Soil salinity alters acemannan content and sodium uptake in Aloe barbadensis Miller plants. A role for root-associated microbial communities?

Abstract Correlated acemannan and Na accumulation in leaf gel in response to soil salinity. Altered root-associated prokaryotic and fungal communities. Root prokaryotes shifted to monoderm bacteria associated with stress tolerance. Aloe barbadensis displays coordinated plant–microbe responses under soil salinity. Salinity adversely impacts soil ecosystems, by inducing osmotic stress, ionic imbalances, water deficit, and oxidative damage in plants. It also alters the composition of plant-associated microbial communities in the rhizosphere and roots, while disrupting microbial processes critical to nutrient cycles. Aloe vera ( Aloe barbadensis Miller), a xerophytic succulent plant, produces acemannan, a bioactive polysaccharide in its leaf gel with pharmaceutical applications. Acemannan contributes to drought tolerance by facilitating water storage within the leaf gel tissue. This study examined the effects of soil salinity on rhizosphere properties, plant nutrient acquisition, acemannan accumulation, and plant-associated microbial communities in A. vera plants grown in the field in Laconia, Greece. Both acemannan and sodium (Na) accumulated in the leaf gel in response to soil salinity, showing a strong positive correlation. Significant differences in the composition and structure of the rhizosphere and root microbial communities were also observed under salinity, with the prokaryotic microbial community in the plant roots showing a pronounced shift towards functionally relevant membership and abundance of monoderms. Moreover, we observed significant co-variation of changes in the acemannan and Na concentrations in the leaf gel with changes in the prokaryotic rhizosphere soil community and the fungal community in the roots. Our findings demonstrate enhanced accemanan production and indicate links between osmolyte accumulation and microbial community adaptation in A. vera under soil salinity.