Assessing Sorghum bicolor biofuel genotypes for potential mycorrhizal benefits

Background/Question/Methods

Fossil fuels are driving planetary alterations that threaten biodiversity and human society. While total energy demands are on the rise, energy portfolios are increasingly emphasizing renewable sources, such as biofuels produced from cellulosic crops. Productivity and nutrient input optimization are key, as fertilizers represent substantial carbon costs. However, belowground traits such as mycorrhizal symbioses are not well explored, despite their potential to reduce fertilizer requirements without reducing agroecosystem productivity. Our research addresses this knowledge gap by examining host-plant interactions with arbuscular mycorrhizal (AM) fungi across three Sorghum bicolor biofuel genotypes (TX08001, TX09063, TX09067) planted at two sites. Site A was cropped for >10 years (Lane, OK: baseline soil = 15 mg kg-1 plant-available P); Site B was recently converted to perennial grassland (Ardmore, OK: 6 mg kg-1 plant-available P). Plants were either not fertilized (controls), fertilized (N and P), or amended with worm compost. Assessments included AM fungal root colonization, soil microbial assessments (determined by PLFA and NLFA), and aboveground production. Presumably due to long-term cultivation at Site A, baseline AM fungal abundance was significantly lower (PLFA = 1.03 nmol g-1, NLFA = 3.51 nmol g-1), compared to site B (PLFA = 1.61 nmol g-1, NLFA = 4.32 nmol g-1).

Results/Conclusions

Linear mixed models show neither fertilization nor genotype significantly influenced plant production at Site A, but the interaction of genotype and fertilization (p = 0.043) influenced production at Site B, with greatest yield in fertilized TX09067, compared to other combinations. There was no significant difference in AM fungal root colonization at Site A; however, genotype (p = 0.027) had a significant influence on root colonization at Site B, with TX08001 averaging ~28% greater inter-radical abundance than other genotypes. At Site B, both genotype (p = 0.029) and fertilizer (p = 0.008) significantly influenced soil microbial abundance, as TX08001 associated with greater active AM fungal biomass (PLFA) and spore production (NLFA), compared to other genotypes, and worm compost also increased AM fungal abundance, compared to commercial fertilizers. At Site A, fertilizer influenced AM spore production (NLFA) (p = 0.022), with worm compost significantly increasing spore production, as compared to commercial fertilizers. These results indicate potentially greater mycorrhizal abundance associated with TX08001 than other genotypes and greater AM fungal biomass following worm compost amendments. Our findings suggest selecting sorghum genotypes that increase AM fungal abundance may lead to more sustainable biofuel production.