Effects of soil biotic and abiotic properties on the growth and mycorrhization of Cedrus atlantica Manetti cedars

Cedrus atlantica Manetti is an emblematic species of great ecological, economic and social value. However, its weak root architecture seriously compromises (re)afforestation and regeneration of the species. Although it is known that mycorrhization is beneficial to cedars growing in unfavourable conditions, our knowledge on the mycorrhization of cedar seedlings is remains patchy. These difficulties show a need to study the interactions between the roots and the soil biotic and abiotic factors and to seek solutions to promote the mycorrhization of cedar seedlings. For this purpose, we studied the responses of cedar seedlings to the physico-chemical, textural, hydromechanical and microbiological factors of the soil and mycorrhization success in juvenile cedars. The response of C. atlantica seedlings to the textural and physico-chemical properties of soils in cedar woods shows that they are highly dependent on organic carbon, nitrogen and phosphorus contents and on the soil's granulometry. These factors stimulate the growth of secondary roots in some soils while in others, they cause seedling growth to predominate. The provenances of C. atlantica show a high nitrogen requirement and different preferences for nitrogen forms. Variations in the cotyledons also reveal different patterns of adaptation to nitrogen nutrition. The hydromechanical properties of the culture medium profoundly affect C. atlantica seedlings, so that in extreme cases, they either over-stimulate the elongation of unbranched main roots or completely inhibit their elongation, producing a great many reduced lateral roots. On the anatomical scale, these responses are more apparent around the cortex. Interactions with the native soil microflora have a determining effect on the growth of C. atlantica seedlings, since the microbial composition of the soil can stimulate growth and decrease the density of roots. The nutrient depletion of 6 soils   allowed the trapping of 15 species of ectomycorrhizal fungi of young C. atlantica seedlings. This indicates the crucial importance of this new range of mycorrhizal fungi, characterized for the first time in C. atlantica seedlings, especially for work aiming to improve the health status of cedar seedlings.