Vegetation types differ in their response to recurrent soil freeze-thaw cycles

Ongoing global warming will increase the recurrence of soil freeze-thaw cycles (FTC) in cool-temperate and other high-latitude regions, which were previously subject to prolonged periods of continuous winter soil frost. Freeze-thaw cycles (FTC) contribute to the microbial release of nutrients in plant available form. However, knowledge on the effects of FTC on plant performance is scarce. Ultimately, the ability of plants to incorporate the released nutrients decides if the nutrient cycling remains closed or if losses from the ecosystem occur. Here, we analyze the effects of recurrent FTC on grassland and heath performance in a controlled field experiment in Central Europe. Five FTC were created by buried heating wires in addition to three natural FTC in winter 2005/06. FTC significantly increased aboveground productivity and vegetation cover of grassland early in the growing season, but root length density was reduced. No significant reaction at any parameter was found for heath. Based on our findings, we propose that the fast and dynamic response of grassland helps to prevent nutrient leaching from the ecosystem. However, the advanced development and decreased root/shoot ratio may increase the susceptibility of grassland to late frost events and drought. Heath systems appear to be more vulnerable to nutrient loss as they lack growth promotion in spring. However, their low resource demand prevents from growth restrictions due to reduced nutrient supply within one year. The decisive power of vegetation type on productivity and nutrient retention following increased FTC is an important finding for future ecosystem management.