Table 3.

The influence of Ca(N0₃)₂, Ca(N0₃)₂H₃B0₃, and N:P:K (24:7:7) fertilization on the freezing tolerance of evergreen oak and holly. Leaves were detached at months 1,2,4, and 8 post-fertilization from trees growing under field conditions and subjected to temperatures of −8°C (18°F) under laboratory conditions. Improvements in tolerance as measured by chlorophyll fluorescence (Fo, Fv/Fm), leaf chlorophyll content (SPAD), and leaf electrolyte leakage values were quantified by repeated measures analysis (regression analysis; the slope value represented by β₁).

Species/fertilizer	Fo			Fv/Fm			SPAD			Lead electrolyte leakage (%)
Species/fertilizer	Intercept	Slope (β₁)	r²	Intercept	Slope (β₁)	r²	Intercept	Slope (β₁)	r²	Intercept	Slope (β₁)	r²
Evergreen oak
Control	350.66	−28.22	68.1	0.546	−0.039	67.9	39.41	−2.78	69.2	47.62	2.46	70.9
Ca(NO₃)₂ (20 g/m²)	340.36	−22.78^ns	67.0	0.611	−0.045^ns	64.2	43.50	−3.20^ns	71.2	42.59	2.59^ns	55.5
Ca(NO₃)₂ (40 g/m²)	282.11	−18.32^*	69.9	0.705	−0.052^*	68.5	48.81	−3.48^*	66.7	40.27	1.87^*	60.0
Ca(NO₃)₂ (80 g/m²)	333.21	−23.08^ns	63.7	0.575	−0.042^ns	59.6	41.20	−2.68^ns	62.5	44.94	2.66^ns	68.7
Ca(NO₃)₂H₃BO₃ (20 g/m²)	281.63	−21.10^*	57.2	0.618	−0.043^ns	70.7	48.38	−3.27^*	64.9	39.83	2.06^*	70.1
Ca(NO₃)₂H₃BO₃ (40 g/m²)	301.25	−20.40^*	70.8	0.661	−0.047^*	68.3	49.54	−3.39^*	67.0	39.94	1.97^*	77.9
Ca(NO₃)₂H₃BO₃ (80 g/m²)	336.67	−24.12^ns	70.1	0.621	−0.040^ns	66.3	40.82	−2.81^ns	67.8	41.26	2.69^ns	66.7
N:P:K (24:7:7) (20 g/m²)	343.12	−23.87^ns	78.1	0.555	−0.037^ns	73.3	48.26	−3.39^*	64.5	44.39	2.49^ns	60.5
N:P:K (24:7:7) (40 g/m²)	345.91	−24.12^ns	69.3	0.563	−0.039^ns	69.1	50.78	−3.44^*	65.6	43.04	3.08^*	68.5
LSD		7.07			0.0062			0.488			0.316
Holly
Control	469.20	−34.01	68.0	0.432	−0.030	67.1	30.21	−2.34	68.4	54.17	2.99	61.4
Ca(NO₃)₂ (20 g/m²)	429.17	−30.31^ns	61.1	0.487	−0.036^*	71.6	35.06	−2.47^ns	69.5	49.26	2.81^ns	67.6
Ca(NO₃)₂ (40 g/m²)	386.43	−24.03^*	70.8	0.560	−0.040^*	68.7	40.03	−2.67^*	65.6	42.15	2.31^*	62.3
Ca(NO₃)₂ (80 g/m²)	440.82	−29.69^ns	67.1	0.461	−0.034^ns	51.2	30.11	−2.13^ns	62.6	48.42	3.27^ns	53.4
Ca(NO₃)₂H₃BO₃ (20 g/m²)	408.17	−26.97^ns	69.9	0.479	−0.033^ns	68.1	38.27	−2.49^ns	64.8	46.29	1.298	26.1
Ca(NO₃)₂H₃BO₃ (40 g/m²)	391.99	−24.63^*	71.2	0.513	−0.036^*	72.4	37.19	−2.69^*	74.7	48.07	2.09^*	49.9
Ca(NO₃)₂H₃BO₃ (80 g/m²)	417.38	−28.67^ns	70.1	0.487	−0.032^ns	70.1	33.56	−2.27^ns	56.9	52.37	3.48^ns	62.6
N:P:K (24:7:7) (20 g/m²)	450.78	−32.61^ns	73.6	0.443	−0.027^ns	69.4	36.81	−2.63^*	64.8	50.91	3.47^ns	44.0
N:P:K (24:7:7) (40 g/m²)	431.22	−31.35^ns	68.9	0.450	−0.029^ns	70.3	38.54	−2.67^*	65.4	53.80	3.22^ns	67.5
LSD		8.52			0.0055			0.253			0.524

Intercept = value through y axis (calculated); slope = rate of Fo, Fv/Fm, SPAD, electrolyte leakage with time.
All values mean of 15 trees, 2 leaves per tree.
↵* = significantly different at P < 0.05, ns = not significantly different from control value.