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Bicharanloo B, Bagheri Shirvan M, Cavagnaro TR, Keitel C, Dijkstra FA. Nitrogen addition and defoliation alter belowground carbon allocation with consequences for plant nitrogen uptake and soil organic carbon decomposition. Sci Total Environ 2022; 846:157430. [PMID: 35863579 DOI: 10.1016/j.scitotenv.2022.157430] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Revised: 06/29/2022] [Accepted: 07/12/2022] [Indexed: 06/15/2023]
Abstract
Grassland plants allocate photosynthetically fixed carbon (C) belowground to root biomass and rhizodeposition, but also to support arbuscular mycorrhizal fungi (AMF). These C allocation pathways could increase nutrient scavenging, but also mining of nutrients through enhanced organic matter decomposition. While important for grassland ecosystem functioning, methodological constraints have limited our ability to measure these processes under field conditions. We used 13CO2 and 15N pulse labelling methods to examine belowground C allocation to root biomass production, rhizodeposition and AMF colonisation during peak plant growth in a grassland field experiment after three years of N fertilisation (0 and 40 kg N ha-1 year-1) and defoliation frequency treatments ("low" and "high", with 3-4 and 6-8 simulated grazing events per year, mimicking moderate and intense grazing, respectively). Moreover, we quantified the consequences for plant nitrogen (N) uptake and decomposition of soil organic C (SOC). Nitrogen fertilisation increased rhizodeposition and AMF colonisation (by 63 % and 54 %), but reduced root biomass (by 25 %). With high defoliation frequency, AMF colonisation increased (by 60 %), but both root biomass and rhizodeposition declined (by 35 % and 58 %). Plant N uptake was highest without N fertilisation and low defoliation frequency, and positively related to root biomass and the number of root tips. Therefore, when N supply is low and the capacity to produce C through photosynthesis is high, belowground C allocation to root production and associated root tips was important to scavenge for N in the soil. In contrast, the strong positive relationship between the rate of rhizodeposition and SOC decomposition, suggests that rhizodeposition may help plants to mine for nutrients locked in SOC. Taken together, the results of this study suggest that belowground C allocation pathways affected by N fertilisation and defoliation frequency affect plant N scavenging and mining with important consequences for long-term grassland C dynamics.
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Affiliation(s)
- Bahareh Bicharanloo
- Sydney Institute of Agriculture, School of Life and Environmental Sciences, The University of Sydney, Camden, NSW 2570, Australia.
| | - Milad Bagheri Shirvan
- Sydney Institute of Agriculture, School of Life and Environmental Sciences, The University of Sydney, Camden, NSW 2570, Australia
| | - Timothy R Cavagnaro
- School of Agriculture, Food and Wine, The University of Adelaide, Adelaide, SA 5005, Australia
| | - Claudia Keitel
- Sydney Institute of Agriculture, School of Life and Environmental Sciences, The University of Sydney, Camden, NSW 2570, Australia
| | - Feike A Dijkstra
- Sydney Institute of Agriculture, School of Life and Environmental Sciences, The University of Sydney, Camden, NSW 2570, Australia
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Wang R, Bicharanloo B, Shirvan MB, Cavagnaro TR, Jiang Y, Keitel C, Dijkstra FA. A novel 13 C pulse-labelling method to quantify the contribution of rhizodeposits to soil respiration in a grassland exposed to drought and nitrogen addition. New Phytol 2021; 230:857-866. [PMID: 33253439 DOI: 10.1111/nph.17118] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2020] [Accepted: 11/24/2020] [Indexed: 05/21/2023]
Abstract
Rhizodeposition plays an important role in below-ground carbon (C) cycling. However, quantification of rhizodeposition in intact plant-soil systems has remained elusive due to methodological issues. We used a 13 C-CO2 pulse-labelling method to quantify the contribution of rhizodeposition to below-ground respiration. Intact plant-soil cores were taken from a grassland field, and in half, shoots and roots were removed (unplanted cores). Both unplanted and planted cores were assigned to drought and nitrogen (N) treatments. Afterwards, shoots in planted cores were pulse labelled with 13 C-CO2 and then clipped to determine total below-ground respiration and its δ13 C. Simultaneously, δ13 C was measured for the respiration of live roots, soils with rhizodeposits, and unplanted treatments, and used as endmembers with which to determine root respiration and rhizodeposit C decomposition using two-source mixing models. Rhizodeposit decomposition accounted for 7-31% of total below-ground respiration. Drought reduced decomposition of both rhizodeposits and soil organic carbon (SOC), while N addition increased root respiration but not the contribution of rhizodeposit C decomposition to below-ground respiration. This study provides a new approach for the partitioning of below-ground respiration into different sources, and indicates that decomposition of rhizodeposit C is an important component of below-ground respiration that is sensitive to drought and N addition in grassland ecosystems.
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Affiliation(s)
- Ruzhen Wang
- Erguna Forest-Steppe Ecotone Ecosystem Research Station, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, 110016, China
- School of Life and Environmental Sciences, Sydney Institute of Agriculture, The University of Sydney, Camden, NSW, 2570, Australia
| | - Bahareh Bicharanloo
- School of Life and Environmental Sciences, Sydney Institute of Agriculture, The University of Sydney, Camden, NSW, 2570, Australia
| | - Milad Bagheri Shirvan
- School of Life and Environmental Sciences, Sydney Institute of Agriculture, The University of Sydney, Camden, NSW, 2570, Australia
| | - Timothy R Cavagnaro
- School of Agriculture, Food and Wine, The University of Adelaide, PMB 1, Glen Osmond, SA, 5065, Australia
| | - Yong Jiang
- Erguna Forest-Steppe Ecotone Ecosystem Research Station, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, 110016, China
| | - Claudia Keitel
- School of Life and Environmental Sciences, Sydney Institute of Agriculture, The University of Sydney, Camden, NSW, 2570, Australia
| | - Feike A Dijkstra
- School of Life and Environmental Sciences, Sydney Institute of Agriculture, The University of Sydney, Camden, NSW, 2570, Australia
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