Effects of biocrusts and lichen-moss mats on plant productivity in a US sand dune ecosystem

Biocrusts are communities of cyanobacteria, algae, bryophytes, and lichens that influence plants and soils worldwide. In the Province Lands sand dunes of Cape Cod, algal biocrusts coexist with extensive bryophyte and lichen mats. The relationship between biocrusts, moss and lichen mats, and plants at this site has never been evaluated. We evaluated the effects of algal biocrusts and moss and lichen mats on soil moisture, plant productivity, and plant tissue water and nutrients of two dune plants, Deschampsia flexuosa and Morella pensylvanica. Soil moisture was highest under lichen-moss mats and lowest under moss-only mats. Algae-only biocrusts and bryophyte and lichen mats significantly affected seedling survivorship, height, biomass, root growth, and tissue water and micronutrients. When compared to controls, algae-only biocrusts and moss-only mats increased seedling survivorship and vigor, while lichen-moss mats decreased these plant responses. However, all biocrusts and mats tended to decrease plant productivity compared to controls. Biocrusts and mats play an important role in plant performance at this site, primarily via their effects on soil moisture, and possibly through their effects on plant tissue nutrients. Plants growing among biocrusts and mats at this site may experience a tradeoff between survivorship and productivity.