Variation of N cycle guilds of the rye rhizosphere microbiome is driven by crop productivity along a tillage erosion catena.

Abstract

Tillage erosion poses threats to crop yields. A transition towards more sustainable agricultural practices may be advanced by harnessing ecosystem services provided by plant microbiomes. However, targeting microbiomes at the agroecosystem scale necessitates bridging the gap to microscale structures of microbiomes. We hypothesized that differences of microbial nitrogen (N) cycle guilds in the rhizosphere of rye align with a soil catena that has been formed by tillage erosion. The rhizosphere was sampled at four sites, which captured a complete tillage erosion gradient from extremely eroded to depositional soils. The gene abundances characteristic of microbial N cycle guilds were assessed via metagenomics. The eroded sites showed the lowest plant productivity and soil mineral N availability, which was associated with an enrichment of glnA in the rhizosphere. Genes associated with dissimilatory nitrate-to-ammonium reducers and diazotrophy prevailed in the eroded soil profiles. The strongest correlations of the biomasses of rye plants along the catena with N cycle functions were observed for norBC. Thus, tillage erosion as a legacy of agricultural management aligns with substantial differences in rhizosphere microbiome functionality in N cycling. These microbiome differences were linked to plant shoot properties. Thus, the dynamics of the microbiome can be indirectly assessed by remote sensing.