Microbiome effects on maize form and function under altered watering conditions

Kelsey R. Carter, John P. Heneghan, L. Turin Dickman, Dea Musa, Jeffrey M. Heikoop, Brent D. Newman and Sanna Sevanto, Earth & Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, NM, Eric R. Moore, Anthony J. Sabella, Michaeline Nelson Albright, Christina R. Steadman, Scott Twary and John M. Dunbar, Bioscience Division, Los Alamos National Laboratory, Los Alamos, NM, Christine M. Anderson-Cook and Abigael C. Nachtsheim, Statistical Sciences, Los Alamos National Laboratory, Los Alamos, NM, Nicholas E. Lubbers, Information Sciences, Los Alamos National Laboratory, Los Alamos, NM, Louise H. Comas, Water Management Research Unit, USDA - Agricultural Research Service, Fort Collins, CO, Chris M. Yeager, Chemical Diagnostics and Engineering Division, Los Alamos National Laboratoy, Los Alamos, NM

Background/Question/Methods
Developing methods to improve maize resistance to drought is essential to provide food security to a growing population. One approach to tackling this complex issue is through identifying microbiomes that improve plant performance under drought conditions. To identify key microbiome-dependent, plant drought resistance traits, we grew two generations of Zea mays, inoculated with microbiomes originating from contrasting environments under two irrigation treatments in a greenhouse using an artificial soil. Well-watered treatment plants were irrigated to pot field capacity (65% relative water content), while the drought treatment plants were maintained at 45% relative water content. For the first generation, we inoculated plants in both watering treatments with a microbiome from a historically droughted agricultural field or a microbiome collected from pine forest soils. At the end of the first generation, we reused the soil from each to inoculate our second generation of maize soil. For the second generation, we either maintained or switched the watering treatment to investigate how water treatment stability affects a microbiome’s ability to alter plant traits. This design allowed us to assess form and function of maize exposed to 1) different microbiomes, 2) different watering treatments, and 3) switched watering treatments.
Results/Conclusions
We found that microbiomes affected both plant form and function; however, modified growth patterns appeared more quickly than changes to plant physiological processes. After one generation, maize plants grown in a microbiome from a historically droughted field were shorter, had smaller stem diameters, and less root biomass, allowing for more soil water conservation. Noticeable differences in plant physiological processes did not occur until the microbiomes had developed under two generations of maize. Independent of microbiome, we found higher water use efficiency in the second-generation droughted plants, compared to the first generation. Plants with microbiomes exposed to the drought treatment for both generations had lower photosynthesis and stomatal conductance compared to plants with microbiomes under full water treatment for both generations. Switching the watering treatment had a stabilizing effect on how the microbiome influenced plant function. Plants with a “switched” watering treatment maintained higher photosynthesis and stomatal conductance in both half and full-water conditions, suggesting a microbiome legacy effect. Our data suggest that microbiomes adapted to drought can quickly promote drought-tolerance changes in plant form; however, it takes greater microbiome selection pressure through prolonged drought exposure (i.e. more microbial generations) to influence maize function.