Nurse shrubs increased the early growth of Cupressus seedlings by enhancing belowground mutualism and soil microbial activity

The influence of shrubs used as nurse plants was tested on the growth of Cupressus atlantica, on microbial activity and on arbuscular mycorrhizal (AM) soil potential in a Mediterranean environment. An experimental plantation was conducted combining uninoculated, arbuscular mycorrhized Cypress seedlings and an association between Lavandula stoechas planted close to newly planted C. atlantica seedlings. After three years plantation, this association between C. atlantica and L. stoechas lead to a higher growth of C. atlantica and better soil microbial characteristics compared to the control treatment. AM mycelium network, total microbial activity, dehydrogenase activity, phosphate-solubilizing fluorescent pseudomonads and N, P nutrient uptake by C. atlantica, were significantly higher in the presence of L. stoechas than those recorded in the other treatments. This pioneer shrubs facilitates the early establishment of Cypress seedlings by improving soil microbial characteristics and AM fungus community development. Given that the facilitative effect of one plant species to another increases with abiotic stress, the benefits of this technique would be useful in reforestation programs undertaken to rehabilitate degraded areas in Mediterranean region.

► This study was carried out in Morocco to assess the influence of shrubs used as nurse plants, on the growth of Cupressus atlantica, on soil microbial activity (enzymatic activities, phosphate solubilizing ability of fluorescent pseudomonads) and more particularly on arbuscular mycorrhizal (AM) soil potential in a Mediterranean environment. We hypothesized that this plant–plant interaction would enhance Cypress growth in field conditions.
► A field experiment was conducted in the Haut Atlas mountains in Morocco combining uninoculated, arbuscular mycorrhized Cypress seedlings and an association between Lavandula stoechas planted close to newly planted C. atlantica seedlings. After 3 years plantation, microbial activity and the structure of AM fungus communities were determined in each soil treatments.
► The results showed that the dual plant cultivation was beneficial to the growth of C. atlantica and to microbial characteristics of the cultural soil in field conditions. In particular, the development of the AM mycelium network, total microbial activity, dehydrogenase activity, phosphate-solubilizing fluorescent pseudomonads and N, P nutrient uptake by C. atlantica, were significantly higher in the presence of L. stoechas than those recorded in the other treatments.
► This pioneer shrub facilitates the early establishment of Cypress seedlings by improving soil microbial characteristics and more particular AM fungus community development.
► Given than the facilitative effect of one plant species to another increases with abiotic stress, the benefits of this technique would be greater in unfavorable environmental characteristics (i.e. water stress) usually encountered in Mediterranean region.