Response of Root Arbuscular Mycorrhizal Fungi Colonization Rate to Biochar, Compost, and Manure: A Global Meta-Analysis

Arbuscular mycorrhizal fungi (AMF) form symbiotic interactions with most terrestrial plants, enhancing nutrient uptake and stress resilience. Organic amendments like biochar, compost, and manure are advocated to improve soil health and promote AMF symbiosis. However, empirical evidence of their effects on root AMF colonization is inconsistent, and a systematic understanding of the governing factors is lacking. Here, we synthesized the responses of root AMF colonization in agricultural systems to biochar, compost, and manure input from 85 studies (663 pairs of observations) globally based on a meta-analysis. Overall, biochar and compost/manure significantly increased root AMF colonization. However, these effects were highly context-dependent. Biochar most strongly promoted colonization in coarse-textured soils with low total potassium (TK ≤ 25 g kg−1) and high total carbon (TC ≥ 11 g kg−1), particularly for fruit and tuber crops. In contrast, compost/manure were most effective in fine-textured soils with high TK (≥25 g kg−1) and low bulk density (BD ≤ 1.3 g cm−3). Notably, compost/manure suppressed colonization in neutral pH (6.5 < pH < 7.5) and high BD soils (>1.3 g cm−3). Key amendment properties drove these responses: biochar with low electrical conductivity (EC < 5 dS m−1), high sodium and low macronutrient content was most beneficial, whereas compost/manure with high total nitrogen (TN > 9 g kg−1) and low organic carbon (OC ≤ 500 g kg−1) performed best. The efficacy of organic amendments in enhancing AMF symbiosis is not universal but dictated by a complex interplay of soil properties and amendment characteristics. Our findings provide a robust, quantitative framework for tailoring amendment strategies to specific agro-ecological contexts, enabling farmers and land managers to selectively use biochar or compost/manure to harness AMF benefits for sustainable crop production.