The soil hydrogel improved photosynthetic performance of beech seedlings treated under drought

The effect of soil amendment with the STOCKOSORB 500 MICRO hydrophilic polymer on the photosynthetic traits in beech seedlings (Fagus sylvatica) during 50 days of dehydration was investigated. Dehydration was detected through osmotic potential in the assimilatory organs of beech seedlings. The addition of Stockosorb positively affected the CO2 assimilation rate (A) and instantaneous water use efficiency (A/T), for severely drought-treated seedlings. In comparison with irrigated plants, the values of A of non-irrigated plants with Stockosorb substrate decreased by 50%, and in non-irrigated plants with common substrate by 88%. The fast kinetics of chlorophyll a fluorescence indicated chronic photoinhibition under drought treatment without Stockosorb, while no significant changes in maximal quantum efficiency (Fv/Fm) were recorded under drought treatment with Stockosorb. The actual quantum efficiency of PSII markedly decreased in both treatments – with and without Stockosorb, though significant differences were found only between control treatments and drought treatment without Stockosorb. Moreover, the thermal energy dissipation (NPQ) was strongly limited under severe drought stress. The capacity to down regulate PSII functionality through non-photochemical quenching was maintained under drought treatment with Stockosorb. The results indicate that an amendment with soil conditioner significantly improved the photosynthetic performance of drought-stressed beech seedlings.