Influence of shading on photosynthesis and antioxidative activities of enzymes in apple trees

Abstract

This study investigated the effects of shading on photosynthesis in 3-year-old potted apple trees. The trees were grown either in full sunlight or in a shade environment with about 50% of sunlight filtered through black plastic nets. Under the shade conditions, the net photosynthetic rate (PN), the stomatal conductance, the transpiration rate, and the intercellular CO2 concentration decreased before midday, which was due to low light energy but the PN of the shaded trees increased relative to the control trees during the afternoon. In addition, the concentrations of chlorophyll (Chl) a, b, and total Chl increased in the shaded trees. In shaded apple trees, the photochemical efficiency increased. There was a lower content of reactive oxygen species and activities of antioxidant enzymes. The results showed that moderate shading can improve the total photosynthetic efficiency, which is mainly attributed to alleviation of photodamage and low accumulation of reactive oxygen species.

Orchard Planting Density and Tree Development Stage Affects Physiological Processes of Apple (Malus domestica Borkh.) Tree

“…A similar effect was obtained by pruning trees [46,47]. Strongly sunny plants can be damaged by sunlight, too intense sun can inhibit photosynthetic processes [26,33,48]. The distance of 1 m between fruit trees resulted the most intensive photosynthesis activity.…”

“…During the growing season, the rate of photosynthesis mostly depends on the photoperiod; however, research showed that young leaves are more photosynthetically active during the long day, and the rate of photosynthesis decreases as the leaves age [26,30]. Significant decrease of stomatal conductance followed by transpiration rate in July and August was observed (Figure 2).…”

“…Higher amounts of sugars stimulate the expression of the major starch synthesis enzyme ADP-glucose pyrophosphoryl (AGPase) resulting more intensive starch synthesis [20]. Moreover, the total amount of starch in the leaves is significantly influenced by day duration, over a longer photoperiod plants accumulate more starch [26]. Changes in the content of soluble carbohydrates and starch are mechanistically linked to transitions in plant freezing tolerance.…”

“…Another factor that affects the rate of photosynthesis and other photosynthesis indices is light. In many cases, the decreased light reduces the rate of photosynthesis [26,[31][32][33]. On the other hand, other authors show, that too much sunlight begins to inhibit photosynthetic processes, saving water, so shading nets or dense planting schemes helps to optimize the intensity of photosynthesis [31][32][33].…”

Partial shade improved the photosynthetic capacity and polysaccharide accumulation of the medicinal plant Bletilla ochracea Schltr.

“…Considering medicinal plants yield and irrigation costs, evapotranspiration can play a guiding role in the cultivation of medicinal plants (Ahemd et al 2016). High light induced leaf temperature rise and excessive transpiration can lead to water deficit, decrease of photosynthetic rate and even plant death (Liu et al 2019. Over-shading also limits transpiration, which can limit photosynthetic rate and affect plant growth, too (Shao et al 2014).…”