Journal of Arboriculture 31(5): September 2005 219 a maximal fluorescence to the J peak) were observed in most cases except one, evergreen oak sprayed with Diuron, for which OJIP curves reflected those at day 0, indicating full recovery of the leaf photosynthetic system. To date, alterations to OJIP curves following application of other herbicides commonly used in urban landscapes, such as glyphosate, chlorotoluron, paraquat, diquat, 2,4-D, mecoprop-P, and dichlorprop, have not been shown to induce the same alterations caused by the plastoquinone B– binding herbicides used in this investigation (Korres et al. 2003; Popovic et al. 2003). This indicates that alterations to the OJIP curve (i.e., OJIP to OJ) can be used to identify tree decline caused by spray drift or inappropriate spraying with plastoquinone B–binding herbicides such as Atrazine, Diuron, and DCMU. Although the physiological principles of chlorophyll fluorescence are complex, the operation of the fluorimeter used in this trial is simple. The practical advantages of using chlorophyll fluorescence include the fact that fluores- cence measurements use a portable piece of equipment, measurements are nondestructive and noninvasive, and readings are obtained within 1 s following 20- to 30-min dark acclimation of a leaf using light-exclusion clips attached to the leaf surface. Consequently, many plants (60 to 80 per hour) can be evaluated and all data downloaded to a standard PC or laptop. The fluorescence software package can then be used to determine Fo and Fv/Fm and graph the OJIP curves. Results demonstrated that fluorescence readings identi- fied herbicide and heat damage as the primary cause of stress 24 h after treatments were applied (i.e., OJIP curves at 24 h were identical to those shown at week 5) (Figures 6 and 7) and that alterations to the OJIP curve could still be observed 12 days (heat) (Figure 5) and 13 weeks (herbicide) (Figures 6 and 7) later. Identification of the cause of tree decline based on visual observation alone (i.e., leaf yellowing and necrosis) would be impossible. In addition, laboratory methodologies to identify, for example, herbicide damage include dose- response assays, radio-labeled compounds, or the measure- ment of metabolic processes at the cellular level. These identification systems can be labor intensive and expensive and require sophisticated analytical equipment and therefore are unsuitable for large numbers of plant samples (Korres et al. 2003). Fluorescence analysis may provide a cheaper and less labor-intensive alternative. In conclusion, results of this investigation strongly indicate how interpretation of a range of fluorescence responses can be used to identify heat and plastoquinone-binding herbicide damage, but not salt, as a primary cause of tree decline in three oak species. Further work is ongoing to use this system to identify other forms of stress frequently encountered in urban environments that contribute to tree decline. LITERATURE CITED Adams III, W.W., B. Demmig-Adams, A.S. Verhoeven, and D.H. Barker, D. H. 1995. Photoinhibition during winter stress: Involvement of sustained xanthophyll cycle dependent energy dissipation. Aust. J. Plant. Physiol. 22:261–276. Bolhar-Nordenkampf, H.R., S.P. Long, N.R. Baker, G. Oquist, U. Schreiber, and E.G. Lechner. 1989. Chlorophyll fluorescence as a probe of the photosynthetic competence of leaves in the field: A review of current instrumentation. Func. Ecol. 3:497–514. Cajanek, M., M. Stroch, I. Lachetova, J. Kalina, and V. Spunda. 1998. Characterization of the photosystem II inactivation of heat-stressed barley leaves as monitored by the various parameters of chlorophyll a fluorescence and delayed fluorescence. J. Photochem. Photobiol. 47:39–45. Demming, B., and O. Björkman. 1987. Comparison of the effect of excessive light on chlorophyll fluorescence (77K) and photon yield of O2 evolution in leaves of higher plants. Planta 171:171–184. Dobson, M.C. 1991. De-icing salt damage to trees and shrubs. Forestry Commission Bulletin 101. Georgieva., K., T. Tsonev, V. Velikova, and I. Yordanov. 2000. Photosynthetic activity during high temperature of pea plants. J. Plant Physiol. 157:169–176. Govindgee. 1995. Sixty-three years since Kautsky: Chlorophyll a fluorescence. Aust. J. Plant Physiol. 22: 131-160. Guisse, B., A. Srivastava, and R.J. Strasser. 1995. The polyphasic rise of the chlorophyll a fluorescence (OKJIP) in heat stressed leaves. Arch. Sci. Geneve 48:147–160. Haldimann, P., and R.J. Strasser. 1999. Effects of anaerobiosis as probed by the polyphasic chlorophyll a fluorescence rise kinetic in pea (Pisum sativum L.) Photosyn. Res. 62:67–83. Hall D.O., and K.K. Rao. 1999. Photosynthesis (6th ed.). Cambridge University Press. pp.174–180. Harris, R.W. 1992. Arboriculture: Integrated Management of Landscape Trees, Shrubs, and Vines (2nd ed). Prentice Hall, New York, NY. Hong, S.S., and D.-Q. Xu. 1999. Light-induced increase in chlorophyll fluorescence Fo level and the reversible inactivation of PSII reaction centers in soybean leaves. Photosyn. Res. 61:269–280. Korres, N.E., R.J. Froud-Williams, and S.R. Moss. 2003. Chlorophyll fluorescence technique as a rapid diagnostic test of the effects of the photosynthetic inhibitor chlorotoluron on two winter wheat cultivars. Ann. Appl. Biol. 143:53–56. ©2005 International Society of Arboriculture
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