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

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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Plant Biology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2022

Author dc:creator

• Seyfried, Georgia S.

Contributors dc:contributor

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

• Plant biology

Statement dc:rights

• Copyright 2021 Georgia Seyfried

Language dc:language

en, eng

Handle dc:identifier

http://hdl.handle.net/2142/113869

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F113869