The ecological, economic and social values of the ectomycorrhizal fungi of the black truffle found in the rural Mediterranean are well known. The inoculation of Pinus halepensis seedlings with mycorrhizal fungi and rhizobacteria can improve the morphology and physiology of the seedlings and benefit the regeneration of arid regions and the reintroduction of inocula of mycorrhizal fungi into these areas. Some rhizobacteria can improve the establishment and functioning of ectomycorrhizal symbiosis. In this study, seedlings of P. halepensis were inoculated with the mycorrhizal fungus Tuber melanosporum and the rhizobacteria Pseudomonas fluorescens CECT 844 under non-limiting greenhouse conditions. Five months after inoculation, we analysed the growth, water parameters (osmotic potential at saturation, osmotic potential at turgor loss and modulus of elasticity), concentrations of mycorrhizal colonies, nutrient concentration and nutrient contents (N, P, K, Ca, Mg and Fe) in roots and aerial parts of the seedlings. Subsequently, tests were performed to estimate the root growth potentials. None of the treatments changed the water parameters or growth potentials of the roots. The inoculations improved the growth and nutrient uptake of the seedlings, although the combination of P. fluorescens CECT 844 and T. melanosporum did not generally lead to a significant improvement over the positive effects of a simple inoculation of T. melanosporum; however, the addition of P. fluorescens CECT 844 did double the rate of the mycorrhization of T. melanosporum. These results may be promising for enhancing the cultivation of truffles.

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© iForest -Biogeosciences and Forestry IntroductionWater and nutrient availability are the main constraints on plant productivity in semi-arid Mediterranean ecosystems. The preservation of mycoflora diversity depends on the status of plant roots (Marulanda et al. 2006). Forest species in these areas often develop specific strategies to improve their water usage in response to drought (Martínez-Ferri et al. 2000).Several studies have been conducted to improve the quality of seedlings produced in nurseries (Caravaca et al. 2005). Several authors reported that soil amendment with ectomycorrhizal fungi and plant-growth-promoting rhizobacteria (PGPR) increased plant survival and seedling quality, especially in soils with low microbial activity (Chanway 1997, Probanza et al. 2001.Pseudomonas fluorescens generally shows several characteristics of an effective PGPR. It is easily cultivated in vitro, and it colonizes a wide range of ecological niches, including plant rhizospheres (Bolton et al. 1993). Additionally, P. fluorescens genomes are highly diverse, which most likely increases the P. fluorescens survival (Silby et al. 2009). The ecological flexibility of such bacteria allows them to exploit a wide variety of nutrients to adapt to environmental changes for survival. P. fluorescens also improves plant growth by producing phytohormones such as auxins (e.g., IAA -Karabaghli et al. 1998). It also has a high capacity for phosphorus solubilization and can produce siderophores (Matthijs et al. 2007). Despite the very well-known positive effects of P. fluorescens on plant survival, only a few studies have been conducted to study its influence on the growth of forest species (Rincón et al. 2008, Ouahmane et al. 2009). We recently demonstrated that the inoculation of Aleppo pine (Pinus halepensis Mill.) with P. fluorescens CECT 844 improved the vegetative growth and N absorption of the P. halepensis seedlings (Dominguez et al. 2012).The use of environmental-friendly natural microbial inocula, such as PGPR or mycorrhizal fungi, is presented in this study as a potential alternative fertilizers. These microorganisms are also beneficial for the maintenance of pre-existing soil microflora, thus contributing to the conservation of soil biodiversity. The amended soil in the nursey increases the vegetative vigor and morphophysiological quality of forest species growth for reforestation purposes (Chanway 1997).Information regarding the productivity of ectomycorrhizal fungi, their ecological functions and their contributions to the productivity and recovery of altered agroecosystems is increasingly valuable in agroforestry. In Spain, the black truffle (Tuber melanosporum Vitt.) is of substantial economic and social value in rural areas of the Mediterranean (Reyna 2007), although studies on the contributions of T. melanosporum to the growth and physiology of forest plants are scarce (Domínguez-Nuñez 2002). Moreover, the ecological value of such symbiosis in the recovery of Mediterranean ecosystems has not been well characterized.The...

Inoculation of mycorrhizal fungi and rhizobacteria in plants can improve their growth and physiological status, which could be particularly important for agricultural and forestry plants used for the revegetation of arid areas. Prosopis juliflora is a forest pioneer species that is drought resistant and has multiple uses (fodder, shade and shelter for livestock; timber and firewood, live fences and windbreaks in agroforestry systems). Azospirillum brasilense is a rhizobacterium that improves the growth of many agricultural crops. The hypothesis of this study was that P. juliflora seedlings produced in the nursery can respond positively to inoculation with A. brasilense CECT 590. Five months after inoculation, we examined the growth, water relations (osmotic potential at full turgor, osmotic potential at zero turgor, and the modulus of elasticity at full turgor), and concentration and content of macronutrients (N, P, K, Ca and Mg) in the seedlings. Subsequently, a trial was conducted to analyse root growth potential. A. brasilense CECT 590 inoculation caused an osmotic adjustment in P. juliflora seedlings but decreased the elasticity of the cell walls. Inoculation with A. brasilense CECT 590 significantly improved plant growth due in part to an increase of N concentration in the seedlings. A. brasilense CECT 590 inoculation also caused an increase in the root growth potential. The increased growth of P. juliflora seedlings inoculated with A. brasilense was probably caused by more than one mechanism. Inoculation with A. brasilense at the nursery may be a suitable technique for producing improved seedling material for restoration purposes.Key words: PGPR; osmotic adjustment; elastic adjustment; mineral nutrition; nursery; root growth potential. Resumen La inoculación de Azospirillum brasilense mejora la calidad de las plántulas de un mezquite (Prosopis juliflora)La inoculación de hongos de micorrizacion y rizobacterias en las plantas puede mejorar su crecimiento y calidad fisiológica, especialmente en plantas agrícolas y forestales empleadas para la regeneración de zonas áridas. Prosopis juliflora es una especie forestal pionera, resistente a la sequía, y de usos múltiples (forraje, sombra y cobijo para el ganado, madera y leña, cercas vivas y cortinas cortavientos en sistemas agroforestales). Azospirillum brasilense es una rizobacteria que mejora el crecimiento de muchos cultivos agrícolas. La hipótesis de este estudio fue que las plántulas de P. juliflora producidas en vivero pueden responder positivamente a la inoculación con A. brasilense CECT 590. Cinco meses después desde la inoculación, se analizó el crecimiento, relaciones hídricas (potencial osmótico en saturación, potencial osmótico en el punto de pérdida de turgencia, y módulo de elasticidad a total turgor), concentración y contenido de macronutrientes (N, P, K, Ca y Mg) en las plántulas. Posteriormente se realizó un ensayo para analizar el Potencial de Crecimiento Radical. La inoculación de A. brasilense CECT 590 causó un ajuste osmótico de las ...

© iForest -Biogeosciences and Forestry IntroductionPinus halepensis is one of the most common tree species in the Mediterranean and is also frequently used for reforestation purposes (Maestre & Cortina 2004). Several studies have been carried out with the aim of improving the quality of P. halepensis seedlings obtained from nurseries (Caravaca et al. 2005). The application of chemical fertilizer treatments to forest seedlings in nurseries is the most common cultivation practice. However, it has been established that soil amendments, including ectomycorrhizal fungi and plant growth-promoting rhizobacteria (PGPR), increase plant survival and seedling quality, especially in soils with low microbial activity (Chanway 1997, Probanza et al. 2001.Pseudomonas fluorescens has several characteristics of an effective PGPR and may function as a plant growth stimulator that efficiently promotes seed germination, accelerates growth in the early stages, induces root initiation, enhances the formation of roots and root hairs, facilitates root regeneration and helps to control pathogens in certain forest species. P. fluorescens is easily cultivated in vitro and colonizes a wide range of ecological niches, including the rhizospheres of plants (Bolton et al. 1993); additionally, P. fluorescens genomes are highly diverse (Silby et al. 2009), which likely increases the survival capacity of this microorganism. P. fluorescens improves plant growth by producing phytohormones, such as auxins (IAA), gibberellins and cytokinins, as well as specific amino acids. Furthermore, these bacteria have a high capacity for phosphorus solubilization and are able to produce siderophores (Matthijs et al. 2007).Despite the well-known positive effects of P. fluorescens on plant survival (Silby et al. 2009), only a small number of studies have examined its influence on the growth of forest species (Ouahmane et al. 2009, LucasGarcía et al. 2004). Some of these effects have been observed specifically in P. halepensis inoculated with P. fluorescens Aur6 (Rincón et al. 2008). Recently, we showed that inoculation of Aleppo pine with P. fluorescens CECT 844 improved both its vegetative growth and N uptake (Dominguez et al. 2012).It has been demonstrated that the frequent use of chemical fertilizers in nurseries leads to soil contamination, as chemical fertilizers are not completely assimilated by the seedlings. Furthermore, the industrial practices necessary for the chemical synthesis of compounds containing inorganic nitrogen require the use of contaminating petroleum products, high temperatures and high pressures. Considering these issues, the use of natural, "environmentally friendly" microbial inoculums, such as PGPR rhizobacteria or mycorrhizal fungi, as alternative fertilizers can be considered as a potential future solution. These microorganisms are also beneficial for the maintenance of pre-existing soil microflora, contributing to the conservation of biodiversity. The amended soil eventually enhances the vegetative vigor and the morphophysiological at...

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