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 NO3 − 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 CO2 concentration, might be smaller than expected at high latitudes if a rise in atmospheric humidity simultaneously takes place.

Elevated air humidity modulates bud size and the frequency of bud break in fast-growing deciduous trees: silver birch (Betula pendula Roth.) and hybrid aspen (Populus tremula L. × P. tremuloides Michx.)

“…2b; for a detailed description of the experimental setup, see Kupper et al 2011). Misting equipment was updated in May 2010, allowing for the production of finer mist, which reduced leaf wetting (for details, see Tullus et al 2012).…”

Migration timing and stopover selection for barnacle geese Branta leucopsis

“…However, bird spring arrival predominantly depends on food availability which depends directly upon temperature (Žalakevicius, 1997). An increase of monthly air temperature during the growing season (May-October) was observed from 2008-2010 in western Europe (Tullus et al, 2012), and spring warming is known to cause increased photosynthetic activity and vegetation growth for northern high latitudes (Myneni et al, 1997). Therefore the time interval between peak GDDjerk and the geese arrival at the consecutive stopover sites was smaller than for colder years with a later onset of spring.…”

“…We think this was due to the extreme weather in northern and western Europe in 2010. The continental temperate climate zone in western Europe was particularly dry for the spring season of 2010, certainly compared with the two previous years (Tullus et al, 2012). This could have led to an earlier start to the growing season at higher latitudes because an increase in the mean annual air temperature in early spring corresponds to an advance in leafing (Chmielewski & Rotzer, 2001).…”

“…All three populations tracked the higher range of GWI in the year 2010. Likewise, a study corresponds that catching the later phenological stage of plant growth might be related to the higher air temperature in the year 2010 compared with the two previous years (Tullus et al, 2012) and the resulted earlier start of growing season (Chmielewski & Rotzer, 2001 Besides GWI, the rate of change in temperature acceleration (GDD jerk) was another successful index to study the spring migration of the geese with respect to green wave of plant phenology (van Wijk et al, 2011). GWI is a direct measure of plant phenology because it is closely related to the amount of photosynthetically active radiation absorbed by vegetation canopies (Loe et al, 2005;Slayback et al, 2003), while GDDjerk is an indirect measure of the same (Kerby & Post, 2013).…”

Testing Subspecies Limits in Monardella villosa

“…Brewer et al (1991;1997) have shown that leaf pubescence density can affect the frequency and duration of water on leaf surfaces (leaf wetness). Increased leaf wetness has been shown to negatively affect plants by decreasing photosynthetic rate (Ishibashi and Terashima, 2006), increasing disease susceptibility (Doss et al, 1987;Hartman et al, 1999), and decreasing growth rate (Tullus et al, 2012). The hairier subspecies franciscana typically found near the coast could be an adaptive divergence in response to the coastal fog influence.…”