Abstract
Successive winter wheat (WW) rotations are associated with a substantial yield decline, and the underlying mechanisms remain elusive. An outdoor experiment was set up using sandy loam soil. WW was grown in rhizotrons, in soil after oilseed rape (KW1), after one season of WW (KW2), and after three successive seasons of WW (KW4). We applied zymography and harvested the plants at the stem elongation stage to observe changes in the activity of β-glucosidase (BGU) and leucine aminopeptidase (LAP), as well as using glucose (GLU) imaging to observe glucose release patterns in the rhizosphere of WW. Several biochemical and microbial properties of the bulk soil and the rhizosphere of the rotational positions were measured. KW2 and KW4 exhibited reduced plant biomass compared to KW1. There was a higher root length density and root mean diameter as well as a lower specific root length for KW1 compared to KW2 and KW4. KW1 soil had a lower mineral N concentration and microbial biomass carbon (C) and nitrogen (N) than KW2 and KW4, which translated to a lower plant C:N ratio. A greater rhizosphere extent of BGU and LAP across the soil profile was also visible for KW1 compared to KW2 and KW4 using zymography. Lower dissolved organic C and hotspot areas of GLU in the rhizosphere of successive WW might explain shifts in the microbial community composition, possibly leading to a dysbiosis with the soil microbes in the rhizosphere. Soil depth and rotational position explained most of the variance in the soil microbial communities. The relative abundance of Acidobacteriota, Gemmatimonadota, Nitrospirota, and Chloroflexi significantly varied among the rotational positions. Our results highlight the effect of WW rotational positions on soil and plant properties, as well as microbial community dynamics, and provide evidence for the pathways driving biomass decline in successively grown WW.
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