沙质草地生长季土壤CO_2排放特征及水热因子分析

Characteristics of Soil CO_2 Emission in Relation to Hydrothermal Factors during the Growing Season in Horqin Sandy Land

草地土壤CO_2排放是陆地生态系统碳循环的关键生态学过程之一,研究其通量特征可以定量评估和预测区域CO_2排放状况,服务于全球气候变化下的区域碳管理。应用LI-8150土壤碳通量测定系统,定位观测并分析科尔沁沙地沙质草地生长季(6—9月)土壤CO_2通量特征,探究水热因子(降水、土壤温度和土壤含水量)对碳排放的影响机制。结果表明,(1)在日动态变化尺度上,晴天和雨天土壤CO_2通量呈现不对称"单峰型"曲线,最高值出现在11:00—16:00,最低值在04:00—06:00。(2)在生长季动态变化尺度上,土壤CO_2日平均通量呈现明显的多峰和季节变化,土壤CO_2月平均日通量分别在7月和9月出现高峰值和低峰值;2016年6月1日—9月30日日平均排放通量最小值(0.35μmol·m^(-2)·s^(-1))出现在晴天(6月8日),最大值(2.68μmol·m^(-2)·s^(-1))出现在雨天(7月23日),生长季平均排放通量为1.26μmol·m^(-2)·s^(-1)。(3)土壤CO_2通量表现为雨天高于晴天,降水事件是扰动土壤CO_2排放的关键因子。(4)土壤CO_2通量与土壤温度和土壤含水量分别表现出不同的时间尺度效应。在日尺度上,无论晴天还是雨天,7月土壤CO_2月平均日通量与表层(5 cm)土壤温度和含水量均呈正相关关系,且相关系数高于其他月份;晴天和雨天土壤含水量和温度的协同作用分别可解释土壤CO_2排放的95.0%和85.5%。在生长季尺度上,晴天的土壤含水量和雨天的土壤温度分别能够解释土壤CO_2排放的63.6%和48.0%;当土壤含水量低于4.87%、土壤温度低于25.94℃时,土壤CO_2排放量随含水量、温度的增加而增加;晴天和雨天土壤含水量和温度的协同作用分别可解释土壤CO_2排放的61.6%和43.7%。

CO2 emission of grassland soil,as one of the key ecological processes of carbon cycle in terrestrial ecosystems,can be used to quantitatively assess and predict regional CO2 emission,and serve the regional carbon management.LI-8150 automatic soil carbon flux measurement system was therefore applied to measure soil CO2 flux in the growing season(June to September)in Horqin sandy land,and explore the effective mechanism of hydrothermal factors(precipitation,soil temperature and soil water content)on carbon emission.The results showed that:(1)For all sunny and rainy days,the diurnal dynamic change of soil CO2 flux showed unsymmetrical“single peak”curve,and the highest value was in the period of 11:00-16:00,the lowest in 04:00-06:00.(2)In the growing season,the daily averaged soil CO2 flux dynamic change showed multi peaks and obvious seasonal changes,higher peak in July and lower peak in September.the minimum value(0.35μmol·m-2·s-1)on the sunny day of June 8th,and the maximum value(2.68μmol·m-2·s-1)on a rainy day of July 23rd in 2016.The average discharge flux in the growth season was 1.26μmol·m-2·s-1.(3)The soil CO2 emission rate was different between the sunny day and the rainy day,and it was higher on the rainy day.Precipitation was the key factor to the soil CO2 emission.(4)On the day scale,the synergistic effect of soil water content and temperature in sunny and rainy days could explain 95%and 85.5%of soil CO2 emission respectively.On the growth season scale,soil water content in sunny days and soil temperature in rainy days could explain 63.6%and 48%of soil CO2 emissions variation,respectively;there is a threshold of soil water content and temperature for soil CO2 emission,when soil water content was below 4.87%and soil temperature below 25.94℃,soil CO2 emission was increased with the increase of water content and temperature;The synergistic effect of soil water content and temperature in sunny and rainy days could explain 61.6%and 43.7%of soil CO2 emission variation respectively.