Masters Theses
Date of Award
12-2019
Degree Type
Thesis
Degree Name
Master of Science
Major
Microbiology
Major Professor
Jennifer DeBruyn
Committee Members
Alison Buchan, Todd Reynolds, Mark Radosevich
Abstract
Plastic mulch films have become widely used in agriculture for altering the soil’s microclimate, lowering water-use, suppressing weed growth, and increasing crop production. The most commonly used plastic mulch films are made from low-density polyethylene plastic (PE mulch). However, the disposal of used PE mulch has resulted in an environmental issue as they are not degradable, nor readily recyclable. Using biodegradable-plastic mulch films (BDMs) provides an alternative to PE mulches, as BDMs are made to be soil degradable or compostable. However, in situ film breakdown is unpredictable, and information on how BDMs influence soil health in the long-term is missing; both becoming barriers for its wide adoption. Soil microorganisms breakdown BDMs, but knowledge about how buried mulch fragments alter soil microbial community remains limited. Across two diverse locations in USA, we used and incorporated into the soil four BDMs, a PE mulch, and paper mulch treatments for four growing seasons. After the first growing season, we took weathered mulch fragments, placed them in 250 micrometer-size meshbags, and buried them 10 to 20 cm deep in our plot rows. After these four years, we sampled bulk soil and the buried mulch fragments inside meshbags for all the available treatments. To determine alterations in microbial community composition and activity, we analyzed total bacterial and fungal abundance, sequenced bacterial community 16S rRNA gene for both samples, and assayed extracellular enzyme activity on the soil samples. Our analysis indicated that mulch treatment did not alter microbial abundance, or enzyme activity of the bulk soil. However, buried mulches had a higher bacterial abundance, and a more specialized community compared to bulk soil. Bradyrhizobium sp. and Nocardioides sp. were some of the bacteria found to be more enriched on the buried mulch fragments. Our results indicate that over four years of use and till-down, BDM use did not significantly alter soil microbial community or several extracellular soil enzyme activities. In addition, the buried mulch pieces carry a specialized community with some taxa which may degrade plastic. This work lays the groundwork for other experiments that further elucidate microbial interactions with buried plastic.
Recommended Citation
Liquet y Gonzalez, Jose, "Effects of long-term use and incorporation of biodegradable plastic mulch films on soil microbial community structure and activity. " Master's Thesis, University of Tennessee, 2019.
https://trace.tennessee.edu/utk_gradthes/5573