the Cinnamomum camphora mixed forest for short),mixed forest of Cunninghamia lanceolata × Phoebe zhennan × Prunus persica ’Atropurpurea’(the Cunninghamia lanceolata mixed forest for short),mixed forest of Prunus persica’Atropurpurea’ × Malus × micromalus(the Prunus persica ’Atropurpurea’ mixed forest for short)and pure forest of Eucalyptus grandis.The main factors affecting soil biological enzyme activities and their stoichioetric characteristics were also analyzed.The main results are as follows:(1)Compared with the pure Eucalyptus grandis forest,all three mixed forests significantly increased the contents of total phosphorus(TP),soil organic carbon(SOC),total nitrogen(TN),and p H in the soil,while decreased soil C: P and N:P and had no significantly effects on C:N;the Cinnamomum camphor mixed forest significantly increased soil water content(SWC).Among the three types of mixed forests,the SOC content in the Prunus persica ’Atropurpurea’ mixed forest was significantly higher than that in the Cunninghamia lanceolata mixed forest,the SWC of the Cinnamomum camphor mixed forest was significantly higher than that in the Prunus persica ’Atropurpurea’ mixed forest and the Cunninghamia lanceolata mixed forest,soil C:P of the Cinnamomum camphor mixed forest was significantly higher than that of the Cunninghamia lanceolata mixed forest.(2)Compared with the pure Eucalyptus grandis forest,all three mixed forests significantly increased the contents of soil MBC and MBN as well as MBC:MBN.Among the three mixed forests,the soil MBC content of the Prunus persica ’Atropurpurea’ mixed forestand and the Cunninghamia lanceolata mixed forest were significantly higher than that of the Cinnamomum camphor mixed forest,the soil MBN content of the Prunus persica ’Atropurpurea’ mixed forest was significantly higher than that of the Cunninghamia lanceolata mixed forest,and the MBC:MBN of the Cunninghamia lanceolata mixed forest was significantly higher than that of the Prunus persica’Atropurpurea’ mixed forest and the Chinese Cinnamomum camphor mixed forest.(3)Compared with the pure Eucalyptus grandis forest,all three mixed forests significantly increased soil NAG activity and decreased soil AP activity,but had no significant impact on soil BG and LAP activities.Among the three mixed forests,except for the Prunus persica ’Atropurpurea’ mixed forest,the soil NAG activity was significantly higher than that of the Cunninghamia lanceolate mixed forest and the Cinnamomum camphor mixed forest,there was no significant difference in other ecological enzyme activities.(4)Compared with the pure Eucalyptus grandis forest,all three mixed forests significantly increased soil ecological enzyme N:P,while significantly reduced soil ecological enzyme C:N,length and angle of ecological enzyme vector,and had no significant impact on soil ecological enzyme C:P.Among the three types of mixed forests,except for the Prunus persica ’Atropurpurea’ mixed forest,the soil ecological enzyme N: P was significantly higher than that of the Cinnamomum camphor mixed forest,there was no significant difference in other soil ecological enzyme quantities and vectors.In addition,the soil ecological enzymes C:N:P were 1:0.72:1.25,1:0.84:1.25,1:0.80:1.23,and1:0.80:1.26 in the pure Eucalyptus grandis forest,mixed Prunus persica ’Atropurpurea’forest,mixed Cunninghamia lanceolate forest,and mixed Cinnamomum camphor forest,respectively.(5)Pearson correlation analysis resluts showed that soil ecological enzyme C:N,soil ecological enzyme vector length and angle were significantly negatively correlated with soil SOC,TN,MBC,and MBN.Soil ecological enzymes C:P and N:P were significantly positively correlated with SOC,TN,MBC,and MBN.The activities of BG,NAG,LAP,and AP were significantly positively correlated with SOC,TN,MBN,enzyme C:P,and enzyme N:P,while significantly negatively correlated with MBC:MBN.The results of Redundancy Analysis(RDA)showed that soil MBC,TN,and MBC: MBN significantly influenced soil ecological enzyme stoichiometry,with explanatory degrees of 56.1%,10.2%,and 2.8%,respectively.Soil TN,C: P,and MBC significantly influenced soil ecological enzyme activities,with explanations of 51.8%,6.1%,and 4.7%,respectively.In summary,the soil microorganisms of the four forest types were all limited by soil carbon and phosphorus.The mixed forest constructed after clear cutting of Eucalyptus grandis pure forest alleviated soil microbial carbon and phosphorus limitations by increasing soil SOC,TN,p H,and MBC:MBN,and decreasing soil C:P and N:P.Soil AP activity was reduced while soil NAG activity was increased in the mixed forests was mainly due to the alleviated soil microbial carbon and phosphorus limitation and increased soil SOC,TN,MBC and MBN and p H.However,there were no significant differences between the three mixed forests in terms of alleviating soil microbial carbon and phosphorus limitations in the initial stage and their effects on soil ecological enzyme activities.Soil MBC,TN,and MBC: MBN were the main factors affecting the initial soil ecological enzyme stoichiometry,and soil TN,C:P;MBC were the main factors affecting the soil ecological enzyme activities.Although as compared to the pure Eucalyptus grandis forest,all three types of mixed forests have alleviated soil microbial carbon and phosphorus limitations,but their soil microorganisms were still limited by carbon and phosphorus.Therefore,to alleviate the soil microbial carbon and phosphorus limitations and promote the soil nutrient balance,we suggest apply organic and phosphorus fertilizers during the management of artificial forests in the research area.