Influence of seedbed, light environment, and elevated night temperature on growth and carbon allocation in pitch pine ( Pinus rigida) and jack pine ( Pinus banksiana) seedlings

Abstract

Jack pine ( Pinus banksiana Lamb.) and pitch pine ( Pinus rigida Mill.) are two autecologically similar species that occupy generally disjunct ranges in eastern North America. Jack pine is boreal in distribution, while pitch pine occurs at temperate latitudes. The two species co-occur in a small number of stands along a ‘tension-zone’ that traverses central Maine. These populations provide an opportunity for studying differences between boreal and temperate species in their adaptation to climatic factors. As seedling establishment and early growth are key life-stages governing tree distribution, we experimentally evaluated the influence of seedbed light environment and substrate on the success and early growth of these species. Under similar environments, first-year jack pine seedlings allocated relatively more biomass to roots and pitch pine more to foliage. This might provide pitch pine with an adaptive advantage when soil moisture was not limiting and an advantage to jack pine if substantial moisture stress occurred. Complex ontogenetic shifts in these allocation patterns occurred over second and third years of growth, which resulted in an equalization of interspecific differences in shoot–root ratios by the end of the third growing season. Night temperatures of 4–5 °C above ambient reduced growth of jack pine seedlings, while that of pitch pine was unaffected. However, foliar respiration and respiratory response to temperature were not significantly different between species and did not explain observed differences in temperature response.