Waiting for the go: Spring recovery of photosynthesis in Siberian Pinus sylvestris (L.)

Abstract

During winter Pinus sylvestris from boreal central Siberian stands encounters severe stress due to low temperatures and high light. This coincides with major seasonal changes in the organisation of the photosystem. In spring, Pinus sylvestris usually achieves full photosynthetic capacity within days. However, the recovery of photosynthesis can be severely interfered by `crazy spring¿ events, when periods with temperatures up to +15°C alternate with prolonged periods with minimum temperatures of -15°C. In this work we studied the effect of these spring events on the recovery of Pinus sylvestris from winter stress. Changes in photosynthetic activity, quenching of excitation energy via xanthophylls, and the final onset of photosynthesis were assessed by means of chlorophyll fluorescence, photosynthetic oxygen production and determination of photosynthetic pigments with high performance liquid chromatography. Optimum quantum yield (Fv/Fm) of late winter/early spring needles was low compared to summer values. However, Fv/Fm measured in needles of different days reflected the severe ambient temperature changes within the observation period. Dark respiration and photosynthetic oxygen production rates, measured at 20°C under laboratory conditions, remained less affected by these temperature changes. Recovery of photosynthesis in late winter/early spring needles was additionally observed in growth chambers at 18°C and 12°C. These experiments revealed an almost complete recovery within only 5 days. The further analysis of photosynthetic pigments suggests that during transition from winter stress to spring activity, xanthophyll cycle dynamics play an important role in the protection of the photosystem of Pinus sylvestris against severe temperature disturbances.