Non-growing-season soil respiration is controlled by freezing and thawing processes in the summer monsoon-dominated Tibetan alpine grassland

• Published in: Global Biogeochemical Cycles
• Main Authors: Wang, Yonghui, Liu, Huiying, Chung, Haegeun, Yu, Lingfei, Mi, Zhaorong, Geng, Yan, Jing, Xin, Wang, Shiping, Zeng, Hui, Cao, Guangmin, Zhao, Xinquan, He, Jin-Sheng
• Format: Article in Journal/Newspaper
• Language: English
• Published: AMER GEOPHYSICAL UNION 2014
• Subjects: winter soil respiration; carbon cycling; alpine ecosystem; soil freezing; Tibetan Plateau; Environmental Sciences; Geosciences; Multidisciplinary; Meteorology & Atmospheric Sciences; CO2 EFFLUX; TEMPERATURE SENSITIVITY; ECOSYSTEM RESPIRATION; MICROBIAL ACTIVITY; ARCTIC ECOSYSTEMS; SOLAR-RADIATION; NORTH-AMERICA; FROZEN SOIL; SNOW DEPTH; WINTER; Environmental Sciences & Ecology; Geology; Arctic; Tundra
• Online Access: http://ir.ibcas.ac.cn/handle/2S10CLM1/27043; https://doi.org/10.1002/2013GB004760

The Tibetan alpine grasslands, sharing many features with arctic tundra ecosystems, have a unique non-growing-season climate that is usually dry and without persistent snow cover. Pronounced winter warming recently observed in this ecosystem may significantly alter the non-growing-season carbon cycle processes such as soil respiration (R-s), but detailed measurements to assess the patterns, drivers of, and potential feedbacks on R-s have not been made yet. We conducted a 4 year study on R-s using a unique R-s measuring system, composed of an automated soil CO2 flux sampling system and a custom-made container, to facilitate measurements in this extreme environment. We found that in the nongrowing season, (1) cumulative R-s was 82-89g C m(-2), accounting for 11.8-13.2% of the annual total R-s; (2) surface soil freezing controlled the diurnal pattern of R-s and bulk soil freezing induced lower reference respiration rate (R-0) and temperature sensitivity (Q(10)) than those in the growing season (0.40-0.53 versus 0.84-1.32 mu mol CO2 m(-2)s(-1) for R-0 and 2.5-2.9 versus 2.9-5.6 for Q(10)); and (3) the intraannual variation in cumulative R-s was controlled by accumulated surface soil temperature. We found that in the summer monsoon-dominated Tibetan alpine grassland, surface soil freezing, bulk soil freezing, and accumulated surface soil temperature are the day-, season-, and year-scale drivers of the non-growing-season R-s, respectively. Our results suggest that warmer winters can trigger carbon loss from this ecosystem because of higher Q(10) of thawed than frozen soils.