Woody encroachment into grasslands is threatening tallgrass prairie ecosystems throughout the U.S. Great Plains, as exemplified at the Konza Prairie Biological Station (KPBS) in eastern Kansas. Many factors can promote this phenomenon, but one that is less well studied is the role of plant-soil-microbe interactions in woody encroachment. Because most plants rely on fungal root symbionts for phosphorus and other plant essential nutrients, we were interested in whether fungi might prevent or promote dominance of matrix tallgrass prairie plant species or woody plant invaders. This study evaluates evidence for a role of fungal interactions in woody encroachment by: i) determining if woody encroaching plants and existing grass species have preferred fungal partners; ii) learning whether land management practices affect the fungal inoculum in the soil and thus the probability of woody plant establishment. Roots and soil were sampled within differing land management histories (grazed, ungrazed, annually burned and unburned) in experimental watersheds at KPBS. Fungal communities were analyzed from total DNA extracted from replicate samples of fine roots of dominant grasses, woody encroachers, as well as adjacent soils, and using Internal Transcribed Spacer metabarcode marker that was PCR-amplified and sequenced (Illumina MiSeq). We used MOTHUR and PhyloSeq to test our hypotheses.
Results/Conclusions
The root-associated fungal communities across all plant species (grasses Andropogon gerardii and Sorghastrum nutans, and shrubs Cornus drummondii and Juniperus virginianus) were influenced by land use (permutational ANOVA: grazed vs. ungrazed, P = 0.003, R2 = 0.027; burned vs. unburned, P = 0.034, R2 = 0.019) but not plant identity (P = 0.628, R2 = 0.031; n = 4 for each species/fire/grazing combination treatment). This was true for all fungal taxa (1187 total OTUs) as well as for “core” taxa present in ≥10% of the samples (56 OTUs). Results also indicated that taxa of arbuscular mycorrhizal fungi (AMF), the most important root symbiont at this site, differed among the treatments and plant species:J. virginianus had both the narrowest range of AMF and the least widespread distribution in the field. Thus, we conclude that available fungal inocula to support plant establishment are affected by land management, and species-specific AMF symbionts may be crucial in mediating plant compositional shifts. Data like these could provide an indicator of rangeland susceptibility to woody invasion, and aid management decisions to prevent further loss of grassland.