| In this experiment,taking the soils of Pinus tabulaeformis Plantation in hilly region,Loess Plateau,through laboratory incubation,using 13C stable isotope labeling method and phospholipid fatty acid technology to study the effects on soil organic carbon pool,basic properties,soil organic carbon mineralization and soil microorganisms following different litters（Pinus tabulaeformis,Robinia pseudoacacia,Pinus tabulaeformis+Robinia pseudoacacia）addition to soils from differentlayers（0-20cm,60-80cm）,in order to further elucidate the microbial processes of soil carbon cycle in forest ecosystem and provide scientific basis for plantation guidance and soil management.The main results are as follows:（1）The total organic carbon,active organic carbon,total nitrogen and C:N in top soil were significantly higher than that in deep soil,and there was no difference in p H.The addition of litters could significantly increase the content of active organic carbon in deep soil,but had no effect on the treatments of top soil.The total organic carbon content of Robinia pseudoacacia treatment was the highest regardless of soil layer.Compared with control treatment,except for Pinus tabulaeformis treatment in deep soil,the total nitrogen content increased significantly,and it was highest in Robinia pseudoacacia treatment among treatments in both soils.C:N of Robinia pseudoacacia treatment was significantly lower than that of Pinus tabulaeformis and mixed litters treatments.On the whole,adding Robinia pseudoacacia litter to soil had the best effect on improving nutrient content.（2）For soil from different layers,the cumulative CO2 mineralization effux and organic carbon mineralization rate of top soil were significantly higher than deep soil.Litters addition significantly increased soil cumulative CO2 mineralization effux and soil organic carbon mineralization rate.Among all amendments in the same layer,the Robinia pseudoacacia treatment litter had the greatest impact on both（P<0.01）.The mineralization rate decreased with the prolongation of incubation.The periods of 0-14 and 0-22 following litters addition to soils were the rapid decomposition stages of organic carbon in top soil and deep soil respectively.At the end of incubation,the mineralization rates of top soil were 10.33%,4.95%,6.99%,12.57%of there initial rates and that in deep soil treatments were 9.51%,11.31%,5.35%;the cumulative CO2 mineralization effux amount top soil were 6.92,6.54,6.99,9.54times of there initial effux,and 9.85,12.96,11.30,4.30 times of that in deep soil treatments.（3）The addition of litters to soils induced different priming effects.For different soil layers,the effect of Pinus tabulaeformis litter and Robinia pseudoacacia litter on the original carbon,the top soil was larger than deep soil,while the mixed litters treatment was the opposite.For top soil,the initial priming of all treatments were negative.On the 14th day of incubation,the priming directions of Robinia pseudoacacia and mixed litters treatments both changed to positive.At the end of incubation,the cumulative priming effect of Pinus tabulaeformis and Robinia pseudoacacia treatments were negative,and the mixed litters treatment was positive.In deep soil,the initial priming effects of all treatments were negative,and turned to positive on the 14th day.At the end of incubation,the cumulative priming effect of Pinus tabulaeformis and mixed litters treatments were positive,and soil with Robinia pseudoacacia litter was negative.For the short-term carbon pool changes by litters addition to soils,Robinia pseudoacacia litter added to different soils could retain soil organic carbon.（4）Soil microbial biomass carbon content,larger in top soil than deep soil,significantly increased following litters addition to soils,and mixed litters treatments had the highest content.There were also significant differences in soil enzyme activities between treatments with the three litters and control.Litters significantly increased the activity of N-acetylglucosaminidase.Except for Pinus tabulaeformis litter treatments,the activities of soilβ-glucosidase,alkaline phosphatase and cellulase were significantly increased in other treatments.Among all,Robinia pseudoacacia litter had the best effect on promoting soil enzyme activities.（5）Litters added to soil can significantly increased the contents of total PLFA,bacteria,fungi,Gram-negative bacteria and F:Bvalue,decreased G+:G-value,but there were no effects on Gram-positive bacteria and mycorrhizal fungi.Robinia pseudoacacia litter had the best effect on the increase of phospholipid fatty acid in soil.Soil active organic carbon,the total organic carbon and total nitrogen were the main factors causing the variation of microbial community structure.The analysis of PLFA sources showed that the PLFAs with larger proportion of litter carbon were 16:0、18:1ω9c、18:1ω7c,in Pinus tabulaeformis treatment,the proportion was 86%,92%,62%;and 73%,78%,64%in Robinia pseudoacacia treatment,66%,68%,53%in mixed litters treatment,respectively. |
