Effects of light quality on leaf growth and photosynthetic fluorescence of Brasenia schreberi seedlings

Brasenia schreberi J. F. Gmel, a perennial floating-leaved macrophyte with high economic value as an aquatic vegetable, has been listed as first-class endangered species in China, mainly due to its habitat loss. Protected cultivation is a potential strategy to meet the demand of both plant conservation and vegetable market, whereas pre-experiments are still needed before series of parameters can be properly set for the large-scale growth of the plants indoor. Light quality is one of the major factors controlling the development of plants and consequently becomes an important factor when planting B. schreberi indoor. This experiment used three artificial light sources to investigate the response of B. schreberi seedlings to different light qualities, including the red-blue LED light (red: blue = 5:1, RB-LED), the white LED light (W-LED) and the white fluorescent (W-Fluo). Our results indicated that the responses of B. schreberi towards varied light qualities differed from those of most terrestrial plants. The total leaf number of the RB-LED treatment was the highest; the number of the submerged leaf and the rolled leaf of the RB-LED treatment was higher than that of the other two treatments, but the number of floating leaves was the lowest. Both the specific leaf weight and the pigment contents per unit leaf area were the lowest in the RB-LED treatment. Quantum yield of PSⅡ (Φ(PSⅡ)), electron transport rate (ETR) and photochemical quenching (qP) measured through light induction curves followed the sequence from high to low as W-Fluo > W-LED > RB-LED, whereas the trend of non-photochemical quenching (NPQ) reversed. The maximum potential ETR (P(s)) and maximum ETR (ETR(m)) derived from ETR curves further verified the trends.