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Nitrogen (N) and phosphorus (P) fertilization has the potential to alter soil respiration temperature sensitivity ( Q 10 ) by changing soil biochemical and crop physiological process. A four-year field experiment was conducted to determine how Q 10 responded to these biochemical and physiological changes in rain-fed agro-ecosystems on the semi-arid Loess Plateau. Soil respiration, as well as biotic and abiotic factors were measured in winter wheat ( Triticum aestivum L.), with three fertilization treatments: (no fertilization (CK), 160 kg N hm − 1 (N), and 160 kg N ha − 1 with 39 kg P ha − 1 (N + P). Mean annual soil respiration rate (calculated by averaging the four years) in the N treatment and N + P treatment was 18% and 48% higher than that in the CK treatment, respectively; and it was increased by 26% (14%–48%) in the N + P treatment as compared with that in the N treatment. The decrease of Q 10 in the N and N + P treatments against the CK treatment was not stable for each year, ranging from 0.01 to 0.28. The maximum decrease of Q 10 in the N and N + P treatments was 10% and 15% in 2014–2015, while in other years the decrease of Q 10 was numerical but not significant. Soil microbial biomass carbon (SMBC) was increased by 10% and 50%, dissolved organic carbon (DOC) was increased by 6% and 21%, and photosynthesis rate was increased ranging from 6% to 33% with N and N + P fertilization. The relative abundance of Acidobacteria, Actinobacteria and Chloroflexi were significantly higher by 32.9%–54.1% in N addition soils (N and N + P) compared to CK treatment, whereas additional P application into soils increased the relative abundance of the family Micrococcaceae, Nocardioidaceae and Chitinophagaceae. Soil respiration was positively related to SMBC, DOC and photosynthesis rate ( p < 0.05). However, variation in Q 10 may be related to the increase of soil mineral N content and variation of the relative abundance of soil microbial community in our study. Nitrogen and additional phosphorus fertilization regimes affect soil respiration and temperature sensitivity differently. [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]

A better understanding of the factors affecting interannual variability in litter respiration is critical to precisely understand local carbon cycling, especially under the changing climate. In this study, litter respiration was obtained by subtracting in situ soil respiration in a control (LCK) treatment by that in a litter removal (LR) treatment for the period 2009–2013 in a 30-year-old black locust plantation ( Robinia pseudoacacia L.) on a ridge slope in a small watershed of Loess Plateau, China. Annual cumulative litter respiration ranged from 48 ± 15 to 165 ± 36 g C m −2 y −1 , with mean value of 113 ± 45 g C m −2 y −1 and coefficient of variation (CV) of 40%; annual contribution rate of litter respiration to total soil respiration (hereafter refer to as litter contribution rate) also exhibited a similar interannual variability (ranged from 8 ± 3% to 20 ± 7%; mean = 15 ± 5%; CV = 31%). Additionally, annual mean soil moisture was highest in 2010 (53.2 ± 8.4% WFPS) and lowest in 2013 (31.4 ± 9.5% WFPS), with mean value of 41.6 ± 7.9% WFPS and CV of 19%; annual litter production rates also exhibited a similar interannual variability (ranged from 379 ± 34 to 565 ± 69 g m −2 y −1 ; mean = 477 ± 71 g m −2 y −1 ; CV = 15%). Annual mean soil moisture was mainly affected by the frequency and distribution of precipitation, and annual litter production rates varied with summer precipitation. Annual cumulative litter respiration and litter contribution rate increased linearly with both annual litter production rates and mean soil moisture content. The contribution of soil water to litter respiration was larger than that of litter production rates. Therefore, litter production rates and soil moisture resulted from precipitation needs to be taken into account for precisely predicting litter respiration in the dryland ecosystems, especially under the changing climate. [ABSTRACT FROM AUTHOR]

The objectives of this study were (i) to determine the stock and distribution of soil organic carbon (SOC) and the quantity and quality of fine root; and (ii) the correlation between SOC stock and fine root quantity and quality in soils of artificial and natural vegetation in the Loess Plateau. Three vegetation types (grassland, shrubland and woodland) and two restoration approaches (artificially and naturally restored from cropland) were investigated in the Yangou watershed of the Loess Plateau. SOC stock, fine root biomass and root C/N ratio at the 0–20, 20–40, 40–60, 60–80, and 80–100 cm depths were determined. The mean SOC stock of natural vegetation at the 0–100 cm depth was significantly greater than that of artificial vegetation, with an increase of 100% for woodland, 15% for shrubland, and 23% for grassland. Natural vegetation restoration led to a significantly greater SOC stock up to a depth of 100 cm for woodland, 40 cm for shrubland, and 40 cm for grassland. The fine root biomass of natural vegetation at the 0–100 cm depth was also significantly greater than that of artificial vegetation, with an increase of 170% for woodland, 140% for shrubland, and 20% for grassland. Natural vegetation restoration led to a significantly greater fine root biomass up to a depth of 100 cm for woodland, 60 cm for shrubland, and only 20 cm for grassland. There was a significant linear correlation between SOC stock and fine root biomass. Thus, natural vegetation restoration could lead to a significantly greater SOC stock, fine root biomass, and fine root C/N ratio than the artificial vegetation restoration. Fine root was an important factor influencing the differences in the SOC stock between artificial and natural vegetation. [ABSTRACT FROM AUTHOR]