海南热带山地雨林林窗对土壤呼吸的影响研究

Under the background of increasing extreme weather and climate events, canopy gaps in the tropical rainforest showed increasing trend. Studying the effect of tropical rainforest canopy gap on soil respiration is becoming a new international frontier and hotspot in the research of forest ecosystem carbon cycling and global climate change. The canopy gaps in the tropical montane rainforest observation sites of the Jianfengling National Natural Reserve on Hainan Island, south of China, were selected as the research objects. Meteorological factors (e.g. air temperature, radiation and precipitation), soil environmental parameters, soil respiration and other indicators were observed and investigated regularly. Based on those long-term observation data, daily and seasonal patterns and differences of soil respiration between the inside and outside of canopy gaps were analyzed. Then, the effect of canopy gaps on soil respiration and its mechanism was illustrated. In addition, the characteristics of the soil respiration in tropical montane rainforest were stimulated by the Denitrification-Decomposition (DNDC) model, and the impact of canopy gap on the annual total amount of soil respiration was quantitatively assessed. The goal of this project is to enrich the data of in-situ observation research of soil respiration in the canopy gaps (typhoon disturbance) of the tropical montane rainforest. The results lay a foundation of long-term data accumulation, which could provide scientific basis and theoretical reference for accurate estimating soil carbon emissions and effective management of soil organic carbon accumulation in the tropical montane forest ecosystem.

在全球极端天气气候事件增多的背景下，热带雨林的林窗呈增加趋势。热带雨林林窗土壤呼吸研究已成为森林生态系统碳循环和全球气候变化研究中的前沿和热点。本项目拟以海南岛尖峰岭热带山地雨林林窗观测场为试验样地，定期监测气象要素、土壤环境和土壤呼吸，并结合土壤活性有机碳、酶活和微生物等理化指标数据，认识林窗形成后土壤呼吸变化过程，揭示林窗对土壤呼吸的影响机制，并利用DNDC模型模拟热带山地雨林土壤呼吸特征，定量评估林窗对年土壤呼吸总量的影响。项目旨在充实热带山地雨林林窗土壤呼吸原位观测研究数据，为台风干扰形成林窗后的土壤碳循环研究积累基础数据，为热带森林生态系统土壤碳排放量的精确估算和土壤有机碳管理提供科学依据。

随着全球气候变暖，极端天气气候（如台风等）呈现出增多增强的变化趋势，因台风导致的森林林窗也呈现增加趋势。研究林窗对森林土壤CO2和CH4通量的影响，对森林土壤温室气体排放的准确估算和有机碳管理具有重要的意义。但林窗对森林土壤温室气体排放的影响及其机制目前还不清楚。本项目通过在尖峰岭站林窗试验样地开展野外观测试验研究，分析了林窗内外气象要素、土壤环境、CO2和CH4通量的异同性，研究了影响土壤CO2和CH4通量的主要环境因子，并利用Forest-DNDC模拟了热带雨林土壤CO2的排放，其主要研究结果如下：.1. 2018年林窗的日均空气温度和相对湿度显著高于林下。整个观测期（2018-2019年）林窗5 cm的土壤温度、全磷、铵态氮与林下均存在显著差异性。林窗土壤微生物群落的多样性略高于林下，但差异不显著。在门分类水平上，土壤主要的古菌群为奇古菌门、广古菌门和泉古菌门。.2. 2018-2019年林窗和林下年均CO2通量分别为3.29±0.94和3.10±1.12 nmol m-2 s-1，CH4通量分别为-0.62±0.43和-0.63±0.43 nmol m-2 s-1。在月和年际尺度上，林窗内外的土壤CO2的排放呈现多峰型曲线变化规律，排放趋势大致相同。2018年的林窗的土壤CO2通量显著高于林下，但2019年林窗和林下的土壤CO2通量无显著差异。土壤CH4通量月变化呈现旱季高雨季低的特点。研究结果表明，林窗对土壤CH4通量没有显著影响。.3. 5 cm土壤温度和脲酶是影响2018年林窗土壤CO2通量的最主要环境因子，分别解释了变异性的26.2%和3.5%；5 cm土壤温度和有机碳是影响林下土壤CO2通量的最主要因素，分别解释了变异性的10.7%和15.8%。土壤CH4通量的最佳结构模型表明，土壤含水量是影响2018-2019年林窗和林下土壤CH4通量最主要的环境因子。.4. Forest-DNDC模型可以较好地模拟尖峰岭热带山地雨林土壤CO2的月排放特征和年排放量，通过模型模拟获得2014、2015年的土壤CO2排放量分别为37.88 t·hm-2·a-1和40.79 t·hm-2·a-1。森林土壤CO2排放的主要敏感因子是5 cm土壤有机碳。模型模拟结果表明，气候变化（气温上升或下降0.2 ℃，降水量增加或降低20%）对土壤CO2排放的影响较小。