The alleviating effects of humic substances on photosynthesis and yield of Plantago ovate in salinity conditions

ABSTRACT: With regard to the rise of concern about environmental issues, the aims of the present research were the assessment of the salt induced changes in photosynthesis and yield of Plantago ovate, an important medicinal plant, as well as evaluation of the possible impacts of the humic substances on the photosynthesis especially in salinity conditions. The effects of three levels of humic acid (0, 50 and 100mgL-1), fulvic acid (0, 50 and 100 mgL-1) and salt (0, 50 and 100 mM) on plants in fifteen different treatment groups were evaluated. In contrast to qN (non photochemical quenching cofficient), salt stress reduced the amounts of Fv/Fm (maximum quantum yield of photosystem II), qPSII (the actual quantum yield), qP (photochemical quenching coefficient) and chlorophyll contents whereas the application of humic acid and fulvic acid, especially the first one, had promoting effects and damages caused by salinity conditions were significantly alleviated by the applied humic substances. In addition, the application of humic acid and fulvic acid not only had enhancing effects on the thousand grain weight but also alleviating ones on the salt induced reduction of yield.