鸡公山麻栎林和水杉林不同凋落物处理下土壤呼吸对降雨强度的响应

Response of Soil Respiration to Simulated Rainfall Pulse in Jigong Mountain,China,Relative to Type of Forest and Volume of Litter

降雨脉冲对土壤呼吸具有瞬间的激发效应,地表凋落物是土壤有机碳的重要来源,并影响降雨的下渗过程和土壤含水量。降雨对土壤呼吸的激发效应是否受地表凋落物的影响?这一问题目前尚不清楚。针对我国亚热带-暖温带气候过渡区麻栎(Quercus acutissima)林和水杉(Metasequoia glyptostroboides)林2种林型开展不同凋落物输入水平(对照、添加凋落物和去除凋落物)下模拟降雨事件对土壤呼吸影响研究,以阐明不同凋落物条件下土壤呼吸对降雨脉冲的响应规律。结果表明:就麻栎次生林而言,对照、添加凋落物和去除凋落物处理土壤呼吸速率在降雨10 min时均达到峰值,分别为4.72、11.68和5.12μmol·m^(-2)·s^(-1),添加凋落物增强了降雨脉冲的激发效应,去除凋落物与对照处理土壤呼吸速率在降雨事件后无显著差异(P>0.05)。地表凋落物层对麻栎次生林在降雨后的土壤呼吸速率变化具有重要影响。水杉林3种凋落物水平下土壤呼吸均不存在降雨激发效应,且凋落物添加与去除均显著降低水杉林土壤呼吸速率(P<0.05)。麻栎林土壤呼吸与土壤湿度呈显著正相关关系(P<0.05或P<0.01)。水杉林添加凋落物条件下土壤呼吸速率与土壤温度呈显著正相关关系(P<0.05)。该研究表明土壤呼吸对降雨脉冲的响应与森林类型、地表凋落物覆盖与否有密切关系,因此森林生态系统碳循环的变化除了考虑气候变化以外,还必须考虑林型和地表凋落物状况。

Rainfall pulse has been widely reported to stimulate soil respiration. Litters on the land surface are the main source of organic carbon in forest soil, and a factor affecting rainfall infiltration process as well as soil water content. However, it is still unclear whether the effects of rainfall pulse on soil respiration vary with the volume of litter and the type of forest. In-situ observations were conducted in a Quercus acutissima secondary forest and a Metasequoia glyptostroboides plantation in the Jigongshan mountain of Henan Province, a transient area between subtropical and warm-temperate zones, of effects of volume of little [ control, （a） with litter added, and （b） with litter removed] and type of forest on soil respiration rate under simulated rainfalls, to illustrate rules of the responses of soil respiration to intensity pulse in soils under different little conditions. The objective of this study was to explore effects of carbon input on birch and to illustrate their mechanisms. In the Q. acutissima secondary forest, soil respiration rate peaked 10 minutes after the rainfall started, reaching up to 4. 72, 11.68, and 5.12 μmol·m^-2·s^-1 in Control and Treatment （a） or （b） , respectively; litter significant- ly enhanced the stimulative effect of rainfall pulses, but no significant difference was found between Control and Treatment b in soil respiration rate （P〉0. 05 ） ; and the litter layer played an important role affecting soil respiration rate after rainfalls. However, in the M. glyptostroboides plantation, stimulative effect of rainfall pulses on soil respiration did not vary much with the litter layer, either thick or thin; and soil respiration rate significantly decreased in either Treatment a and Treatment b （ P〈0. 05）. In the Q. acutissima secondary forest, soil respiration rate was found significantly and positively related to soil moisture at 5 cm depth （P〈0. 05 or P〈0. 01）, while in the M. glyptostroboides plantation it was to soil temperature at 10 cm depth （P〈0. 05）. The findings in this study suggest that response of soil respiration to rainfall pulse is closely related to type of the forest and existence of a litter layer. Therefore, in studying variations of carbon recycling in forest ecosystems, it is essential to take into account type of the forest and existence of a litter layer in addition to climate change.