| For centuries,forests have been destroyed to varying degrees due to human and natural causes,and ecologists and governments have paid more and more attention to the study of forest restoration process.Natural restoration and artificial forest are two main restoration models.Soil microorganisms,as the main decomposers in the ecosystem,can directly or indirectly affect plant growth,and the changes of soil microbial community structure can also reflect the changes of soil environment.However,most of the current research focuses on the single natural restoration process or the plantation growth process,and less on the comparison of the two restoration modes.The research was carried out in Baisha Forest Farm(25°04 '? 25°15'N,116°30 '?116°38' E)in Shanghang County,Longyan City,Fujian Province.This study selected forest natural recovery and Chinese fir plantation recovery after clear cutting(forest age:4-5 a?8-12a?18-22a?25-30a?35-40a)as research object,and the primary forest(forest age > 100 a)for comparison,to study the soil microbial community structure and function.The main conclusions of the study are as follows:1)Soil depth had significant effects on soil Microbial biomass carbon(MBC),Microbial biomass nitrogen(MBN),and Microbial quotient(MQ).With the increase of soil depth,MBC and MBN were significantly decreased.In the same soil layer and stand age,the MBC,MBN and MQ of secondary forest were significantly higher than those of Chinese fir plantation,indicating that natural restoration was more conducive to soil microbial growth and nutrient accumulation.The MBC,MBN and MQ of different soil layers had different responses to stand age,but the change trend of MQ with stand age was consistent with that of MBC and MBN.The MBC,MBN and MQ of primary forest were not significantly different from those of 35-40-year-old secondary forest,but were significantly higher than those of 35-40-year-old Chinese fir forest.Soil nutrient indices(ammonium nitrogen,total carbon,total nitrogen)were significantly positively correlated with MBC and MBN,indicating that soil nutrient availability was an important factor affecting soil microbial biomass.There was a negative correlation between soil C/N ratio and microbial carbon quotient.2)The restoration model had no significant effect on soil microbial community structure.There was no significant difference in soil microbial community structure of secondary forest and Chinese fir plantation with different stand ages.RDA showed that mineral nitrogen,total carbon and p H were the main influencing factors of microbial community structure in the growth process of Chinese fir forest,while AP,total carbon,soil water content and p H were the main influencing factors of microbial community structure in the growth process of secondary forest.3)The molar percentage of soil bacteria was the largest in secondary forest and Chinese fir plantation of different age.Soil depth had significant effects on the Fungi to bacteria ratio(F:B)and gram-positive to gram-negative bacteria ratio(GP: GN).With the increase of soil depth,soil F:B decreased and GP: Gn increased.The restoration mode had a significant effect on GP: GN,and the GP: GN of Chinese fir plantation was significantly higher than that of secondary forest of the same stand age.There was no significant difference in F:B,GP:GN between primary forest and 35-40 year old secondary forest and35-40 year old Chinese fir plantation.Soil F:B was significantly positively correlated with C/N ratio,and significantly positively correlated with soil nutrient indexes(ammonium nitrogen,total carbon,total nitrogen),while GP: GN was significantly or significantly negatively correlated with soil nutrient indexes(ammonium nitrogen,nitrate nitrogen,mineral nitrogen,available phosphorus,total nitrogen,etc.).4)The depth of soil layer and forest age had significant effects on Cellobiohydrolase(CBH),?-glucosidase(?G),Acid phosphatase(AP),N-acetyl-?-D-glucosaminidase(NAG),Peroxidase(PER)and Polyphenol oxidase(PPO).With the increase of soil depth,the activities of four hydrolases decreased significantly.The response of different enzyme activities to stand age was not consistent.CBH,?G,AP,NAG and PER in Chinese fir plantation were significantly higher than those in secondary forest,while ?G,AP and NAG in secondary forest were significantly higher than those in Chinese fir plantation.Soil nutrient indexes(ammonia nitrogen,available phosphorus,etc.)were positively correlated with enzyme activities,while p H was negatively correlated with hydrolase and positively correlated with peroxidase.The microbial biomass was significantly or extremely significantly positively correlated with enzyme activity.There were significant positive or negative correlations among the activities of different enzymes,indicating that the various enzymatic reactions were not only specific,but also interrelated.Therefore,this study suggests that natural restoration is more conducive to the recovery of soil microbial and enzyme activities than that of Cunninghamia lanceolata plantation.Stand age and stand type affect soil microbial and enzyme activities,and this effect decreases with soil depth increasing.Soil microorganisms will eventually reach their pre-disturbed state after being disturbed. |
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