Mediating role of root-exuded secondary metabolites in intraspecific interactions with Haloxylon ammodendron

Root exudates are pivotal in soil carbon and nutrient cycling, enhancing nutrient availability and plant resource utilization efficiency under stress. Despite challenges in obtaining accurate soil-borne signaling chemical information, further exploration of belowground plant interactions mediated by root exudates is essential.

We conducted a planting density experiment using Haloxylon ammodendron seedlings, including single-plant (D-1), two-plant (D-2), and three-plant (D-3) conditions.

Single-plant trials exhibited the largest biomass, while two-plant trials had the highest plant nutrient content, and three-plant trials had the highest soil total phosphorus (STP) content, with an enrichment of Sphingobacteriales and Vicinamibacteria in the rhizosphere. The abundance of compounds released by roots initially decreased and then increased with planting density, with flavonoids as the predominant differential secondary metabolites. 7-deoxyloganate, podophyllotoxin, and myristic acid exhibited positive correlations with biomass and negative correlations with root total phosphorus (RTP), soil total nitrogen (STN), STP, pH, and Sphingomonadales. Ecgonine, raucaffricine, and neohesperidin were positively correlated with plant biomass, soil pH and Sphingomonadales. O-methylandrocymbine, and gibberellin A8 displayed positive correlations with soil nutrients, Vicinamibacteria, and Sphingomonadales but negative correlations with Cyanobacteria.

Plant root exudates can influence the root bacterial community, soil properties, and plant competition outcomes, providing insights for H. ammodendron vegetation regeneration and desert ecosystem protection.