Salinity of irrigation water selects distinct bacterial communities associated with date palm (Phoenix dactylifera L.) root.

Saline water irrigation has been used in date palm (Phoenix dactylifera L.) agriculture as an alternative to non-saline water due to water scarcity in hyper-arid environments. However, the knowledge pertaining to saline water irrigation impact on the root-associated bacterial communities of arid agroecosystems is scarce. In this study, we investigated the effect of irrigation sources (non-saline freshwater vs saline groundwater) on date palm root-associated bacterial communities using 16S rDNA metabarcoding. The bacterial richness, Shannon diversity and evenness didn't differ significantly between the irrigation sources. Soil electrical conductivity (EC) and irrigation water pH were negatively related to Shannon diversity and evenness respectively, while soil organic matter displayed a positive correlation with Shannon diversity. 40.5% of total Operational Taxonomic Units were unique to non-saline freshwater irrigation, while 26% were unique to saline groundwater irrigation. The multivariate analyses displayed strong structuring of bacterial communities according to irrigation sources, and both soil EC and irrigation water pH were the major factors affecting bacterial communities. The genera Bacillus, Micromonospora and Mycobacterium were dominated while saline water irrigation whereas contrasting pattern was observed for Rhizobium, Streptomyces and Acidibacter. Taken together, we suggest that date-palm roots select specific bacterial taxa under saline groundwater irrigation, which possibly help in alleviating salinity stress and promote growth of the host plant.

Fungal community assemblage of different soil compartments in mangrove ecosystem.

The fungal communities of different soil compartments in mangrove ecosystem are poorly studied. We sequenced the internal transcribed spacer (ITS) regions to characterize the fungal communities in Avicennia marina root-associated soils (rhizosphere and pneumatophore) and bulk soil compartments. The rhizosphere but not pneumatophore soil compartment had significantly lower fungal species richness than bulk soil. However, bulk soil fungal diversity (Shannon diversity index) was significantly higher than both pneumatophore and rhizosphere soil compartments. The different soil compartments significantly affected the fungal community composition. Pairwise sample analyses showed that bulk soil microbial community composition significantly different from rhizosphere and pneumatophore soil compartments. There was, however no significant difference observed between rhizosphere and pneumatophore soil fungal community composition and they shared relatively more OTUs between them. Further, there was a significant correlation observed between fungal community compositional changes and carbon or nitrogen availability of different soil compartments. These results suggest that few characteristics such as fungal richness and taxa abundance of rhizosphere and pneumatophore soil compartments were significantly different in mangrove ecosystem.

Pyrosequencing-Based Seasonal Observation of Prokaryotic Diversity in Pneumatophore-Associated Soil of Avicennia marina.

Pneumatophores are aerial roots developing from the main roots of mangrove plants away from the gravity. The below ground pneumatophore-associated soil prokaryotic community of Avicennia marina was studied by amplicon pyrosequencing (39,378 reads) during monsoon and summer seasons. Apart from the most dominant phylum Proteobacteria in both seasons, the second most were Acidobacteria (summer) and Cyanobacteria/Chloroplast (monsoon). Similarly, Acidobacteria_Gp10 and Cyanobacteria were the second most abundant at class level during summer and monsoon, respectively. Archaeal phylum Thaumarchaeota was the most abundant followed by Crenarchaeota and Euryarchaeota. The classes detected in our study were Thermoprotei, Halobacteria, and Methanomicrobia. The highest richness and diversity were observed during summer for bacteria, whereas the same phenomena for archaea in monsoon at 97% sequence similarity. To the best of our knowledge, this is the first attempt to catalog the prokaryotic diversity of pnueumatophore-associated soil.