Effect of pendimethalin on growth and photosynthetic activity of Protosiphon botryoides in different nutrient states

The effect of pendimethalin on the green alga Protosiphon botryoides was investigated. Results indicate that specific growth rate, cell number, chlorophyll a level, and dry weight yield significantly decrease with increasing pendimethalin concentrations, while protein and carbohydrate contents increase significantly. On the other hand, photosynthetic activity decreases whereas dark respiration increases with high pendimethalin concentrations. High doses of pendimethalin exhibited no clear trend with 77 K fluorescence (Fv/Fm). Increasing nitrate and phosphate levels led to a decrease in cell number, chlorophyll a, and dry weight as compared with the control at high doses of pendimethalin. The results obtained revealed that N:P < 1 increases the inhibitory effect of high doses of the herbicide.