Abstract
The objective of this study was to evaluate the activity of antioxidant enzymes, the functioning of the photosystem II and quality of C. xanthocarpa seedlings cultivated under intermittent water deficit and shading levels and the influence of shading on recovery potential after suspension of the stress conditions. The seedlings were subjected to three levels of shading (0, 30, and 70%), six periods of evaluation (start: 0 days; 1st and 2nd photosynthesis zero: 1st and 2nd P0; 1st and 2nd recovery: 1stand 2nd REC; and END), and two forms of irrigation (control: periodically irrigated to maintain 70% substrate water retention capacity, and intermittent irrigation: suspension of irrigation). The plants subjected to intermittent irrigation conditions at 0% shading showed a reduction in water potential (Ψw) and potential quantum efficiency of photosystem II (Fv/Fm) and maximum efficiency of the photochemical process (Fv/F0) and an increase in basal quantum production of the non-photochemical processes (F0/Fm). Superoxide dismutase (SOD) activity was higher in the leaves than in the roots. The C. xanthocarpa is a species sensitive to water deficit but presents strategies to adapt to an environment under temporary water restriction, which are more temporary are most efficient under shading. The seedlings with water deficit at all levels of shading exhibited higher protective antioxidant activity and lower quality at 0% shading. The shading minimizes prevents permanent damage to the photosystem II and after the re-irrigation, the evaluated characteristics showed recovery with respect to the control group, except POD and SOD activities in the leaves.
Highlights
Previous studies have shown that climate change is responsible for irregular patterns of precipitation and temperature, resulting in different types of stress that alter the metabolism and development of plants
These results suggest that seedlings under water deficit were stressed when compared with the control seedlings
In periods of lower water availability, in general, the initial fluorescence (F0) and the basal quantum production of non-photochemical processes in photosystem II (F0/ Fm) showed an increase and the photochemical process in photosystem II (Fv/F0) showed maximum efficiency. This behavior of the characteristics of the chlorophyll a fluorescence may be related to the reduction of the chlorophyll content in the leaves in the same period, and we believe that a smaller amount of energy was absorbed by the antenna complex, that is, it was not transmitted, leading to greater changes in photosynthetic capacity due to stress caused by water deficiency
Summary
Previous studies have shown that climate change is responsible for irregular patterns of precipitation and temperature, resulting in different types of stress that alter the metabolism and development of plants. It is important to study the behaviour of plants exposed to environmental stresses because some of these plants are not adapted to areas with little soil water availability or variations in luminosity (Reis et al, 2016; Chirino et al, 2017), which makes them vulnerable. Water deficit due to alterations in luminosity may impair the development of plants, and photosystem II is affected by intense radiation, making it necessary to alter the photosynthetic apparatus and dissipate the excess energy absorbed; this alters the fluorescence parameters of chlorophyll a (Franco et al, 2005; Costa et al, 2015). Excess light usually increases the ambient temperature and vapour pressure deficit, intensifying the effects of the water deficit and closure of the stomata and resulting in the lower uptake of CO2 and, lower photosynthetic rate (Favaretto et al, 2011)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
