Table 3 Effect of different concentrations of Put, CQDs, and Put-CQD NPs on chlorophyll fluorescence parameters of Vitis vinifera cv. ‘Sultana’ under salinity stress (CQDs, carbon quantum dots; Put, putrescine, Put-CQD NPs, carbon quantum dots functionalized by putrescine nanoparticles). Different letters indicate significant differences based on Duncan’s post-hoc analysis at P ≤ 0.05

NaCl (0 mM) + No Treatment

2.455 ± 0.09^c

2.631 ± 0.08^d

1.072 ± 0.08^ab

0.933 ± 0.03^d

2.291 ± 0.01^d

0.674 ± 0.01^c

NaCl (0 mM) + Put 5 mg L^− 1

2.567 ± 0.03^ab

2.252 ± 0.07^e

1.069 ± 0.04^ab

1.139 ± 0.01^c

2.401 ± 0.04^c

0.672 ± 0.02^c

NaCl (0 mM) + Put 10 mg L^− 1

2.579 ± 0.06^ab

2.137 ± 0.09^g

1.021 ± 0.02^b

1.206 ± 0.02^b

2.691 ± 0.03^ab

0.677 ± 0.03^c

NaCl (0 mM) + CQDs 5 mg L^− 1

2.033 ± 0.08^g

2.213 ± 0.08^ef

1.035 ± 0.01^ab

0.918 ± 0.06^de

2.0918 ± 0.01^ef

0.672 ± 0.03^c

NaCl (0 mM) + CQDs 10 mg L^− 1

2.123 ± 0.07^f

1.766 ± 0.07^f

0.976 ± 0.08^c

1.202 ± 0.02^b

2.375 ± 0.01^cd

0.666 ± 0.01^d

NaCl (0 mM) + Put-CQD NPs 5 mg L^− 1

2.432 ± 0.07^cd

2.001 ± 0.08^ef

1.034 ± 0.08^ab

1.215 ± 0.02^b

2.552 ± 0.4^b

0.687 ± 0.03^b

NaCl (0 mM) + Put-CQD NPs 10 mg L^− 1

2.731 ± 0.01^a

1.564 ± 0.04^h

0.975 ± 0.04^c

1.749 ± 0.03^a

2.748 ± 0.03^a

0.698 ± 0.04^ab

NaCl (100 mM) + No Treatment

2.052 ± 0.07^g

3.677 ± 0.04^a

0.861 ± 0.04^d

0.558 ± 0.05ⁱ

1.328 ± 0.02^hi

0.667 ± 0.01^d

NaCl (100 mM) + Put 5 mg L^− 1

2.227 ± 0.02^ef

3.375 ± 0.06^ab

1.028 ± 0.02^b

0.659 ± 0.01^h

1.746 ± 0.01^g

0.696 ± 0.03^ab

NaCl (100 mM) + Put 10 mg L⁻¹

2.263 ± 0.08^e

2.809 ± 0.03^bc

1.071 ± 0.09^ab

0.805 ± 0.02^fg

1.985 ± 0.05^f

0.695 ± 0.01^ab

NaCl (100 mM) + CQDs 5 mg L⁻¹

2.131 ± 0.09^f

3.185 ± 0.07^ab

1.138 ± 0.07^a

0.669 ± 0.04^h

1.272 ± 0.03ⁱ

0.692 ± 0.04^ab

NaCl (100 mM) + CQDs 10 mg L⁻¹

2.205 ± 0.05^ef

2.953 ± 0.09^b

0.867 ± 0.03^d

0.746 ± 0.01^g

1.343 ± 0.01^h

0.675 ± 0.03^c

NaCl (100 mM) + Put-CQD NPs 5 mg L⁻¹

2.403 ± 0.06^d

2.805 ± 0.07^bc

0.986 ± 0.01^c

0.855 ± 0.03^f

2.037 ± 0.04^ef

0.709 ± 0.02^ab

NaCl (100 mM) + Put-CQD NPs 10 mg L⁻¹

2.506 ± 0.09^b

2.738 ± 0.05^c

0.813 ± 0.06^e

0.905 ± 0.06^e

2.201 ± 0.03^e

0.721 ± 0.02^a