Assessment of arbuscular mycorrhizal fungi in flax production
Arbuscular mycorrhizal fungi (AMF) play an important role in nutrient cycling and growth of flax (Linum usitatissimum L.). However, limited information is available regarding the symbiotic association between flax and AMF in field environments. A study was conducted to survey AMF communities colonizing flax grown in Saskatchewan. Additionally, field and growth chamber studies investigated the impact of AMF inoculation on nutrient uptake and growth of flax. Eighteen commercial flax fields were surveyed to assess mycorrhizal colonization of flax and to assess the impact of agricultural practices and soil abiotic factors on AMF activity. The flax root-associated AMF communities were explored using a 454 sequencing method, together with microscopic-based measurements of root AMF colonization and soil spore density. High levels of root colonization were detected in most flax fields. Of the 222 AMF operational taxonomic units (OTUs) identified in flax roots, 181 OTUs clustered as Funneliformis-Rhizophagus, 19 as Claroideoglomus, 14 as Paraglomus, six as Diversisporales and two as Archaeospora. Results suggest that tillage influenced the composition of AMF communities colonizing flax, and reduced relative AMF abundance and species richness. Additionally, AMF community characteristics were related to soil abiotic factors such as pH, EC, available phosphorus and nitrogen. Field experiments were conducted over two years (two sites per year) using a commercial AMF inoculant applied at three rates (0, 1X, and 2X the recommended rate) with or without P fertilizer (16.8 kg ha-1). The response of flax cultivars to AMF inoculation was examined in a growth chamber experiment. In addition, 454 sequencing was employed to examine the impact of AMF inoculation on root-associated AMF communities. Under field conditions, only one site showed increased root colonization with AMF inoculation. Flax responded to AMF inoculation differently under different field conditions. At the two sites with intermediate initial soil P level, evidence of increased above-ground biomass and plant nutrient uptake with AMF inoculation was observed. However, such an effect was not detected when P fertilizer was combined with the inoculation. At a low P site and an irrigated site, P application accounted for all of the increases in plant nutrient uptake and biomass of flax, whereas no responses to AMF inoculation were detected. The 454 sequencing revealed different inoculation-induced changes in the diversity and composition of root-associated AMF communities between sites, which was possibly related to different field environments and native AMF communities. In the growth chamber, AMF inoculation resulted in general increases of plant nutrient uptake among cultivars, but only one cultivar showed enhanced biomass with inoculation. The diversity of AMF communities colonizing different flax cultivars was generally reduced by AMF inoculation. Community composition shifted under AMF inoculation, and the shifts appeared to be cultivar specific. These results suggested that benefits of AMF inoculation in flax production are limited and currently not predictable, and the degree of response is likely dependent on a myriad of soil and environmental conditions.
arbuscular mycorrhizal fungi, flax growth, flax nutrient uptake, 454 sequencing, community assembly
Master of Science (M.Sc.)