Low inorganic phosphorus (Pi) supply limits the photosynthetic process and hence plants growth and development. Contradictory reports exist in the literature on whether mycorrhyzal association can attenuate the negative effects of low Pi supply on photosynthesis and growth. In the present paper, the effect that low Pi supply may have on photosynthesis and growth of papaya Maradol plants was evaluated in intact plants and in those inoculated with two different strains of the arbuscular mycorrhizal fungi Glomus intraradices. Plant growth was significantly reduced as the Pi supply decreased. However, inoculation with any strain of G. intraradices was able to attenuate such effect. Without Pi in the nutrient solution, the mycorrhizal plants had on average 6.1 times and 7.5 higher photosynthesis than non mycorrhizal plants. The chlorophyll fluorescence values were significantly higher in mycorrhizal than in non-mycorrhizal plants. These results could be associated to an increased ability of mycorhyzal plants to take up Pi from the substrate, as they had higher Pi content than non-mycorrhizal plants. A high correlation was found between internal Pi content and plant biomass. The lower correlation between Pi content and photosynthesis, suggests that some photosynthates could had been used to maintain the symbiosis. 1. Introduction The scarcity of nutrients is a factor that limits physiological processes in plants, including photosynthesis, their growth, and development [1]. Phosphorus (P) deficiency normally reduces the root system development and plant establishment because it has an important role in cell division, growth, photosynthesis (Pn), respiration, energy storage, and transfer [2–4]. So that, in many agricultural systems, it is necessary to supply P in order to have good productivity [5]. When plants grow with nutrient scarcity, some of them are capable of modifying their root architecture, to exude organic acids, or to establish associations with some beneficial organisms as strategies to compensate for the low concentration of nutrient in the substrate. Among the beneficial organisms for plants, the arbuscular mycorrhizal (AM) fungi have a very important role in plant nutrition [6, 7]. It is through AM association that plants increase their capacity to take up organic phosphorus (Pi) from the soil solution [8–10] that normally translates into better growth than that of non-AM plants [11, 12]. Nevertheless, it has been reported that AM association could be more or less beneficial to the plant growth depending on the plant species and the AM fungi
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