Journal of Arboriculture 31(1): January 2005 13 Measurements of Fo and leaf electrolyte leakage were 50% higher, while measurements of Fv/Fm and SPAD values were 50% lower in newly formed spring leaf tissue (new leaves; Tables 5 and 6) sampled at month 8 compared to leaf tissue sampled at month 8 that was present at the time of fertilizer application (existing leaves; Tables 3 and 4), irrespective of form of stress applied and tree species (Tables 4 through 7). Previous research has shown that newly formed leaves produced in spring are highly suscep- tible to a range of environmental stresses such as freezing, heat, and salinity compared to older, more mature leaf tissue due to the new leaves’ inability to acclimate (Cannel and Smith 1986; Cameron and Dixon 1997). A significant effect of fertilizer and concentration applied was recorded (Table 1). Such a response is reflected in the results where, compared to nonfertilized controls, significantly lower (P < 0.05) Fo and electrolyte leakage regression values (20% to 40%), coupled with significantly higher (P < 0.05) Fv/Fm and SPAD regression values (30% to 40%), indicate that the freezing and salinity tolerance of evergreen oak and holly can be increased by fall application of Ca(NO3 g/m2 (1.4 oz/ft2 )2 and Ca(NO3 ) (Tables 3 and 4). Results also show that )2 H3 BO3 increases in freezing and salinity tolerance were apparent in newly formed spring leaf tissue measured at month 8 (Tables 5 and 6). This finding indicates that fall fertilization with Ca(NO3 only the freezing and salinity tolerance of existing leaf material through the winter months but also that of newly formed leaf tissue in spring. )2 and Ca(NO3 H3BO3 at 40 g/m2 )2 Improvements in freezing and salinity hardiness of plants following calcium fertilization have been shown to be achieved via alterations to a number of plant physiological processes. The structural stability of cell walls and plasma membranes results from calcium links between phosphate and plasma lipids. Consequently, applications of calcium can physically increase the strength of the plant cell wall (Legge et al. 1982). Calcium has also been implicated in controlling enzyme activity, important in improving freezing resistance. For example, cold temperatures increase levels of a calcium- dependent NAD kinase, which, in turn, is responsible for activating enzymes that cause the production of proteins necessary to alter the transcription of genes specific to cold acclimation. The progress of freezing injury can be also be halted by bathing or washing freeze-thaw–injured tissue in a calcium-based solution. (Monroy et al. 1993; Berbezy et al. 1996). Electrolyte leakage is widely used to measure freezing damage via alterations in membrane structural integrity (McKay 1992; Percival and Galloway 1999). Reduced electrolyte leakage values in trees fertilized with Ca(NO3 Ca(NO3 H3BO3 at a concentration of 40 g/m2 following freezing damage indicate increased membrane )2 (1.4 oz/ft2 )2 ) can improve not at a concentration of 40 structural stability and cell wall strength caused by calcium fertilization in both test species. Importantly, improvements in freezing and salinity tolerance were recorded by month 1 (Tables 3 and 4), indicating calcium fertilization works rapidly to induce stress resistance in both evergreen oak and holly. Increased tolerance to salinity and freezing stress as a result of calcium fertilization at 40 g/m2 may also have contributed toward the significantly increased (P < 0.05) plant dry weights recorded at the cessation of the experiment (Table 7). Although Fo and electrolyte leakage regression values were generally lower in both test species supplemented with Ca(NO3 (0.7 oz/ft2 ) and Fv/Fm, SPAD regression values and plant dry weights were generally higher compared to controls; in few instances were they significantly so (Tables 3 through 7). This finding indicates that applications of calcium-based fertilizers at 20 g/m2 )2 and Ca(NO3 H3BO3 at a concentration of 20 g/m2 )2 conferred no significant protectant properties in the two test species. Likewise, applications of both calcium fertilizers at a concentration of 80 g/m2 oz/ft2 (2.8 ) had no significant effect on freezing and salinity tolerance or plant dry weights (Tables 3 through 7). Symp- toms of fertilizer burn were observed in both tree species at this concentration (marginal necrosis of the leaf peripheral edges) indicating phytotoxicity of both calcium fertilizers at 80 g/m2 , which may account for this result. a concentration of 40 g/m2 per metric ton at farm gate prices. Such knowledge may prove of importance to those involved in urban tree care, when the cost–benefit ratio involved with calcium fertiliza- tion needs to be considered. fertilizers are commercially available at a cost of US$288 (£160) for Ca(NO3 )2 and $US304 (£169) for Ca(NO3 )2 H3 Nitrogen fertilization has been shown to reduce winter hardiness in apple (Way 1953; Edgerton 1957), pear (Raese 1997), and peach (Proebstring 1961). Contrary to these findings, work elsewhere suggests nitrogen fertilization can enhance winter hardiness in Picea ruben (Dehaynes et al. 1998) and Juniperus chinensis (Pellet and White 1969), while Smiley and Shirazi (2000) suggest nitrogen fertilization has no significant effect on winter hardiness in Forsythia, maple (Acer spp.), Leyland cypress (× Cupressocyparis leylandii), and oak (Quercus spp.). and Irrespective of species, chlorophyll fluorescence (Fo, Fv/ Fm) and electrolyte leakage regression values did not significantly differ from controls following freezing and salinity stresses following fall fertilization with a high- nitrogen (N:P:K 24:7:7) fertilizer (Tables 3-7). This result indicates that fertilization of evergreen oak and holly with a N:P:K (24:7:7) fertilizer did not enhance or increase susceptibility to freezing and salinity damage. However, ©2005 International Society of Arboriculture Irrespective of species, there was no marked difference in freezing and salinity tolerance and dry weight values between trees treated with Ca(NO3 (Tables 3 through 7). Both )2 and Ca(NO3 )2 H3 BO3 at BO3
January 2005
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
