Asymmetric Response of Soil Heterotrophic Respiration and Its Temperature Sensitivity in a Desert Steppe Under Climate Change

Soil heterotrophic respiration ( R h ) and its temperature sensitivity ( Q 10 ) are important variables reflecting the intensity of feedback between the grassland carbon cycle and climate change. However, the factors regulating R h and Q 10 in desert grasslands under climate change remain unclear, and the asymmetric response of R h during warming and cooling remains unquantified. We collected and measured the physicochemical properties of soils after 8 years of elevated temperature and precipitation (ambient temperature, T0, +2°C, T1, +4°C, T2, ambient precipitation, P0, +25%, P1, and +50%, P2). To quantify the asymmetric response of R h , we continuously monitored R h during warming and cooling at six incubation temperature levels in the laboratory (5°C, 10°C, 15°C, 20°C, 25°C, and 30°C). Results indicated that elevated temperature and precipitation significantly affected soil moisture, soil organic carbon, R h , and Q 10 . Compared with the T0P0 treatment, the T2P2 treatment enhanced R h and Q 10 by 11.72% and 1.56%, respectively. In addition, R h was significantly affected by periodic changes in incubation temperature during both warming (5°C–30°C) and cooling (30°C–5°C), and R h was 15.05% higher under warming than cooling. Variation partitioning analysis showed that R h was primarily governed by soil carbon content, whereas Q 10 was largely driven by soil water content. In summary, soil carbon and water content are limiting factors for R h and Q 10 in the desert steppe, and periodic temperature changes should be taken into account when quantifying R h and Q 10 .