A minireview on adaption of young leaf redness

It is well known that the leaves of many woody plant species flush red rather than green during particular stages across their life span. Non-green leaf coloration caused by active synthesis of anthocyanin in plant organs at these stages costs the plant significant resources and energy, resulting in a reduction of primary photosynthesis. Therefore, it is likely that the coloration change is an active process and not simply a by-product of metabolism. Various hypotheses formulated to explain the potential reasons for coloration change can be divided into two categories: (1) those that suggest it is physiological adaptation for resistance to severe environments (high light, drought and low temperatures); and (2) those that suggest it protects against herbivory damage (coevolution, unpalatability, camouflage and anticamouflage, etc.). To date, there is no consensus on the relative validity of these ideas. The majority of previous work has focused on only a few species and autumn leaf color change. The relatively few studies done on red young leaves in spring mostly focused on red coloration as an independent visual signal. Future studies need to consider the chemical and mechanical defense of leaf redness, as well as the anthocyanins presented in other plant organs (thorns, stems and particularly, flowers), which may experience similar selection as leaves. The quantification of environmental factors and herbivore selection would be helpful in expansion our understanding in young leaf redness.