Plant carbon allocation drives turnover of old soil organic matter in permafrost tundra soils. (17th June 2020)

• Record Type: Journal Article
• Authors: Street, Lorna E.; Garnett, Mark H.; Subke, Jens‐Arne; Baxter, Robert; Dean, Joshua F.; Wookey, Philip A.
• Is Part Of: Global change biology. Volume 26:Number 8(2020)
• Page Start: 4559
• Page End: 4571
• Publication Date: 2020-06-17
• Subjects: arctic -- below‐ground -- isotopes -- mycorrhiza -- priming -- radiocarbon -- rhizosphere -- root -- shrub -- vegetation change; Climatic changes -- Environmental aspects -- Periodicals; Troposphere -- Environmental aspects -- Periodicals; Biodiversity conservation -- Periodicals; Eutrophication -- Periodicals; 551.5
• DOI: 10.1111/gcb.15134
• Languages: English
• ISSNs: 1354-1013

Abstract

Abstract: Carbon cycle feedbacks from permafrost ecosystems are expected to accelerate global climate change. Shifts in vegetation productivity and composition in permafrost regions could influence soil organic carbon (SOC) turnover rates via rhizosphere (root zone) priming effects (RPEs), but these processes are not currently accounted for in model predictions. We use a radiocarbon (bomb‐ 14 C) approach to test for RPEs in two Arctic tall shrubs, alder ( Alnus viridis (Chaix) DC.) and birch ( Betula glandulosa Michx.), and in ericaceous heath tundra vegetation. We compare surface CO2 efflux rates and 14 C content between intact vegetation and plots in which below‐ground allocation of recent photosynthate was prevented by trenching and removal of above‐ground biomass. We show, for the first time, that recent photosynthate drives mineralization of older (>50 years old) SOC under birch shrubs and ericaceous heath tundra. By contrast, we find no evidence of RPEs in soils under alder. This is the first direct evidence from permafrost systems that vegetation influences SOC turnover through below‐ground C allocation. The vulnerability of SOC to decomposition in permafrost systems may therefore be directly linked to vegetation change, such that expansion of birch shrubs across the Arctic could increase decomposition of older SOC. Our results suggest that carbon cycle models that do not include RPEs risk underestimating the carbon cycle feedbacks associated with changing conditions in tundra regions. Abstract : We show, for the first time, that recent plant photosynthate drives mineralisation of older (>50 years old) soil organic carbon (SOC) under birch shrubs and ericaceous heath tundra. By contrast, we find no evidence of rhizosphere priming effects in soils under alder. This is the first direct evidence from permafrost systems that vegetation influences SOC turnover through differences in belowground C allocation.