Nitrogen supply increases Cucumis sativus L. low temperature tolerance by improving cucumber growth, nitrogen...

Nitrogen (N) is one of the main limiting nutrients in crops, and continuous low temperature (LT, 15 °C/8 °C，day/night) significantly inhibits crop growth. However, there is a lack of clarity regarding the intrinsic linkage between N supply under LT on the chlorophyll fluorescence response of cucumber and other physiological biochemistry. Consequently, we studied the effects of different N supply on 'Bonai 526' and 'Jinyou No.1' cucumber biomass, chlorophyll, root morphology, fast chlorophyll fluorescence, N accumulation and N metabolism under LT. 'Jinyou No.1' had higher maximum chlorophyll fluorescence intensity, photosystem II (PSII) specific activity parameters, quantum yield and driving force under LT, with above parameters average increase of 8.5 %, 14.2 %, 18.3 % and 42.6 % compared with 'Bonai 526', which was attributed to the high N-metabolizing enzyme activity and related genes expression in 'Jinyou No.1'. In addition, the response of different cucumber genotypes to N supply was significantly different under LT. Compared with 'Bonai 526', 7 mM N supply was more favorable to promote root growth and biomass accumulation of 'Jinyou No.1' under LT, significantly increasing N metabolism enzyme activity and chlorophyll content, improving quantum yield captured and absorbed per reaction center and electron chain end driving force, promoting PSII primary photochemical reaction mechanism activity and performance, and thus improving cucumber LT tolerance.