Effect of simulated acid rain on mycorrhizae of Aleppo pine (Pinus halepensis Miller) in calcareous soil

Mycorrhiza formation and plant growth, in particular root development, of Pinus halepensis were studied in relation to the influence of pH from simulated rain in pot cultures. Four treatments of water (7.5, 6.0, 4.5 and 3.0) were established by adding a mixture of sulphuric and nitric acids (2:1, v/v) Or 10% NaOH to distilled water. Three experiments were carried out: i) seedlings growing in calcareous forest soil; ii) 2-year-old naturally mycorrhizal seedlings, transplanted into vermiculite in order to differentiate old and new-formed roots; and iii) seedlings growing in peat vermiculite, inoculated with mycelial inoculum of Suillus collinitus. Although no visible effects on the aerial part were observed, a reduction of root length in the most acidic treatment was noted. Enhancement of ectomycorrhizae formation was also recorded in this treatment in the three experiments. In substrata of neutro-basic pH, short-term exposures to acid rain positively affected ectomycorrhizal fungi, in particular, Suillus species.