西南高山地区土壤异养呼吸时空动态

土壤异养呼吸是陆地和大气之间的重要通量,是决定陆地生态系统碳源汇的关键因素之一,与气候变化紧密相关。西南高山地区是响应气候变化的重点区域,研究西南高山地区土壤异养呼吸动态及其对气候变化的响应,对于评估区域碳循环对全球气候变化的贡献具有重要意义。应用生态系统模型(CEVSA)模型估算了1954-2010年西南高山地区土壤异养呼吸(HR)的时空变化,分析了其对气候变化的响应。结果表明:(1)西南高山地区1954-2010年平均异养呼吸量为422 g C·m^-2·a^-1,在空间分布上,HR自东南向西北递减,与年平均温度(r=0.721,P<0.01)、年降水量(r=0.564,P<0.01)均显著正相关;(2)在时间尺度上,西南高山地区1954-2010年 HR总量增加趋势显著(P<0.05),变化范围为197-251 Tg C/a,平均每年增加0.710 Tg C,其中主要植被类型草地、常绿针叶林和常绿阔叶林均增加趋势显著(P<0.01),增加速度分别为1.621、1.496和1.055 g C·m^-2·a^-2。(3)土壤HR的年际变化主要受温度影响,且西北部高海拔地区较东南部低海拔对温度变化更为敏感,主要植被类型温度敏感系数Q₁₀从大到小依次为草地(2.35)、常绿针叶林(2.34)、常绿阔叶林(1.93)。

Temporal-spatial variation of heterotrophic respiration in alpine area of southwestern China

Soil heterotrophic respiration is a major flux of CO₂ between terrestrial ecosystems and the atmosphere. It is defined as the sum of carbon releases as gaseous products in the microbial decomposition of soil carbon pool. Soil heterotrophic respiration plays a critical role in regulating the global carbon cycle and is potentially sensitive to climate changes in the future. The alpine area of southwestern China is one of the most sensitive areas to climate change. Therefore, it is of great importance to investigate the response of soil heterotrophic respiration to climate in this region for evaluating the contribution of regional carbon cycle to global climate changes. A process-based biogeochemical model CEVSA (Carbon Exchange between Vegetation, Soil, and the Atmosphere) was used to estimate the temporal and spatial variations of soil heterotrophic respiration (HR) in alpine area of southwestern China during the period from 1954 to 2010. We conducted CEVSA model with observation-based data sets of climate (ten days mean value of temperature, precipitation, relative humidity, and cloudiness), atmospheric CO₂ concentration, and soil and vegetation distribution at a spatial resolution of 0.1°. Using the climate, vegetation and soil data, firstly, we ran the model with the average climate data from 1954 to 2010 until an ecological equilibrium was reached, then conducted dynamic simulations with climate data at a time-step of ten days from 1954 to 2010. Also, the correlation coefficients between soil HR and climate variables were calculated to analyze the response of soil heterotrophic respiration to climate change. To achieve the results, various kinds of computer software were used, such as ANUSPLIN4.1, Fortran 90, Arcgis 9.3, SPSS18.0. The results showed that: (1) The mean values of soil HR density was 422 g C·m^-2·a^-1 during the period of 1954-2010 in alpine area of southwestern China. The soil HR showed a decreasing trend from southeast to northwest and had significant positive correlation with both annual mean temperature (r = 0.721,P < 0.01) and annual total precipitation (r = 0.564,P < 0.01). (2)Total annual soil HR showed an increasing trend with the rate of 0.710 Tg C/a (P<0.05), and varied between 197 and 251 Tg C/a. The increasing rate was 1.621, 1.496 and 1.055 g C·m^-2·a^-2 in grassland, evergreen coniferous forest and evergreen broad-leaved forest (P<0.01), which were three main vegetation types in alpine area of southwestern China, respectively. (3) Annual variation of soil HR was mainly influenced by temperature. The temperature sensitivity of soil HR (Q₁₀) in the high-elevation northwestern areas was higher than that in the low-elevation southeastern areas, and it is 2.35, 2.34 and 1.93 in grassland, evergreen coniferous forest and evergreen broad-leaved forest in this area, respectively. Soil heterotrophic respiration is an extremely complex process involving a variety of biological and non-biological factors. Climate and vegetation changed with topography and high space heterogeneity existed in alpine area of southwestern China. For these reasons, we suggest that the model resolution should be improved and validation of the simulation result should be strengthened in future to reduce uncertainty.