| Soil organic carbon pool is the main component of carbon pool in terrestrial ecosystem.One of the important ways for forest ecosystem to release CO2to atmosphere is decomposition of soil organic matter.Under the background of global warming,the accurate assessment of the sensitivity of soil organic matter decomposition to temperature(Q10)has become a hot topic in the study of soil carbon cycle in terrestrial ecosystems.So far,there is still a huge heterogeneity in vertical space of Q10.While Q10in horizontal space has received more attention,there are few studies on Q10in vertical space,and the regulatory mechanism and influencing factors leading to vertical heterogeneity of Q10are still highly uncertain.Global warming will increase the quality of litter that enters the soil by promoting plant growth.In the short term,litter input can strongly change the decomposition rate of soil organic carbon,which is usually called priming effect.The increase of litter input changes Q10mainly through nutrient changes and microbial community composition and activity.However,soil nutrient,microbial community composition and activity may change with the elevation gradient.Therefore,there is considerable uncertainty in the response of Q10to litter input,particularly along elevation gradients.To solve the above problems,forest soil samples at three elevations（750,950 and 1150m）were collected in the transition zone of subtropical and warm temperate zones and incubated with 13C-labeled fir litter at 15°C and 17.4°C for 97 days,respectively.Chinese fir litters with carbon content of 5%of soil organic carbon were added and a 13C abundance was 255‰.By measuring the cumulative mineralization amount of soil organic carbon at different elevations and litter-adding treatment and calculating the value of Q10,the temperature sensitivity of soil organic matter decomposition and the response to exogenous carbon addition at different elevations were discussed,and the potential mechanism was analyzed.The main findings are as follows:（1）Soil organic carbon and total nitrogen contents ranged from 37.86-70.67 g C/kg and 3.6-5.28g N/kg,respectively.The soil sample has the highest sand content at 950 m.In addition,the incubation process was divided into two stages（0-37 days and 38-97 days）according to the gradual decline of CO2release rate in 0-37 days followed by some fluctuations but basically unchanged.The values of fungi,fungal bacteria ratio and Gram-negative bacteria were the highest at 750 m and the lowest at 950 m,and there were significant differences between the two elevations.Elevation significantly affects soil organic carbon accumulative mineralization.The cumulative mineralization of soil organic carbon was significantly higher at the middle elevation（950 m）than at the other two elevations during the whole culture period from 0-97 days.The addition of exogenous carbon significantly affected the cumulative mineralization of soil organic carbon.The interaction between the elevation gradient and the addition of exogenous carbon had a significant effect on the cumulative mineralization of soil organic carbon only in the second stage（38-97 days）.In the first stage,there were significant differences in litter decomposition at different altitudes,which were 950>750>1150 m.In the second stage,the decomposition amount of litters at low altitude was significantly different from that at950 m.（2）Q10in the first stage did not change significantly with the increase of elevation,because p H was similar at all elevations and Q10in the first stage was regulated by p H.Soil C/N ratio is the main factor regulating Q10in the second stage.Q10at the elevation of 950m is significantly higher than that at the elevation of 1150 m,indicating that the decomposition Q10of high quality organic matter is lower than that of low quality organic matter,which is consistent with the carbon-quality temperature hypothesis.There is no respond for Q10to litter input at an elevation of 750 m,and Q10at an elevation of 950 m decreased significantly after litter input in both two stages.After litter input,Q10at 1150 m increased in the first stage and remained stable in the second stage.The change of Q10with litter input was mainly limited by the availability of soil phosphorus.（3）The priming effect induced by exogenous carbon addition are all positive.The Q10of priming effect of different elevations in the first stage is higher than that of the second stage.Unstable exogenous organic carbon was preferentially utilized by soil microorganisms,and relatively difficult to decompose carbon sources（cellulose,etc.）in the second stage limited the utilization of exogenous carbon by microorganisms,which was in line with research expectations.The characteristic of priming effect is more intense in the early stage and gradually stable in the late stage.In general,the trend of priming effect of different elevations showed that the priming intensity of medium-elevation soil was higher than that of low-elevation and high-elevation soil,and warming basically increased the intensity of priming effect.In addition,the interaction between soil physical properties and enzyme activity accounted for 35%of the total variation.The response of priming effect to warming is mainly limited by nutrient.In the first stage,Q10of the priming effect was mainly regulated by nitrogen limitation,which verified the theory of microbial nitrogen mining.However,Q10of the priming effect in the second stage is limited by phosphorus,which indicates that after the addition of exogenous carbon,the nutrient restriction of soil is not fixed for a certain nutrient,but constantly changes with time.These findings suggest that soil p H and C/N ratio are the main factors regulating the vertical heterogeneity of Q10in forest ecosystem.After adding litters,Q10prediction indexes were more regulated by soil enzyme activities and soil available nutrients.In addition,the interaction between and litter had a significant effect on Q10only in the second stage.The priming effect of Q10was limited by N and P in two stages. |
