The influence of Ca(NO3)2, Ca(NO3)2H3BO3, and N:P:K (24:7:7) fertilization on the freezing tolerance of spring foliage of evergreen oak and holly. Newly emerged leaves were detached at month 8 post-fertilization from trees growing under field conditions and subjected to −8°C (18°F) under laboratory conditions. Improvements in tolerance were measured by chlorophyll fluorescence (Fo, Fv/Fm), leaf chlorophyll content (SPAD), and leaf electrolyte leakage.
| Species/fertilizer | Fo | Fv/Fm | SPAD | Leaf electrolyte leakage (%) |
|---|---|---|---|---|
| Evergreen oak | ||||
| Control | 159.9 (24.33) | 0.261 (0.028) | 18.5 (4.07) | 70.7 (14.66) |
| Ca(NO3)2 (20 g/m2) | 150.3ns (31.42) | 0.281ns (0.063) | 20.4ns (6.11) | 66.4ns (16.10) |
| Ca(NO3)2 (40 g/m2) | 121.3* (17.68) | 0.325* (0.041) | 24.3* (5.32) | 56.9* (15.40) |
| Ca(NO3)2 (80 g/m2) | 146.5ns (19.60) | 0.244ns (0.031) | 18.9ns (3.87) | 66.8ns (17.21) |
| Ca(NO3)2H3BO3 (20 g/m2) | 131.9* (26.55) | 0.295* (0.037) | 23.6* (4.46) | 57.0* (13.28) |
| Ca(NO3)2H3BO3 (40 g/m2) | 124.6* (30.13) | 0.312* (0.040) | 23.3* (4.17) | 62.3ns (16.75) |
| Ca(NO3)2H3BO3 (80 g/m2) | 137.5ns (19.75) | 0.284ns (0.018) | 19.9ns (6.25) | 67.7ns (13.26) |
| N:P:K (24:7:7) (20 g/m2) | 141.2ns (18.80) | 0.259ns (0.020) | 24.1* (8.08) | 65.8ns (13.58) |
| N:P:K (24:7:7) (40 g/m2) | 146.5ns (22.62) | 0.264ns (0.038) | 24.3* (7.13) | 72.9ns (16.50) |
| LSD | 27.54 | 0.0311 | 4.66 | 13.11 |
| Holly | ||||
| Control | 207.7 (32.20) | 0.204 (0.019) | 14.3 (3.14) | 79.0 (15.21) |
| Ca(NO3)2 (20 g/m2) | 195.1ns (38.54) | 0.219ns (0.022) | 15.7ns (3.70) | 72.1ns (17.49) |
| Ca(NO3)2 (40 g/m2) | 157.5* (31.49) | 0.253* (0.034) | 18.7* (4.13) | 64.8* (14.11) |
| Ca(NO3)2 (80 g/m2) | 190.4ns (40.36) | 0.189ns (0.015) | 14.6ns (4.39) | 78.2ns (20.79) |
| Ca(NO3)2H3BO3 (20 g/m2) | 171.3* (22.66) | 0.230ns (0.027) | 18.2* (5.66) | 59.3* (11.96) |
| Ca(NO3)2H3BO3 (40 g/m2) | 161.7* (30.21) | 0.243* (0.034) | 17.9* (6.13) | 65.0ns (13.57) |
| Ca(NO3)2H3BO3 (80 g/m2) | 178.8ns (26.39) | 0.221ns (0.021) | 14.7ns (5.71) | 82.1ns (18.60) |
| N:P:K (24:7:7) (20 g/m2) | 183.5ns (28.48) | 0.202ns (0.022) | 18.6* (7.60) | 83.4ns (16.23) |
| N:P:K (24:7:7) (40 g/m2) | 190.2ns (24.30) | 0.206ns (0.022) | 18.7* (5.28) | 80.4ns (15.63) |
| LSD | 34.76 | 0.0288 | 3.16 | 11.67 |
All values mean of 15 trees, 2 leaves per tree.
↵* = significantly different at P < 0.05, ns = not significantly different from control value.
Values in parentheses represent the standard error of the mean.