Abstract: In desert ecosystems, biological soil crusts (biocrusts) play a crucial role in regulating soil nutrient dynamics and plant productivity. However, their cascading effects on aboveground biomass (AGB) mediated through soil-plant-microbe interactions remain poorly understood. To address this gap, we conducted a field experiment in the Gurbantunggut Desert of Central Asia, focusing on Erodium oxyrrhynchum, a dominant ephemeral species. We compared biocrust successional stages (from bare sand to moss crust) and ephemeral plant germination seasons (spring vs. autumn), assessing soil properties, plant traits, and phyllosphere microbial communities. Significant differences in leaf traits and AGB were observed between spring- and autumn-germinated plants across biocrust successional stages. Autumn-germinated plants exhibited higher AGB and more resource-acquisitive traits, whereas spring-germinated plants showed stronger stress tolerance but reduced AGB. AGB declined along the biocrust successional gradient (bare sand > algal crust > lichen crust > moss crust). Structural equation modeling revealed that soil moisture and nutrient availability were the dominant drivers of AGB, followed by phyllosphere microbial composition and plant traits. Biocrusts influenced plant biomass primarily through bacteria-mediated pathways that modified soil conditions. These findings highlight a trade-off between biocrusts-driven nutrient enrichment and water limitation, that collectively shape desert ecosystem productivity. They also provide a mechanistic foundation for predicting ecosystem responses to environmental change and for developing effective restoration strategies in arid regions.

Key words: Aboveground biomass, Biological soil crusts, Erodium oxyrrhynchum, Leaf functional traits, Phyllosphere microorganisms, Plant life-history