Unveiling the Microbiota Diversity of the Xerophyte Argania spinosa L. Skeels Root System and Residuesphere

Abstract

The microbiota associated to xerophyte is a “black box” that might include microbes involved in plant adaptation to the extreme conditions that characterize their habitat, like water shortage. In this work, we studied the bacterial communities inhabiting the root system of Argania spinosa L. Skeels, a tree of high economic value and ecological relevance in Northern Africa. Illumina 16S rRNA gene sequencing and cultivation techniques were applied to unravel the bacterial microbiota’s structure in environmental niches associated to argan plants (i.e., root endosphere, rhizosphere, root-surrounding soil), not associated to the plant (i.e., bulk soil), and indirectly influenced by the plant being partially composed by its leafy residue and the associated microbes (i.e., residuesphere). Illumina dataset indicated that the root system portions of A. spinosa hosted different bacterial communities according to their degree of association with the plant, enriching for taxa typical of the plant microbiome. Similar alpha- and beta-diversity trends were observed for the total microbiota and its cultivable fraction, which included 371 isolates. In particular, the residuesphere was the niche with the highest bacterial diversity. The Plant Growth Promotion (PGP) potential of 219 isolates was investigated in vitro, assessing several traits related to biofertilization and biocontrol, besides the production of exopolysaccharides. Most of the multivalent isolates showing the higher PGP score were identified in the residuesphere, suggesting it as a habitat that favor their proliferation. We hypothesized that these bacteria can contribute, in partnership with the argan root system, to the litter effect played by this tree in its native arid lands.

Isolation and Functional Analysis of a PISTILLATA-like MADS-Box Gene from Argan Tree (Argania spinosa)

“…Besides the differences, we observed higher homogeneity among trees from Korbous, Sousse, and Sfax sites than within the botanical garden population. In addition, trees from Sousse and Sfax seem to be more closely related, in agreement with previous analyses [ 7 , 11 ].…”

“…Other than their considerable socioeconomic value, Argan trees have a great ecological interest. This species has no requirements for the type of soil and tolerates a wide pH range and high concentration of limestone [ 7 ]. Furthermore, Argan trees improve the quality of soil and water around them [ 8 ], and the root structures of this species and its high tolerance to aridity and high temperature make it a unique tool to counteract desertification [ 6 ].…”

“…Furthermore, Argan trees improve the quality of soil and water around them [ 8 ], and the root structures of this species and its high tolerance to aridity and high temperature make it a unique tool to counteract desertification [ 6 ]. The study of the argan tree population from Tunisia revealed large variability both within and between the studied sites [ 7 ]. The characterization and preservation of these populations could improve biodiversity in arid and semi-arid areas of Tunisia.…”

“…While many studies have been previously carried out to characterize the fruits, kernels, and leaves of the Argan [ 7 , 9 , 10 , 11 ], there is limited information concerning flower development [ 12 , 13 , 14 , 15 ]. Even more, to date, there is no available information of genes specifically involved in flower or fruit development in these species.…”

Microbial Diversity of Upland Rice Roots and Their Influence on Rice Growth and Drought Tolerance

“…Many bacterial strains with PGP potential have been screened in the laboratory. The production of EPS by some PGPB can ameliorate the water-holding capacity of the soil and promote the stability of soil aggregates, which is particularly relevant in arid environments [ 92 ]. Moreover, despite widespread claims of efficacy of inoculation with PGPB under laboratory conditions, many studies have been unable to attribute the beneficial effects to a specific trait and suggest that untapped mechanisms await discovery [ 93 ], and there is limited evidence of inoculation success and subsequent benefits for plant growth under drought stress [ 12 ].…”