Date of Award
Master of Science (MS)
The Southeastern United States is a biological hot-spot for carnivorous plants, with over half of the North American species occurring along the Gulf Coast. Pinguicula planifolia Chapman is one of six carnivorous perennial butterwort species found in the Florida Panhandle. Among these species, only P. planifolia expresses a distinct variation of red coloration on its leaves. The functional role of foliar anthocyanins may include stress response to drought and nutrient deficiency, herbivory defense, free radical scavenging, and photoprotection. Carnivorous plant leaves face strong selection pressures to optimize prey capture and nutrient absorption. Given the frequency of these red pigments in such specialized trapping leaves of carnivorous plants, their presence may be providing some type of physiological adaptation. The objectives of this study were: 1 ) to determine how environmental factors impact foliar anthocyanin production in P. planifolia, 2) to investigate how light manipulation affects foliar anthocyanin content of green and red plants over time, 3) to determine how foliar anthocyanins affects prey capture, and 4) to investigate how leaf gland density differs in red and green leaves.
Three field studies (quadrat, light manipulation, and prey capture) were conducted at 7 populations within the Florida Panhandle, and 2 lab studies (chamber and gland density) were conducted at Eastern Illinois University. In the quadrat study, chlorophyll and anthocyanin content indexes in leaves of plants selected in quadrats along a transect were measured as a factor of light intensity, water depth, soil nutrients, water nutrients, and habitat structure. In the light manipulation study, three treatments (control, clipped, and caged) were established for red and green plants. These treatments tested the effects of normal, heightened, and lowered solar radiation on red and green plants over time. The prey capture study employed artificial sticky traps painted to match leaf colors (red or green), which were established next to plants with red or green leaves. Prey was collected from artificial traps and leaves to determine how color affects prey capture. The chamber study tested ex situ responses of P. planifolia anthocyanin production to artificial environmental cues by growing plants in controlled growth chambers under varying conditions including light intensity, nutrient levels, and substrate moisture levels. In the gland density study, leaf clearings were performed to conduct density counts of stalked and sessile glands on red and green leaves.
Foliar anthocyanin content is correlated positively with light intensity and negatively with water depth and vegetation height. In soil, calcium and pH levels are positively correlated with foliar anthocyanins. In water, bicarbonates and pH levels are positively correlated with foliar anthocyanins. In water, ammonium is negatively correlated with foliar anthocyanins. In field and laboratory settings, exposing red plants to decreased light intensity significantly reduced foliar anthocyanin content, while exposing green plants to increased light intensity significantly increased foliar anthocyanin content. Rosette diameter and leaf number of plants grown in artificial high light conditions (1200-1500 μmol/m2/s) were significantly higher than of plants grown in artificial low light conditions (500-800 μmol/m2/s). Growing plants with fertilizer (16-16-16 diluted to 0.9 g/1 L) added to underlying water reduced survival by over 70%. Green traps (both artificial and leaves) captured significantly more prey than red traps. The most abundant taxon captured on leaves, regardless of color, was Collembola (62-67%). Red leaves contained a significantly higher number of stalked glands (12.7) compared to green leaves (9.9), while sessile gland density did not differ between leaf colors.
This study provides evidence that light intensity alone can effectively increase or decrease anthocyanin production in P. planifolia. Further work is needed to determine if anthocyanins may serve as a type of protective screening from UV radiation in this species. Increased calcium availability along with higher pH in soils may serve to enhance anthocyanin production. Increased bicarbonates and higher pH in water also may be linked to increased foliar anthocyanins. Plants at the germination to seedling stage thrive in higher light intensities, likely due to increased photosynthetic activity. This species exhibits a strong resiliency to low nutrient/anoxic soil conditions, as plants thrived in completely submerged conditions for over 4 months, producing the largest plants of all chamber study treatments. Anthocyanins do not appear to play a role in prey attraction. The target prey (Collembola) may be attracted to olfactory or other cues emitted by these plants. While leaf color affected stalked gland density on P. planifolia leaves, where they had sporadic occurrence compared to sessile glands, which were more evenly spaced. Since stalked glands are the first step to prey consumption, they may be more sensitive to the environmental change s that affect leaf color, compared to sessile glands.
While there is much more to learn about the physiological role of foliar anthocyanins and its importance to the conservation of this species, we can conclude that light exposure is the principal factor linked to anthocyanin production in Pinguicula planifolia.
Annis, Jenna, "Seeing Red in a Sea of Green: Anthocyanin Production in a Carnivorous Plant, Pinguicula planifolia" (2016). Masters Theses. 2478.
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