Inhibition of photosynthesis by freezing temperatures and high light levels in cold‐acclimated seedlings of Scots pine (Pinus sylvestris). – II. Effects on chlorophyll fluorescence at room temperature and 77 K.

Abstract

Strand, M, and Oquist, G, 1985, Inhibition of photosynthesis by freezing temperatures and high liglit levels in cold-acclimated seedlings of Scots pine {Pinus sylvestris). -II. Effects on chlorophyll fluorescence at room temperature and 77 K. -Physiol, Plant. 65: 117-123, Shoots of cold-acclimated seedlings of Pinus sylvestris L, were exposed to a temperature of -7°C for 4 h, in darkness or at a photon flux density of 1 300 fimol m"~ s^B efore and after freezing, fluorescence kinetics of intact needles and isolated chioropiast membranes were measured at both room temperature and 77 K, Maximum and variable fluorescence yield of photosystem II both at room temperature and 77 K decreased strongly after freezing in light, whereas the initial fluorescence yieid was little affected. Quenching of maximum and variable fluorescence of photosystem I at 77 K also occurred. The results show that freezing in light damages photosystem Ii, thereby increasing the radiationless decay at the reaction centres of photosystem II, This is a typical symptom of photoinhibition of photosynthesis. Freezing in d.arkness did not significantiy reduce fluorescence yieid of photosystem il or photosystem I, Moreover, electron transport capacity was not significantly affected. We therefore suggest that the inhibition of the CO, assimilation in pine seedlings by freezing alone does not involve thyiakoid inactivation.Additional key words -Eiectron transport, freezing stress, photoinhibition, M. Strand (reprint requests) andG. Oquist,

Modifications in Photosynthetic Pigments and Chlorophyll Fluorescence in 20-Year-Old Pine Trees after a Four-Year Exposure to Carbon Dioxide and Temperature Elevation

“…The depression is much greater on days with marked water stress, as observed in several tree species (Epron and Dreyer 1993, Epron et al 1994, Valentini et al 1995. Such changes are often related to thermal deexcitation of PS2 (Strand and Öquist 1985), and maintain a balance between light-driven linear electron flow and requirements of reducing power for both carboxylation and oxygenation of RuBP (Krause and Weis 1991). The CO 2 -induced decrease in the efficiency of open PS2 centres can thus make an important contribution to the greater CO 2 -induced depression of ∆F/F' m at high VPD.…”

“…A low temperature, often accompanied by high irradiance in spring and autumn, can lead to cold acclimation in trees, which could involve changes in membrane composition and RuBPCO content, so that photosynthesis is depressed (Strand and Öquist 1985, Leverenz and Öquist 1987. Elevated temperatures may therefore greatly reduce the period during which natural acclimation results in depression of photosynthetic capacity and allow trees to utilise photons intercepted during the spring and autumn with greater efficiency (Long and Hutchin 1991).…”

Seasonal variation in energy and water fluxes in a pine forest: an analysis based on eddy covariance and an integrated model

“…7). Studies have indicated that the early spring recovery of photosynthesis depends greatly on the acclimation of the foliage to the previous winter's low temperatures and radiation (Strand and Öquist, 1985;. In view of the coupled relationship between stomatal resistance and photosynthesis, the difference in stomatal resistance between the years during the spring could be partly attributed to stomatal acclimation to low temperatures and radiation during the previous winter.…”

“…Since there did not occurred a relatively low wind speed in this period (Fig. 3), and foliage photosynthesis or stomatal conductance was in its recovery stage from winter low temperatures (Strand and Öquist, 1985;, the larger H e was the result of a combination of relatively high incoming radiation but a low mean air temperature (Fig. 4) and canopy stomatal conductance (Fig.…”

“…Meanwhile, the low water-holding capacity of the soil may also make easily expose the Scots pines to stress from soil moisture deficits (Kellomäki and Wang, 2000a). Solar radiation and soil water content are relatively high in early spring, whereas evaporation rates in a forest stand may be relatively low, as the canopy conductance of Scots pines is still in its recovery stage following the low winter temperatures (Strand and Öquist, 1985; and the cold soils may restrict the uptake of soil water by the roots ). In addition, the level of soil freezing and the snow depth in the previous winter can affect the early spring soil fluxes .…”