W K Ma

Publications (3)3.69 Total impact

• Article: Soil formate regulates the fungal nitrous oxide emission pathway.

  W K Ma, R E Farrell, S D Siciliano
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  ABSTRACT: Fungal activity is a major driver in the global nitrogen cycle, and mounting evidence suggests that fungal denitrification activity contributes significantly to soil emissions of the greenhouse gas nitrous oxide (N(2)O). The metabolic pathway and oxygen requirement for fungal denitrification are different from those for bacterial denitrification. We hypothesized that the soil N(2)O emission from fungi is formate and O(2) dependent and that land use and landforms could influence the proportion of N(2)O coming from fungi. Using substrate-induced respiration inhibition under anaerobic and aerobic conditions in combination with (15)N gas analysis, we found that formate and hypoxia (versus anaerobiosis) were essential for the fungal reduction of (15)N-labeled nitrate to (15)N(2)O. As much as 65% of soil-emitted N(2)O was attributable to fungi; however, this was found only in soils from water-accumulating landforms. From these results, we hypothesize that plant root exudates could affect N(2)O production from fungi via the proposed formate-dependent pathway.
  Applied and environmental microbiology 10/2008; 74(21):6690-6. · 3.69 Impact Factor
• Article: Relationship between nitrifier and denitrifier community composition and abundance in predicting nitrous oxide emissions from ephemeral wetland soils

  W.K. Ma, A. Bedard-Haughn, S.D. Siciliano, R.E. Farrell
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  ABSTRACT: The link between differences in the community composition of nitrifiers and denitrifiers to differences in the emission of nitrous oxide (N2O) from soils remains unclear. Nitrifier and denitrifier community composition, abundance and N2O emission activity were determined for two common landscapes characteristic of the North American “prairie pothole region”: cultivated wetlands (CW) vs. uncultivated wetlands (UW). The hypotheses of this study were: (1) landscape selects for different nitrifier and denitrifier communities, (2) denitrification was the dominant N2O emitting process, and (3) a relationship exists between nitrifier and denitrifier community composition, their abundance, and N2O emission. Comparisons were made among soils from three CW and three UW at the St. Denis National Wildlife Area. Denaturing gradient gel electrophoresis was used to compare community composition, and quantitative polymerase chain reaction was used to estimate community size. Incubation experiments on re-packed soil cores with 15N-labeled nitrate were performed to assess the relative contributions of nitrification and denitrification to total N2O emission. Results indicate: (1) nitrification was the primary source of N2O emission, (2) cultivation increased nitrifier abundance but decreased nitrifier richness, (3) denitrifier abundance was not affected by cultivation but richness was increased by cultivation, and (4) differences in nitrifier and denitrifier communities composition and abundance between land-use and landform did not correspond to differences in N2O emission.
  Soil Biology and Biochemistry.
• Article: A PCR-DGGE method for detecting arbuscular mycorrhizal fungi in cultivated soils

  W.K. Ma, S.D. Siciliano, J.J. Germida
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  ABSTRACT: Arbuscular mycorrhizal (AM) fungi (AMF) are important components of agro-ecosystems and are especially significant for productive low-input agriculture. Molecular techniques are used to investigate fungal community composition in uncultivated, disturbed, or contaminated soils, but this approach to community analysis of AMF in agricultural soils has not been reported. In this study, a polymerase chain reaction and denaturing gradient gel electrophoresis (PCR-DGGE) procedure for the detection of fungal 18S ribosomal RNA gene was developed with reference cultures of seven isolates (representing five AMF species). These reference cultures were chosen because isolates of their species were putatively identified in a previous survey of farm field soils in the province of Saskatchewan, Canada. A reference PCR-DGGE profile was generated using DNA extracted and amplified from the spores of these cultures. The effectiveness of the procedure was tested by its application to soil samples from 38 farms. Prominent bands from the PCR-DGGE profiles of these samples were excised for sequence analysis. The total number of species recovered was low in comparison to other AMF community surveys of temperate climate locations. The majority of the sequences recovered were Glomus species. Scutellospora calospora, a previously undetected AM fungus in Saskatchewan was found. Though not without its drawbacks, this approach to community composition analysis of AMF was faster than conventional trap cultivation methods.
  Soil Biology and Biochemistry.