Grassland types and season-dependent response of ecosystem respiration to experimental warming in a permafrost region in the Tibetan Plateau

- Warming effect on ecosystem respiration (ER) was greater in alpine meadow than swamp meadow.
- Non-growing season ER responded stronger to warming compared with growing season.
- ER may be stimulated for 6 years under climate warming whether in dry or moist soil conditions.
- ER was mainly affected by soil temperature, aboveground biomass and duration of thaw days.
- The temperature sensitivity of ER (Q10) decreased with increase temperature.

Information regarding the response of ecosystem respiration (ER) to various warming levels, especially in different grassland types and seasons, is scarce at the field scale in the permafrost region of the Tibetan Plateau (TP). In this study, we examined how different warming levels during different seasons affected ER in Tibetan alpine meadow and swamp meadow after 6 years experimental warming. The interpolated annual ER of swamp meadow (387.0 gC m−2) was higher than that of alpine meadow (284.5 gC m−2) in natural conditions. A moderate warming of 2.4 °C increased ER by 62.2% and 36.6%, and a high warming of 5.3 °C increased ER by 101.3% and 52.0% in alpine meadow and swamp meadow, respectively. The warming effects on ER were greater in the non-growing season compared with the growing season; this significantly increased the contribution of non-growing season emissions to annual ER from 25% in natural conditions to 31% in high warming treatments. ER was significantly affected by soil temperature, aboveground biomass and the duration of thaw days. The temperature sensitivity of ER (Q10) was higher in the non-growing season (3.02-5.02) than in the growing season (2.11-2.75) and decreased with increasing temperature. Our results indicated that the magnitude of warming-induced increases in ER differed by grassland type and season, and there was strong potential for the non-growing season to serve as a positive feedback to annual carbon balance.