They absorb green and yellow wavelengths (two dominant colors of the spectrum), they attract “friendly” insects to assist with pollination, they repel “hostile” pests that would exploit them, and they can tolerate environmental stress better than green-leafed plants because of their slower metabolism.
They [exist] in habitats as diverse as the Antarctic shoreline and the tropical rainforests, are as abundant in arid deserts as in freshwater lakes, and seem equally at home in the light-starved forest understorey (ground-lower level) as in the sun-drenched canopy (upper level-top).”[2] While the existence of red leaves is transient in some plants (e.g.
The focus of this article is on the plants with red leaf pigments that exist for the duration of their lives.The “Red” in LeavesAnthocyanins (mainly cyanidin-3-O-glucoside)[3], which belong to the flavonoid family are the key water-soluble pigment responsible for giving a plant its red color.
[7] “Interestingly [though], the amount of red light that is reflected from red leaves often… correlates [poorly] to anthocyanin content; leaf morphology (structure and form) and the amount and distribution of chlorophyll are… stronger determinants of red reflectance.”[8] Although chlorophyll is the pigment responsible for giving most plants their green color, an experiment showed that it can play a role in red reflectance.
[However] the differences in [the] average rates of photosynthesis were not significantly different.”[14]Another experiment compared the photoperiodic sensitivity of green-leafed (Perilla frutescens) and red-leafed (Perilla crispa) Perilla (flowering Asian annuals) or how long it took each of the Perilla plants to reach the same level of growth or flowering based on exposure to different light conditions.
When the rate of photosynthesis was measured at the “cellular, tissue, and whole leaf levels to understand the role of anthocyanin pigments on patterns of light utilization” of red- and green-leafed Quintinia serrata, it was found that “anthocyanins in the mesophyll (photosynthetic tissue between the upper and lower epidermis of a leaf) restricted absorption of green light to the uppermost [section of the] mesophyll [and that] distribution was further restricted when anthocyanins were also present in the upper epidermis.”[16]Accordingly, “mesophyll cells located beneath a cyanic (blue or bluish) light filter assumed the characteristic features of shade-adapted cells, [with red leaves showing] a 23% reduction in CO2 assimilation under light-saturating conditions, and a lower threshold of irradiance (density of radiation occurrence) for light-saturation, relative to those of green leaves.”[17] In short, the findings were consistent with the previous two experiments in which red leaves displayed slower rates of photosynthesis, exhibiting photosynthetic characteristics of “shade-acclimated plants.”[18]Although green-leaves appear to hold the advantage when it comes to photosynthesis, this advantage should not be overstated since to compensate for their slower rate of photosynthesis, red-leafed plants exhibit slower metabolism as established by an experiment using Iodine to test for the presence of starch.
