Land management alters arbuscular mycorrhizal fungal community structure and function through selection for spore traits

Background/Question/Methods

Land management techniques like prescribed fire and bison (i.e., grazing) are commonly used to maintain grassland and savanna ecosystems. Despite the importance of land management in preserving ecosystem health, we have a poor understanding of how management disturbance affects belowground soil biota and their function. Since soil biota like arbuscular mycorrhizal (AM) fungi can directly promote plant community diversity and ecosystem productivity, it is important that we understand the effect of management disturbance on AM fungal communities and mutualisms, as well as how AM fungal spore traits mediate this effect. This work tested how fire and grazing influenced AM fungal community structure and symbioses with plants through selection for spore traits. We hypothesized that fire and grazing would favor specific spore traits related to management disturbance (e.g., spore volume, color, size, etc.), and that this selection would drive differences in AM fungal community composition, and plant growth. Using paired field and greenhouse studies, we assessed how bison and prescribed fire effects on AM fungal spore traits like saturation, volume, intensity, and luminance, altered AM fungal community structure and effects on the growth of Schizachyrium scoparium.

Results/Conclusions

Land management activity altered AM fungal communities through selection for specific spore traits. In grazed sites, spores were lighter in color and smaller in volume than those in burned sites. In the absence of grazing however, fire selected for spores that were darker in color. This selection for spore traits also drove differences in AM fungal spore community composition between burned and no burn sites, with burned communities displaying higher heterogeneity and decreased spore abundance. Land management also influenced plant-AM fungal interactions, however, this was not due to differences in AM fungal community composition. While the presence of AM fungi (live vs. sterile) promoted S. scoparium growth, this effect did not differ between spores from burned vs. grazed sites. However, AM fungi from burned sites were associated with lower plant root:shoot ratios relative to sterile treatments. In summary, prescribed fire and grazing select for different AM fungal spore traits and drove the formation of distinct AM fungal communities. Despite these changes, management effects on AM fungal communities did not appear to influence S. scoparium growth, but AM fungi in burned sites may have helped S. scoparium plants take advantage of post-fire nutrient flushes and allocate more resources to aboveground growth.