Isotopic evidence for increased carbon and nitrogen exchanges between peatland plants and their symbiotic microbes with rising atmospheric CO2 concentrations since 15,000 cal. year BP |
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Authors: | Qiannan Yang Ziping Liu Benjamin Z Houlton Decai Gao Qing Chang Hongkai Li Xianlei Fan Bai Liu Edith Bai |
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Institution: | 1. Key Laboratory of Geographical Processes and Ecological Security of Changbai Mountains, Ministry of Education;2. School of Geographical Sciences, Northeast Normal University, Changchun, China;3. Department of Ecology and Evolutionary Biology and Department of Global Development, Cornell University, Ithaca, New York, USA |
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Abstract: | Whether nitrogen (N) availability will limit plant growth and removal of atmospheric CO2 by the terrestrial biosphere this century is controversial. Studies have suggested that N could progressively limit plant growth, as trees and soils accumulate N in slowly cycling biomass pools in response to increases in carbon sequestration. However, a question remains over whether longer-term (decadal to century) feedbacks between climate, CO2 and plant N uptake could emerge to reduce ecosystem-level N limitations. The symbioses between plants and microbes can help plants to acquire N from the soil or from the atmosphere via biological N2 fixation—the pathway through which N can be rapidly brought into ecosystems and thereby partially or completely alleviate N limitation on plant productivity. Here we present measurements of plant N isotope composition (δ15N) in a peat core that dates to 15,000 cal. year BP to ascertain ecosystem-level N cycling responses to rising atmospheric CO2 concentrations. We find that pre-industrial increases in global atmospheric CO2 concentrations corresponded with a decrease in the δ15N of both Sphagnum moss and Ericaceae when constrained for climatic factors. A modern experiment demonstrates that the δ15N of Sphagnum decreases with increasing N2-fixation rates. These findings suggest that plant-microbe symbioses that facilitate N acquisition are, over the long term, enhanced under rising atmospheric CO2 concentrations, highlighting an ecosystem-level feedback mechanism whereby N constraints on terrestrial carbon storage can be overcome. |
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Keywords: | elevated CO2 Holocene mycorrhizal fungi nitrogen fixation northern peatlands Pleistocene Sphagnum moss δ15N |
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