KIU Publications

Background: Polyphenols from root exudates and polyphenol-rich organicinputs may shape soil microbiomes, enzyme activities, and crop nutrientoutcomes, with relevance to regenerative agriculture.Objectives: To quantify the effects of plant- and soil-derived polyphenols/polyphenol-rich soil inputs on i) soil microbial alpha-diversity and enzymeactivity and ii) crop yield and nutrient quality and to summarise mechanisticpathways and evidence certainty.Methods: Following the Preferred Reporting Items for Systematic Reviews andMeta-Analyses (PRISMA) 2020 statement, we searched PubMed, Web of Science,Scopus, Embase, and CAB Abstracts (1990–March 2025) plus grey literature.Fifteen controlled studies (163 observations) met the Population, Intervention,Comparator, Outcomes, and Study design (PICOS) eligibility. Random-effectsmeta-analysis pooled standardised mean differences (SMDs; Hedges’ g) forcontinuous outcomes. To ensure reproducibility and statistical independence,we prespecified decision rules for selecting endpoints/time points andaggregated multiple within-study outcomes into study-level composites withineach domain. We explored moderators [polyphenol source class, purified vs.complex inputs, environment (field vs. controlled), soil pH, soil organic carbon(SOC), duration, and dose, where reported] via subgroup analyses and mixedeffects meta-regression. We assessed certainty using the Grading ofRecommendations, Assessment, Development and Evaluation (GRADE) approach.Results: Polyphenol inputs increased soil microbial alpha-diversity (pooledacross Shannon/Simpson indices) [SMD = +0.58, 95% confidence interval (CI)0.32–0.83; high certainty] and soil enzyme activity (SMD = +0.49, 95% CI 0.240.73; moderate certainty). Crop yield increased modestly (+6.8%, 95% CI 2.710.9; moderate certainty), while micronutrients iron (Fe) and zinc (Zn) improved modestly (low–moderate certainty) due to limited reporting and imprecision.Yield and nutrient-quality outcomes were secondary endpoints in most includedstudies and were available in a smaller, uneven subset, limiting generalisability.Heterogeneity was moderate (I2 ≈ 50%) and was partly consistent withdifferences between purified compounds vs. complex organic amendmentsand field vs. controlled environments.Conclusion and future directions: Plant- and soil-derived polyphenol inputsmeaningfully enhance soil microbial diversity and enzyme activity and maydeliver smaller, context-dependent gains in yield and crop micronutrientquality; future multi-season field trials with standardised polyphenol chemistry/dose reporting and functional multi-omics are needed to clarify persistence,dose–response relationships, and causal mechanisms.