Combined effects of glufosinate ammonium and temperature on the growth, photosynthetic pigment content and oxidative stress response of Chlorella sp. and Pseudokirchneriella subcapitata

There has been concern over the potential adverse effects of glufosinate ammonium, a widely used herbicide, on microalgae. This study aimed to assess the combined effects of glufosinate and temperature on Chlorella sp. CHSS262, which was isolated from a farmland in Malaysia, in comparison with the model microalga Pseudokirchneriella subcapitata. The following parameters were assessed: growth, pigment content and oxidative stress response. Results showed that Chlorella sp. (EC25 = 120 mu g mL(-1)) was more tolerant to glufosinate than P. subcapitata (EC25= 43 mu g mL(-1)) when grown at 28 degrees C. Both microalgae were then exposed to glufosinate at EC25 at different temperatures (10, 18, 28, 33 and 38 degrees C) for 8 days. While P. subcapitata could grow from 10 to 38 degrees C, with optimal temperature between 18 and 28 degrees C, the lower temperature limit of Chlorella sp. was 18 degrees C. There was only minimal growth inhibitory effect of glufosinate on Chlorella sp. over the range of temperatures tested. In comparison, the inhibitory effect of glufosinate on P. subcapitata was less pronounced at extreme temperatures (10 and 38 degrees C) compared to that at 18 to 33 degrees C. High ROS levels and increased lipid peroxidation were detected in P. subcapitata at 10 and 38 degrees C in both the control and glufosinate-treated cultures. Principal component analysis (PCA) showed that there was significant correlation between ROS and lipid peroxidation in P. subcapitata but not in Chlorella sp. Overall, the results showed that Chlorella sp. and P. subcapitata responded differently to temperature and glufosinate, especially in regard to oxidative stress response although both species were highly resistant to the herbicide.