非生长季刺槐林土壤CH4通量的变化特征及其影响因子

目的]探讨在非生长季不同天气条件下45年生刺槐林土壤CH₄通量的日变化和季节变化特征,并确定其主要影响因子.方法]2014年10月-2015年4月(非生长季),在华北低山丘陵区黄河小浪底森林生态系统定位研究站,利用基于离轴积分腔输出光谱技术的土壤CH₄通量自动观测系统,对土壤CH₄通量进行连续观测,同步观测林内大气温度和相对湿度、5 cm深处土壤温度和土壤湿度、林内总辐射以及降雨量,分析各因子间的相互关系并确定影响土壤CH₄通量的主要因子.结果]表明:(1)在非生长季,刺槐人工林土壤为大气CH₄重要的汇,变化范围为-0.15~-2.34 nmol·m^-2·s^-1 .晴天的林地土壤吸收CH₄能力 (-0.78 nmol·m^-2·s^-1) 明显高于阴天(-0.61 nmol·m^-2·s^-1)、降雨或降雪天气 (-0.58 nmol·m^-2·s^-1),而且呈"V"型日际变化特征;在2014年11月-2015年1月,土壤吸收CH₄能力逐渐下降,并维持相对较低的水平,直至2015年3月达到最大值 (-2.34 nmol·m^-2·s^-1);(2)土壤CH₄通量与大气温度、5 cm深处土壤温度呈显著负相关,与相对湿度呈正相关;在2015年1月,土壤CH₄通量与总辐射呈正相关;(3)在生长末期土壤上冻阶段和冬季土壤冻结阶段,大气温度和相对湿度为影响土壤CH₄通量的主要因子;而在生长季初期,主要的影响因子为大气温度和5 cm深处土壤温度.结论]非生长季刺槐林土壤表现为大气CH₄的汇,在非生长季初期土壤吸收CH₄的能力最弱,主要受大气温度和相对湿度的影响,而在非生长季末期土壤吸收CH₄的能力逐渐增加,主要受大气温度和土壤温度的影响.

Change of Soil CH4 Fluxes of Robinia pseudoacacia Stand During Non-growing Season and the Impact Factors

Objective]To investigate the diurnal and seasonal variation of CH₄ fluxes in different weather conditions, and explore the effects of soil and meteorological factor on CH₄ fluxes in black locust forest soil. Method]The automatic observation system with the near infrared laser and infrared laser analysis composite technology was used to measure the CH₄ fluxes of soil in Robinia pseudoacacia L. plantation in low hilly land of north China from October 2014 to April 2015. Meanwhile, the atmospheric temperature and relative humidity, soil temperature and soil water content (5 cm), global radiation and precipitation were concurrently measured. The principal component analysis and stepwise regression analysis were used to analyze the relationship among the factors and determine the main factor of soil CH₄ flux. Result](1) The soil of R. pseudoacacia plantation was the important atmospheric CH₄ sink during the non-growing season with the range from-0.15 to-2.34 nmol·m^-2·s^-1. The diurnal variation of CH₄ fluxes showed diurnal characteristics of "V-shape",and had higher absorption capacity in a clear day (-0.78 nmol·m^-2·s^-1) but lower in cloudy (-0.61 nmol·m^-2·s^-1), rainy or snowy day (-0.58 nmol·m^-2·s^-1). From November 2014 to January 2015, a gradual decline in the absorption capacity of soil was found. The remained fairly low until the spring when the soil started thawing. The soil CH₄ absorption capacity reached the maximum (-2.34 nmol·m^-2·s^-1) in March 2015. (2) There was a significant negative correlation relationship between soil CH₄ fluxes and atmospheric temperature, soil temperature.The soil CH₄ fluxes was positively correlated with atmospheric relative humidity. In March and April 2015, the most significant positively correlation was observed between CH₄ fluxes and global radiation. (3) The factors of atmospheric temperature and relative humidity became the leading elements in terminal growth and winter while the atmospheric temperature and soil temperature (5 cm in depth) were the primary factors of soil CH₄ fluxes in early growing season. Conclusion]The R. pseudoacacia forest soil was the sinks of atmospheric CH₄ during non-growing season. The absorption capacity of CH₄ was the weakest in early non-growing season, while the absorption capacity of the soil gradually increased at the end of non-growing season. In the early period, the soil CH₄ fluxes were mainly affected by atmospheric temperature and relative humidity. In the latter period, the soil CH₄ fluxes were influenced by air temperature and soil temperature.