Photosynthesis Research

, 94:437

Chilling and freezing stress in live oaks (Quercus section Virentes): intra- and inter-specific variation in PS II sensitivity corresponds to latitude of origin


    • Department of Ecology, Evolution and BehaviorUniversity of Minnesota
Research Article

DOI: 10.1007/s11120-007-9215-8

Cite this article as:
Cavender-Bares, J. Photosynth Res (2007) 94: 437. doi:10.1007/s11120-007-9215-8


Sensitivity to cold and freezing differs between populations within two species of live oaks (Quercus section Virentes Nixon) corresponding to the climates from which they originate. Two populations of Quercus virginiana (originating from North Carolina and north central Florida) and two populations of the sister species, Q. oleoides, (originating from Belize and Costa Rica) were grown under controlled climate regimes simulating tropical and temperate conditions. Three experiments were conducted in order to test for differentiation in cold and freezing tolerance between the two species and between the two populations within each species. In the first experiment, divergences in response to cold were tested for by examining photosystem II (PS II) photosynthetic yield (ΔF/F m′) and non-photochemical quenching (NPQ) of plants in both growing conditions after short-term exposure to three temperatures (6, 15 and 30°C) under moderate light (400 μmol m−2 s−1). Without cold acclimation (tropical treatment), the North Carolina population showed the highest photosynthetic yield in response to chilling temperatures (6°C). Both ecotypes of both species showed maximum ΔF/F m′ and minimum NPQ at their daytime growth temperatures (30°C and 15°C for the tropical and temperate treatments, respectively). Under the temperate treatment where plants were allowed to acclimate to cold, the Q. virginiana populations showed greater NPQ under chilling temperatures than Q. oleoides populations, suggesting enhanced mechanisms of photoprotective energy dissipation in the more temperate species. In the second and third experiments, inter- and intra-specific differentiation in response to freezing was tested for by examining dark-adapted F v/F m before and after overnight freezing cycles. Without cold acclimation, the extent of post-freezing declines in F v/F m were dependent on the minimum freezing temperature (0, −2, −5 or −10°C) for both populations in both species. The most marked declines in F v/F m occurred after freezing at −10°C, measured 24 h after freezing. These declines were continuous and irreversible over the time period. The North Carolina population, however, which represents the northern range limit of Q. virginiana, showed significantly less decline in F v/F m than the north central Florida population, which in turn showed a lower decline in Fv/F m than the two Q. oleoides populations from Belize and Costa Rica. In contrast, after exposure to three months of chilling temperatures (temperate treatment), the two Q. virginiana populations showed no decline in F v/F m after freezing at −10°C, while the two Q. oleoides populations showed declines in F v/F m reaching 0.2 and 0.1 for Costa Rica and Belize, respectively. Under warm growth conditions, the two species showed different F 0 dynamics directly after freezing. The two Q. oleoides populations showed an initial rise in F 0 30 min after freezing, followed by a subsequent decrease, while the Q. virginiana populations showed a continuous decrease in F 0 after freezing. The North Carolina population of Q. virginiana showed a tendency toward deciduousness in response to winter temperatures, dropping 58% of its leaves over the three month winter period compared to only 6% in the tropical treatment. In contrast, the Florida population dropped 38% of its leaves during winter. The two populations of the tropical Q. oleoides showed no change in leaf drop during the 3-months winter (10% and 12%) relative to their leaf drop over the same timecourse in the tropical treatment. These results indicate important ecotypic differences in sensitivity to freezing and cold stress between the two populations of Q. virginiana as well as between the two species, corresponding to their climates of origin.


Chilling and freezing sensitivity Chlorophyll fluorescence Irreversible decline in F v/F m F 0 Non-photochemical quenching Population and species-level variation Ecotypes Climatic gradient Live oaks


F 0

Fluorescence level when leaf is in a non-energized (dark) state, all non-photochemical processes are at a minimum and plastoquinone electron acceptor pool (Qa) of PS II is fully oxidized

F m

Maximum fluorescence level in a dark leaf when Qa is transiently fully-reduced and non-photochemical processes are at a minimum

F m

Fluorescence level in an illuminated leaf when Qa is transiently fully-reduced

F v

Maximum variable chlorophyll fluorescence (F mF 0) in a dark leaf when all non-photochemical processes are at a minimum

F s

Steady state fluorescence in an illuminated leaf


Variable fluorescence in an illuminated leaf (F m′–F s)

F v/F m

Maximum photochemical efficiency of photosystem II in a dark leaf when non-photochemical processes are at a minimum

ΔF/F m

Photochemical efficiency of photosystem II in an illuminated leaf


Non-photochemical quenching of excited chlorophyll calculated as (F mF m′)/F m′ (Stern-Volmer relationship)


Photosynthetically-active radiation (between wavelengths 400 nm and 700 nm)


Photosystem I


Photosystem II

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© Springer Science+Business Media B.V. 2007