Photosystem II Activity of Alhagi sparsifolia is Low under Natural Light after Initial Exposure to Shaded Conditions

Light is one of the most important environmental factors that regulate the development of the photosynthetic system in higher plants. As the source of energy for carbon fixation, light exhibits a regulatory function in plant growth.

The photosynthetic plasticity of plants varies in response to different light conditions. Many previous studies investigated the response of leaves transferred from low-light intensity to high-light intensity. However, these studies rarely focused on typical desert plants grown under high irradiance conditions.

Alhagi sparsifolia, commonly regarded as a sun plant, is the main vegetation found in the forelands of Taklamakan desert and exhibits an important function in wind prevention and sand fixation at the transition zone. A. sparsifolia could adapt to shaded conditions after a period of exposure to low-light conditions. However, whether or not the sun plant A. sparsifolia can adapt to natural light intensity after initial exposure to shaded conditions remains unknown.

To investigate whether or not desert plant can adapt to natural light intensity after exposure to shaded conditions, LI Lei et al. examined the characteristics of the photosystem II (PSII) of A. sparsifolia exposed to natural light after the initial treatment under shaded lighting conditions. In this study, A. sparsifolia samples in the same sampling plot were randomly selected and shaded with a piece of nylon net on April 10, 2012. After 4 months, four of the eight nylon nets were taken down after which the PSII of the plants was characterized. A. sparsifolia was then exposed to natural light. On August 20 and 30, 2012, another set of PSII characterization was also carried out.

The results indicated that the PSII activity of A. sparsifolia under the specified condition was low; the thickness of leaves was reduced and occurred as an adaptive response to capture high amounts of light and exhibit high intensity of light-use efficiency. Shade leaves differed in terms of chlorophyll. Furthermore, the excess excitation energy has been converted to thermal dissipation energy to maintain energy balance. Shade-grown plants cannot adapt to strong irradiance, which is normal in plants for a short period when they are initially maintained under low-light conditions. Therefore, A. sparsifolia should not be considered as a typical sun plant.

The results of this study could provide information to understand the relationship between leaf development and varying light intensity. The study was published in Trees in 2014.