Soil algae in arable land: changes in the genotypic community composition across time points and farming systems-a...

Soil algae, including Cyanobacteria, in the topsoils of arable land are essential for many valuable effects on soil texture and fertility. However, the constant changes and disturbances caused by agricultural practices create a challenging environment. We tested for responses in soil algal diversity across principal time points during the growth of Triticum aestivum, a typical winter cereal under Central European agricultural practices, and examined the effects of contrasting farming systems.

We employed a metabarcoding analysis based on amplicons from multiple markers to assess changes in the genotypic community composition.

Relationships among the detected key groups of soil algae, i.e., Chlorophyta (Chlorophyceae, Trebouxiophyceae), Stramenopiles (Xanthophyceae, Diatomeae), and Cyanobacteria, varied significantly across the three principal time points of the wheat's growth season. The eukaryotic algae (118 genera) alone accounted for approximately one-third in March to approximately one-half in July of all microeukaryote ASVs in the surface soils. The 23S UPA marker, used to amplify eukaryotic algae and Cyanobacteria in a single step, and the 18S marker differed in their estimates of ASV numbers for Chlorophyta and Xanthophyceae. However, in combination with markers specifically targeting the green algal ITS2 and the rbcL genes of Stramenopiles and Chlorophyta, consistently the same distinct distribution patterns of the soil algal genotypes were found. Stramenopile genotypes were preferentially found in March and November at cold and high bare-soil availability, whereas Chlorophyta genotypes were most abundant in July at higher temperatures and minimal bare-soil availability. No Klebsormidiophyceae were found in March. The conventional management system favored algal biomass and ASV richness of Xanthophyceae, Diatomeae, and the green algal classes Ulvophyceae and Klebsormidiophyceae compared with organic farming. It negatively influenced the diversity of Cyanobacteria. Within conventional farming, Zea mays, as another crop, significantly increased the ASV richness of Chlorophyceae and Ulvophyceae, whereas that of Cyanobacteria decreased. A large fraction of genotypes, however, remained invariant without response to environmental disturbances; it mainly consisted of Chlorophyta and the Eustigmatophyceae (Stramenopiles).