Impact Of Chinese Pine Plantation On Soil Enzymatic Activities And Microorganism In The Loess Plateau

Chinese pine(Pinustabulaeformis Carr.)represents the most predominant pioneer tree species for artificial reforestation and is widely planted due to its high stress tolerance to cold,drought,and poor quality of soil in the Loess Plateau of northwest China.The previous studies found that the changes with the development of afforestation of Chinese pine and seasonal variations will have a series of changes on soil physical and chemical properties,which will have a deeply effect on soil microbial biomass and soil enzyme activity,subsequently affect to the growing of Chinese pine plantation and seedling regeneration.To date,however,little studies had been conducted in this field,especially in relation of the impact mechanism.Hence,it is necessary to understanding the seasonal variations of soil environmental effects on the Chinese pine plantation development and generation characteristic of forest renewal.The present study was to explain the effects of Chinese Pine plantation on soil enzymatic activities and microbial biomass and its seasonal shifts coinciding with forest development in the Loess Plateau.In addition,such information will be helpful in future studies investigating the effects of soil restoration on forest ecosystems and fertility.We studied on soil physio-chemical properties,four types of soil enzyme activities,microbial biomass carbon(Cmic)and nitrogen(Nmic)during four seasons in Chinese pine plantations aged 8(PF8),22(PF22),and 42(PF42)years at Fuxian county in the middle of Loess Plateau,China.The natural secondary Chinese pine forest sites which was aged more than 70 years(NF)was considered as the control.Final,the Chinese pine regeneration characteristic has investigated in two types of Chinese pine forest,where the seeding germination was observed,there are in Chinese pine plantation forest 42 years and natural forest.Both of forest age and sampling season had significant effects on almost soil physiochemical properties except TN.The values of soil p H,TN,SOC and P were found to be higher in the summer,whereas the ratio of C and N reached a peak in autumn but not in soil moisture or porosity.The variability in the soil physio-chemical properties were dissimilar across Chinese pine forest ages.For example,the values of BD,t,NO3--N,NH4+-N,TN,TP,and P decreased due to forest development in the order of PF8 > PF22 > PF42.In contrast,the variation in the values of SMC,porosity,TK,K,and SOC gradually increased when the forest matured from PF8 to PF42.The content of soil nutrient elements in the natural secondary forest of Chinese pine was higher than that of Chinese pine plantation forest,and the seasonal variation was higher in summer and autumn than in spring and winter.Both of Cmic and Nmic were higher in summer season than autumn,spring and winter seasons.This can be understood as: the surviving biomass can utilize the cell debris;the strong photosynthetic capacity of plants in summer led to increased carbohydrate secretion of roots,and promote soil microbial activity increased.The concentration of Cmic in the forest development was systematically increased from PF8 < PF42 < PF22.The higher content of microbial biomass C from PF8 to PF22 than in PF42,this point suggested that the accumulation of microbial biomass mainly occurred at early successional stages.While the content of Nmic was gradually decreased from PF8 > PF22 > PF42.The concentration of Nmic decreased from PF8 to PF42,this may be due to the rapid rate of N mineralization and N leaching in the temperate plantation forest soils.The highest values of both Cmic and Nmic concentrations occurred in the NF as compared to the three stages of Chinese pine plantation forest.In contrast,lower values were found in the NF than all stages of plantations in Cmic/Nmic,Cmic/SOC,and Nmic/TN.The highest values of both Cmic/SOC and Nmic/TN were observed in PF22.The activities of the four studied soil enzymes(urease,alkaline phosphatase,invertase and peroxidase)were significantly higher in the summer,when plant photosynthetic activity also peaked,than in the rest seasons of the year.The mean values of urease and invertase were significantly different during all four seasons,while alkaline phosphatase activity was significantly different only in the spring and summer.Additionally,the changes in three types of hydrolase enzyme were more pronounced during the various forest stages.Such as,in urease the decreasing trend was found: PF8 > PF22 > PF42,while alkaline phosphatase was increasing in forest aged: PF8 < PF22 < PF42,however invertase was increased and then decreased: PF8 < PF42 < PF22.As compare with soil plantation forest,the activities of urease,alkaline phosphatase,invertases in the natural forest were higher.The relationship between soil physio-chemical and microbial activity was changed in seasonal variations.In spring,all of the four enzymes were significantly correlated with soil physio-chemical.However,the non-significant correlation between soil physio-chemical and activity of peroxidase was found in summer and autumn seasons,while three types of hydrolase were expressed high significant correlation in both of the summer and autumn seasons.The correlation between soil Nmic and TN was closely significant in all of the four seasons.However,the close relationship between SOC and Cmic was found in spring,summer and autumn seasons.The total of Chinese pine seeding found in PF42 was 244/375m2,wherein around 4% seedlings was appearances with the ages 10 years over.While the quantity of seeding in NF was counted 547/375m2,with 16 % of seedlings in year over than 10 years.This result suggests that the quantity of regenerating Chinese pines is relatively large in Chinese pine forest,but the effect is not significant.The development of regenerating seeding is evidently better in natural forests than in planted forests.This may suggest that the NF stands have an advantage in terms of sustaining soil fertility.Through the redundancy analysis,the result shows soil environment factors such as: TLL,VC,p H,SMC,SOC,NO3--N,P,TP,K,TK,urease,invertase,Nmic,Cmic were significantly affected to Chinese pine generation.This result can reaffirm that regenerating Chinese pine characteristics are affected by soil properties.In overall the soil physio-chemical properties,soil microbial biomass and enzyme activity were significant shifted along with season-change and forest development stages(p<0.05).Soil microbial biomass C and N concentration were significantly higher in summer,autumn seasons than in the spring and winter seasons.The concentration of Cmic in the forest development was systematically increased from PF8 < PF42 < PF22.While the content of Nmic was gradually decreased from PF42 > PF22 > PF8.The activities of the four studied soil enzymes(urease,alkaline phosphatase,invertase and peroxidase)were significantly higher in the summer,when plant photosynthetic activity also peaked,than in the restseasons of the year.The highest values of Cmic,Nmic,urease,alkaline phosphatase and invertase occurred in the NF as compared to the three stages of plantation forest.The relationship between soil physio-chemical and four types of enzymeswere changed in seasonal variations.The correlation between soil Nmic and TN was closely significant in all of the four seasons.Besides,the close relationship between SOC and Cmic was found in spring,summer and autumn seasons.The results suggesting that soil microbes are closely related to soil nutrient dynamics and could also be considered indicators for evaluating the status of soil fertility.The development of regenerated trees in natural forests is evidently better than planted forests.Soil environment factors such as: TLL,VC,p H,SMC,SOC,NO3--N,P,TP,K,TK,urease,invertase,Nmic,Cmic were significantly affected to Chinese pine regeneration.In overall,the natural forest is better in sustaining the microbial biomass carbon,nitrogen and soil organic matter quality than Chinese pine plantation in Loess plateau,China.This calls for cautions in large-scale conversions of the native forests to coniferous plantations as a forest management practice on concerns of sustainable soil productivity.