Effects of short-term treatment with various light intensities and hydroponic solutions on nitrate concentration of lettuce

Figures & data

Table I. Sub-treatment codes and the corresponding hydroponic constitution.

Sub-treatment codes	Composition of hydroponic solutions for sub-treatment
1	Full nutrient solution (10 mM nitrogen)
2	Nitrogen-free nutrient solution
3	Phosphorus and potassium solution (0.75 mM K2SO4, 0.5 mM KH2PO4 and 0.1 mM KCl)
4	KCI (0.1mM) solution
5	K2SO4 (0.75 mM) solution
6	Ammonium molybdate solution (5×10^-5 mM)
7	NaCl solution (10 mM)
8	Microelement solution (the same concentrations as the full nutrient solution)

Table II. Leaf SPAD of lettuce treated with different hydroponic solutions and light intensities.

	Shading		Non-shading
Treatments	Expanded leaves	New leaves	Expanded leaves	New leaves
1	14.6c	14.1b	19.6a	16.7a
2	16.4abc	14.1b	17.2a	16.5a
3	15.4bc	12.6c	18.7a	17.9a
4	16.9abc	15.3ab	17.2a	17.7a
5	17.3ab	15.6ab	17.9a	14.6a
6	18.6a	15.8a	19.0a	17.5a
7	16.4abc	14.2ab	17.5a	14.7a
8	17.2abc	14.7ab	18.6a	18.1a
In the same column, the different letters following the averages represent significant difference at p < 0.05.

Table III. Nitrate concentrations of the new leaves, expanded leaves and petiole of lettuce treated with different hydroponic solutions and light intensities (mg kg^-1).

	Shading			Non-shading
Sub-treatments	New leaves	Expanded leaves	Petioles	New leaves	Expanded leaves	Petioles
1	2658a	2902a	2509a	2197a	1684a	2350a
2	636b	1676b	1848b	466b	163c	666c
3	564b	1566b	1767b	334b	396bc	1085bc
4	749b	1390b	1751b	392b	563bc	1131bc
5	1097b	1232b	1692b	329b	270c	784c
6	915b	1468b	1869b	595b	306c	730c
7	889b	1576b	1980b	617b	521bc	926bc
8	1163b	1555b	1505b	374b	872b	1457b
In the same column, the different letters following the averages represent significant difference at p < 0.05.

Table IV. Effects of shading on leaf SPAD and nitrate concentration.

Treatments	SPAD of expanded leaves	SPAD of new leaves	Nitrate concentration in expanded leaves (mg kg^−1)	Nitrate concentration in new leaves (mg kg^−1)	Nitrate concentration in petiole (mg kg^−1)
Shading	14.6ab	16.6ab	1084a	1671a	1865a
Non-shading	16.7a	18.2a	663b	442b	969b
In the same column, the different letters following the averages represent significant difference at p < 0.05.