Rhizosphere Cercozoa reflect the physiological response of wheat plants to salinity stress

Plant salinity stress index correlates with rhizosphere Cercozoa.

Protists are essential components of the rhizosphere microbiome, which is crucial for plant growth, but little is known about the relationship between plant growth and rhizosphere protists under salinity stress. Here we investigated wheat (Triticum aestivum L.) rhizosphere protistan communities under naturally occurring salinity (NOS) and irrigation-reduced salinity (IRS), and linked a plant salinity stress index (PSSI) to different protistan groups in a nontidal coastal saline soil. We found that the PSSI was significantly correlated with rhizosphere cercozoan communities (including bacterivores, eukaryvores, and omnivores) and that these communities were important predictors of the PSSI. Structural equation modeling suggested that root exudation-induced change in bacterial community composition affected the communities of bacterivorous and omnivorous Cercozoa, which were significantly associated with the PSSI across wheat cultivars. Network analysis indicated more complex connections between rhizosphere bacteria and their protistan predators under IRS than under NOS, implying that alleviation of salinity stress promotes the predation of specific cercozoans on bacteria in rhizospheres. Moreover, the Cercomonas directa inoculation was conducive to alleviation of salinity stress. Taken together, these results suggest that the physiological response of wheat plants to salinity stress is closely linked to rhizosphere Cercozoa through trophic regulation within the rhizosphere microbiome.