集水区尺度下东北东部森林土壤呼吸的模拟

IBIS模型是陆地碳循环模拟的有利工具,土壤呼吸是陆地碳循环的关键生态学过程,利用IBIS模型模拟估算土壤呼吸对陆地碳循环和全球变化研究具有重要意义。在地形数据、植被参数、土壤质地参数和气象数据支持下,利用改造后的IBIS模型模拟2004年张家沟集水区5种森林类型的土壤呼吸,以实测数据对模拟结果进行验证,并分析土壤呼吸时空格局及其与土壤温湿度的关系。结果表明:(1)改造后的IBIS模型模拟的土壤呼吸值与实测值相关性显著,可较好地用于集水区尺度的森林土壤呼吸模拟估算。(2)土壤呼吸年均值为571 gC m^-2 a^-1,年土壤呼吸空间格局与生长季土壤呼吸空间格局相似,均表现为高值区主要分布在北部、西南和东南区域,低值区主要分布在沟谷附近,该格局与集水区的地形、植被及其组合等因素有关。(3)生长季内,5种森林类型土壤呼吸的季节性变化均呈单峰曲线形式,土壤呼吸峰值均出现在7月,其中落叶松林峰值最低,为85.5 gC/m²,杂木林峰值最高,为146.3 gC/m²。(4)5种森林类型的土壤呼吸值与5 cm深土壤温度存在极显著的指数关系,与土壤湿度的相关性较低,土壤温度的变化可以解释土壤呼吸约70%的季节变化。

Simulation of soil respiration in forests at the catchment scale in the eastern part of northeast China

The Integrated Biosphere Simulator (IBIS) model is an important tool for terrestrial carbon cycle simulation. One of the key ecological processes of the terrestrial carbon cycle is soil respiration. Modeling soil respiration and revealing its space-time pattern using the IBIS model is of great significance to the study of the terrestrial carbon cycle and global change. However, the application of the IBIS model to a catchment with complicated terrain has not been attempted because of problems with the model mechanism. In this study, the IBIS model was improved by addition of a terrain analysis module, and modification of the redistribution module of soil water and the calculation module of solar radiation received at the ground surface. Soil respiration of the five forest types in the Zhangjiagou catchment of Heilongjiang province in northeast China was then simulated in 2004 using the improved IBIS model. The model was driven by terrain data, vegetation parameters, soil texture parameters and climate variables. The simulated values were validated with measurements, and the temporal-spatial patterns of forest soil respiration and the relationship between soil respiration and soil temperature and humidity were analyzed. The five forest types were: Larch plantation, Oak forest, Aspen-birch forest, Hardwood forest and Mixed deciduous forest. Results showed that: (1) The simulated daily soil respiration by the improved IBIS model had a significant relationship with the measured daily soil respiration. The improved IBIS model can be better used in simulating and estimating soil respiration of forests at the catchment scale, which may provide a favorable tool for carbon cycle simulation at the catchment scale. (2) The annual highest soil respiration of forests was 700 gC m^-2 a^-1 and the annual mean soil respiration of forests was 571 gC m^-2 a^-1 in the Zhangjiagou catchment. The spatial pattern of the annual soil respiration was similar to the spatial pattern of soil respiration for the growing season, which showed that high values of soil respiration were distributed in the north, southwest and southeast of the catchment, and the low values were largely in nearby valleys. The spatial pattern of soil respiration was closely related to topography, vegetation and other factors. (3) During the growing season, the five forest types showed a similar seasonal pattern in simulated soil respiration, characterized by a mono-peak curve, with a summer maximum and an early and late growing season minimum. The peak soil respiration value of the five forest types occurred in July, and was 146.3 gC/m² in the Mixed deciduous forest, >121 gC/m² in the Oak forest, >118.3 gC/m² in the Aspen-birch forest, >114.9 gC/m² in the Hardwood forest and >85.5 gC/m² in the Larch plantation. (4) In the growing season, the simulated soil respiration of the five forest types showed a significant index correlation (P<0.001) with the simulated soil temperature at 5 cm depth, and could explain approximately 70% of the seasonal variation in soil respiration. The correlation coefficients varied from 0.6873 in the Hardwood forest to 0.7205 in the Larch plantation. There was no obvious correlation between the simulated soil respiration and the simulated soil moisture for all forest types at 5 cm depth. This showed that the dominant factor of seasonal variation in soil respiration was soil temperature and the effect of soil moisture on soil respiration was not notable.