Plant-biochar interactions drive the negative priming of soil organic carbon in an annual ryegrass field system |
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| Institution: | 1. School of Environmental and Rural Sciences, University of New England, Armidale, NSW 2351, Australia;2. NSW Department of Primary Industries, Wollongbar Primary Industries Institute, Wollongbar, NSW 2477, Australia;3. NSW Department of Primary Industries, Elizabeth Macarthur Agricultural Institute, Woodbridge Rd, Menangle, NSW 2568, Australia;4. NSW Department of Primary Industries/University of New England, Armidale, NSW 2351, Australia;5. CSIRO Agriculture, Waite Campus, Glen Osmond, SA 5064, Australia;1. University of Zurich, Department of Geography, Winterthurerstrasse 190, 8057 Zurich, Switzerland;2. Swedish University of Agricultural Sciences, Uppsala BioCentre, Department of Chemistry, Box 7015, 750 07 Uppsala, Sweden;3. University of Florence, Department of Plant, Soil and Environmental Sciences, Piazzale delle Cascine 18, 50144 Florence, Italy;1. Faculty of Agriculture and Environment, The University of Sydney, NSW 2006, Australia;2. NSW Department of Primary Industries, Elizabeth Macarthur Agricultural Institute, Menangle, NSW 2568, Australia;1. Soil and Crop Sciences, School of Integrative Plant Science, Cornell University, Ithaca, NY 14850, USA;2. Department of Soil Science, University of Wisconsin, Madison, WI 53706, USA;3. Atkinson Center for a Sustainable Future, Cornell University, Ithaca, NY 149850, USA;1. Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN 47907, USA;2. Purdue Climate Change Research Center, Purdue University, West Lafayette, IN 47907, USA;3. School of Earth and Environmental Sciences, Queens, College, City University of New York, Flushing, NY 11367, USA;4. Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109, USA;5. Department of Agronomy, Purdue University, West Lafayette, IN 47906, USA;1. Faculty of Agriculture and Environment, The University of Sydney, NSW 2006, Australia;2. NSW Department of Primary Industries, Elizabeth Macarthur Agricultural Institute, Menangle, NSW 2568, Australia |
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| Abstract: | There is a knowledge gap on biochar carbon (C) longevity and its priming effects on soil organic carbon (SOC) and recent root-derived C under field conditions. This knowledge would allow the potential of biochar in long-term soil C sequestration to be established. However, most studies on biochar C longevity and its priming effect have been undertaken in plant-free laboratory incubations.A 388 d field study was carried out in the presence of an annual ryegrass (C3) growing on a rhodic ferralsol with established C3/C4 plant-derived SOC (δ13C: ?20.2‰) in a subtropical climate. A 13C-depleted hardwood biochar (δ13C: ?35.7‰, produced at 450 °C) was applied at 0 and 30 dry t ha?1 and mixed into the top 100-mm soil profile (equivalent to 3% w/w). We report on the differentiation and quantification of root respiration and mineralisation of soil-C and biochar-C in the field. Periodic 13CO2 pulse labelling was applied to enrich δ13C of root respiration during two separate winter campaigns (δ13C: 151.5–184.6‰) and one summer campaign (δ13C: 19.8–31.5‰). Combined soil plus root respiration was separated from leaf respiration using a novel in-field respiration collar. A two-pool isotope mixing model was applied to partition three C sources (i.e. root, biochar and soil). Three scenarios were used to assess the sensitivity associated with the C source partitioning in the planted systems: 1) extreme positive priming of recent SOC derived from the current ryegrass (C3) pasture; 2) equivalent magnitude of priming of SOC and labile root C; and 3) extreme positive priming of the native C4-dominant SOC.We showed that biochar induced a significant negative priming of SOC in the presence of growing plants but no net priming was observed in the unplanted soil. We also demonstrated the importance of experimental timeframe in capturing the transient nature of biochar-induced priming, from positive (day 0–62) to negative (day 62–388). The presence/absence of plants had no impact on biochar-C mineralisation in this ferralsol during the measurement period. Based on a two-pool exponential model, the mean residence time (MRT) of biochar varied from 351 to 449 years in the intensive pasture system to 415–484 years in the unplanted soils. |
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| Keywords: | Biochar C longevity Root respiration Mean residence time Three-pool C source partitioning |
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