Mycorrhizal fungi affect growth of an endemic bunchgrass in pine savannas.
Abstract
1. Planting or sowing native perennial bunchgrasses is a common restoration practice in grasslands disturbed by agricultural or forestry operations. Bunchgrasses provide fine fuel loads for reinstating fire regimes that promote native plant community development. Wiregrass (Aristida beyrichiana) is a dominant bunchgrass used in the restoration of south-eastern US pine savannas. Amending disturbed soils with native soils or inoculating them with mycorrhizal fungi are restoration practices used to enhance plant growth or establishment. It is unknown, however, whether these practices increase wiregrass biomass, which would promote fire spread and reinstatement of frequent fire regimes. 2. We grew wiregrass from seed in four treatments: (1) undisturbed soil from an undisturbed pine savanna (reference treatment), (2) soil disturbed by plantation forestry, (3) disturbed soil mixed with a small amount of undisturbed soil and (4) disturbed soil inoculated with commercial arbuscular mycorrhizal inoculum. After 6 months, we harvested plants and weighed above- and below-ground biomass. We compared total biomass, soil spore counts and root colonization between treatments. 3. Although the undisturbed and disturbed soils used in the experiment did not initially differ in nutrients or mycorrhizal inoculum potential, spore counts were significantly higher in the disturbed soils we collected. At the end of the experiment, total plant biomass (above- and below-ground) was significantly lower in the undisturbed treatment than in all other treatments, which were not significantly different from each other. There were no significant differences in percent root colonization at the end of the experiment, but soil spore counts were significantly higher in the disturbed and commercially inoculated soils than in the undisturbed and mixed soils. 4. Our results suggest that the mycorrhizal relationship might be enhanced in disturbed soils as arbuscular mycorrhizal fungi mobilize nutrients needed by wiregrass; alternatively, disturbed and commercially inoculated soils might harbour a different fungal community than native soils. Although plants had lower biomass in the undisturbed soils, this difference may disappear over time. 5. Practical implication. If the goal of savanna restoration is to re-establish fire regimes using wiregrass, inoculation is likely unnecessary. In contrast, inoculating the soil may support other objectives, such as increasing biodiversity or accelerating succession.