Influence Of Shaded Conditions On Development Of Asteraceae Species Native to Kansas, is a well researched Biology Master’s Thesis topic, it is to be used as a guide or framework for your Academic Research.
Due to the heterogeneity of habitats, all plants are exposed to at least some degree
of shade during their lifetime. Reduced light intensity, drops in R: FR ratio and limited blue light are cues for plants to perceive competition; the shade avoidance syndrome (SAS) is common for grassland species while shade tolerance (ST) is common for forest species when the competition is perceived.
SAS is characterized by elongation of stems and petioles, reduced branches, decreased leaf area, decreased shoot biomass, and increased number of ramets. ST is characterized by little elongation of stems and petioles, high chlorophyll content and high chlorophyll a/b ratio in leaves, low root-shoot ratio, and thinner leaves.
In this study, germination of six native Asteraceae species was tested against 10%, 50%, and 100% of natural light in a greenhouse.
Measurements of growth and reproduction were made in two species under the same light conditions. Shaded conditions decreased the germinabilities of seeds in all species that were tested.
Increased light conditions resulted in increased growth for both species. When exposed to shaded conditions, both species
displayed several traits that are related to shade tolerance modifications such as little
elongation of stems and petioles, higher specific leaf area, higher chlorophyll a/b ratio, reduced leaf area and root/shoot biomass, and fewer and thinner leaves.
In summary, plants displayed unexpected strategies and high resilience to grow and develop under shaded conditions.
Environmental factors, such as local weather, climate, seasons, or position of the
plant in the community, directly alter the quality and intensity of light that is available for
plants, strongly influencing their entire life cycle (Kami et al., 2010; Bian et al., 2014, Patel et al., 2017).
Therefore, due to the heterogeneity of habitats, all plants are exposed to at least some degree of shade during their lifetime (Valladares and Niinemets, 2008).
The light signal is perceived by three classes of specialized information-transducing
plant photoreceptors: red (R) and far-red (FR) light-absorbing phytochromes, the blue/UV-A light-absorbing cryptochromes, and phototropins (Franklin, 2008).
Plant photoreceptors continuously sense and respond to fluctuating light conditions and modulate plant growth and development accordingly (Fiorucci and Fankhauser, 2017).
Interactions among the different classes of photoreceptors and their downstream signaling pathways mediate both adaptive responses, such as phototropism and developmental transitions, such as germination and flowering (Kami et al., 2010; Dierck et al., 2017).
Plants usually grow and develop in dynamic environments, competing with surrounding neighbors over limited resources such as light, water, and nutrients (Keuskamp
et al., 2010).
Reduced light intensity, drops in R: FR ratio and limited blue light are cues for plants to perceive competition and display two contrasting mechanisms of response, the Shade avoidance syndrome and shade tolerance (Gommers et al., 2013).
Additionally, while shade avoidance responses are also induced by cues that indicate neighbor proximity, such mechanical stimulation, and presence of plant volatile substances, shade-tolerance responses are known to be elicited in plants mainly via decreases in light intensities
(Gruntman et al., 2017).
Shade avoidance syndrome and its metabolic pathways are well described in the literature for model species such as Arabidopsis thaliana (Ciolfi et al., 2013) and crop species (Carriedo et al., 2016).
Shade avoidance syndrome is a group of responses such as enhanced growth of the hypocotyl and petioles, more erect position of the leaves, and reduced branching, causing substantial changes in plant body form and function (Casal, 2012; Gommers, et al., 2013; Ballaré and Pierik, 2017).
Also, responses such as acceleration of flowering, reduced resources for storage and reproduction associated with reduced seed set, and truncated fruit development are also common if the shaded condition
is prolonged (Morelli and Ruberti, 2002).
These responses are often accompanied by
reductions in leaf area, shoot biomass, and the size of harvestable organs, a likely
a consequence of the reallocation of resources towards reproductive structures (Franklin, 2008).