高寒草地土壤异养呼吸对温度响应随培养时间延长而下降的主要影响因素研究

Decrease in temperature response of heterotrophic soil respiration with incubation time has been observed in many field and control experiments. However, the influencing factors on decreasing temperature response of heterotrophic soil respiration and their impact mechanisms have not been well understood, which caused difficulties in accurately predicting the feedbacks between soil carbon pools and future climate change. In this research, we design three experiments utilizing the surface soils of alpine meadow, alpine grassland and alpine desert steppe which are different in substrate quality: (1) Incubate the three soils under two different moisture and three temperature conditions for 64 days. The CO2 fluxes, soil microbial community characters (by molecular biology techniques) and carbon fractions will be detected throughout the incubation; (2) Separate the soil substrate and microbes by soil sterilization and microbial extraction and cross incubate them for 64 days under the same culture condition as experiment 1. The fluxes of CO2 will be detected throughout the incubation period too; (3) On the basis of experiment 1, the soil substrate and microbes of the soil incubated for 0 and 64 days will be separated and cross incubated under the same culture condition. The fluxes of CO2 will be detected throughout the incubation period. Our study could get a better understanding of the effects of moisture, microbial shifts and substrate quality and availability on decreasing temperature response of heterotrophic soil respiration with incubation time and thus has theoretical significance in raising awareness of feedbacks between the main soil carbon pools in Tibetan Plateau and future climate change.

国内外多数研究发现土壤异养呼吸(Rh)对温度的响应程度均随增温时间的延长而逐步下降，但对其变化的驱动因素和机制缺乏统一的认识，导致土壤碳库与气候变化的反馈存在较大不确定性。本研究选择青藏高原高寒草甸、高寒草原和高寒荒漠草原三种土壤质量类型的表层土壤，设计3个实验：(1) 3种土壤在3种温度和2种湿度条件下培养64天，定期监测CO2通量、微生物群落(利用分子生物学技术)和土壤碳组分变化；(2) 通过土壤灭菌和微生物浸提将3种土壤的底物和微生物分离并交叉培养64天，培养条件同实验1，定期监测CO2通量；(3)在实验1的基础上，分离培养0天和64天的土壤的底物和微生物并交叉培养30天，培养条件不变，定期监测CO2通量。研究湿度、土壤底物质量和可利用性及微生物变化对Rh温度响应变化的驱动作用，探讨Rh对温度响应随时间衰减的过程和机制，对提高认识青藏高原主要类型土壤碳库与气候变化反馈具有重要意义。

青藏高原土壤碳库巨大且对气候变化响应敏感。因此认识青藏高原土壤碳库对气候变化的响应过程和机制对于预测当地甚至全球的气候变化具有重要意义。国内外多数研究包括青藏高原相关工作发现土壤异养呼吸（Rh）对温度的响应程度均随增温时间的延长而逐步下降，但对其变化的驱动因素和机制缺乏统一的认识，导致土壤碳库与气候变化的反馈存在较大不确定性。本项目在青藏高原选择了高寒草甸，高寒草原和高寒荒漠草原三种典型青藏高原植被类型，利用2步交叉培养实验研究了Rh对温度增加的响应规律和机制。为了消除气压，氧含量等因素对结果的影响，本项目培养工作在中国科学院青藏高原研究所那曲生态环境综合观测研究站开展。第一步将土壤在不同温度和水分条件下培养，监测Rh及微生物群落特征变化，直至Rh¬显著降低。第二步是在第一步基础上将培养结束后的土壤灭菌并接种新鲜土壤微生物研究土壤底物限制对Rh的影响；同时提取第一步培养结束后土壤中微生物接种到新鲜土壤中，研究微生物温度适应对Rh的影响。第一阶段培养结果表明, Rh在增温初期显著增加，微生物群落特征但随着增温时间的延长Rh增加的程度逐渐降低。土壤易分解有机质在培养过程中显著降低，微生物群落特征也发生了显著变化。荒漠草原土壤微生物群落特征的变化主要是由于底物降低导致的，其Rh降低的主要原因是由于土壤中微生物底物的限制导致的。因此，在未来气候变暖情形下，荒漠草原土壤碳库会显著降低。而高寒草甸和高寒草原土壤微生物群落特征的变化是由于底物降低和温度增加共同导致的，其Rh的降低主要是由于土壤中微生物底物的限制和微生物的温度适应共同作用的结果。由于微生物的温度适应，未来气候变暖条件下高寒草甸和高寒草原碳库的降低速度显著低于预期水平。该结果为准确分析和预测未来高寒生态系统土壤碳库变化提供必要的参数估计和模型验证，对于理解全球气候变化情形下青藏高原碳库响应过程和机制具有重要的理论意义。