Bryophyte Microhabitat Control Over Seed Germination and Early Growth of Vascular Plants in the Sub‐Arctic

ABSTRACT Questions Plant interactions shape community composition, but most research on this topic is done on vascular plants with less focus on bryophytes, despite their dominance in many ecosystems. Bryophytes modulate the soil microclimate and thereby also the conditions for germination and early growth of vascular plants. Vascular plants typically grow faster than bryophytes, but their potential dominance requires successful germination which, in turn, is modulated by the moisture, temperature, and pH conditions created by different bryophyte species. Location Sub‐Arctic heath and peatlands in northern Sweden. Method To quantify if, and in case how, bryophyte species affect seed germination timing and growth of vascular plants we sowed seeds of Taraxacum officinale , Deschampsia cespitosa , and Plantago major in patches dominated by seven bryophyte species in northern Sweden. To quantify how the surface structure of bryophyte stands affects vascular plant germination and growth, we performed a surface removal treatment. In addition, to identify if bryophytes' exudates affect germination timing and efficiency, we included a laboratory assay using species‐specific extracts of the surface‐removed bryophyte parts. Results Bryophyte effects on vascular plant establishment are highly species specific: Flexitrichum flexicaule allowed for earlier germination and more vigorous plant growth, while Tetralophozia setiformis and Racomitrium lanuginosum inhibited germination completely. Emergence of D. cespitosa occurred earlier among darker bryophytes, most likely because of the interplay of bryophyte reflectance and temperature. Overall, plant biomass was best explained by bryophyte pH and moisture, but not consistently among vascular plant species. Conclusions These findings indicate that bryophytes can greatly influence vascular plant establishment. The mechanisms by which this takes place are highly species specific and dependent on the bryophyte as well as the vascular plant species. Expansion of vascular plants in bryophyte‐dominated communities is likely for Arctic ecosystems, but invasion success will vary and depend on the traits of the dominant bryophyte species.