Light-emitting diodes (LEDs) have been widely applied in the controlled environment agriculture, which are characterized by relatively narrow-band spectra and energetical efficiency.  Most recently, the spectrum of Sunlike LEDs has been engineered and it closely resembles solar spectrum in the range of photosynthetic active radiation (PAR, 400–700 nm).  To investigate how plant growth responses to the spectrum of Sunlike LEDs, cucumber and lettuce plants were cultivated and their responses were compared with the conventional white LEDs as well as composite of red and blue LEDs (RB, R/B ratio was 9:1).  We observed that although Sunlike LEDs resulted in a longer stem in cucumber, dry weight and leaf area were similar as those under RB LEDs, and significantly higher than those under white LEDs.  Moreover, cucumber leaves grown under Sunlike and white LEDs showed higher photosynthetic capacity than those grown under RB LEDs.  For lettuce, plants grown under Sunlike LEDs showed larger leaf area and higher dry weight than the other two treatments.  However, the leaf photosynthetic capacity of lettuce grown under Sunlike LEDs was the lowest.  In this context, the spectrum induced plant functions are species-dependent.  Furthermore, the three types of LEDs show distinct light spectra and they are different in many aspects.  Therefore, it is difficult to attribute the different plant responses to certain specific light spectra.  We conclude that plants grown under Sunlike LEDs exhibit larger leaf area, which may be due to some specific spectrum distributions (such as more far-red radiation), and consequently are favorable for light interception and therefore result in greater production.

 

Sixteen cotton cultivars widely planted in China were sowed under five different drought concentrations (0, 2.5, 5, 7.5, and 10%) using PEG₆₀₀₀ to screen the indices of drought resistance identification and explore the drought resistance of different cotton cultivars.  Eighteen physiological indices including root, stem, and leaf water contents (RWC, SWC, and LWC), net photosynthetic rate (P_n), the maximum photochemical quantum yield (F_v/F_m), the actual photochemical quantum yield (Φ_PSII), non-photochemical quenching coefficient (NPQ), leaf water potential (LWP), osmotic potential (Ψs), leaf relative conductivity (REC), leaf proline content (Pro), leaf and root soluble protein contents (LSPC and RSPC), leaf and root malondialdehyde (MDA) contents (LMDA and RMDA), root superoxide dismutase, peroxidase, and catalase activities (RSOD, RPOD, and RCAT) were measured.  Results indicated the 18 physiological indices can be converted into five or six independent comprehensive indices by principal component analysis, and nine typical indices (F_v/F_m, SWC, LWP, Pro, LMDA, RSPC, RMDA, RSOD, and RCAT) screened out by a stepwise regression method could be utilized to evaluate the drought resistance.  Moreover, the 16 cotton cultivars were divided into four types: drought sensitive, drought weak sensitive, moderate drought resistant, and drought resistant types.  The resistance ability of two selected cotton cultivars (drought resistant cultivar, Dexiamian 1; drought sensitive cultivar, Yuzaomian 9110) with contrasting drought sensitivities were further verified by pot experiment.  Results showed that the responses of final cotton biomass, yield, and yield composition to drought were significantly different between the two cultivars.  In conclusion, drought resistant cultivar Dexiamian 1 and drought sensitive cultivar Yuzaomian 9110 were screened through hydroponics experiment, which can be used as ideal experimental materials to study the mechanism of different cotton cultivars with contrasting drought sensitivities in response to drought stress.