ICN Graduate student researches microscopic pioneers of ecosystem succession

by Sarah Castle, University of Montana

When glaciers recede, previously buried land surfaces are exposed that may have been uninhabited by life for thousands of years or more. Substrates closest to the glacial terminus are the youngest while substrates furthest from the terminus are older. In some cases, continually melting glacial ice creates an annually resolved age-gradient. Soil organisms quickly colonize these barren substrates and begin the long process of soil formation that ultimately leads to the development of mature ecosystems. 

Bacteria, fungi, and soil animals are responsible for decomposing organic matter, mineralizing nutrients, weathering primary minerals, and, in some ecosystems, are responsible for a majority of primary production. Despite their importance, we know very little about how communities of soil organisms change with time during succession or whether the process happens differently in various parts of the world. That is to say, do all early successional microbial communities start out with the same community members conducting the same functions? Further, do early developing communities follow the same successional trajectories throughout ecosystem development? 

Measuring how soil biota and the soil environment develop with time in these relatively simple deglaciated landscapes may help us to unravel the relationships between community structure and ecosystem function that may be otherwise obscured in more complex soil systems. 

In order to understand the generality of microbial community succession, we have examined microbial community structure and function along glacial chronosequences in both North and South American continents. Each site is unique in climatic and soil edaphic characteristics that are known to have a strong influence on soil communities. We show that immediately following retreat, soil communities vary dramatically between the geographically distant sites. However, despite very different starting conditions, microbial communities become more alike through time and converge both in terms of which types of microbes are present and how they function. We suspect that this convergence is driven mostly by changes in soil chemistry, specifically changes in soil organic carbon chemistry, which are the result of increasing plant-derived carbon inputs as plants colonize these newly deglaciated lands.  

Glacial retreat is one specialized type of ecosystem disturbance, but there are many other natural and human caused disturbances that influence microbial communities and their functions. The study of natural gradients may offer us some insight into how to maintain and restore degraded systems.

Sarah Castle is a PhD student in Cory Cleveland’s lab (Soil Biogeochemistry) at the University of Montana. As part of the ICN, the Interdisciplinary Collaborative Network, she works with other graduate student researchers to address the need for transformative research by connecting Montana researchers from varying professional levels, universities, and disciplines. Visit interdisciplinarycollaborativenetwork.org

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