Regeneration failure of Pinus halepensis Mill.: The role of autotoxicity and some abiotic environmental parameters

Our study deals with ecological parameters that could influence early recruitment including germination and seedling growth with emphasis on the establishment of Pinus halepensis fire free forests in Mediterranean basin. Because plant secondary compounds (terpenoids and/or phenolic compounds) may govern competition, those produced by P. halepensis were investigated in terms of autotoxicity and implication in natural regeneration. In a laboratory experiment, two ecological factors as: (i) soil and litter conditions, (ii) light availability and three allelopathic processes: (i) the successional stage (age of pines), (ii) organ source of allelochemicals, (iii) and dose effect of allelochemicals were tested together in order to understand their interactions in natural regeneration of P. halepensis. The results showed a potential autotoxicity implied in germination rate and seedling growth. This phenomenon of autotoxicity was modulated by the biotic factors studied here: (i) young Aleppo pines exhibited a toxic effect on germination whereas old pines showed the most important effect on seedling growth and (ii) needle extracts presented an important dose effect on germination compared to roots. Autotoxicity was also modulated by environmental factors: (i) autotoxicity effect on germination and growth was more important on sterile soil, bringing to light the key role of microorganisms in this functional process, (ii) litter seems to be an important parameter influencing germination rates by favouring both drought conditions during germination and high mortality rate and (iii) light availability did not influence either germination or growth rate of early recruitment, but is well known to play an important role in saplings stage. Hence, our study showed that autotoxicity is a potential functional process that could influence natural regeneration of P. halepensis, but field conditions studies are necessary.