MARY A. TOPA, PHD
Adjunct Professor of Biology
Research Interests
The biotic and abiotic interactions that occur between tree roots and the soil rhizosphere environment are easily the most complex and least understood interactions in plants. The opacity of the soil and complex nature of the root/rhizosphere biotic system pose unique challenges to tree biologists studying below-ground biodiversity and root system (roots plus rhizosphere biota) function. The technological difficulty in monitoring in situ root system function has resulted in a markedly biased understanding of “whole-tree” and ecosystem function that is often defined solely by shoot characteristics, or is a derivation of highly controlled seedling and mesocosm studies. However, to scale from seedlings to mature trees, root system biologists must consider how root growth, development and function change as seedlings mature in situ, and how biodiversity of rhizosphere microorganisms in the field alters tree root system function. As a seedling ages, whole-plant source/sink relationships for both nutrients and carbon change, with growth and metabolism relying more on carbon and nutrient stores than recently-acquired resources. As a seedling matures into a sapling and a tree, its roots will modify the physical, chemical and microbiological characteristics of its soil environment to enhance acquisition of limiting soil resources or to survive soil environmental stresses.
My current and long-range research interests focus on the following areas, with an emphasis on examining in situ root system function, in particular, how: 1) Root systems of long-lived perennials respond to natural edaphic stresses and resource heterogeneity, and anthropogenic stresses, 2) Root system responses may account for the wide variation in above-ground growth that is generally observed in tree populations, and 3) Rhizophere biota alter root system and belowground ecosystem function.
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