东北黑土典型坡耕地土壤呼吸特征的研究

Characteristics of soil respiration on typical cropland slope in mollisol region of Northeast China

本研究以东北黑土典型坡耕地为研究对象,利用LI-8100土壤呼吸测量仪对玉米全生育期土壤呼吸进行了原位监测,分析了坡耕地不同部位(坡顶、坡肩、坡背、坡趾)土壤呼吸速率变化规律、土壤呼吸总量、土壤呼吸速率与土壤水热因子之间的关系。结果表明:该地区土壤呼吸速率呈现"春秋季低夏季高"的季节性变化规律,坡趾位置土壤呼吸峰值显著高于坡顶、坡肩、坡背位置(P<0.05)。不同部位土壤呼吸速率与土壤温度呈现显著线性关系(P<0.05),与土壤含水量相关性不显著(P>0.05)。土壤呼吸总量以坡趾位置最高[523.97 g(CO_2-C)×m^(-2)],显著高于坡背[443.13 g(CO_2-C)×m^(-2)]、坡肩[426.81 g(CO_2-C)·m^(-2)]、坡顶[388.5g(CO_2-C)·m^(-2)]3个位置18.5%、22.8%和34.9%(P<0.05)。说明黑土坡耕地不同位置土壤呼吸存在显著差异,准确评价黑土坡耕地土壤呼吸需要综合考虑坡耕地不同坡位的差异,减少引用平地监测结果来评估坡耕地土壤呼吸量所造成的偏差。

The characteristics of soil respiration in cropland slopes are different from those in cropland plains.In order to accurately evaluate greenhouse gases emission in Northeast China farmland,it was necessary to study the patterns and factors influencing soil respiration in different cropland slopes.The study was conducted on a typical cropland slope in a mollisol region in Northeast China.An entire cropland slope was divided into four slope positions based on change in gradient― summit,shoulder-slope,back-slope and toe-slope.The LI-8100probe was used to monitor soil respiration throughout the maize growing period.Water content and temperature of the surface soil(0?20cm soil layer)were respectively measured using soil moisture meter and thermometer.The relationship between soil carbon dioxide(CO2)flux and the impact of temperature,soil moisture content were then analyzed for different slop positions(summit,shoulder-slope,back-slope and toe-slope).The study laid the basis for scientific evaluation of soil respiration and carbon balance in mollisol in cropland slopes.The results showed that CO2flux in summer was higher than in spring and autumn.Peak soil respiration occurred during the period from maize silking to tasseling,which was from July3to August23in the study area.During this period,the cumulative respiration was58.7%–59.9%of total soil respiration for the whole growing period of maize across the four slope positions,indicating it was the main period of soil respiration in mollisol regions in Northeast China.The peak rate of soil respiration was significantly different in each slope position(P<0.05).It was significantly higher in the toe-slope position[7.56μmol(CO2)·m-2·s-1]than at the summit[5.60μmol(CO2)·m-2·s-1],shoulder-slope[6.08μmol(CO2)·m-2·s-1]and back-slope[6.47μmol(CO2)·m-2·s-1].The results showed that soil respiration rates among different slope positions in typical mollisol regions were significantly different,especially in summer.CO2flux had a positive,linear correlation with soil temperature for all the slope positions(P<0.05).The exponential equation best expressed the relationship between soil temperature and soil respiration rate.Then temperature sensitivity(Q10)was the strongest for the back-slope position,compared with the others.There was an insignificant correlation between soil respiration and soil volumetric water content.These results indicated that change in soil temperature significantly influenced soil respiration rate.The cumulative emission of CO2in toe-slope[523.97g(CO2-C)·m-2]was18.5%,22.8%and34.9%higher than in back-slope[443.13g(CO2-C)·m-2],shoulder-slope[426.81g(CO2-C)·m-2]and summit[388.50g(CO2-C)·m-2],respectively.This was caused by the migration and redistribution of organic carbon,the change in soil bulk density,and the related effect on soil under the different environmental factors.The results of the study suggested that it was necessary to consider the respiration characteristics of different slope positions in order to limit any deviations in the monitoring results based on cropland plains respiration in the scientific evaluation of soil respiration on cropland slopes.