Prescribed fire timing influences smut infection in a native warm season bunch grass
Season of burning effects on sexual reproduction fire dependent communities are widely reported, though the mechanisms are unresolved. Fire might act at various points, from increasing the number of flowering stems through pollination, fertilization and seed development, and interact with other factors like site quality. Disease can affect seed production directly; however, a disease-causing organism itself may be affected by fire and change the host’s reproductive success indirectly. We asked how prescribed fire timing and soil affect the infection of wiregrass (Aristida spp.) by a smut (tentatively, Langdonia sp.), which produces fruiting bodies in the ovaries of developing flowers. We predicted that earlier dates would increase smut infection. In 2014 we sampled 85 sites (nested within 15 properties). Samples were distributed across the middle and south Atlantic coastal plain, 4 soil orders, and burning in every month from December 2013 through July 2014. At each site we tallied presence at 10-m intervals along transects, and collected culms (from 24 clumps) that were tallied for flower production and smut presence by flower. We quantified smut presence at site, clump, and culm levels.
Both burn month and soil order had significant effects (ANOVA; p<.05) on stand smut abundance; the interaction was not significant. Clump and culm infection were correlated (Pearson; r =.53; p<.01) and showed patterns similar to the stand level. Sites burned in May-July had significantly higher rates than early burns, contrary to expectation. Sites on ultisols had higher infection rates than on sandy spodosols and entisols. Results suggest that the vigor of individual plants may moderate infection. Wiregrass typically dominates sandy soils, while mixed graminoids share dominance on ultisols resulting in increased competition for resources. This is consistent with smaller plant size and reduced culm production on silty compared to sandy sites, and potentially decreased plant vigor that facilitates smut reproduction.