Abstract Detail

Ecology

Argiroff, William [1], Zak, Donald [1], Pellitier, Peter [2], Upchurch, Rima [1], Belke, Julia [1].

Decay by ectomycorrhizal fungi modifies soil organic matter biochemistry and soil carbon storage.

The interaction between nitrogen (N) availability and microbial decay is an important control over soil organic matter (SOM) dynamics and soil carbon (C) storage. Experimental nitrogen (N) deposition enhances SOM formation and soil C storage by slowing the fungal decay of lignin. However, it remains unclear whether these principles apply to naturallyhigh inorganic N availability, which is instead typically assumed to enhance decay and reduce soil C storage. If naturally high inorganic N availability enhances soil C storage, it could do so through two fungal mechanisms. First, naturally high inorganic N availability could reduce the relative abundance of ligninolytic saprotrophic fungi decaying lignin-rich plant litter (e.g., fine roots), paralleling patterns observed from N deposition experiments. Alternatively, naturally high inorganic N could reduce the relative abundance of ectomycorrhizal (ECM) fungi that produce lignin-degrading peroxidase enzymes, thereby limiting the extent to which ECM fungi decay SOM. We addressed these hypotheses by characterizing SOM biochemistry using pyrolysis gas chromatography-mass spectrometry (py-GC/MS), soil C storage, and fungal community composition using DNA barcoding in soil and decaying fine root litter across a natural gradient of soil inorganic N availability in northern temperate forests.
Lignin-derived SOM (generalized additive mixed model [GAMM]; P = 0.045, n = 68) and soil C (P = 0.016) increased with increasing inorganic N availability, suggesting that high inorganic N availability enhances soil C storage by reducing the decay of lignin-derived compounds. This pattern contrasts with the widespread assumption that naturally high inorganic enhances decay and reduces soil C storage, and therefore represents a novel coupling between the terrestrial C and N cycles that is not currently part of our conceptualizations of SOM dynamics. Surprisingly, this pattern was driven by a reduction in the relative abundance of ECM fungi in soil with peroxidase enzymes encoded in their genomes (P < 0.001). Lignin-derived SOM (P = 0.039) and soil C storage (P = 0.016) were significantly negatively related to the relative abundance of these ECM fungi. By contrast, ligninolytic fungi did not respond to inorganic N availability and were unrelated to lignin-derived SOM and soil C storage (P > 0.05). Thus, our findings provide some of the first evidence that certain ECM fungi directly reduce soil C storage by decaying SOM while liberating organically bound N for their plant hosts. Importantly, this process is contingent on ECM community composition, as only ECM fungi with peroxidases appear able to extensively decay SOM.

1 - University of Michigan, School for Environment and Sustainability, 440 Church St., Ann Arbor, MI, 48109, USA
2 - Stanford University, Department of Biology, 371 Serra Mall, Stanford, CA, 94305, USA

Keywords:
mycorrhizal fungi
saprotrophic fungi
fine roots
nitrogen
lignin
decomposition
soil carbon
plant-soil interactions.

Presentation Type: Oral Paper
Session: ECO8, Ecology: Interactions
Location: /
Date: Friday, July 23rd, 2021
Time: 11:15 AM(EDT)
Number: ECO8006
Abstract ID:460
Candidate for Awards:None