Abstract
Winter warming and its accompanying predicted decrease in snow pack for northern temperate regions may increase frost damage to plants induced by an increase in freeze-thaw cycles (FTCs) due to reduced insulation. FTC frequency, minimum temperature during freezing and pre-existing local adaptations potentially all influence site-specific plant responses to future climatic changes. Within a chamber experiment, frost sensitivity towards recurrent FTCs was determined in 12 Dactylis glomerata populations from various European sampling sites differing in temperature and precipitation. After winter hardening, plants were frozen at -4 and -8 °C at frequencies of one, three and seven FTCs within a 1-week treatment phase. The control was kept at 4.5 °C. Plant survival, leaf elongation, chlorophyll content and above-ground net primary productivity (ANPP) decreased with lower minimum temperatures and higher FTC frequencies, while lower freezing temperatures generally proved more influential than increased freezing frequencies. Plant survival rates correlated with the amount of annual precipitation at seed origin, as individuals from comparably drier sites exhibited higher survival rates. This response, however, was limited in its effect to low freezing temperatures (-8 °C) and low and medium freezing frequencies (1 and 3 FTCs). In the set of surviving plants, water availability at seed origin best explained the plants' growth responses to FTC treatment. The observed intraspecific variation emphasizes the ecological importance of potential local adaptations within a more variable future winter climate.
Highlights
Climate change scenarios suggest an increase in the frequency of soil freeze-thaw cycles (FTCs) in many northern temperate regions, currently insulated and thermally stabilized by snow cover (Henry 2008; Pauli et al 2013).As strong changes in seasonality and precipitation patterns accompany global warming, air frost (−30 to −45 %) and snow cover days (−30 to −40 %) will be strongly reduced across northern Europe (Jylhä et al 2008)
Survival rates among plants experiencing freezing at −4 °C decreased with increasing freezing frequency from 98.3 to 96.7 and 93.2 %
This effect was only partly observed in the −8 °C category: following the addition of two additional freezing cycles survival rates decreased by twothirds, but did not further decrease upon the addition of four additional freezing cycles
Summary
Climate change scenarios suggest an increase in the frequency of soil freeze-thaw cycles (FTCs) in many northern temperate regions, currently insulated and thermally stabilized by snow cover (Henry 2008; Pauli et al 2013).As strong changes in seasonality and precipitation patterns accompany global warming, air frost (−30 to −45 %) and snow cover days (−30 to −40 %) will be strongly reduced across northern Europe (Jylhä et al 2008). Freeze-thaw cycles can disrupt soil microorganism and soil aggregate dynamics, affecting belowand above-ground ecological processes (Oztas and Fayetorbay 2003; Schadt et al 2003; Six et al 2004; Sjursen et al 2005; Vankoughnett and Henry 2013). Their effect on local plant populations differs significantly depending on their timing, duration, severity and frequency. Short-term warming during winter may deharden acclimatized plant tissue within several days (Strimbeck et al 1995; Kalberer et al 2006) or even hours (Rapacz et al 2000) increasing soil frost-related root injury upon (re-)freezing and in turn negatively affecting fine-root dynamics, primary productivity and nutrient cycling on-site (Fitzhugh et al 2001; Tierney et al 2001, 2003; Kreyling et al 2008, 2010)
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