The need for phosphate: at the root of the mycorrhizal symbiosis

Effects of P nutrition on growth and photosynthetic activity of tomato plants inoculated or not with AM fungi

Arbuscular mycorrhizal (AM) fungi colonize plant roots, improving mineral nutrition and promoting photosynthesis. Phosphorus (P) has a key role in plant physiology, affecting the photosynthetic process and being involved in sugar/carbon metabolism. The aim of this work was to investigate the effects of the arbuscular mycorrhizal symbiosis and P nutrition on the growth parameters and photosynthetic activity of tomato plants grown in controlled conditions. Plants were maintained in a growth chamber for 50 days and watered three times a week with a Long Ashton nutrient solution at three different P levels (32, 96 and 288 μM, respectively). At harvest, mycorrhizal colonization, biomass production, P and photosynthetic pigment concentrations were measured. Moreover, the photosynthetic efficiency relating to the activity of the two photosystems and the biochemical analysis of proteins extracted from thylakoid membranes were also performed. Results showed that inoculation did not affect growth parameters. AM symbiosis was strongly inhibited at the highest P level. Plant biomass production was positively correlated with increasing level of P. The analysis of chlorophyll fluorescence in inoculated plants highlighted that Y(I), Y(II), ETR(I), ETR(II) varied proportionally to the AM colonization and inversely proportionally to the P supply, whether this effect on NPQ and ETR occurs by a modulation of the xanthophyll cycle, remains to be established.

Impact of Plant-Microbe Interactions with a Focus on Poorly Investigated Urban Ecosystems-A Review

The urbanization process, which began with the Industrial Revolution, has undergone a considerable increase over the past few decades. Urbanization strongly affects ecological processes, often deleteriously, because it is associated with a decrease in green spaces (areas of land covered by vegetation), loss of natural habitats, increased rates of species extinction, a greater prevalence of invasive and exotic species, and anthropogenic pollutant accumulation. In urban environments, green spaces play a key role by providing many ecological benefits and contributing to human psychophysical well-being. It is known that interactions between plants and microorganisms that occur in the rhizosphere are of paramount importance for plant health, soil fertility, and the correct functioning of plant ecosystems. The growing diffusion of DNA sequencing technologies and "omics" analyses has provided increasing information about the composition, structure, and function of the rhizomicrobiota. However, despite the considerable amount of data on rhizosphere communities and their interactions with plants in natural/rural contexts, current knowledge on microbial communities associated with plant roots in urban soils is still very scarce. The present review discusses both plant-microbe dynamics and factors that drive the composition of the rhizomicrobiota in poorly investigated urban settings and the potential use of beneficial microbes as an innovative biological tool to face the challenges that anthropized environments and climate change impose. Unravelling urban biodiversity will contribute to green space management, preservation, and development and, ultimately, to public health and safety.

Role and potentialities of bacteria associated with Tuber magnatum: A mini-review

Among the hypogeous ectomycorrhizal fungi, the white truffle Tuber magnatum Picco is the species of greatest interest, both from an ecological and economic point of view. The increasing market demand of the precious white truffle along with the fall in its natural production led to a growing interest in cultivation techniques and encouraged truffle growers and researchers to deeper investigate factors that could affect and improve T. magnatum productivity. In this context, microbial communities play a central role. Indeed, in the last few years, the hypothesis of a potential link between microbial community composition and truffle orchard productivity is arousing a greater attention. Moreover, since the value of the prized T. magnatum can vary in relation to its provenience, the need to define a reliable tracking system is also emerging and bacteria appear to be a promising tool. Accordingly, the present mini-review summarises the knowledge currently available on T. magnatum microbial communities, focusing on the role of truffle-associated bacteria and highlighting similarities and differences between samples of different origin, to address the following issues: (i) Is there a correlation between microbial taxa and truffle ground productivity? (ii) Can bacteria actually be used as markers of T. magnatum geographic origin? The identification of microorganisms able to promote T. magnatum formation may represent an important advance in the field of truffle farming. Similarly, the detection of bacterial taxa that can be used as markers of T. magnatum origin could have a considerable impact on truffle industry and trade, even at local scale.