Soil respiration and its temperature sensitivity in agricultural and afforested poplar plantation systems in northern Alberta
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The effect of land use change from agricultural to short rotation woody crops on soil respiration and its temperature sensitivity is not fully understood. We studied the effect of land use change on soil respiration, in a factorial experiment, 4 years after converting an agricultural field to a Walker poplar (Populus deltoides × Populus × petrowskyana var. Walker) plantation in the boreal region of northeastern Alberta. Overall, total soil respiration was greater in the agricultural plots (planted to alfalfa, Medicago sativa L.) than in the poplar plots. Soil respiration and soil temperature at the 10-cm depth in both land uses had similar seasonal and diurnal variations. The season-long temperature sensitivity (Q10) of daily and nighttime soil respiration in the alfalfa plots was greater than that in the poplar plots, with Q10 values of 5.4 vs. 4.9, respectively. Our data also show that, 4 years after land use conversion, the heterotrophic respiration was smaller in the poplar plots than in the adjacent agricultural plots, indicating potential benefits of plantation establishment in reducing heterotrophic respiration. However, the temperature sensitivity of soil respiration based on monthly nighttime rates, which minimizes the plant phenological influences, was greater in the poplar plantation, suggesting that soil respiration could become greater in the poplar plantation under a future warmer climate. We conclude that establishment of poplar plantations, which are known to have a fast rate of biomass production for long-term carbon storage, may help mitigate climate change by reducing heterotrophic and total soil respiration in the Canadian boreal region, but the long-term implications (e.g., changes in the temperature sensitivity of soil respiration over time) need to be further studied.
KeywordsClimate change Short rotation woody crop Hybrid poplar Land use change Boreal forest Alfalfa Crop rotation
We thank Dan Saurette, Sarah Pattison, Tesfay Teklay, Gary Sargeant, Michelle Marler, Pak Chow, Pete Presant, and others in the Forest Soils laboratory for assistance in the laboratory and field and Dave Kamelchuk at Alberta-Pacific Forest Industries Inc. for assistance in the field. The technical assistance from Professor Andy Black’s group, particularly Zoran Nezic, of the University of British Columbia on the automated soil respiration systems was appreciated. Professor Robert Grant contributed in discussions. We sincerely thank Alberta-Pacific Forest Industries Inc., BIOCAP Canada Foundation, and the Natural Science and Engineering Council of Canada (NSERC) for the financial support for this project. The second author was also partially supported by a scholarship from the University of Alberta. Kangyi Luo assisted in formatting the manuscript. We thank the constructive comments from four anonymous reviewers that substantially improved the quality of an earlier version of this manuscript.
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