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Energy Dissipation and Photoinhibition in Douglas‐Fir Needles with a Fungal‐Mediated Reduction in Photosynthetic Rates
Author(s) -
Manter Daniel K.
Publication year - 2002
Publication title -
journal of phytopathology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.53
H-Index - 60
eISSN - 1439-0434
pISSN - 0931-1785
DOI - 10.1046/j.1439-0434.2002.00801.x
Subject(s) - photoinhibition , xanthophyll , photosynthesis , photosynthetic reaction centre , biology , chlorophyll fluorescence , photosystem ii , botany , horticulture , photosynthetic pigment , chlorophyll , chlorophyll a , photochemistry , chemistry
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 CO 2 assimilation rates from ca. 6 μ mol/m 2 /s to 1.5 μ mol/m 2 /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 ( F v / F m ) in response to a 1 h high light treatment (PPFD=2000 μ mol/m 2 /s) also suggests that infected needles absorb greater amounts of excess light. In this experiment, declines in F v / F m 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.