Early physiological consequences of fire as an abiotic stressor in metabolic source and sink of young Brutian pine (Pinus brutia Ten.)

Climatic change causes gradual deforestation, partly through forest fires. However, fire has not been seen as an oxidative stressor on surviving forest trees. In addition, discrimination of stress-induced responses from acclimation steps cannot be examined under prolonged stress. Thus, four young Brutian pine (Pinus brutia Ten.) trees, a fire-related species, were subjected to a simulation of a crown-fire event to evaluate its impact on the availability of soluble carbon (C) and nitrogen (N) and the redox status near fire-afflicted tissue. Total soluble sugars, amino acids and non-structural (NS) proteins in needles and phloem, the antioxidant ascorbic acid (AsA) and reactive oxygen species (ROS) in needles were investigated together with the phloem transport velocity. To examine the temporal progress of these parameters, samples were obtained prior to fire (pre-fire), 2 h after fire, the following day (Day 1) and the following week (Week 1). Findings were categorized into shock reactions (2 h) and acclimation steps. Phloem transport accelerated 2 h postfire by almost 30% and correlated negatively to phloem sugars. At the same time the phloem ratio of sugars/amino acids correlated negatively to needle ROS. The trees' main response at 2 h and particularly on Day 1 was a massive increase in phloem NS proteins. The acclimation process involved also significant increases in needle NS proteins and AsA, as well as significant depletion of phloem amino acids by 65% by Week 1. The highest availability of soluble C and N was recorded on Day 1 in the phloem. Regression models explained significantly the variability of most soluble compounds postfire. Our findings suggest sink control over the source and an advanced role of phloem transport in defense processes.