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 treatments) and the ecosystem carbon exchange was measured using open-top chambers (OTCs) and infrared analyzer, respectively, over three consecutive growing seasons. Our results showed that: 1) compared to the control, 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 scenarios, accordingly.