Effects of elevated CO2 and arbuscular mycorrhizal fungi on root exudates of black locust seedlings grown in cadmium-polluted soils by 13C isotope tracer

Abstract

Root exudates contribute to heavy metal migration in soils, which are easily influenced by many factors such as arbuscular mycorrhizal fungi (AMF) and atmospheric CO₂. To understand the effect of increasing atmospheric CO₂ and AMF on root exudates of plants exposed to heavy metals, we investigated the impacts of elevated CO₂ (eCO₂) and AMF strain Funneliformis mosseae (FM) on root exudates of black locust (Robinia pseudoacacia L.) cultivated in cadmium (Cd)-polluted soils using ¹³C isotope tracer under sterile conditions. 93 metabolites were identified from root exudates including phenolic acids, amino acids, other organic acids and soluble sugars. 56 differential metabolites were identified under FM colonization using orthogonal partial least squares-discriminant analysis. The eCO₂ contributed 11.31, 163.00 and 8.31 μg kg^-1 to total phenolic acids, amino acids, and soluble sugars, respectively. The top 10 eCO₂-contributed compounds under FM included nine monosaccharides, such as β-d-allopyranose and d-(+)-galactopyranose, and sarosine, and five differential compounds, such as maltose and sarcosine, between eCO₂ + FM and eCO₂ existed in starch and sucrose metabolism, amino sugar and nucleotide sugar metabolism, and arginine and proline metabolism pathways. Elevated CO₂ and FM affected (p < 0.05) root exudates under Cd pollution by regulating plant metabolism. Overall, responses of root Cd and soil C and N to eCO₂ and F. mosseae affected (p < 0.05) root exudates. The results will help us understand the combined contribution of increasing CO₂ and AMF on phytoremediation of heavy metal-polluted soils, providing the possibility to select bioremediation measures under global change scenarios.

Keywords: (13)C isotope tracer; Funneliformis mosseae; Gas chromatography-mass spectrometry; Metabolism pathways; Root exudates.