Photosynthetic and antioxidant-related properties in blueberry under low- and high-density covering material

Covering material is an important tool to reduce damage from extreme weather events, especially in horticultural species. However, physiological and biochemical responses to covering material are still limited in woody plants. Thus, this study aimed to evaluate covering material effects on photosynthetic and antioxidant performance in blueberry cv. Legacy to high-density polyethylene (HDPE) and low-density polyethylene (LDPE) covering treatments under field conditions during two consecutive seasons. Our results showed that net photosynthesis (P-n) was reduced in LDPE compared to uncovered treatment during the first season. Interestingly, P-n increased 10% in HDPE compared to uncovered and LDPE treatments. Stomatal conductance (g(s)) was not affected by covering material; meanwhile, the transpiration (E) only showed a 22% increment in LDPE. HDPE exhibited the highest chlorophyll a in the 2018/2019 season compared to the uncovering treatment, as well as chlorophyll b and chlorophyll a/b ratio, but during the 2017/2018 season. A tendency to decrease chlorophyll a level in uncovered plants and LDPE treatment was observed during the 2018/2019 season. Antioxidant activity showed no differences among covering materials. By contrast, phenols increased in LDPE treatment followed by control plants, showing HDPE treatment the lower values during 2018/2019. In conclusion, this study demonstrated that blueberry plants subjected to HDPE treatment showed better P-n and chlorophyll levels than uncovered and LDPE treatments, which could be associated with the diffuse transmittance in HDPE, whereas a high E and phenols were observed in LDPE, whereas intrinsic water use efficiency was lower, which is related to high direct transmittance in this covering material during the summer season.