Allelopathic effects of dominant ground vegetation species on initial growth of Pinus sylvestris L. seedlings in response to different temperature scenarios

Abstract: The dominant species of ground vegetation cover in clear-cuts impact the regeneration of Scots pine forests due to the biochemical properties of these dominant species. Environmental conditions in clear-cuts, specifically increased light and temperature, can alter the biochemical impact of dominant species on subsequent Scots pine regeneration processes. To investigate this, plant species diversity, frequency and cover were estimated in order to identify the dominant species of ground vegetation in clear-cut areas over a two-year period. Afterward, the impact of dominant species extracts on pine seed germination and seedling physiology at different temperature scenarios was evaluated. The species Pleurozium schreberi (Brid.) Mitt., Vaccinium vitis-idaea L. and Calluna vulgaris (L.) Hull were recorded as dominant in 1-yr-old clear-cut areas, and Vaccinium vitis-idaea L., Rumex acetosella L., and Calamagrostis epigejos (L.) Roth were dominant in 2-yr-old clear-cut areas. The prepared aqueous extracts of all dominant species exhibited strong inhibitory effects on pine seed germination and seedling morpho-physiological traits (the length of the radicle and hypocotyl; chlorophyll a, b, a/b and carotenoid content), resulting in the reduction of ex situ pine adaptive capacity at higher air temperature (24°C) compared to that at lower temperature (20°C). Significantly (p<0.05) stronger inhibitory effects of root and shoot extracts produced from all dominant species on chlorophyll a, b and a/b content were recorded at higher temperature (22-24°C) compared to lower (20°C) temperature. A significantly lower content of carotenoids was observed in the control (24°C) temperature. Thus, a high increase of ambient temperature may cause unfavourable conditions for Scots pine seedling growth in boreal forests.