Light-Root Microbiome Interactions in Vegetable Crops: From Photoreceptor Signaling to Exudate-Mediated Recruitment.

In protected cultivation, light intensity, spectral quality, red/far-red ratio, photoperiod and diel fluctuation can alter the belowground biological environment by modifying carbon allocation, root architecture, root exudation, nutrient acquisition, immune tone and rhizosphere physicochemistry. Direct community-level evidence in vegetables remains sparse, but targeted experiments on bacterial colonization, arbuscular mycorrhizal symbiosis, beneficial fungi and root pathogens show that light can condition specific plant-microbe interactions. This review develops a molecular framework for light-root-microbiome interactions in protected vegetable crops and distinguishes direct community evidence, targeted colonization or symbiosis evidence, crop-specific indirect evidence and mechanistic analogues. We synthesize how photoreceptors and PIF-, HY5-, hormone- and immunity-related pathways regulate root niche construction, while also considering direct microbial photoreception. Experimental examples include tomato rhizosphere responses to shading, R:FR-dependent colonization by Serratia plymuthica, phyB-HY5-strigolactone control of tomato mycorrhization, light-intensity effects on lettuce-AMF interactions, spectrum-dependent Trichoderma harzianum colonization and light sensing by Ralstonia pseudosolanacearum. The evidence supports the view that light acts as a conditional regulator whose effects depend on crop genotype, microbial partner, substrate, nutrient status and developmental stage. Progress will require factorial lighting experiments coupled with exudomics, stable-isotope tracing, absolute microbial quantification, isolate genomics, synthetic communities and pathogen-challenge assays.