High Nitrogen Supply Induces Physiological Responsiveness to Long Photoperiod in Barley

Photoperiod and nutrient nitrogen (N) supply influence the growth, development, and productivity of crops. This study examined the physiological, biochemical, and morpho-anatomical traits of NA5 and NA9, two barley cultivars with contrasting photoperiod lengths, under the combined treatment of photoperiod regime and N supply. Under long photoperiod, high N supply decreased net photosynthesis; decreased chlorophyll a and chlorophyll a/b; decreased ascorbate peroxidase (APX), catalase (CAT), and superoxide dismutase (SOD) activities; decreased ascorbate, glutathione, soluble protein, and soluble sugar; destroyed mesophyll cell integrity; and increased [Formula: see text] , malondialdehyde, and proline in both NA5 and NA9. Under short photoperiod, high N content increased net photosynthesis; increased chlorophyll a and chlorophyll a/b; increased APX, CAT, and SOD activities; and increased antioxidants, soluble protein, and soluble sugar in NA9 but decreased the same parameters in NA5. These results indicated that N supply strongly affected photosynthetic capacity and the balance of reactive oxygen species in response to short and long photoperiod. High N supply enhanced the sensitivity of long-day barley to photoperiod change by inhibiting photosynthesis and decreasing antioxidant defense ability. High N mitigated the undesirable effects of shortened photoperiod in short-day barley. Therefore, the data from this study revealed that N status affects adaptation to photoperiod changes by maintaining redox homeostasis and photosynthetic capacity.