Soil Phosphorus Conditions Drives Arbuscular Mycorrhizal Fungal Community Differentiation and Modulate the Growth of Cenchrus pauciflorus

Cenchrus pauciflorus is a major invasive plant in the sandy lands of northern China, with the Horqin Sandy Land being a hotspot of its invasion, where soil phosphorus availability may influence its spread through arbuscular mycorrhizal fungi (AMF). To elucidate the effects of soil phosphorus on AMF communities and their role in the invasion of C. pauciflorus, we conducted a field survey at two sites with contrasting phosphorus backgrounds: Chajintai Ranch (high phosphorus) and Bahuta Sumu (low phosphorus). Rhizosphere soil and root samples of C. pauciflorus and the co-occurring native grass Setaria viridis were collected for high-throughput sequencing of 18S SSU rRNA gene to analyze AMF community composition and diversity. Two AMF species, Funneliformis mosseae and Diversispora epigaea, were selected for a pot experiment with C. pauciflorus. Five phosphorus treatments were established under high- and low-phosphorus conditions using different phosphorus forms. The effects of the two AMF species on the growth and reproduction of C. pauciflorus under different phosphorus treatments were analyzed. The results showed that Glomeraceae and Glomus were the predominant family and genus, respectively. Under Bahuta Sumu, Diversispora was relatively enriched in the roots of C. pauciflorus compared with S. viridis roots. However, other nutrient factors also varied between the two field sites, the independent effect of phosphorus on AMF community composition and diversity could not be fully disentangled. The pot experiment revealed that AMF inoculation did not significantly promote the growth of C. pauciflorus under high-phosphorus treatment. In contrast, when phosphorus was low and supplied in insoluble forms, both AMF species significantly promoted the growth and reproduction of C. pauciflorus. D. epigaea exhibited a stronger growth-promoting effect than F. mosseae, with significantly higher colonization rates in most treatments. In summary, C. pauciflorus is associated with the enrichment of specific AMF taxa in low-phosphorus habitats, which may in turn promote its growth by enhancing the acquisition of insoluble phosphorus. This may represent an important belowground symbiotic mechanism underlying its successful invasion in nutrient-poor sandy habitats.