Mycobiont contribution to tundra plant acquisition of permafrost-derived nitrogen
Abstract
As arctic soils warm, newly thawed permafrost releases nitrogen (N) that could stimulate plant productivity and thus offset soil carbon (C) losses from tundra ecosystems. The role of mycorrhizal fungi in providing plants access to N from cold, newly thawed permafrost soils is unknown. We characterized depth profiles of ecto- and ericoid mycorrhizal fungi (EMF and ERM) on roots and soil fungal communities at the thaw front below the maximum rooting depth of host plants in tussock and shrub vegetation communities at Eight Mile Lake, Alaska. We tested the relationships between root and deep soil fungal composition and plant uptake of an isotopically labeled 15N tracer applied at the permafrost boundary at maximum active layer thaw. Fungal composition was characterized by DNA and RNA sequencing of the internal transcribed spacer gene region. Plant acquisition of the deep 15N tracer was quantified using Isotope Ratio Mass Spectrometry. Deep soil communities at the thaw front occurred at 73 ± 5 cm depth in tussock tundra and 46 ± 2 cm depth in shrub tundra; while the maximum rooting depth of the host plants ranged from 23-41 cm depth across these two vegetation communities. There was strong continuity between deep, thawed soil RNA and DNA profiles demonstrating that deep fungal DNA communities are mostly active rather than representing a dormant spore bank (A = 0.018). Of 709 deep soil fungal taxa, 142 were mycorrhizal. Of the 194 mycorrhizal taxa observed in the root community, 72 were observed at the thaw front, providing evidence of mycelial connectivity between shallow root systems and the thaw front environment. The occurrence of EMF and ERM in RNA profiles of deep soil fungi beyond the deepest roots of their host plants demonstrates the potential for mycobionts to access deep permafrost N late in the growing season when the thaw front is deepest. There was gradual assimilation of tracer by EMF and ERM host plants the year after tracer addition. This may indicate immediate fungal immobilization of tracer and subsequent transfer to host plants as foliar sink strength increases over the growing season. Thus, the mycorrhizal symbiosis may be a mechanism for the vertical redistribution of deep, permafrost-derived nutrients in tussock and shrub tundra with the potential to fertilize tundra as it warms.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.B43M3008H
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 0476 Plant ecology;
- BIOGEOSCIENCESDE: 0486 Soils/pedology;
- BIOGEOSCIENCESDE: 1630 Impacts of global change;
- GLOBAL CHANGE