1. Introduction
Light is a predominant source of energy for plant photosynthe-sis and also an important signal for plant growth and development.
It is well known that plants are not only able to respond to light
quality but also able to its intensity (Fu et al., 2012; Tu et al.,
2012; Wang et al., 2009). Plants in greenhouse are always affected
by low light intensity. The light intensity of greenhouse is about
85–150 mol m−2
s
−1
in higher latitudes during winter seasons.
Moreover, as a consequence of recent haze weather, diming and
shading have become major challenges to vegetable production in
many areas of the world (Mu et al., 2010). Previous studies had
shown that weak light or shading could significantly affect growt