土壤湿度对中国南部热带森林土壤甲烷吸收的影响

森林土壤是一个重要的大气甲烷的汇。然而，相较于寒带和温带，在热带尤其是东南亚地区，森林土壤甲烷通量的观测较少，这限制了目前对热带森林土壤甲烷通量与环境因子之间关系的认识，也给热带森林土壤甲烷汇的估算带来了一定的不确定性。在中国海南省吊罗山国家森林公园的热带森林土壤，采用激光光谱法测量了2016年9月至2018年9月逐月的土壤甲烷通量，并分析了其与周围环境因子的关系。结果表明：研究区土壤是甲烷的汇，山顶样地的年平均吸收量为0.95 kg CH₄-C hm^-2 a^-1,山脚样地的年平均吸收量为1.93 kg CH₄-C hm^-2 a^-1。干季(11月—次年4月)的甲烷吸收通量明显高于湿季(5—10月),占到全年甲烷吸收的68%。山顶样地年平均土壤湿度为19.2%,年内的波动较小(2.8%)。而山脚样地的年平均湿度相对较低，为12.7%,且年内波动大(5.4%)。土壤湿度是控制甲烷吸收最主要的环境因子，可以解释月际甲烷吸收变化的76%,甲烷吸收通量与土壤温度的相...

Effects of soil moisture on methane uptake in a tropical forest of southern China

Forest soils contribute substantially to the global methane uptake. However, compared with the cold and temperate zones, measurements of methane flux from the soils in the tropical forests are still sparse, especially in Southeastern Asia. This gap limits our understanding of the relationship between the methane flux from the soils and the environmental factors, which leads to large uncertainty in the estimation of the methane uptake flux from the tropical forest soils. This study was conducted in Diaoluoshan National Forest Reserve in Hainan Province, China. We measured monthly methane flux from the tropical forest soils by near-infrared laser greenhouse analyzers from September 2016 to September 2018. Soil moisture and soil temperature were measured simultaneously by Decagon 5 TM sensors. Furthermore, we analyzed the relationship between the methane flux with the environmental factors. The results revealed that the soils of the study area served as the sink of atmospheric methane during a 2-year period. The methane uptake in tropical forest soils at the top of the mountain was 0.95 kg CH₄-C hm^-2 a^-1, while that in tropical forest soils at the foot of the mountain was 1.93 kg CH₄-C hm^-2 a^-1. The methane uptake flux in the dry season (from November to April next year) was significantly higher than that in the wet season (from May to October). The former one accounted for about 68% of the methane uptake flux of the whole year. The mean annual soil moisture at the top of the mountain was 19.2% with an intra-annual variance of 2.8%. And the mean annual soil moisture at the foot of the mountain was 12.7% with a bigger intra-annual variance (5.4%) than that at the top of the mountain. Soil moisture acted as the significant predictor of the methane uptake flux and accounted for 76% of the variance. There was no significant correlation between methane uptake flux and soil temperature. For soil moisture lower than 20% (v/v), the relation between soil moisture and methane flux was best fitted with linear regression. For soil moisture higher than 20% (v/v), the tropical forest soils of the study area turned from the sink to the source of the methane flux. According to the relationship between soil moisture and methane flux in the tropical forests, we estimated the annual methane uptake of the tropical forest soils was 1.72 Tg CH₄-C/a. Our results have important implications for long-term methane flux measurements in Southeastern Asia and the estimation of the magnitude of the methane uptake from tropical forest soils.