Research Focus: We study how roots and soil fungi interact with soils and whole-plant processes to create functional plant strategies.
Our Vision is to fundamentally change how belowground systems are perceived in both basic and applied research communities, highlighting the importance of root and rhizosphere processes to the overall health, resilience, and productivity of terrestrial ecosystems.
Key Words: Fine roots, mycorrhizal fungi, ecosystem ecology, global change biology, forest ecology, plant physiology, drought, urban forestry, ecological modelling, biogeochemistry
Our Vision is to fundamentally change how belowground systems are perceived in both basic and applied research communities, highlighting the importance of root and rhizosphere processes to the overall health, resilience, and productivity of terrestrial ecosystems.
Key Words: Fine roots, mycorrhizal fungi, ecosystem ecology, global change biology, forest ecology, plant physiology, drought, urban forestry, ecological modelling, biogeochemistry
Fine-root dynamics and aboveground-belowground linkages in trees
Figure. The importance and seasonal patterns of leaf emergence, maturation, and senescence are well known for most tree species (spring, summer, fall, winter seasons shown in top panels), but there is relatively little information concerning the patterns and drivers of belowground processes such as root growth and fungal dynamics (bottom panels) in most terrestrial ecosystems.
Together with the leaves and stems that we more commonly observe aboveground, the production and turnover of roots belowground play important roles mediating carbon and nutrient cycling within plants and across terrestrial ecosystems. However, basic patterns of phenology, lifespan, and decomposition of fine roots are poorly understood. In fact, compared to leaves aboveground, we know little about how different plant species allocate resources to build and maintain roots belowground, how temporal patterns in resource allocation to roots are linked with other components of trees and forests, and how these differences manifest diverse strategies for soil resource acquisition across seasons and years. Through long-term observations established in mature forestry plots at The Morton Arboretum as well as through external collaborations, we are working to understand linkages between fine-root dynamics belowground and broader patterns of plant growth and resource investment aboveground. Moreover, we are targeting our observations across a diverse suite of species representing different taxonomic groups, mycorrhizal associations, woody anatomy, fine-root traits, and whole-plant traits. From this we can develop broader understanding of functional plant variation across major plant groups that are especially relevant for the development of terrestrial biosphere models.
Trees and water stress
Figure. Sugar maple leaf showing acute signs of water stress.
Too little and too much water both present challenges to trees. As a result, trees have developed many strategies to adapt to drought and waterlogging conditions. Aspects of physiological, anatomical, and morphological adapations are well studied aboveground. Despite being the primary point of contact between plants and soil water, we have comparatively poor understanding of how roots respond to water stress and and how unique adaptations at the root level can facilite better tree growth under stressful conditions. We are interested to address this knowledge gap and better understand how roots mediate plant responses to drought and waterlogging conditions. We are further interested to use this information to better predict whole-tree responses and inform management of trees in urban environments.
Evolutionary history and global variation in fine-root traits
Figure. Heat map of oak root traits (dark color=larger trait values); taken McCormack et al. 2020, doi: 10.1111/nph.16804
Working with a collaborative group across Europe, China and the North America, this project utilizes an extensive collection of woody plant species at The Morton Arboretum, including many species that are underrepresented in global surveys. We are addressing basic research questions regarding how diverse fine-root strategies have evolved across species, ecosystems, and biomes. We are further interested in how these different strategies impact plant performance, ecosystem nutrient cycling and soil carbon storage. Our recent work has suggested a reduction in plant reliance on symbiotic soil fungi (i.e. mycorrhizal fungi) among more recently derived angiosperm species and these changes within the angiosperm lineage have led to broad shifts in plant strategies for belowground resource acquisition. However, it is unclear if this pattern is consistent across all plants and if the pattern of narrowing fine-root diameter and reduced fungal reliance found in angiosperms is the same with different types of mycorrhizal associations. We also have precious little understanding of how fine-root traits vary at narrower phylogenetic scales (e.g. within genus or species). At present, exceptions to the rule seem nearly as common as the expected pattern itself suggesting that there is much left to be understood and many questions left to be answered.
Functional trade-offs in the root-mycorrhizal symbiosis
Figure. Root tips of pine colonized by the ectomycorrhizal fugus Tuber sp.
The function of fine roots belowground is intricately linked with mycorrhizal fungi reflecting a symbiosis that has existed since shortly after plants emerged on land. With the exchange of carbohydrates from the plant and belowground resources from the fungi, both partners may realize significant benefit. However, the trade-offs and potential advantages of greater or lesser reliance by plants on mycorrhizal fungi are not well understood. At the same time, these trade-off largely determine competitive plant strategies for belowground resource acquisition strategies across environments. Our ongoing work aims to quantify functional trade-offs between fine roots and their mycorrhizal partners recognizing that the relative benefit to each partner likely changes with environmental conditions and based on the individual plant and fungal species involved.
Meet FRED: the Fine-Root Ecology Database
Figure. Distribution of root trait observations in FRED 3.0 across the globe; taken from Iversen and McCormack, https://doi.org/10.1111/nph.17326
Trait-based approaches provide a framework to investigate plant strategies for resource acquisition, growth, and competition, as well as plant impacts on ecosystem processes. Despite significant progress capturing trait variation within and among stems and leaves, identification of trait syndromes within fine-root systems and between fine roots and other plant organs is limited. This empirical roadblock is also partly responsible for the highly simplistic and descriptions of fine-root and belowground ecology in terrestrial biosphere models. With support from the Department of Energy’s Office of Biological and Environmental Research and in collaboration with Oak Ridge National Laboratory and Colleen Iversen, we compiled the Fine-Root Ecology Database (FRED) from published literature and unpublished data. For more information visit the FRED Website.