Contrasting responses of soil respiration and temperature sensitivity to land use types: Cropland vs. apple orchard on the Chinese Loess Plateau

Land use plays an essential role in regional carbon cycling, potentially influencing the exchange rates of CO2 flux between soil and the atmosphere in terrestrial ecosystems. Temperature sensitivity of soil respiration (Q(10)), as an efficient parameter to reflect the possible feedback between the global carbon cycle and climate change, has been extensively studied. However, very few reports have assessed the difference in temperature sensitivity of soil respiration under different land use types. In this study, a three-year field experiment was conducted in cropland (winter wheat, Triticum aestivum L.) and apple orchard (Malus domestica Borkh) on the semi-arid Loess Plateau from 2011 to 2013. Soil respiration (measured using Li-Cor 8100), bacterial community structure (represented by 16S rRNA), soil enzyme activities, and soil physicochemical properties of surface soil were monitored. The average annual soil respiration rate in the apple orchard was 12% greater than that in the cropland (2.01 vs. 1.80 mu mol m(-2) s(-1)), despite that the average Q(10) values in the apple orchard was 15% lower than that in the cropland (ranging from 1.63 to 1.41). As to the differences among predominant phyla, Proteobacteria was 26% higher in the apple orchard than that in the cropland, whereas Actinobacteria and Acidobacteria were 18% and 36% lower in the apple orchard. The beta-glucosidase and cellobiohydrolase activity were 15% (44.92 vs. 39.09 nmol h(-1) g(-1)) and 22% greater (21.39 vs. 17.50 nmol h(-1) g(-1)) in the apple orchard than that in the cropland. Compared to the cropland, the lower Q(10) values in the apple orchard resulted from the variations of bacterial community structure and beta-glucosidase and cellobiohydrolase activity. In addition, the lower C: N ratios in the apple orchard (6.50 vs. 8.40) possibly also contributed to its lower Q(10) values. Our findings call for further studies to include the varying effects of land use types into consideration when applying Q(10) values to predict the potential CO2 efflux feedbacks between terrestrial ecosystems and future climate scenarios. (C) 2017 Elsevier B.V. All rights reserved