[Effects of water supply tension on photosynthetic characteristics and root activity of greenhouse cucumber].

ABSTRACT

To study the effects of soil water content on the photosynthesis, fluorescence parameters, and root growth of greenhouse cucumber (Cucumis sativus L.), a pot experiment was conducted, using a negative pressure water supplying and controlling device to control soil moisture regime. Seven levels of water supply tension (WST), i. e., 1, 3, 5, 7, 9, 11, and 13 kPa, were designed. The WST was inversely proportional to soil water content, and the gravimetric soil water content was maintained in the range of 14.23%-42.32%. With increasing WST, the leaf net photosynthetic rate (P(n)) in different growth periods showed a parabolic trend, being higher when the WST was 7-11 kPa at initial flowering stage, and was 3-5 kPa at fruiting stage. The reason for the decreased P(n) at 9-13 kPa WST was stomatal limitation. Under 1-5 kPa WST, the actual photochemical efficiency (phi(PS II) had a high value, and the possibility of photo inhibition was small. Both the leaf transpiration rate and the chlorophyll content were positively correlated with leaf P(n) in different growth periods. Root growth and activity also had a parabolic trend with increasing WST. The maximum root dry mass and root activity happened at 7 kPa and 5 kPa WST, respectively. Our results indicated that a WST of 3-7 kPa was more profitable for the leaf photosynthesis and root growth of greenhouse cucumber.