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Understanding the response mechanisms of litter respiration to soil moisture in water-limited semi-arid regions is of vital importance to better understanding the interplay between ecological processes and the local carbon cycle. In situ soil respiration was monitored during 2010–2012 under various conditions (normal litter, no litter, and double litter treatments) in a 30-year-old artificial black locust plantation (Robinia pseudoacacia L.) on the Loess Plateau. Litter respiration with normal and double litter treatments exhibited similar seasonal variation, with the maximum value obtained in summer (0.57 and 1.51 μmol m−2s−1 under normal and double litter conditions, respectively) and the minimum in spring (0.27 and 0.69 μmol m−2s−1 under normal and double litter conditions, respectively). On average, annual cumulative litter respiration was 115 and 300 g C m−2 y−1 under normal and double litter conditions, respectively. Using a soil temperature of 17°C as the critical point, the relationship between litter respiration and soil moisture was found to follow quadratic functions well, whereas the determination coefficient was much greater at high soil temperature than at low soil temperature (33–35% vs. 22–24%). Litter respiration was significantly higher in 2010 and 2012 than in 2011 under both normal litter (132–165 g C m−2 y−1 vs. 48 g C m−2 y−1) and double litter (389–418 g C m−2 y−1 vs. 93 g C m−2 y−1) conditions. Such significant interannual variations were largely ascribed to the differences in summer rainfall. Our study demonstrates that, apart from soil temperature, moisture also has significant influence on litter respiration in semi-arid regions. [ABSTRACT FROM AUTHOR]

Temperature sensitivity of soil respiration ( Q 10 ) is an important mechanism for the possible feedback between global carbon cycle and climate system. Knowledge of how crop types and nitrogen (N) fertilization affect Q 10 is critical for estimating soil respiration and carbon cycling in agro-ecosystem. A two-year field experiment was conducted with cold-resistant (winter wheat; Triticum aestivum L.) and thermophilic (spring maize; Zea mays L.) crops at two N fertilization levels (no fertilization (CK) and 160 kg N hm −1 ) from October 2013 to September 2015 in semi-arid Loess Plateau. Annual mean soil respiration and Q 10 in maize were 20% (1.85 vs. 1.54 μmol m −2 s −1 ) and 36% (2.49 vs . 1.83) higher than that in wheat. Nitrogen fertilization resulted in a 35% increase in annual mean soil respiration (1.95 vs. 1.44 μmol m −2 s −1 ) and a 11% decrease in Q 10 (2.05 vs . 2.28) compared with the CK treatment. Soil respiration was positively related to root biomass, whereas no significant relationship was found between root biomass and Q 10 . Therefore, it can be concluded that soil respiration and temperature sensitivity of soil respiration are significantly influenced by crop types and N fertilization regimes, which should be considered in calculating carbon budget in agro-ecosystem using carbon models. [ABSTRACT FROM AUTHOR]