Mechanistic drivers of mycorrhizal type effects on soil carbon and nitrogen cycling across scales

Seyfried, Georgia S.

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Description

Title

Mechanistic drivers of mycorrhizal type effects on soil carbon and nitrogen cycling across scales

Author(s)

Seyfried, Georgia S.

Issue Date

2021-12-01

Director of Research (if dissertation) or Advisor (if thesis)

Yang, Wendy

Doctoral Committee Chair(s)

Yang, Wendy

Committee Member(s)

• Kent, Angela
• Dalling, James
• Fraterrigo, Jennifer

Department of Study

Plant Biology

Discipline

Plant Biology

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Ectomycorrhizal fungi
• Arbuscular mycorrhizal fungi
• Soil carbon
• Soil nitrogen
• Tropical forests
• Soil organic matter

Abstract

A large portion of terrestrial carbon (C) and nitrogen (N) are stored in soil organic matter (SOM) yet the factors driving the balance between C and N storage versus loss from SOM remain unclear. Tree-mycorrhizal association has emerged as a promising predictor of SOM dynamics with ECM stands characterized by slow C and N cycling and AM stands characterized by rapid C and N cycling. This dissertation investigates the mechanisms driving formation of distinct mycorrhizal nutrient syndromes at the neighborhood, stand and watershed scales. First, I found that ECM effects on SOM dynamics and N cycling can differ in magnitude and direction between watersheds that differ in soil pH and fertility, demonstrating the potential for intrinsic soil properties to mediate the effects of ECM trees and associated fungi on SOM formation and persistence in the tropics. Second, I found that underlying soil acid-base chemistry can shape fungal communities that lead to variation in ECM effects on SOM accumulation and N cycling. Third, I found that litter chemical quality and environmental conditions mediate the manifestation of slower decomposition in ECM stands such that leaf litter decomposition rates cannot be predicted directly from litter mycorrhizal type or stand mycorrhizal type. Finally, I show that gross N mineralization rates can be greater in ECM relative to AM stands despite slow nitrification and minimal N losses, demonstrating that suppressed mineralization of low quality ECM leaf litter does not directly drive closed N cycling in ECM stands. This work revealed the central role of environmental and geologic context in determining the mechanisms driving ectomycorrhizal (ECM) effects at spatial scales from individual trees to forest stands to watersheds. I conclude that the mechanisms driving mycorrhizal effects can vary across ecosystems, informing efforts to predict mycorrhizal effects at the global scale.

Graduation Semester

2021-12

Type of Resource

Thesis

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Copyright 2021 Georgia Seyfried

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