investigation the response of some photosynthetic attributes of stevia (stevia rebaudiana bertoni) to different active coal concentrations with several solvents

background and objectives: active coal is applied in tissue culture media as the absorbant of phenolic compounds and toxic materials; but no research has been done regarding its direct application like spray on plants. application of this material as the carbone source is based on researches done by sucrose; which had highly positive effect on plant growth and development. thus; a hypothesis was brought that applied active coal could be absorbed by charged particles on the plant surface, a portion via cuticle and others via stomata, then entered into carbon fixation cycle. the aim of this study was to investigate the application of active coal in order to increase stevia plant required carbon during photosynthesis beside the other carbon dioxide sources. since this plant possesses high supply of carbohydrate which prepares suitable system for such researches, it was selected for application of mentioned treatments.materials and methods: in order to investigate the effect of different concentrations of active coal on some photosynthetic attributes of stevia, an experiment was carried out in a factorial based on randomized complete blocks design (rcbd) with four replications. evaluated treatments consisted of different concentrations of active coal solution of 0, 0.2, 0.4 and 0.6 percent. thus, the mentioned material was diluted in solvents such as methanol 15%, borric acid 3 ppm, acetic acid 1 ppm and distilled water. treatments were sprayed on plants with intervals of 10-day until plants start flowering stage. chlorophyll fluorescence components such as min fluorescence under dark acclimated condition (fo), max fluorescence under dark acclimated condition (fm), variable florescence (fv), min fluorescence under light acclimated condition (fo'), max fluorescence under light acclimated condition (fm'), electron transport rate (etr), maximum photochemical quantum yield of photosystem (fv/fm), chlorophyll a, b and total chlorophyll were measured at beginning of flowering. additionally, the leaf dry matter and stevioside content of the leaves were also measured.results: results showed that application of active coal as a source of carbon is possible; and different concentrations of active coal in different solvents are significantly effective on all of the recorded parameters. based on means comparison analysis, the most optimum amount of photosynthetic parameters were related to concentration 0.6% of active coal; while other concentrations placed in next orders. also, the highest and the lowest optimum photosynthetic parameters were recorded in the solvents methanol (15%) (m), boric acid (3 ppm) (b), acetic acid (1 ppm) (a) and distilled water (control; c); respectively. also, different solvents (pconclusionfinally, it can be concluded that application of active coal with its appropriate solvent could decrease the obsulute plant requirement to carbon source existing in the environment or to be substituted. the applied result of this research is that application of mentioned treatments could increase the absorbed carbon by plant. increase of absorbed carbon might be oxidized and intered the photosynthetic cycle in plant, and no increase of atmospheric carbon would be occurred.