Rhizosphere effect on soil pH decrease in the arid area but not humid area across global agricultural ecosystems

The pH of rhizosphere significantly influences crop growth, stress resistance, and yield by regulating soil nutrient transformation, microbial activity, and crop hormone metabolism in agroecosystem. Despite its pivotal role, the comprehensive global-scale quantification of magnitude, direction, and driving factors of rhizosphere effect on soil pH is lacking. Thus, a comprehensive meta-analysis including 906 individual cases of the rhizosphere effect on soil pH from 102 target literatures together with biotic and abiotic variables was conducted across the worldwide agricultural ecosystem. Our results revealed that the overall rhizosphere effect on soil pH significantly decreased by 1.04 ± 0.20%, but this trend varied across climatic regions, management practices, and soil properties. Specitively, rhizosphere effect on soil pH significantly decreased by 1.34 ± 0.10% in arid areas (aridity index 0.65). Besides climatic factors, the rhizosphere demonstrated a pronounced pH-reducing effect in soils with initial soil pH of 6.5-7.5 and soil organic carbon of 10-20 g kg-1. Soybean, identified as the most sensitive crop, caused a significant 3.00% and 1.73% reduction for rhizospheric pH in arid and humid areas, respectively. Soil nutrients and microbial communities and functions in humid areas proved more susceptible to changes induced by rhizospheric pH compared with arid areas. In summary, our findings underscore the potential for agricultural activities, particularly soybean cultivation in arid regions, to contribute significantly to soil acidification on a global scale, especially in neutral soils.