title: Climate change at northern latitudes: rising atmospheric humidity decreases transpiration, N-uptake and growth rate of hybrid aspen.
abstract: At northern latitudes a rise in atmospheric humidity and precipitation is predicted as a consequence of global climate change. We studied several growth and functional traits of hybrid aspen (Populus tremula L.×P. tremuloides Michx.) in response to elevated atmospheric humidity (on average 7% over the ambient level) in a free air experimental facility during three growing seasons (2008-2010) in Estonia, which represents northern temperate climate (boreo-nemoral zone). Data were collected from three humidified (H) and three control (C) plots, and analysed using nested linear models. Elevated air humidity significantly reduced height, stem diameter and stem volume increments and transpiration of the trees whereas these effects remained highly significant also after considering the side effects from soil-related confounders within the 2.7 ha study area. Tree leaves were smaller, lighter and had lower leaf mass per area (LMA) in H plots. The magnitude and significance of the humidity treatment effect--inhibition of above-ground growth rate--was more pronounced in larger trees. The lower growth rate in the humidified plots can be partly explained by a decrease in transpiration-driven mass flow of NO(3) (-) in soil, resulting in a significant reduction in the measured uptake of N to foliage in the H plots. The results suggest that the potential growth improvement of fast-growing trees like aspens, due to increasing temperature and atmospheric CO(2) concentration, might be smaller than expected at high latitudes if a rise in atmospheric humidity simultaneously takes place.
authors.affiliation: Department of Silviculture, Institute of Forestry and Rural Engineering, Estonian University of Life Sciences, Tartu, Estonia.
authors.forename: Arvo
authors.initials: A
authors.lastname: Tullus
authors.forename: Priit
authors.initials: P
authors.lastname: Kupper
authors.forename: Arne
authors.initials: A
authors.lastname: Sellin
authors.forename: Leopold
authors.initials: L
authors.lastname: Parts
authors.forename: Jaak
authors.initials: J
authors.lastname: Sõber
authors.forename: Tea
authors.initials: T
authors.lastname: Tullus
authors.forename: Krista
authors.initials: K
authors.lastname: Lõhmus
authors.forename: Anu
authors.initials: A
authors.lastname: Sõber
authors.forename: Hardi
authors.initials: H
authors.lastname: Tullus
mesh_terms: D000531:Altitude; D001272:Atmosphere; D057231:Climate Change; D004957:Estonia; D006813:Humidity; D006824:Hybridization, Genetic; D009584:Nitrogen / Q000378:metabolism*; D018515:Plant Leaves / Q000502:physiology; D018547:Plant Stems / Q000033:anatomy & histology; D018526:Plant Transpiration / Q000502:physiology*; D032107:Populus / Q000254:growth & development* / Q000378:metabolism; D011891:Rain; D012621:Seasons; D013696:Temperature; D014867:Water / Q000378:metabolism
chemical_list: D014867:Water; D009584:Nitrogen