Competitive interactions in two different plant species: Do grassland mycorrhizal communities and nitrogen addition play the same game?

In the Tibetan Plateau grassland ecosystems, nitrogen (N) availability is rising dramatically; however, the influence of higher N on the arbuscular mycorrhizal fungi (AMF) might impact on plant competitive interactions. Therefore, understanding the part played by AMF in the competition between and and its dependence on the N-addition status is necessary. To address this, a glasshouse experiment was conducted to examine whether the grassland AMF community's inocula (AMF and NAMF) and N-addition levels (N-0 and N-15) alter plant competition between and . Two harvests took day 45 (1 harvest) and day 90 (2 harvest), respectively. The findings showed that compared to , AMF inoculation significantly improved the competitive potential of the . In the occurrence of AMF, was the strongest competitor being facilitated by in both harvests. While under N-15, AMF significantly enhanced tissue N:P ratio in mixed-culture at 1 harvest, the opposite trend was observed in 2 harvest. The mycorrhizal growth dependency slightly negatively affected mixed-culture compared to monoculture under both N-addition treatments. The aggressivity index of AMF plants was higher than NAMF plants with both N-addition and harvests. Our observation highlights that mycorrhizal associations might facilitate host plant species in mixed-culture with non-host plant species. Additionally, interacting with N-addition, AMF could impact the competitive ability of the host plant not only directly but also indirectly, thereby changing the growth and nutrient uptake of competing plant species.