Dynamics of carbon flux of alpine meadows along a degradation gradient

Alpine meadow is one of the main vegetation types in the Qinghai-Tibet Plateau. Alpine meadows are variably degraded under the influence of climate change and human activities. The carbon flux in alpine meadows changes with the degradation. However, the characteristics of carbon flux components during degradation in alpine meadows are still unclear, hindering our understanding of the transition between carbon sink and source in responding to global changes. In this study, four degradation degrees of alpine meadows, including enclosure as control check, lightly degraded, moderately degraded, and severely degraded meadows were studied. The net ecosystem exchange (NEE), ecosystem respiration (ER), gross ecosystem productivity (GEP), methane (CH₄) fluxes, and related environmental factors were measured during the growing season by the static chamber method. Results showed that: 1) Alpine meadows with different degrees of degradation in summer were significant CO₂ sinks, with NEE ranging from −1437.55 to −98.45 mg·(m²·h)⁻¹ (CO₂); NEE, ER, and GEP decreased significantly with the degradation of alpine meado(CH₄)w (P < 0.05). The alpine meadow presented a weak CH₄ sink with a mean rate of 0.029 mg·(m²·h)⁻¹ (CH₄), showing no significant difference among degradation degrees (P > 0.05). 2) Soil organic carbon content and vegetation coverage were the two main environmental factors that affected NEE, GEP, and ER. Our study found that the capacity of carbon sequestration of alpine meadows decreased by 55% from lightly degraded to moderately degraded in the growing season, indicating that more attention should be paid to the succession of alpine meadows from light to moderate degradation, which is crucial to maintaining the carbon sequestration function of alpine meadow.