Effects of di-n-butyl phthalate and di (2-ethylhexyl) phthalate on the growth, photosynthesis, and chlorophyll fluorescence of wheat seedlings

• The decrease of Pn was due to chlorophyll, Gs, Tr, Ci, and chlorophyll fluorescence.
• Stomatal limitation led to a reduction of Pn at 5 and 10 μg/mL DBP/DEHP.
• Stomatal and non-stomatal limitations caused the decrease in Pn at 20 μg/mL DBP/DEHP.
• The toxicity of DBP was significantly greater than that of DEHP.

Phthalates are commonly used man-made chemicals that can be released into soil, water, and the atmosphere. The potential toxicity of phthalates on wheat seedlings has not been well studied. To better understand the deleterious effects of di-n-butyl phthalate (DBP) and di (2-ethylhexyl) phthalate (DEHP) on wheat seedlings, their influences on the following were investigated: plant growth, net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), intercellular CO2 concentration (Ci), chlorophyll content, initial fluorescence (F0), maximal photochemical efficiency (Fv/Fm), photochemical quenching (qP), non-photochemical quenching (qN), effective quantum yield of photosystem II (ΦPSII), and photosynthetic electron transport rate (ETR). Compared with the control, the growth indices (plant height, fresh and dry weights of shoots, fresh and dry weights of roots), Pn, Gs, Tr, Ci, chlorophyll content, Fv/Fm, qP, ΦPSII, and ETR decreased in the 5 μg mL−1 and 10 μg mL−1 DBP and DEHP treatments, whereas F0 and qN increased. When wheat seedlings were treated with 20 μg mL−1 of DBP and DEHP, the growth indices, Pn, Gs, Tr, chlorophyll content, Fv/Fm, qP, qN, ΦPSII, and ETR decreased significantly, whereas Ci and F0 increased. A decrease in the Pn of wheat seedlings was mainly caused by stomatal limitation in the 5 μg mL−1 and 10 μg mL−1 DBP and DEHP treatments. However, stomatal and non-stomatal limitations may have caused the reduction in Pn in the 20 μg mL−1 DBP and DEHP treatments. Notably, the noxious effect of DBP on the wheat seedlings was significantly greater than that of DEHP.