Identification of aqueous extracts from Artemisia ordosica and their allelopathic effects on desert soil algae

Desert vascular plants coexist extensively with biological soil crusts (BSCs) in arid lands, but limited information is known about the impacts of shrub litterfall on soil microalgae. In this study, the components of aqueous extracts (AEs) from Artemisia ordosica leaves were identified, and the growth and physiological responses of two BSC-dominated algae, namely, Chlorella vulgaris and Nostoc sp., to AEs were investigated. The AEs contained humic and fulvic acid-like fluorescence components with high aromaticity. They also comprised four main chemical components, namely alcohols, phenols, organic acids and saccharides. Low AE concentrations enhanced the growth rate and chlorophyll fluorescence yield of C. vulgaris. Conversely, high AE concentrations inhibited the growth and photosynthetic activities of both soil microalgae, resulting from the decrease of superoxide dismutase and catalase activities and the accumulation of reactive oxygen species and malondialdehyde contents. The tolerance concentration of the green alga C. vulgaris to the AEs was greater than that of the cyanobacterium Nostoc sp. The AEs from A. ordosica exerted different degrees of stimulatory or inhibitory effects on the growth rates and physiological activities of Nostoc sp. and C. vulgaris, which might affect soil microalgal community structure and BSC formation in drylands. This study reveals the response mechanisms of soil algae to shrub leachates and improves our understanding of the role of vascular plants in shaping BSC communities.