Soil respiration of alpine meadow is controlled by freeze-thaw processes of active layer in the permafrost region of the Qinghai-Tibet Plateau

Freezing and thawing action of the active layer plays a significant role in soil respiration (R-s) in permafrost regions. However, little is known about how the freeze-thaw processes affect the R-s dynamics in different stages of the alpine meadow underlain by permafrost in the Qinghai-Tibet Plateau (QTP). We conducted continuous in situ measurements of R-s and freeze-thaw processes of the active layer at an alpine meadow site in the Beiluhe permafrost region of the QTP and divided the freeze-thaw processes into four different stages in a complete freeze-thaw cycle, comprising the summer thawing (ST) stage, autumn freezing (AF) stage, winter cooling (WC) stage, and spring warming (SW) stage. We found that the freeze-thaw processes have various effects on the Rs dynamics in different freeze-thaw stages. The mean Rs ranged from 0.12 to 3.18 mu molm(-2) s(-1) across the stages, with the lowest value in WC and highest value in ST. Q10 among the different freeze-thaw stages changed greatly, with the maximum (4.91 +/- 0.35) in WC and minimum (0.33 +/- 0.21) in AF. Patterns of R-s among the ST, AF, WC, and SW stages differed, and the corresponding contribution percentages of cumulative R-s to total Rs of a complete freeze-thaw cycle (1692.98 +/- 51.43 gCO(2) m(-2)) were 61.32 +/- 0.32 %, 8.89 +/- 0.18 %, 18.43 +/- 0.11 %, and 11.29 +/- 0.11 %, respectively. Soil temperature (T-s) was the most important driver of Rs regardless of soil water status in all stages. Our results suggest that as climate change and permafrost degradation continue, great changes in freeze-thaw process patterns may trigger more R-s emissions from this ecosystem because of a prolonged ST stage.