Matgrass sward plant species benefit from soil organisms

Soil organisms are important in the structuring of plant communities. However, little is known about how to apply this knowledge to vegetation management. Here, we examined if soil organisms may promote plant species of characteristic habitats, and suppress plant species of disturbed habitats. We classified nineteen fields into four types: characteristic and disturbed matgrass swards and successfully and unsuccessfully restored fields. We recorded the vegetation composition and measured biotic and abiotic soil characteristics of the sites. In a pot experiment, we mixed non-sterilized (with soil organisms) or sterilized (without soil organisms) soil inoculum from each field with a common sterilized background soil. We planted seedlings of characteristic matgrass species Antennaria dioica and Nardus stricta, of disturbance indicators Deschampsia flexuosa and Agrostis capillaris, or a combination of the four species. At harvest, we measured root and shoot dry mass of all plants.The vegetation composition of characteristic matgrass swards differed from the disturbed and unsuccessfully restored fields. The successfully restored fields were intermediate. The composition of the nematode community tended to follow the same pattern. In the pot experiment, addition of soil organisms increased the biomass of A. dioica, N. stricta and D. flexuosa, but decreased the biomass of A. capillaris. However, the effect of soil organisms on plant biomass was not related to field type. A. dioica showed a large variation in biomass in non-sterilized, but not in sterilized soil. Soil organisms from some sites increased plant biomass, whereas soil organisms from other sites did not. The biomass of characteristic matgrass plants was lower in the presence of plants from disturbed swards, irrespective of the presence of soil organisms. Probably A. capillaris was so much larger than the other species, that this overruled effects of added soil organisms. Soil organisms promoted growth of plant species characteristic of matgrass swards, whereas they reduced growth of a plant species characteristic of disturbed fields. Soil organisms did not change the outcome of plant interactions, which was won by a disturbance indicator. Nevertheless, measurement of the growth stimulating capacity of a soil may be used to assess opportunities for reintroduction of characteristic plant species.

► Soil communities from original matgrass swards differed from disturbed sites.
► Successful restoration changed both plant and soil community composition.
► Soil organisms from some sites increased biomass of original matgrass sward plants.
► Plant response to soil inoculation was not related to our field type classification.
► Soil organisms are important for reintroduction of characteristic plant species.