Effects of Chlamydomonas debaryana and Arthrospira maxima Biostimulants on Maize Performance, Soil Properties, and Microbial Community Responses in an Arid Agroecosystem

Microalgal biostimulants are promising inputs for improving crop performance and soil quality, but integrated evidence linking plant, soil, and microbial responses under arid field conditions remains limited. Independent but complementary pot and field experiments were conducted in the Hexi Corridor using a live Chlamydomonas debaryana cell suspension (CM) and spray-dried Arthrospira maxima biomass (AM), with water (CK) and NPKZn fertilizer (NPK) as controls. The pot experiment included three biological replicates per treatment, and the field experiment comprised three independent plots per treatment. Both microalgal treatments promoted root development, increased catalase (CAT) and superoxide dismutase (SOD) activities, and reduced malondialdehyde (MDA) accumulation in maize seedlings. Under field conditions, CM increased net photosynthetic rate and Soil Plant Analysis Development (SPAD) value by 30.0% and 21.4%, respectively, and increased kernel number per ear and ear weight by 14.3% and 21.7% relative to CK. CM significantly increased soil organic matter and available N, P, and K, whereas AM significantly increased soil organic matter and available N and K, with available P showing a numerical but nonsignificant increase. Both microalgal treatments significantly reduced soil electrical conductivity. Microbial responses were comparatively limited: bacterial richness changed under the treatments, whereas fungal alpha diversity and overall bacterial and fungal community composition were not significantly affected. Nevertheless, selected bacterial co-occurrence network attributes differed among treatments, including higher absolute negative-to-positive cohesion ratios under CM and AM than under CK and NPK. Exploratory random forest and correlation analyses further identified associations of soil nutrient status and bacterial network attributes with maize yield-related traits. These findings support the agronomic potential of microalgal biostimulants for improving maize performance and soil nutrient conditions under the tested arid field conditions.