Effects of soil freeze–thaw cycles differ between experimental plant communities

Soil freeze–thaw cycles (FTC) influence nutrient cycling, but their consequences for productivity and composition of vegetation are not well investigated. Ongoing global warming will increase the recurrence of FTC in cool-temperate and high-latitude regions.Here, we report on the above- and belowground biomass production as well as the nitrogen nutrition of two common vegetation types, grassland and heath, after more frequent FTC in a controlled field experiment in Central Europe. Furthermore, we analyze the duration of the observed effects. Five FTC were induced by buried heating wires in addition to three naturally occurring FTC during winter 2005/06. More frequent FTC significantly increased aboveground production of experimental grassland early in the following growing season. However, no reaction was found for experimental heath within the first growing season. Biomass production of heath communities dropped significantly and C/N ratio increased in the freeze–thaw treated plots in the second year after the manipulation, whereas production in the grassland communities was no longer affected significantly, except for an increase in C/N ratio. This response can at least partly be explained by changes in nutrient availability, as plant available nitrate increased in the manipulated grassland plots and decreased in the manipulated heath plots.The results show the high ecological importance of climate changes during winter, with the outcomes differing strongly between contrasting vegetation types. Furthermore, we show that short term climatic events can cause long-lasting effects, sometimes emerging in the vegetation only after considerable time lags (here: one growing season).