16 research outputs found
Climate Change at Northern Latitudes: Rising Atmospheric Humidity Decreases Transpiration, N-Uptake and Growth Rate of Hybrid Aspen
<div><p>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 (<em>Populus tremula</em> L.Ă<em>P. tremuloides</em> Michx.) in response to elevated atmospheric humidity (on average 7% over the ambient level) in a free air experimental facility during three growing seasons (2008â2010) 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 â inhibition of above-ground growth rate â 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<sub>3</sub><sup>â</sup> 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<sub>2</sub> concentration, might be smaller than expected at high latitudes if a rise in atmospheric humidity simultaneously takes place.</p> </div
FAHM experimental area: a) locations (<i>X</i>: distance from the west edge, <i>Y</i>: distance from the south edge) of control (empty circles) and humidification plots (filled circles), b) general layout of a humidification plot comprising trees - hybrid aspens (filled triangles) and silver birches (empty triangles), <i>L</i> indicates the distance between opposite vent pipe pairs and c) photo of the humidification plot taken in July 2009.
<p>FAHM experimental area: a) locations (<i>X</i>: distance from the west edge, <i>Y</i>: distance from the south edge) of control (empty circles) and humidification plots (filled circles), b) general layout of a humidification plot comprising trees - hybrid aspens (filled triangles) and silver birches (empty triangles), <i>L</i> indicates the distance between opposite vent pipe pairs and c) photo of the humidification plot taken in July 2009.</p
Chemical properties of the soil humus horizon in the experimental plots.
<p>Chemical properties of the soil humus horizon in the experimental plots.</p
Comparison of foliar characteristics (mean ± standard error) in control (C) and humidified (H) plots during individual study years (asterisks indicate <i>p</i>-values based on <i>t</i>-test: 0.01<<i>p</i><0.05*; 0.001<<i>p</i><0.01**; <i>p</i><0.001***) and summary effect of the treatment through the years: âTrueâ if <i>q</i><0.05.
<p>Comparison of foliar characteristics (mean ± standard error) in control (C) and humidified (H) plots during individual study years (asterisks indicate <i>p</i>-values based on <i>t</i>-test: 0.01<<i>p</i><0.05*; 0.001<<i>p</i><0.01**; <i>p</i><0.001***) and summary effect of the treatment through the years: âTrueâ if <i>q</i><0.05.</p
Comparison of physiological traits: a) <i>F</i> â total sap flow, b) <i>F<sub>D</sub></i> â sap flux density, c) WUE â water-use efficiency of hybrid aspens at the ages of 3 and 4 years in control (C) and humidified (H) plots (<i>t</i>-test) and summary effect of the treatment over two years (model), whiskers denote ± standard error.
<p>Comparison of physiological traits: a) <i>F</i> â total sap flow, b) <i>F<sub>D</sub></i> â sap flux density, c) WUE â water-use efficiency of hybrid aspens at the ages of 3 and 4 years in control (C) and humidified (H) plots (<i>t</i>-test) and summary effect of the treatment over two years (model), whiskers denote ± standard error.</p
Analysed variables.
a<p><i>H</i>, <i>D</i> and <i>V</i> of the previous year were used as explanatory variables while predicting the current year increments.</p>b<p>soil variables characterise A-horizon.</p
The interaction between treatment and size of the trees at the end of the previous (<i>t</i>â1) growing season for predicting the current year (<i>t</i>) increment in control (C) and humidified (H) plots: a) stem diameter (<i>D</i>), b) stem volume (<i>V</i>).
<p>Points represent individual measurements across three years of the experiment.</p
Weather conditions expressed as daily averages in the study area during the growing seasons (MayâOctober) of the study period (2007â2010).
<p>Weather conditions expressed as daily averages in the study area during the growing seasons (MayâOctober) of the study period (2007â2010).</p