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Harvard Forest Symposium Abstract 2019

• Title: Resolving controls on lignin decomposition at the continental scale to reconcile classical and modern paradigms of soil organic matter
• Primary Author: Steven Hall (Iowa State University)
• Abstract:

  Lignin is an important component of plant tissues that provides protection from herbivores and pathogens due to its complex chemical structure. When plant tissues die and enter the soil food web, lignin is often among the last components to be decomposed. However, despite the generally slow decay rates of lignin, recent work has suggested that many soils ultimately contain very little lignin-derived carbon in their organic matter. This apparent contradiction presents a key challenge for our understanding of soil organic matter persistence, a topic which is critically linked to environmental services including soil fertility, water quality, and carbon storage. This research seeks to understand the environmental factors that control lignin decay rates and the ultimate contributions of lignin to soil organic matter at sites in the National Ecological Observatory Network (NEON)—including Harvard Forest. In particular, the influence of differences in soil microorganisms and minerals on lignin decomposition across these diverse ecosystems will be assessed.
  
  This research seeks to resolve lingering inconsistencies in the modern paradigm of soil organic matter, where the context-specific importance of lignin may have been neglected due to spatial and methodological sampling biases. Interactions among lignin, soil geochemical characteristics, and microbial community composition may have significant impacts on lignin residence times and mineral sorption that only clearly emerge when examined across continental-scale environmental gradients. Data collected from NEON sites across North America and the Caribbean will be combined with new experiments to test two hypotheses: (1) Lignin decomposition rates and abundance in soil organic matter predictably vary with soil geochemical characteristics and microbial community composition at the continental scale, in contrast to both classical and modern paradigms of soil organic matter; (2) Representations of lignin decomposition and carbon cycling in a state-of-the-art mechanistic ecosystem model can be improved by inclusion of geochemical and microbial parameters, in addition to the traditional variables of climate, residue quality, and nutrient availability. The NEON data will be combined with field and laboratory incubations of carbon isotope-labeled lignins and nuclear magnetic resonance spectroscopic measurements to test these hypotheses.
  

• Research Category: Regional Studies
  Soil Carbon and Nitrogen Dynamics