在气候变化背景下,干旱频率和强度的增加将对森林生态系统的碳循环过程产生重要影响,掌握土壤呼吸及其敏感性对干旱的响应规律有助于评价土壤在碳收支过程中的源汇角色.本研究用顶棚法野外模拟毛竹林干旱下凋落物不变(LU)、添加(LA)、移除(LR)处理对土壤呼吸动态及其温度敏感性的影响和滞留效应.结果表明:对照(自然降雨)和干旱条件下凋落物不变处理年均土壤呼吸速率分别为3.15和2.34 mumol·m~(-2)·s~(-1).凋落物移除处理较凋落物添加处理对土壤呼吸的影响大,对照和干旱条件下凋落物移除处理较不变处理分别下降21.0%和20.9%,仅干旱条件下凋落物添加处理较不变处理增加5.3%;说明干旱条件下凋落物添加和移除处理对土壤呼吸的影响均较不变处理明显.干旱条件下土壤呼吸的温度敏感性较对照降低8.4%,凋落物添加处理和凋落物移除处理温度敏感性分别下降15.4%和7.6%.对照和干旱条件下18个月土壤碳累积排放量分别为7.35和5.40 kg CO_2·m~(-2),对照和干旱条件下凋落物添加处理较不变处理分别增加1.8%和10.7%,凋落物移除处理分别下降19.9%和18.0%.凋落物添加处理或移除处理对毛竹林土壤呼吸速率的影响呈非线性,因土壤水分的减少直接影响根系生长和微生物活性致使滞留效应明显,干旱条件下凋落物量对土壤碳排放的影响更明显,凋落物量的变化是气候变化背景下土壤碳排放不可忽视的影响因素.
英文摘要:
Increases in drought frequency and intensity under climate change will have great impacts on the carbon cycle of forest ecosystems. Understanding the responses of soil respiration and its temperature sensitivity to drought is necessary,when we assess whether soil is a carbon sink or source. The effects of litterfall input on soil respiration,temperature sensitivity and its lagging effect were studied in moso bamboo forests under simulated drought by ceiling method in the field with three litterfall treatments,i.e.,ambient litterfall (unchanged,LU) ,litter addition (LA) and litter removal (LR) . The results showed that LU decreased annual soil respiration rate in drought treatment (2.34 mumol·m~(-2)·s~(-1)) ,compared with that in the control (3.15 mumol·m~(-2)·s~(-1)) with ambient natural rainfall. LR showed stronger effect on soil respiration than LA. Compared with LU,LR decreased soil respiration rate by 21.0% in ambient condition and by 20.9% in drought treatment,while LA led to 5.3% increase only in drought treatment. Such a result indicated that the effects of LA and LR on soil respiration rate were stronger than LU in the drought condition. Drought decreased the temperature sensitivity of soil respiration by 8.4%,while LA and LR reduced that by 15.4% and 7.6%,respectively. The cumulative CO_2 emissions during the whole 18 months were 7.35 and 5.40 kg CO_2·m~(-2) in the control and drought treatment. Compared with LU,LA increased the cumulative CO_2 emissions by 1.8% and 10.7%,and LR decreased that by 19.9% and 18.0% in the control and drought treatments. Our results indicated that the relationship between the litterfall amount (addition or removal) and soil respiration rate was nonlinear. The significant lagging effect may be caused by the decrease in root growth and microbial activity due to decreased soil water availability in drought treatment. Litterfall played a more important role in soil CO_2 emission under drought,and thus litterfall was a crucial factor in soil carbon emission in the context of climate change.