Rhizosheath–Mycorrhizal Interactions in Kengyilia hirsuta Enhance Phosphorus Efficiency

Phosphorus deficiency is a key factor limiting plant growth in desertified grasslands. Elucidating the adaptive strategies of pioneer plants that integrate root morphology and microbial interactions is crucial for understanding the natural restoration of ecosystems. This study investigated the strategies employed by <i>Kengyilia hirsuta</i>, a pioneer grass species in desertified grasslands, to adapt to low-phosphorus environments. By conducting sand culture experiments under varying phosphorus levels (low, optimal, and high), we focused on elucidating the synergistic adaptive mechanisms involving the root-rhizosheath system. The results showed that the rhizosheath serves as a critical micro-ecological niche for enriching arbuscular mycorrhizal fungi (AMF) and enhancing phosphatase activity. Under low-phosphorus stress, the plant strengthened root hair development and its symbiotic association with AMF, which markedly increased acid phosphatase activity and led to the highest phosphorus use efficiency. At the optimal phosphorus level, the plant developed an efficient "rhizosheath-mycorrhiza" synergistic system, characterized by high AMF colonization and spore density, facilitating optimized carbon-phosphorus exchange. Under phosphorus-sufficient conditions, the adaptive strategy transitioned towards root morphological plasticity, exemplified by increased surface area and branching. Multivariate analysis revealed that the phosphorus absorption efficiency of <i>K. hirsuta</i> is co-regulated by both morphological adaptation and symbiotic optimization. This study elucidates the mechanisms of nutrient stress adaptation in desertified grassland plants, providing a theoretical foundation for understanding the natural restoration processes of degraded ecosystems.