PNNL

Abstract

Arbuscular mycorrhizal (AM) fungi are ancient plant symbionts and nutrient exchange forms the basis of this plant-microbe relationship. Plants provide carbon (C) to AM fungi and the fungi provide the plant with nutrients such as nitrogen (N) and phosphorous (P). Nutrient addition can alter this symbiotic coupling in key ways, such as reducing AM fungal root colonization and changing the AM fungal community composition. However, environmental parameters that differentiate ecosystems and drive plant distribution patterns (e.g. pH, moisture) are also known to impact AM fungal communities. Identifying the relative contribution of factors impacting AM fungal distribution patterns is important for predicting biogeochemical cycling patterns and plant-microbe relationships across ecosystem types. To evaluate the relative impacts of local environmental conditions and long-term nutrient addition on AM fungal abundance and composition across the temperate grassland biome, we studied a set of experimental plots amended for 10 years with N, P, or N and P fertilizer in different grassland ecosystem types, including tallgrass prairie, montane, shortgrass prairie, and desert grasslands. Ecosystem type, not nutrient treatment, was the main driver of AM fungal root colonization, diversity, and community composition, even when accounting for site-specific nutrient limitations. Environmental characteristics identified as being important drivers of grassland ecosystem AM fungal distribution patterns include aridity, mean annual temperature, root moisture, and soil pH. We also provide empirical evidence for niche partitioning strategies of AM fungal functional guilds. These results emphasize the importance of long-term, large scale research projects to provide ecologically relevant context to laboratory models.