Energy Dissipation and Photoinhibition in Douglas-Fir Needles with a Fungal-Mediated Reduction in Photosynthetic Rates

• Published in: Journal of phytopathology Vol. 150; no. 11-12; pp. 674 - 679
• Main Author: Manter, Daniel K.
• Format: Journal Article
• Language: English
• Published: Berlin, Germany Blackwell Verlag GmbH 01.12.2002; Blackwell
• Subjects: Biological and medical sciences; Chlorophyll fluorescence; foliar disease; Fundamental and applied biological sciences. Psychology; Fungal plant pathogens; non-photochemical quenching; Pathology, epidemiology, host-fungus relationships. Damages, economic importance; Phaeocryptopus gaeumannii; photoinhibition; photosynthesis; Phytopathology. Animal pests. Plant and forest protection; Chlorophyll; non-photochemical quenching; Mycosis; Pseudotsuga menziesii; Fungi; Infection; Chlorophyll fluorescence; Photosystem 2; foliar disease; Energy dissipation; Softwood forest tree; Gymnospermae; Phaeocryptopus gaeumannii; Photoinhibition; Coniferales; Spermatophyta; Needle(conifer); Photosynthesis; Photooxidation; Thallophyta
• ISSN: 0931-1785; 1439-0434
• DOI: 10.1046/j.1439-0434.2002.00801.x

The dissipation of absorbed light and potential for photooxidative damage was explored in Douglas‐fir (Pseudotsuga menziesii ) seedlings with and without Phaeocryptopus gaeumannii infection. The presence of P. gaeumannii significantly reduced net CO2 assimilation rates from ca. 6 μmol/m2/s to 1.5 μmol/m2/s, without any significant impact on chloroplast pigments. The partitioning of absorbed light‐energy to photochemistry or thermal dissipation was determined from chlorophyll fluorescence measurements. Maximum thermal dissipation for both control and infected needles was ca. 80%, consistent with the similar xanthophyll pool sizes in the two treatments. At high photosynthetic photon flux density (PPFD), when thermal dissipation was maximized, the lower photochemical utilization in infected needles resulted in greater amounts of excess absorbed light (ca. 20 and 10% for the infected and control needles, respectively). A second experiment, monitoring changes in photosystem II (PSII) efficiency (Fv/Fm) in response to a 1 h high light treatment (PPFD=2000 μmol/m2/s) also suggests that infected needles absorb greater amounts of excess light. In this experiment, declines in Fv/Fm were 1.5 times greater in infected needles, despite the similar xanthophyll pool sizes. Furthermore, increases in minimum fluorescence (178 and 122% of initial values for the infected and control needles, respectively) suggest that the reduction in PSII efficiency is largely attributable to photooxidative damage. Finally, reductions in PSII efficiency under high light conditions provide a plausible explanation for the greater pathogenicity (e.g. premature needle abscission) of P. gaeumannii in sun‐exposed foliage.