Inner Mongolian steppe arbuscular mycorrhizal fungal communities respond more strongly to water availability than to nitrogen fertilization.

Plant community productivity and species composition are primarily constrained by water followed by nitrogen (N) availability in the degraded semi-arid grasslands of Inner Mongolia. However, there is a lack of knowledge on how long-term N addition and water availability interact to influence the community structure of arbuscular mycorrhizal (AM) fungi, and whether AM fungi contribute to the recovery of degraded grasslands. Soils and roots of the dominant plant species Stipa grandis and Agropyron cristatum were sampled under two water levels and N) rates after 8 years. The abundance and diversity of AM fungi remained relatively resilient after the long-term addition of water and N. Variation in the AM fungal communities in soils and roots were affected primarily by watering. AM fungal abundance and operational taxonomic unit (OTU) richness were significantly correlated with average aboveground net primary productivity and biomass of plant functional groups. Hyphal length density was significantly correlated with plant richness, the average biomass of S. grandis and perennial forbs. Both water and plant biomass had a considerable influence on the AM fungal assemblages. The tight linkages between AM fungi with aboveground plant productivity highlight the importance of plant-microbe interactions in the productivity and sustainability of these semi-arid grassland ecosystems.