A SWEET Challenge: Less Sugar for Rhizospheric Microbiome Under the Successive Wheat Cultivatoin

Considering the crucial role of root exudates, we hypothesized that continuous wheat cultivation would lead to lower glucose release, resulting in lower microbial growth, activity, and biomass. For the first time in situ glucose imaging was optimized for studying the interactions in the first (W1) and third (W3) wheat after break crop plots in the field. Glucose imaging method combined with soil microbial respiration, enzyme kinetics and the quantification SWEET genes expression levels in wheat plants. W3 had the lowest proportion of hotspots for glucose release with 1.35 % of the total soil surface area, indicating a 17.7 % decline compared to W1. Also, the expressions of functional orthologous genes of SWEET1a in wheat roots were significantly upregulated in W3 compared to W1. The growing microbial biomass in the rhizosphere soil of W1 was about five times higher than W3. Differences in SWEET gene expression and shift in glucose release is linked to altered root physiology and exudation processes, potentially reflecting the plant's strategy to create a less favourable environment for opportunistic pathogens. Hence, this study provides novel insights into the complex interactions between continuous wheat cultivation, root exudation, microbial dynamics, gene expression, and enzymatic activities. Overall design: This study examines the impacts of continuous wheat cultivation on glucose release, microbial growth and activity, and the expression of sugar transporter genes. We propose the following hypotheses: i) continuous wheat cultivation differentially alters sugar transporter gene expression in roots and leaves; ii) reduced SWEET gene expression lowers glucose release, decreasing microbial growth, activity, and biomass in the rhizosphere; and iii) diminished glucose exudation reduces microbial functionality, reflected in lower enzyme activity and efficiency. These hypotheses were tested using root window installations, in situ glucose imaging, gene expression analysis of SWEET genes in roots and leaves, and destructive soil analyses of microbial growth and enzyme kinetics in first- and third-year wheat plots following a break crop at the Hohenschulen field, CAU Kiel.