The aim of this study was to evaluate the growth of rape (Brassica napus L.) seedlings under different light intensities to select appropriate conditions for cultivation in an indoor system.  Seedlings were grown under different light intensities of red and blue light provided by light-emitting diodes (LEDs) and their self-adjustment ability and changes in leaf microstructure were evaluated.  Light was supplied by red LEDs with peak wavelengths of 630 (R₁) and 660 nm (R₂) and by blue LEDs (B) with a peak wavelength of 445 nm (the light intensity ratio of R₁:R₂:B was 3:3:2), at intensities of 400 (R₁R₂B400), 300 (R₁R₂B300), and 200 μmol m^–2 s^–1 (R₁R₂B200).  Natural solar light served as the control (C).  Plant height, stem diameter, root length, leaf area, and dry weight of rape seedlings gradually increased with increasing light intensity.  The seedlings in the R₁R₂B400 treatment grew more vigorously, while those in the R₁R₂B200 treatment were weaker.  The photosynthetic pigment contents did not differ significantly between the R₁R₂B400 treatment and C, but were significantly lower in the R₁R₂B300 and R₁R₂B200 treatments.  The highest intercellular CO₂ concentration, stomatal conductance, and transpiration rate were in the R₁R₂B300 treatment.  The highest photosynthetic rate was in the R₁R₂B400 treatment, and was related to more compact leaves, thicker and tidier palisade and spongy tissues, and well-developed chloroplasts.  In contrast, the seedlings in the R₁R₂B200 treatment had disordered mesophyll cells, round chloroplasts, and fractured and fuzzy grana lamellae, all of which inhibited plant growth.  In conclusion, the seedlings in the R₁R₂B400 treatment had well-developed leaves, which favored photosynthesis.  Compared with the light intensities below 300 μmol m^–2 s^–1, the light intensity of 400 μmol m^–2 s^–1 provided by a combination of red and blue LEDs was beneficial for cultivating strong and healthy rape seedlings in an artificial system.  

The North China Plain (NCP), one of the most important agricultural regions in China, is facing a major water-resource crisis evoked by excessive exploitation of groundwater. To reduce water use while maintaining high crop production level, improving variety water use efficiency (WUE) is an urgent need, especially because other water-saving measures such as water delivery, irrigation, and agricultural practices have already achieved most possible progresses. Evaluation of variety WUE can be performed accurately at the individual plant level (WUEp). Reviewing the studies on physiological factors affecting WUEp performed up to date, stomatal conductance was considered to be an important trait associating closely with WUEp. The trait showed a large degree of varietal variability under well-watered conditions. Crop varieties differ highly in sensitivity of stomata to soil and air drying, with some varieties strongly reducing their stomatal conductance in contrast with those lightly regulating their stomata. As a result, difference among varieties in WUEp was enlarged under water deficit conditions in contrast with those under well-watered conditions. The relationship between stomatal conductance and yield depends on water availability of whole growing period in local areas. Usually, large stomatal conductance results in a high yield under good irrigation system, whereas a low stomatal conductance can lead to yield benefit under limited stored soil moisture conditions. In the NCP, winter wheat is the largest consumer of irrigation water, improvement strategies for high WUE aiming at wheat crops are in urgent need. We suggest, for the well-irrigated areas with excessive exploitation of groundwater, the wheat breeding program need to combine medium stomatal conductance (0.35 mmol H2O m-2 s-1 or so), high carboxylation efficiency, and high harvest index. Areas with partial/full access to irrigation, or infrequent drought, should target wheat varieties with high stomatal conductance under no water stress and low sensitivity of stomata to soil water deficit. Drought-prone rain-fed areas characterized by frequent and long terminal drought should target wheat varieties with low stomatal conductance under no water stress and high stomata sensitivity to soil drying to make water available during grain filling.