COS 60-4 - Cover cropping reduces the negative effect of salinity soil microbiome complexity

Abstract: Around one-third of the global cropped area under irrigation is tainted by the stress of soil salinization. Crops growing on such soils are subject to unfavorable growth conditions, including high osmotic stress, nutritional limitations and toxicities, which can result in up to 50% loss in yield. It also affects microbial communities and functions in soil, potentially jeopardizing vital ecosystem services and functions. It is believed that practices like cover cropping, that link to water management, can be deployed to ameliorate stress caused by soil salinity. However, we lack in-depth knowledge on how it impacts soil microbial communities. We hypothesized that microbial diversity and network complexity will be reduced in saline as compared to non-saline soils, and the reduction will be countered by inclusion of cover crops. We conducted a field study at four experimental cropping sites in North Dakota, all of which comprise of two levels of salinity (saline: SS, and non-saline: NS) and cover cropping with cereal rye (cover-cropped: CC, and non-cover-cropped: NC) – giving us four treatment combinations. Soil samples were analyzed for physico-chemical properties and phospholipid fatty acid (PLFA). We assessed microbial diversity and community composition by performing Illumina MiSeq sequencing of bacterial 16S rRNA and fungal ITS genes. We also employed the Illumina NovaSeq 6000 platform to determine changes in microbial functional attributes in response to salinity and cover cropping. Phospholipid fatty acid (PLFA) analyses revealed that cover crops had significant effect on the fatty acid concentration of fungi and gram-negative bacteria in soil. The overall microbial diversity was significantly increased under cover-cropping (p< 0.05), and it was indifferent to salinity levels. However, salinity led to significant changes in bacterial community structure. Affirming our hypothesis, we saw that incorporation of cover crops, in both saline and non-saline soils, led to more complex microbial networks with higher number of nodes, edges and average degrees. The bacterial family JG30-KF-CM45 of class Chloroflexia emerged as a prominent keystone taxon across all treatments, indicating it may be crucial for structuring the microbial communities. Genes involved in transcription and folate metabolism significantly varied across treatments. To the best of our knowledge, our study is the first looking into microbial networks of soils under combined salinity and cover cropping conditions. Altogether, our results identify key microbial players under salinity stress and identify the potential of utilizing cover crops to mediate negative effects of salinity on soil microbiomes.