Unravelling the Mechanisms Responsible for Crop Rotation and Sequencing Effects on Plant Performance

Abstract

Rhizosphere microbiomes are critical to plant productivity and can be altered by preceding plant species. Rhizosphere microbiomes are therefore essential in agricultural systems where we use crop rotation, plant communities organized in space and time, to optimize productivity. Crop rotations create soil legacies, changing soil abiotic and biotic properties over time, that in turn affect rhizosphere microbiome composition and plant health. However, it is difficult to distinguish between long-term crop rotation and preceding species effects on rhizosphere microbiomes. We used a greenhouse study to isolate the immediate legacy of previous species identity with a conditioning-response design. We tested the preceding species effects of maize, soybean, pea, and sunflower on maize seedling rhizosphere microbiomes and of spring wheat, soybean, and maize on soybean seedling rhizosphere microbiomes. Pea preceding maize resulted in the highest maize seedling biomass and was correlated with reduced arbuscular mycorrhizal fungal abundance and higher bacterial diversity. Soybean seedlings showed small differences in biomass among treatments, but soybean-soybean treatments resulted in qualitatively higher soybean biomass. Comparing results of this greenhouse study to results of long-term soil legacy studies in the same system suggests that some rotation effects we see in the field are strongly influenced by the preceding plant species for maize-soybean, soybean-maize, and pea-maize pairs, and these effects are mediated by specific assemblages of rhizosphere bacteria and fungi. Other rotation benefits, like those seen in spring wheat-soybean and sunflower-maize pairs in field studies, may derive more from long-term effects on soil properties.

Keywords: Rhizosphere microbiome, soil legacy, plant host identity, crop rotation