Public Abstract

DE-SC0025299: Incorporating ericoid mycorrhizal shrubs into biogeochemical models

Award Status: Active

Institution: University of Georgia Research Foundation, Inc., Athens, GA
UEI: NMJHD63STRC5
DUNS: 004315578

Most Recent Award Date: 08/28/2024
Number of Support Periods: 1
PM: Stover, Daniel

Current Budget Period: 09/01/2024 - 08/31/2025
Current Project Period: 09/01/2024 - 08/31/2027
PI: Wurzburger, Nina

Supplement Budget Period: N/A

Public Abstract

Incorporating ericoid mycorrhizal shrubs into biogeochemical models Nina Wurzburger, University of Georgia (Principal Investigator) Caitlin Hicks Pries, Dartmouth College (Co-Investigator) Richard Lankau, University of Wisconsin (Co-Investigator) Benjamin Sulman, Oak Ridge National Lab (Unfunded Collaborator) Current biogeochemical frameworks focus on the role of ectomycorrhizal (EcM) and arbuscular mycorrhizal (AM) trees in carbon (C) and nitrogen (N) cycling. Ericaceous shrubs, although smaller in stature, are commonly found in temperate forests, boreal forests, and tundra, but they associate with ericoid mycorrhizal (ErM) fungi. The limited evidence available suggests that ErM shrubs have strong effects on C and N cycling by slowing decomposition and reducing soil N availability. A lack of consideration for ErM shrubs in biogeochemical frameworks could lead to the misattribution of such patterns to forest trees. ErM shrubs are expanding in response to disturbances such as fire exclusion, timber harvesting, and species invasions. Given the prevalence of ErM shrub understories in forests of the eastern US, and the increasing pace of biotic and abiotic disturbances predicted for this region, it is imperative that we understand ErM shrub effects on biogeochemistry to accurately predict changes in soil C and N cycling in response to rapid environmental change. We lack an understanding of which functional attributes of ErM shrubs and ErM fungi drive observed patterns in soils. We hypothesize that there are three main mechanisms by which ErM shrubs affect soil biogeochemical cycles. First, ErM shrub litter is high in tannins that can form complexes with proteins and thereby reduce soil N availability. Second, ErM fungal necromass (dead material) may be higher in melanin than other fungal necromass. Melanin can slow necromass decay and, like tannin from ErM shrub litter, can form organic N complexes. Third, ErM fungi have the ability to mine N from organic matter, and may therefore be able to access N in these organic N complexes putting decomposers and other types of mycorrhizal fungi at a competitive disadvantage. No coordinated experiments have tested how ErM litter tannins, ErM fungal necromass, and ErM fungal N mining affect organic matter formation and plant N acquisition. Our overarching objective is to mechanistically understand how ErM shrubs influence soil C and N cycles. We will use observations across two temperate forests with ErM shrub understories–in North Carolina and Connecticut–and targeted isotopic tracing experiments to tease apart these mechanisms. We will use these data to parameterize and validate a soil biogeochemical model to project the consequences of expanding ErM shrub understories on soil C and N. Our work will address the following specific objectives: Objective 1: Quantify mycorrhizal fungal productivity, turnover and melanin concentration in AM-EcM co-dominated forests with and without an understory of ErM shrubs. Objective 2: Isolate which functional attributes of ErM shrubs and ErM fungi affect soil organic matter formation and plant N uptake within AM-EcM co-dominated forests. Objective 3: Extend and parameterize a plant-mycorrhizal soil C-N model with the addition of the ErM association and use the model to project soil C and N cycling under ErM shrub expansion. We hypothesize that the combination of ErM shrub litter, ErM fungal necromass and ErM fungal mining facilitate ErM shrubs’ disproportionate access to organic N relative to non-ErM plants, while stabilizing decay-resistant material in particulate organic matter. Our proposed research supports DOE ESS objectives. We will expand understanding of plant and microbe interactions in the rhizosphere by testing and modeling the mechanisms by which ErM associations affect soil organic matter formation and N acquisition. Because ErM shrubs are expanding due to disturbances, this research also addresses the effects of rapid environmental change. ErM understory shrubs appear to play a key functional role in biogeochemistry, but are currently poorly represented in models and frameworks. We will quantify the biogeochemical importance of the ErM functional type using observations, experiments, and models to better predict future soil C and N cycling.

Incorporating ericoid mycorrhizal shrubs into biogeochemical models

Nina Wurzburger, University of Georgia (Principal Investigator)

Caitlin Hicks Pries, Dartmouth College (Co-Investigator)

Richard Lankau, University of Wisconsin (Co-Investigator)

Benjamin Sulman, Oak Ridge National Lab (Unfunded Collaborator)

Current biogeochemical frameworks focus on the role of ectomycorrhizal (EcM) and arbuscular mycorrhizal (AM) trees in carbon (C) and nitrogen (N) cycling. Ericaceous shrubs, although smaller in stature, are commonly found in temperate forests, boreal forests, and tundra, but they associate with ericoid mycorrhizal (ErM) fungi. The limited evidence available suggests that ErM shrubs have strong effects on C and N cycling by slowing decomposition and reducing soil N availability. A lack of consideration for ErM shrubs in biogeochemical frameworks could lead to the misattribution of such patterns to forest trees. ErM shrubs are expanding in response to disturbances such as fire exclusion, timber harvesting, and species invasions. Given the prevalence of ErM shrub understories in forests of the eastern US, and the increasing pace of biotic and abiotic disturbances predicted for this region, it is imperative that we understand ErM shrub effects on biogeochemistry to accurately predict changes in soil C and N cycling in response to rapid environmental change.

We lack an understanding of which functional attributes of ErM shrubs and ErM fungi drive observed patterns in soils. We hypothesize that there are three main mechanisms by which ErM shrubs affect soil biogeochemical cycles. First, ErM shrub litter is high in tannins that can form complexes with proteins and thereby reduce soil N availability. Second, ErM fungal necromass (dead material) may be higher in melanin than other fungal necromass. Melanin can slow necromass decay and, like tannin from ErM shrub litter, can form organic N complexes. Third, ErM fungi have the ability to mine N from organic matter, and may therefore be able to access N in these organic N complexes putting decomposers and other types of mycorrhizal fungi at a competitive disadvantage. No coordinated experiments have tested how ErM litter tannins, ErM fungal necromass, and ErM fungal N mining affect organic matter formation and plant N acquisition. Our overarching objective is to mechanistically understand how ErM shrubs influence soil C and N cycles. We will use observations across two temperate forests with ErM shrub understories–in North Carolina and Connecticut–and targeted isotopic tracing experiments to tease apart these mechanisms. We will use these data to parameterize and validate a soil biogeochemical model to project the consequences of expanding ErM shrub understories on soil C and N. Our work will address the following specific objectives:

Objective 1: Quantify mycorrhizal fungal productivity, turnover and melanin concentration in AM-EcM co-dominated forests with and without an understory of ErM shrubs.

Objective 2: Isolate which functional attributes of ErM shrubs and ErM fungi affect soil organic matter formation and plant N uptake within AM-EcM co-dominated forests.

Objective 3: Extend and parameterize a plant-mycorrhizal soil C-N model with the addition of the ErM association and use the model to project soil C and N cycling under ErM shrub expansion.

We hypothesize that the combination of ErM shrub litter, ErM fungal necromass and ErM fungal mining facilitate ErM shrubs’ disproportionate access to organic N relative to non-ErM plants, while stabilizing decay-resistant material in particulate organic matter. Our proposed research supports DOE ESS objectives. We will expand understanding of plant and microbe interactions in the rhizosphere by testing and modeling the mechanisms by which ErM associations affect soil organic matter formation and N acquisition. Because ErM shrubs are expanding due to disturbances, this research also addresses the effects of rapid environmental change. ErM understory shrubs appear to play a key functional role in biogeochemistry, but are currently poorly represented in models and frameworks. We will quantify the biogeochemical importance of the ErM functional type using observations, experiments, and models to better predict future soil C and N cycling.