Effects of summer frost oh the gas exchange of field‐grownPinus sylvestrisL. seedlings

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Abstract
The effect of night temperatures on the gas exchange of naturally established Scots pine (Pinus sylvestris L.) seedlings was investigated at a site with frequent summer frosts in northern Sweden. During the growing season, a reversible inhibition of light‐saturated rates of CO2‐assimilation was observed after nightfrosts. Stomatal conductance decreased or increased in parallel with changes in the CO2‐assimilation rate. The inhibition of photosynthesis was not primarily the result of stomatal closure, since intercellular CO2‐concentration increased after night frosts. Naturally regenerated Scots pine seedlings survived repeated frosts during the growing season and showed no visible damage although air temperatures as low as ‐8.2°C were recorded during the period of shoot elongation