Supplementing green light under strong sunlight improves growth and functional ingredients of ginger (Zingiber officinale Rosc.) in summer

Abstract

Abstract The green light for ginger growth may not be as unimportant as often assumed, but still now the roles of green light in ginger remain poorly understood. To investigate this issue, the ‘Shandong No. 1’ginger cultivar was grown and treated with two contrasting light environments: sunlight (CK treatment), supplementing green light under strong sunlight (T1 treatment), and this study explored morphological alterations, photosynthetic responses and gene expression of ginger in response to supplementing green light under strong sunlight, based on ginger s own species characteristics. The results showed as follows. One hand, supplementing green light under strong sunlight promoted expression of gibberellin biosynthesis gene and altered the morphological characteristics of ginger. In response to supplementing green light under strong sunlight, ginger presented not only shade avoidance symptoms characteristics, but also promotion of number of shoots, and thus rendered higher crown density and greater crown volume. When exposed to supplementing green light under strong sunlight condition, the strategies implemented by ginger to deal with stem elongation and branching increase seemed to be a species-specific response. On the other hand, the positive effect of supplementing green light under strong sunlight on ginger also depends on the growth conditions. Previous research confirmed that ginger did not grow well under green light only treatment. In contrast, supplementing green light under strong sunlight resulted in higher crown density and greater crown volume, which played a role in shading for the inner leaves and young pseudostems under summer sunlight, although strong summer light posed a threat to ginger growth. In addition, supplementing green light under strong sunlight led to upregulation of chlorophyll metabolism gene and an increase in Chlorophyll a content. Also, the enhancement of green light radiation effectively increased expressions of photosynthetic genes and photosynthesis rate. These all contributed to the improvement of photosynthetic efficiency of ginger leaves, as a way to increase light energy consumption, and thus reduced chloroplast senescence caused by excess light energy in summer. Furthermore, higher photosynthesis rate contributed to accumulation of photosynthetic products, and supported the material requirements for increasing biomass and improving rhizome functional ingredients. Taken together, this study will lay the foundations of a better understanding of the importance of green light to ginger.