The aim of the experiment was to determine the effect of subsoil inoculation with fungi of the genus Trichoderma on the cadmium phytoavailability and process of photosynthesis of oat (Avena sativa). A two-factor pot experiment was established, in which the 1st variable factor was the presence or absence of Trichoderma fungi in the substrate, while the 2nd order factor was the increasing soil content of cadmium. During the plant growing season, disturbances in the photosynthesis process were monitored by measurements of the chlorophyll content and fluorescence parameters (on the first, third and flag leaf). The following parameters were determined: F0 – zero fluorescence of objects adapted to darkness, FM – maximum fluorescence, FV – variable fluorescence, FV/F0 – maximum efficiency of water splitting at the donor side of PSII and FV/FM - maximum photochemical efficiency of PSII.  After completion of the pot experiment, the yield of the plant and the content of cadmium in roots and aerial parts were determined. The results indicate that an increasing cadmium concentration in the soil did not influence the yield of roots and straw of oat, although it caused a significant decrease of grain yield. The cadmium concentration in roots and aerial parts of oat was increasing proportionally to the increasing amount of this metal in the soil, and the addition Trichoderma fungi did not influence significantly the yield and cadmium phytoavailability by roots and aerial parts of oat. The biggest changes in values of chlorophyll fluorescence parameters were noted on the first leaf. The addition of Trichoderma fungi to the subsoil had a positive influence on the content of chlorophyll in leaves.

23.2.2018