Responses of the Corylus avellana Colonized by the Tuber Melanosporum Mycorrhiza to Short-Term Rhizosphere Disturbance

We hypothesized that Tuber melanosporum colonization enhances growth and photosynthetic performance in Corylus avellana seedlings. Forty-eight seedlings were assessed for root colonization (stereomicroscopy, ITS sequencing) and photosynthetic traits (Li-6800F) under short-term disturbed and undisturbed rhizosphere conditions. Mycorrhizal colonization was found in 97.9% of seedlings (47/48). The mean colonization was 33.1% (SD = 16.1), 16.7% of seedlings showed more than 50% colonization per seedling, and 65.0% showed more than 30% colonization per seedling. Colonization declined with root depth and correlated with seedling length (r = 0.371, p = 0.01). In disturbed roots, longer root length predicted higher Gsw (r = 0.60), PhiCO2 (r = 0.77), and PhiPSII (r = 0.70), while collar diameter negatively affected transpiration (r = −0.60). In undisturbed roots, collar-proximal colonization improved PhiPSII (r = 0.69, p = 0.02). Undisturbed seedlings showed ~2× higher CO2 assimilation, stomatal conductance, quantum yield, and transpiration. These findings confirm that T. melanosporum enhances seedling physiology, especially under undisturbed conditions.