Inoculate soil with mycorrhiza before seeding/planting
Overall effectiveness category Evidence not assessed
Number of studies: 5
Background information and definitions
Modern agricultural practices such as ploughing and application of pesticides and fertilizer may reduce the abundance of mycorrhizal fungi (Helgason et al. 1998, Johnson 1993). As a result, addition of mycorrhiza to degraded habitats may help natural plant communities to establish.
Inoculating soil with mycorrhizal fungi often involves the transfer of soil or plant material where mycorrhiza are already present to new areas. These microorganisms can increase nutrient uptake and protect against root pathogens (Smith & Read 2008). In grasslands, mycorrhizal fungi can increase species diversity and productivity (Van der Heijden et al. 1998).
The studies detailed in this intervention are direct tests of the effectiveness of inoculating soil with mycorrhiza before seeding or planting (e.g. by comparison with an untreated but seeded or planted plot). Studies that represent comparisons of seeding to unseeded plots can be found in the actions ‘Sow grass seeds’, ‘Sow grassland forb species’ or ‘Sow native grass and forbs’.
Helgason, T., Daniell, T., Husband, R., Fitter, A. & Young, J. (1998) Ploughing up the wood-wide web? Nature, 394, 431.
Johnson, N.C. (1993) Can fertilization of soil select less mutualistic mycorrhizae? Ecological applications, 3, 749–757.
Smith, S.E. & Read, D.J. (2008) Mycorrhizal symbiosis. Academic Press, USA.
Van der Heijden, M.G., Klironomos, J.N., Ursic, M., Moutoglis, P., Streitwolf-Engel, R., Boller, T., Wiemken, A. & Sanders, I.R. (1998) Mycorrhizal fungal diversity determines plant biodiversity, ecosystem variability and productivity. Nature, 396, 69.
Supporting evidence from individual studies
A replicated, randomized, paired, controlled study in 1992–1994 in a former mine in Minnesota, USA (Noyd et al. 1996) found that inoculating soil with mycorrhizal fungi before sowing seeds had mixed effects on plant cover. After two years, plant cover was higher in areas that were inoculated with mycorrhizal fungi and sown with seeds (36%) than in areas where seeds were sown but no mycorrhizal fungi were added (28%). However, after three years, plant cover was not significantly different in areas that were inoculated with mycorrhizal fungi and sown with seeds (50%) and areas where seeds were sown but no mycorrhizal fungi were added (37%). In May 1992, four blocks consisting of two 4 × 2.5 m plots were established. In each block, one 4 x 2.5 m plot was inoculated with mycorrhizal fungi by applying 2.5 g of Sorghum sudanense root material infected with fungi, and one plot was not inoculated. All plots were sown with a mixture of native plant species at a rate of 30.4 kg/ha. Plant cover was measured in all plots in August 1993 and 1994 using three 1-m wide transects.Study and other actions tested
A replicated, controlled study in 1998–1999 in a greenhouse and a former arable field in Arizona, USA (Richter & Stutz 2002) found that adding mycorrhizal fungi to soil before seeding did not alter the biomass or emergence success of giant sacaton Sporobolus wrightii plants, although after one year plants with added mycorrhiza were taller. Eight weeks after seeding in a greenhouse, emergence and biomass did not differ significantly between seeds sown in soil with added mycorrhiza (emergence: 71%; biomass: 0.44 g) and those sown in untreated soil (emergence: 62%; biomass: 0.46 g). Twelve months after the plants were transplanted to a field, those with added mycorrhiza were taller (79–85 cm) than those grown in untreated soil (63–79 cm). Survival of plants grown in soil with added mycorrhizal fungi was 90–100% compared to 82–95% for plants grown in untreated soil, although these results were not tested for statistical difference. Plants were grown in pots filled with heat-treated soil. Mycorrhizal fungi from local soil was added to the soil in 105 pots, while 105 pots were left untreated. Pots were sown with either three or ten seeds and watered regularly. Emergence was monitored weekly for eight weeks. Plants were transplanted into a former arable field in July 1998 and measured after 2, 4, 10 and 12 months.Study and other actions tested
A replicated, randomized, controlled study in 2008–2010 in 11 urban wasteland sites in Hellersdorf, Germany (Fischer et al. 2013) found that inoculating soil with mycorrhizal fungi and sowing seeds of grassland species did not alter overall plant species richness or the proportion of target species. In the three years after sowing, average plant species richness did not differ significantly between plots where seeds were sown in soil inoculated with mycorrhizal fungi (47–52 species) and plots where seeds were sown in untreated soil (43–50 species). The percentage of vegetation consisting of target species of local conservation priority also did not differ significantly (inoculated plots: 35–50%; untreated plots: 29–46%). In autumn 2008, one 4 x 4 m plot at each of 11 sites was sown with seeds and the soil inoculated with mycorrhizal fungi (0.75 l/plot). One plot at each site was sown with seeds and the soil was left untreated. Plots were mown and tilled prior to sowing. Seed mixes contained 27 species from the study region. In spring, early and late summer in 2009–2010, a 3 x 3 m quadrat was placed in the centre of each plot and plant cover mapped.Study and other actions tested
A replicated, controlled study in 2008–2011 in a greenhouse in Wisconsin, USA (Paluch et al. 2013) found that adding mycorrhizal fungi to soil before seeding did not alter the dry weight of three native grass and forb species. Dry weight of plants did not differ significantly between those grown in soil with added mycorrhizal fungi and those grown in untreated soil for the native grasses Canada wild rye Elymus canadensis (mycorrhiza added: 0.06–0.15 g; untreated: 0.09–0.13 g) and little bluestem Schizachyrium scoparium (mycorrhiza added: 0.02–0.07 g; untreated: 0.02–0.04 g), or the forb heath aster Aster ericoides (mycorrhiza added: 0.01–0.11 g; untreated: 0.05–0.06 g). Seeds of each species were sown into twenty 50-ml tubes containing sieved soil in December 2008. Sixteen tubes were treated with one of four commercial mycorrhizal treatments at a rate of 149–597 g/m3, and four were left untreated. All species were over-seeded and then thinned to one individual/tube, and watered regularly. Total plant dry weight was calculated 83 days after sowing.Study and other actions tested
A controlled study in 2009–2011 in an urban prairie restoration site in San Antonio, Texas, USA (Leonard & Lyons 2015) found that adding soil microbes and nutrients when planting increased cover of two of 38 native prairie species but did not alter overall cover of herbaceous or woody species. Two years after planting, two of 38 native prairie species had higher average cover in the area with microbes and nutrients added (Texas cupgrass Eriochloa sericea: 3.4%; bluegrama Boutouloua gracilis: 2.2%) than in the untreated area (Texas cupgrass: 1.2%; bluegrama: 0.6%). Cover of the other 36 plant species did not differ significantly between areas (see original paper for data). There was also no significant difference in average overall cover of herbaceous plant species (with microbes: 53%; untreated: 56%) and woody species (with microbes: 10%; untreated: 9%). Woody vegetation was cleared from the 9.4-ha site, and in September 2009, grass plugs of seven native species were planted at 4 plants/m2. Half the area was planted with plugs from seeds inoculated with nutrients and a slurry containing 17 microbial strains, at a rate of 1 g slurry/1,600 g seed. The other half of the area was planted with plugs from untreated seeds. The treated plants were also sprayed with fertiliser one month after planting. The whole site was sown with a native prairie seed mix (0.001 kg/m2) before and after planting, and mowed in December 2010. Vegetation cover was surveyed in October 2011 in ten 1 x 1 m quadrats placed along five 50-m transects in the inoculated and untreated areas.Study and other actions tested