Mat-forming lichens support contrasting micro-arthropod density

Mat-forming lichens are important components of tundra and alpine vegetation, and affect soil microclimatic conditions, which in turn may influence micro-arthropod communities. Here, we compare the density of Collembola and Oribatida within lichen mats and their abundance in the underlying soil across four different mat-forming lichens at Finse, southern Norway. The lichen mats consisted of Alectoria ochroleuca, Cetraria islandica, Cladonia rangiferina/stygia, or Flavocetraria nivalis. We hypothesized that lichens with high water holding capacity (WHC) create a cool and stable microclimate with few freeze-thaw cycles which sustains a high micro-arthropod density in lichen and abundance in soil. We further test how lichen monocultures affect soil element availability. The abundance of micro-arthropods differed among lichen species. Cladonia rangiferina/stygia supported the highest Collembola density, and lichens with high WHC supported higher densities, and relatively more Collembola in the lichen than the soil underneath. Oribatida were less responsive than Collembola but increased in lichen mats relative to soil with increasing WHC. Lichen mat density, soil temperature and freeze-thaw cycles did not correlate to micro-arthropod abundance. Element availability was higher in bare soil compared to soil covered with lichens driven by differences in temperature and freeze-thaw cycles, which possibly affect microbial activity. Lichen cover in boreal and tundra ecosystems is expected to decrease due to environmental change, which may significantly impact micro-arthropod communities in lichen-dominated vegetation.