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Title:Interactions between cover crop residue and microbial community affect weed suppression
Author(s):Lou, Yi
Director of Research:Yannarell, Anthony
Doctoral Committee Chair(s):Kent, Angela
Doctoral Committee Member(s):Davis, Adam; Leakey, Andrew
Department / Program:Natural Resources & Environmental Sciences
Discipline:Natural Resources & Environmental Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):Microbial ecology
Weed suppression
Cover crop
Abstract:The environmental and health risks from the use of herbicides have led to interest in developing alternative methods for agricultural weed control. Incorporation of cover crop residues is an important approach that contributes to alternative weed management systems. The cover crop residue-associated allelochemicals can inhibit weed germination, growth and production. Soil microbial communities are especially important for the allelochemical potential of a cover crop residue, because microorganisms can modify residues and allelochemicals to make them more or less phytotoxic. In addition to their effects on allelochemicals, soil microbial communities can also directly suppress weeds. To improve weed biocontrol, it is critical to understand how soil microorganisms interact with cover crop residues to suppress weed. The goal of this dissertation is to evaluate the contributions of microbes, cover crop residues, and their interactions to weed suppression. The first experiment examined the temporal dynamics of weed suppression over time to determine the microbial suppression, residue suppression, and their interactions. Results show that microbial activity directly suppressed weed germination and seedling growth, but also indirectly helped weeds by degrading cover crop-derived allelochemicals. These results suggest that the weed suppression shifted from a predominantly chemical phase to a predominantly microbial phase. To identify putative weed suppressive microbes, the microbial communities associated with diseased and stunted seedlings were characterized, and organisms present were examined for desirable weed suppressive traits. The identified putative weed suppressive microbes can be considered as a starting point for future selection of biocontrol agents. To determine the effects of management practices on weed suppression, I investigated the interactions between microbial communities and cover crop residues in three agricultural management systems (tillage, no tillage and organic system). Overall, the organic and tillage management systems offered higher microbial and cover crop-derived weed suppression than the no-tillage system. Different microbial communities were associated with dead seeds and diseased seedlings. These microbes also differed among the three agricultural management systems. This result indicates the potential of managing the soil microbiome for desirable weed suppression. The cover crop associated allelochemicals negatively affected microbial attacks to seedlings. However, the allelochemicals also induced seedling leakage that made seedling more susceptible to microbial attacks by triggering microbial chemotactic behaviors. Understanding how soil microbial communities interact with cover crop residues in agricultural systems has important implications for the weed biocontrol strategies. This dissertation suggests that naturally occurring soil microbial communities can be used and managed for sustainable weed control in agricultural systems.
Issue Date:2015-12-01
Type:Thesis
URI:http://hdl.handle.net/2142/89211
Rights Information:Copyright 2015 Yi Lou
Date Available in IDEALS:2016-03-02
Date Deposited:2015-12


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