浙江古田山亚热带常绿阔叶林不同干扰强度下土壤呼吸的日动态与季节变化

Diurnal and seasonal patterns of soil respiration in subtropical evergreen broad-leaved forests with different degrees of human disturbance in Gutianshan,Zhejiang Province

在浙江古田山常绿阔叶林区域选择了4个具代表性的不同干扰强度森林类型：常绿阔叶老龄林（OF）、一次皆伐后自然恢复的天然次生林Ⅰ（SFI）、皆伐后自然恢复过程中经历一次重度择伐的天然次生林Ⅱ（SFⅡ）、人工杉木林（AF）为研究对象，进行了为期1年的土壤呼吸动态监测，定量分析了不同林型土壤呼吸的昼夜和季节变化，同时结合相关环境和生物因子的监测，从日尺度和季节尺度上探讨了影响我国亚热带常绿阔叶林区不同森林土壤呼吸的主要驱动因子，并就不同的森林管理方式对亚热带森林土壤碳释放的可能影响做出了初步评估．研究发现4种林型土壤碳日累积释放量呈现显著的季节变化，从5月份开始各林型土壤碳日累积释放量以较快速率升高，老龄林8月中旬达到最大，次生林I在7月中旬达最大，次生林II和人工林在6月中旬达最大，之后各林型持续下降到翌年1月份，而后开始缓慢回升．4种林型年平均土壤碳日累积释放量分别为1．48，1．48，1．51，0．87gcm-2d-1，人工林的土壤碳日累积释放量显著低于其他3种林型．各林型的土壤呼吸速率的日变化幅度均不显著．土壤表层温度是影响该地区土壤呼吸季节动态的主要因素，二者呈显著的指数相关关系，相关系数舻为0．88～0．94；土壤表层含水量与土壤呼吸之间没有显著的相关关系．老龄林土壤温度敏感性（Qzo值）显著高于其他林型．上述结果表明，受干扰强度最大的人工林的土壤呼吸速率显著降低，对温度变化的敏感性显著降低：受干扰强度相对较小的次生林其土壤呼吸速率和温度敏感性基本上和老龄林保持一致．古田山不同林型土壤呼吸季节变化的主要驱动因子均为土壤温度．这些结论说明不同干扰强度对亚热带森林土壤碳释放的影响不同，这为精确估算该地区不同植被类型碳收支提供了重要依据，此外土壤呼吸无显著昼夜变化的结论将对该区域后续的动态监测工作起到积极的指导作用．

The aims of this study were to investigate the diurnal and seasonal variations in soil respiration in different broad-leaved forest types with different degrees of human disturbance, to identify the major abiotic and biotic factors affecting the daily and seasonal patterns of soil respiration, and to evaluate the effects of different forest management types and human disturbance on soil respiration in subtropical forests. We selected four different 1 hm2 forests with different degrees of human disturbance in Gutianshan, Zhejiang Province： An old-growth forest （OF, almost no human disturbance）; two secondary forests （SF1, a secondary forest regrown after clear cutting about 50 years ago, and SF2, a secondary forest regrown after clear cutting about 50 years ago and selective cutting about 20 years ago）; and a plantation forest （AF, planted about 20 years ago）. We measured the diurnal and seasonal changes in soil respiration rates in each plot every month from May 2011 to July 2012. We also measured soil temperature and water content of the surface soil layer during sampling. The annual means of daily accumulated soil carbon release were 1.48, 1.48, 1.51, and 0.87 g C m 2 d-l in OF, SF1, SF2, and AF plots, respectively. The soil respiration rate in AF was significantly lower than those in the other three forest types. On the diurnal scale, there were no significant variations in soil respiration rates among the four forest types. Our results indicated that the rate of soil respiration measured any time during the day can be used to predict daily accumulated soil carbon release. Significant positive relationships were found between soil respiration and surface soil temperature （R2=0.88-0.94） for all four forest types. There were no significant relationships between soil respiration and soil water content. The Q10 value of OF was significantly higher than those of the other three forest types. The results showed that the soil respiration rate and its sensitivity to temperature were significantly decreased in the plantation with the most intense human disturbance （AF）. The soil respiration rates and Ql0 values of both SF forests were similar to those of OF forest. Soil temperature was the most important driving factor for soil respiration. Together, our results implied that different degrees of human disturbance had different effects on soil respiration in these forests. This information is important to estimate the role of human interference in regional carbon cycles. Also, the finding that there was no significant variation in the diurnal soil respiration rates is very important for guiding further research on soil respiration in related regions.