Periodic Reporting for period 1 - MYCO-SoilC (Mycorrhizal Types and Soil Carbon Storage: A mechanistic theory of fungal mediated soil organic matter cycling in temperate forests)
Okres sprawozdawczy: 2022-06-01 do 2024-11-30
The world's soils are the largest terrestrial reservoir of organic carbon (C). Feedbacks between soil organic C and atmospheric CO2 will determine the future trajectory of climate change. However, predictions are largely uncertain because we still lack fundamental knowledge of the complex interplay between plants and microorganisms and its influence on C turnover.
Most terrestrial plants live in symbiosis with mycorrhizal fungi. Previous work suggests that on a global scale soil C stocks are linked to the distribution of arbuscular mycorrhizal (AM) or ectomycorrhizal (ECM) plants. To date, it is not clear whether there is a causal relationship between mycorrhizal type and soil C storage. Answering this key question requires novel concepts that consider the mechanistic link between short-term C fluxes from plants to mycorrhizal fungi and C storage as an emerging ecosystem property.
MYCO-SoilC will yield a comparative, systematic understanding of the dynamics of C input by mycorrhizal fungi to soil, their effects on C turnover and their implications for C storage in temperate forests dominated by AM or ECM trees. Achieving this ambitious goal, which involves a multitude of processes on different spatio-temporal scales, requires the development of ground-breaking technological innovations. Key innovations of MYCO-SoilC are 1) real-time visualization of 11C allocation in plant-soil systems, 2) construction of the first moving greenhouse for 13CO2-labeling of mini-forests, 3) coupling of quantum dot nanotechnology with isotope labeling to visualize organic nutrient uptake by fungi and 4) combining isotope analysis with biomarker approaches to quantify the fungal necromass contribution to soil C. MYCO-SoilC will create substantial knowledge on mycorrhizal mediated C turnover and facilitate predictions of soil-climate feedbacks.
Most terrestrial plants live in symbiosis with mycorrhizal fungi. Previous work suggests that on a global scale soil C stocks are linked to the distribution of arbuscular mycorrhizal (AM) or ectomycorrhizal (ECM) plants. To date, it is not clear whether there is a causal relationship between mycorrhizal type and soil C storage. Answering this key question requires novel concepts that consider the mechanistic link between short-term C fluxes from plants to mycorrhizal fungi and C storage as an emerging ecosystem property.
MYCO-SoilC will yield a comparative, systematic understanding of the dynamics of C input by mycorrhizal fungi to soil, their effects on C turnover and their implications for C storage in temperate forests dominated by AM or ECM trees. Achieving this ambitious goal, which involves a multitude of processes on different spatio-temporal scales, requires the development of ground-breaking technological innovations. Key innovations of MYCO-SoilC are 1) real-time visualization of 11C allocation in plant-soil systems, 2) construction of the first moving greenhouse for 13CO2-labeling of mini-forests, 3) coupling of quantum dot nanotechnology with isotope labeling to visualize organic nutrient uptake by fungi and 4) combining isotope analysis with biomarker approaches to quantify the fungal necromass contribution to soil C. MYCO-SoilC will create substantial knowledge on mycorrhizal mediated C turnover and facilitate predictions of soil-climate feedbacks.
To study the role of mycorrhizal types in soil carbon (C) storage, the first two years of the project were largely devoted to the development and implementation of novel innovative technologies. To trace C flux from the atmosphere through plants to mycorrhizal mycelium and ultimately to the soil or back to the atmosphere, experimental setups ranging from microcosms (Petri dishes), pots, and mesocosms (lysimeters) to field conditions have been established.
In microcosms, we investigated the carbon use efficiency (CUE) of various fungal species, including both saprotrophs and ectomycorrhizal fungi, depending on substrate quality and nutrient availability. A system using isotope labeling coupled with cavity ring-down spectrometry to measure real-time fungal respiration was developed to estimate CUE. Additionally, methods to extract representative sample solutions from the medium in Petri dishes were tested and established for measuring hydrolytic and oxidative enzyme activities. This will help to elucidate the decomposition mechanisms of individual fungi depending on chemistry of the substrates provided.
Using 13C-CO2 pulse labeling of plants in pots combined with high-time resolution measurements of soil CO2 and its isotopic composition, we acquired data for modeling C allocation within the plant-soil system. The modeling exercise was conducted in collaboration with project partners at the TUM, Munich, Germany. A first version of the model is established and will further be refined and validated with data from laboratory experiments.
The model will later be used to predict C allocation in mini-forest experiments. The MYCO-SoilC mini-forests are established. They consist of ten tree species, half of which have arbuscular mycorrhizal associations and the other half have ectomycorrhizal associations. A newly developed system for 13C-CO2 pulse labeling of trees in the mini-forests allow us to trace C allocation from trees to fungal partners and soil over three consecutive years. The flux of 13C via mycorrhizal mycelium to soil organic matter fractions (particulate and mineral-associated organic matter) will further be studied, aiming to understand the contributions of different mycorrhizal types and fungal residues to soil C stabilization.
Together with partners from the Indiana University Bloomington, USA, we conducted research to examine how different mycorrhizal types contribute to soil carbon stabilization and the formation of mineral-associated organic matter in a temperate forest. To estimate the contribution of mycorrhizal fungal residues to particulate and mineral-associated organic matter, we informed Bayesian mixing models with 13C and 15N natural abundances of particulate and mineral-associated organic matter sources, i.e. leaves, roots, arbuscular mycorrhizal hyphae, ectomycorrhizal and saprotrophic sporocarps. Overall, our results suggest fungal, not plant residues, as the main source of mineral-associated organic matter in temperate forests and highlight the critical role of mycorrhizal types for soil C stabilization.
In microcosms, we investigated the carbon use efficiency (CUE) of various fungal species, including both saprotrophs and ectomycorrhizal fungi, depending on substrate quality and nutrient availability. A system using isotope labeling coupled with cavity ring-down spectrometry to measure real-time fungal respiration was developed to estimate CUE. Additionally, methods to extract representative sample solutions from the medium in Petri dishes were tested and established for measuring hydrolytic and oxidative enzyme activities. This will help to elucidate the decomposition mechanisms of individual fungi depending on chemistry of the substrates provided.
Using 13C-CO2 pulse labeling of plants in pots combined with high-time resolution measurements of soil CO2 and its isotopic composition, we acquired data for modeling C allocation within the plant-soil system. The modeling exercise was conducted in collaboration with project partners at the TUM, Munich, Germany. A first version of the model is established and will further be refined and validated with data from laboratory experiments.
The model will later be used to predict C allocation in mini-forest experiments. The MYCO-SoilC mini-forests are established. They consist of ten tree species, half of which have arbuscular mycorrhizal associations and the other half have ectomycorrhizal associations. A newly developed system for 13C-CO2 pulse labeling of trees in the mini-forests allow us to trace C allocation from trees to fungal partners and soil over three consecutive years. The flux of 13C via mycorrhizal mycelium to soil organic matter fractions (particulate and mineral-associated organic matter) will further be studied, aiming to understand the contributions of different mycorrhizal types and fungal residues to soil C stabilization.
Together with partners from the Indiana University Bloomington, USA, we conducted research to examine how different mycorrhizal types contribute to soil carbon stabilization and the formation of mineral-associated organic matter in a temperate forest. To estimate the contribution of mycorrhizal fungal residues to particulate and mineral-associated organic matter, we informed Bayesian mixing models with 13C and 15N natural abundances of particulate and mineral-associated organic matter sources, i.e. leaves, roots, arbuscular mycorrhizal hyphae, ectomycorrhizal and saprotrophic sporocarps. Overall, our results suggest fungal, not plant residues, as the main source of mineral-associated organic matter in temperate forests and highlight the critical role of mycorrhizal types for soil C stabilization.
The overarching goal of MYCO-SoilC is to understand the role of mycorrhizal fungi in soil C storage. The research programm is driven by the need to gain detailed knowledge of mycorrhizal-mediated soil organic matter turnover, which is of utmost importance for predicting feedbacks between soil C sequestration and atmospheric CO2, and hence, the future trajectory of climate change.
The progress made so far, which goes beyond the state of the art, has been tackled regarding the three following central research question:
1) How do different mycorrhizal types affect the dynamics of plant C input to soil?
The impact of mycorrhizal types on plant C allocation and C input to soil has remained the largely unexplored hidden side of forest ecology despite its significance for soil C storage. In MYCO-SoilC, we investigate differences between AM and ECM trees in their dynamics of C allocation and C input to the soil with consequences for soil C cycling.
2) What are the mechanisms of AM and ECM fungi to decompose soil organic matter?
The mechanistic link between the impact of distinct mycorrhizal types and saprotrophic microorganisms (i.e. facilitation and suppression) and the decomposition of soil organic matter remains largely unknown. To shed light on the role of mycorrhizal fungi for soil organic matter decomposition, we focus our research activities on a process-based understanding of interactions in distinct tree-fungus combinations.
3) What is the contribution of AM and ECM fungal residues to mineral-associated organic matter?
We still lack crucial knowledge about the contribution of plant and microbial residues to the mineral-associated organic matter pool in forests dominated by AM and ECM trees. The history of facilitation and suppression of saprotrophs by mycorrhizal fungi may be reflected in the composition of C compounds sorbed to minerals. Using Bayesian mixing models informed with natural abundance isotope data, and detailed decomposition studies on isotopically labeled fungal necromass and plant litter, we aim to show that the composition of mineral-associated organic matter is an emerging ecosystem property governed by mycorrhizal types as mediators of soil C cycling.
The outcomes of MYCO-SoilC will help to explain observations at the ecosystem scale and to improve the representation of soil organic matter dynamics influenced by plant-fungal interactions in ecosystem and Earth system models to enhance their predictive capabilities.
The progress made so far, which goes beyond the state of the art, has been tackled regarding the three following central research question:
1) How do different mycorrhizal types affect the dynamics of plant C input to soil?
The impact of mycorrhizal types on plant C allocation and C input to soil has remained the largely unexplored hidden side of forest ecology despite its significance for soil C storage. In MYCO-SoilC, we investigate differences between AM and ECM trees in their dynamics of C allocation and C input to the soil with consequences for soil C cycling.
2) What are the mechanisms of AM and ECM fungi to decompose soil organic matter?
The mechanistic link between the impact of distinct mycorrhizal types and saprotrophic microorganisms (i.e. facilitation and suppression) and the decomposition of soil organic matter remains largely unknown. To shed light on the role of mycorrhizal fungi for soil organic matter decomposition, we focus our research activities on a process-based understanding of interactions in distinct tree-fungus combinations.
3) What is the contribution of AM and ECM fungal residues to mineral-associated organic matter?
We still lack crucial knowledge about the contribution of plant and microbial residues to the mineral-associated organic matter pool in forests dominated by AM and ECM trees. The history of facilitation and suppression of saprotrophs by mycorrhizal fungi may be reflected in the composition of C compounds sorbed to minerals. Using Bayesian mixing models informed with natural abundance isotope data, and detailed decomposition studies on isotopically labeled fungal necromass and plant litter, we aim to show that the composition of mineral-associated organic matter is an emerging ecosystem property governed by mycorrhizal types as mediators of soil C cycling.
The outcomes of MYCO-SoilC will help to explain observations at the ecosystem scale and to improve the representation of soil organic matter dynamics influenced by plant-fungal interactions in ecosystem and Earth system models to enhance their predictive capabilities.