PS 19-25
Microbial and allelopathic effects on weed suppressions
Bio-control approaches, such as the introduction of allelochemicals and microbial antagonists, may be important tools to manage weed with low environmental risk. Incorporation the cover crop residues to release allelochemicals shortly before crop sowing can suppress early-season weed germination and offer a competitive advantage for crops. The overall effects of weed suppression depend on the multiple microbial roles in the release and transformation of phytotoxic compounds as well as acting as weed pathogens, and these roles may change over time. Thus, it is critical to know the strengths of each microbial role and the dynamic changes of microbe- and allelochemical-induced suppression after residue incorporation. Residue incorporation experiments were conducted by incorporating water-soluble chemicals, residues after water extraction and fresh residues with sterilized and non-sterilized soil in a time series experiment. Weed germination rate and radicle length were measured in seed germination bioassays. Allelopathic phenolic compounds were extracted from soil and the total content was measured by Folin-Ciocalteu method. The dynamic changes of allelopathic weed inhibitions on germination and radicle length were described by negative exponential decay functions. Structural equation modeling (SEM) were used to partition multiple effects of microbes and allelochemicals and quantify their effects magnitude.
Results/Conclusions
Without allelochemicals, microbes reduced weed germination rate and radicle growth rate by 50%. However, in the presence of allelochemicals, microbial activity reduced the potency of these chemicals such that they no longer suppressed weed germination or growth after two days. In comparison, slow, microbe-assisted release of allelochemicals from fresh residues extended their period of effective weed suppression to 30 days post incorporation. As direct antagonists to weed seedlings, microbial infection significantly reduced seedling growth (P-value <0.001). SEM showed that overall microbial antagonistic effects were secondary to that of allelopathy, and these antagonistic effects were offset by the detoxification of allelochemicals. But microbial roles dynamic changed during residue decomposition, microbial roles shifted from detoxification in high allelopathic environment to direct pathogenicity in low allelopathic environment. This work suggests that microbial community could be manipulated to optimize weed suppression potential.