杉木人工林不同深度土壤CO_2通量

Analysis of vertical profiles of soil CO_2 efflux in Chinese fir plantation

土壤CO2通量具有明显的时间和空间变异性。土壤温度和含水量是影响土壤CO2通量的重要因素,同时,不同深度的土壤CO2通量对温度和含水量变化的响应差异较大,因此,研究土壤CO2通量和影响因素随土壤深度的变化,对于准确评估土壤碳排放具有重要意义。选择福建三明杉木人工林(Cunninghamia lanceolata)作为研究对象,利用非散射红外CO2浓度探头和Li-8100开路式土壤碳通量系统,并使用Fick扩散法计算了0—60cm深度土壤CO2的通量,结果表明:(1)5种扩散模型计算的表层(5cm)CO2通量与Li-8100测量结果均具有显著相关性(P<0.01),Moldrup气体扩散模型计算结果较好。(2)土壤CO2浓度随深度的增加而升高,但60cm深度以下土壤CO2浓度开始降低;不同深度土壤CO2浓度的日变化均呈现单峰型;0—60cm土壤CO2通量日通量均值变化范围为0.54—2.17μmol m-2 s-1;(3)指数拟合分析显示,5、10cm和60cm深度处土壤CO2通量与温度具有显著相关性,Q10值分别为1.35、2.01和4.95。不同深度土壤含水量与CO2通量的相关性不显著。

CO2 flux from the soil to the atmosphere represents a major flux in the global carbon cycle.But there remains some limitations on predicting this flux because of multiple control mechanisms that interact at temporal and spatial scales.Soil can be described in successive layers and the processes and soil properties were described separately for each layers.The CO2 flux between the layers was driven by diffusion,which depended on CO2 concentration,porosity,soil temperature and moisture content.Soil CO2 flux and its major driving factors,especially in vertical profile,may change with great temporal and spatial variability.Compared to deep soil,soil surface have great difference in temperature and moisture content.Therefore,investigation of the differences and influencing factors of soil CO2 flux changed with soil depth could be essential for accurate evaluation of soil carbon emission.At present,the soil CO2 vertical gradient measurement method is rapidly gaining popularity because it allows to continuously and automatically measure soil CO2 flux at different temporal scales with minimal disturbance to the natural soil structure.It is also comparable with other methods.The soil CO2 gradient method uses Fick′s first law to calculate soil CO2 efflux,relying on both measurements of soil CO2 profile and on the CO2 diffusion coefficient in the soil（Ds）.Determining the latter with confidence is a challenge.Modelling as an approach can potentially be used to determine Ds.It is possible if the detailed information on some important soil properties（i.e.total soil porosity and air-filled porosity） are available. In this study,Fick′s diffusion method and five kinds of diffusion coefficient models,including Penman,Marshall,Quirk,and Moldrup,were used to estimate soil CO2 flux at different depth of the Chinese fir Plantation（Cunninghamia lanceolata） in a Base of Forest Management and Technology in Sanming（26°191,117°361）,Fujian Province,China.The modeling soil CO2 flux were also compared with the results measured by Li-8100 automated soil CO2 flux system.The results were as follows：（1） Calculation of surface（at 5cm） CO2 flux estimated by 5 kinds of diffusion models had significant correlation with Li-8100 measurement result（P0.01）.Among the models obtaining diffusion coefficient,soil CO2 efflux measured by Moldrup model were the closest to the results of the soil chamber;（2） CO2 flux in soil different depths had obvious daily variation patterns,and the mean flux were（2.17±0.06）,（2.18±0.13）、0.54±0.04、（1.65±0.20） and（1.74±0.04） μmol m-2 s-1 at 5,10,20,40,and 60cm depth respectively（mean±SD）;And（3） by plotting CO2 efflux vs.soil temperature,we found that CO2 efflux correlated exponentially with soil temperature at the depth of 5cm,10cm,60cm,with Q10 of 1.35,2.01,4.95,respectively.But soil water content was not significant correlation with soil CO2 efflux.Using CO2 solid concentration detector can automatically and continuously monitor CO2 concentration in soil of different depth soil.The estimated CO2 efflux using this method was close to chamber measurements,suggesting that this method can be use for long-term continuous measurements of soil CO2 efflux.