Cross-Polarized Magic-Angle Spinning (sup13)C Nuclear Magnetic Resonance Spectroscopic Characterization of Soil Organic Matter Relative to Culturable Bacterial Species Composition and Sustained Biological Control of Pythium Root Rot

Abstract

We report the use of a model system that examines the dynamics of biological energy availability in organic matter in a sphagnum peat potting mix critical to sustenance of microorganism-mediated biological control of pythium root rot, a soilborne plant disease caused by Pythium ultimum. The concentration of readily degradable carbohydrate in the peat, mostly present as cellulose, was characterized by cross-polarized magic-angle spinning 13 C nuclear magnetic resonance spectroscopy. A decrease in the carbohydrate concentration in the mix was observed during the initial 10 weeks after potting as the rate of hydrolysis of fluorescein diacetate declined below a critical threshold level required for biological control of pythium root rot. Throughout this period, total microbial biomass and activity, based on rates of [ 14 C]acetate incorporation into phospholipids, did not change but shifts in culturable bacterial species composition occurred. Species capable of inducing biocontrol were succeeded by pleomorphic gram-positive genera and putative oligotrophs not or less effective in control. We conclude that sustained efficacy of naturally occurring biocontrol agents was limited by energy availability to this microflora within the organic matter contained in the potting mix. We propose that this critical role of organic matter may be a key factor explaining the variability in efficacy typically encountered in the control of pythium root rot with biocontrol agents.

Sustaining Soil Quality in Intensively Managed High Tunnel Vegetable Production Systems: A Role for Green Manures and Chicken Litter

“…These results are important for vegetable growers to consider, because soil microbial activity directly contributes to crop productivity and has potential to help make crop systems more resistant to biotic and abiotic stress. For example, greater microbial activity as measured by FDA hydrolysis has been correlated with potential N mineralization (Drinkwater et al, 1995) and suppression of pathogens in pepper and tomato production (Boehm et al, 1997;Kim et al, 1997aKim et al, , 1997b. Whereas disease was not observed in this study, our results indicate that fertility management does directly influence soil microbial activity, and these changes could potentially influence crop productivity in the presence of pathogens or other plant stress factors.…”

Suppression of Seedling Damping-Off Caused by Pythium ultimum, P. irregulare, and Rhizoctonia solani in Container Media Amended with a Diverse Range of Pacific Northwest Compost Sources

“…For soilless container media amended with composted hardwood bark, Chen and coworkers (5) reported a minimum rate of fluorescein diacetate hydrolysis and minimal level of microbial biomass needed for predictable suppression of P. ultimum. More recently, the potential for organic matter to support suppression of Pythium damping-off has been related to the substrate biological energy availability using carbon 13 cross-polarization magic angle spinning nuclear magnetic resonance spectroscopy and diffuse reflectance Fourier transform infrared spectroscopy (3,43). These methods require laboratory equipment not readily available to compost producers and users; a more accessible and cost-effective method for the industry is needed.…”

Similarity of bacterial communities in sawdust- and straw-amended cow manure composts

“…Cow manure was amended with two different exogenous carbon sources (either straw or sawdust) prior to composting, resulting in mature composts with chemical profiles that differed substantially, particularly with regards to levels of mineral nitrogen. These composts were then amended to peat-based potting mixes to emulate common greenhouse potting mixes [29]. Analyses of bacterial community composition, by PCR-DGGE and sequencing, revealed striking similarities between the two composts, and between potting mixes amended with the composts.…”