Effects of Land-Use and Vertical Compartmentalization on Eukaryotic Soil Algal Community Turnover in Peri-Urban Mexico City

Soil algae are important photoautotrophs, yet drivers of their diversity in peri-urban landscapes and across soil horizons remain poorly resolved. We used ITS2 metabarcoding to profile eukaryotic algal and fungal communities in 34 samples from Mexico City’s peri-urban conservation soils. Samples represented three Soil Systems: agricultural mineral soil, forest mineral soil, and forest litter, collected in two boroughs (Xochimilco and Tlalpan). We inferred amplicon sequence variants (ASVs), then alpha diversity and Bray–Curtis turnover were analyzed against edaphic and stoichiometric variables using random forests and PERMANOVA, and compared algal with fungal turnover. We recovered 662 algal ASVs spanning eight classes dominated by Trebouxiophyceae and Chlorophyceae. Litter was the richest and most distinct compartment with a high prevalence and abundance of lichen-associated taxa, whereas mineral soils were dominated by Chlorophyceae. Random forests ranked N/P ratio as the top predictor of both diversity indices. PERMANOVA indicated that the Soil System explained the largest single fraction of turnover. Algal and fungal turnover were positively correlated in mineral soils. Together, soil management practices, vertical compartmentalization and measured edaphic gradients were associated with community differences. These results point to potential algal management practices that could enhance peri-urban soil conservation and agroecological productivity.