Influence of high-temperature convective flow on viability of Scots pine needles (Pinus sylvestris L.)

Abstract

During a forest fire, plants are affected by high temperatures causing stress. At the time of burning, it is difficult to record temperature changes in tree crowns and the associated effects on photosynthesis. This paper presents the results of modelling a high-temperature effect simulating a convective flow from a ground fire. Evaluation of the response was carried out by the parameters of rapid fluorescence (Fv/Fm, ETR), the state of the pigment complex, and the relative water content in the needles. To characterize the degree of heat endurance and short-term effects concerning thermal damage, saplings of Scots pine (Pinus sylvestris L.) were used at different times during the growing season (June, July, August, September). Experimental heating at 55 °C lasted for 5 and 10 min. There were different levels of heat resistance by the needles. Data in June show that heating of the saplings significantly suppressed photosynthesis. In July, August, and September, the photochemical quantum yield (Fv/Fm) was restored to 75% and 60% from the initial level after 5- and 10-min heating, respectively. The electron transport rate (ETR) for saplings in September was restored to their initial level within 3 days after a short heat exposure. Restoration of the photosynthetic activity in needles was observed after a 5-min impact, but by the end of the study period, restoration had not reached control values. A longer heating of 10 min resulted in an irreversible suppression of photosynthesis and destruction of the photosynthetic apparatus, as evidenced by the decrease in the number of photosynthetic pigments.