梯度增温对青藏高原高寒草甸生态系统碳交换的影响

高寒草甸是青藏高原主要的草地生态系统类型,对气候变化非常敏感,研究高寒草甸生态系统碳交换对升温的响应具有重要的理论和现实意义。在青藏高原中部地区的高寒草甸,使用开顶箱法(open-top chambers,OTCs)设置不增温对照(T_0)以及4个不同程度的增温处理(T_1、T_2、T_3、T_4),采用CO_2红外分析仪对生长季期间的碳交换进行连续3年的观测。结果表明,4个增温处理的5cm土壤温度较之于不增温对照分别增加1.73(T_1)、1.83(T_2)、3.03(T_3)以及3.53℃(T_4);土壤水分没有发生梯度变化。观测期间,净生态系统碳交换(net ecosystem carbon exchange,NEE)基本为负值,因此高寒草甸表现为碳汇。增温小于2℃促进总生态系统生产力(gross ecosystem productivity,GEP),但对生态系统呼吸(ecosystem respiration,ER)影响较小,因而促进NEE,即促进高寒草甸的碳吸收;但增温大于3℃则抑制GEP,对ER影响较小,因而总体上对NEE产生抑制作用。综上所述,在高寒草甸生态系统,适度增温促进碳吸收,增温过度则降低碳吸收。

Ecosystem carbon exchange of an alpine meadow under simulated gradient warming in the Tibetan Plateau,China

Alpine meadow is one of the primary alpine grassland ecosystems in the Tibetan Plateau region, which is sensitive to climatic changes,including global warming.Therefore,it is crucial to investigate how the ecosystem carbon exchange of the alpine meadow varies with increasing temperature.In the present study,we conducted a five-level warming experiment (T0 ,no warming;T1-T4 represent the different warming treat-ments)and the ecosystem carbon exchange was measured using open-top chambers (OTCs)and infrared analy-zer,respectively,over three consecutive growing seasons.Our results showed that:1 )compared to the con-trol,warming enhanced the temperature of 5 cm soil layer by 1.73 (T1 ),1.83 (T2 ),3.03 (T3 )and 3.53 ℃(T4 ),respectively for four warming treatments;but soil moisture changed in a non-linear fashion.2)The negative values of the net ecosystem carbon exchange (NEE)indicated that the alpine meadow acted as a carbon sink.3)Warming that less than 2 ℃ substantially improved the gross ecosystem productivity (GEP),but had no significant effect on ecosystem respiration (ER),resulting in a net increase in NEE value.In other words, moderate warming could stimulate carbon sequestration in the alpine meadows,but in a warmer scenario (e.g. temperature increased by more than 3 ℃),carbon sequestration would be restricted due to the decrease in GEP. These findings suggest that the alpine meadow will uptake more/less CO2 in moderate/outranged warming sce-narios,accordingly.