Stress Response of Dominant Forest Tree Species South of the Caspian Sea in Relation to Soil from Coast to Upland

Distribution and growth of plant species is affected by many factors including abiotic (topography, altitude and soil) and biotic (root symbiosis) factors. In light of global warming, recent findings advocate microhabitats and micro-conditions of the root zone and canopy ambiance as determining factors in sustaining of plant populations. Although, occurrence of ectomycorrhizal (ECM) and non-mycorrhizal plants in forests south of the Caspian Sea have been studied extensively, stress response of tree species in relation to altitude and soil (texture and contents of heavy metals) has not been investigated much. This research investigated the antioxidant stress response of three dominant tree species (Alnus subcordata C.A.Mey, Acer velutinum Boiss. and Carpinus betulus L.) of three selected hyrcanian forests south of the Caspian Sea (Javaherdeh, Dalkhani and Tonekabon) at 4 altitudes (sea level, 500, 1000 and 1500 m above sea level). Results showed some nonenzymatic antioxidants, such as flavonoids and anthocyanins contents correlated with ectomycorrhizal root colonization, differed amongst trees in corresponding altitudes and was generally greater in upper altitudes. Activity of antioxidant enzymes like catalase and peroxidase and total protein content were affected by soil physicochemical factors. A.velutinum grew better in sandy soils while A.subcordata dominanted clay soils. Although, nutrient status of the soil was different within each soil type, cation competition between Ca and Mg and high concentration of Fe in soil most likely affected root performance and consequentially pigment content in leaves, particularly in upper altitudes where temperatures were low and UV radiation was strong. UV radiation induces anthocyanin biosynthesis which mainly protects the DNA from damage. In this research, Chllorophyll/ Carotenoid ratio reduced with increasing altitude perhaps because of photoprotection.