Start and end of the growing season determine important ecosystem processes, such as the uptake of carbon through photosynthetic assimilation, leading to a shift from a carbon sink over summer to a carbon source over winter. Drivers of plant phenology may differ between autumn and spring, above-and belowground, as well as between different plant communities. This study compares above- and belowground spring and autumn phenology, as well as their abiotic drivers in four typical, but also contrasting temperate plant communities in Central Europe. We measured root growth in-situ with minirhizotrons in spring and autumn in four contrasting vegetation types (beech forest, alder carr, phragmites reed, sedge reed) along with abiotic parameters (temperature, water level and soil moisture). Dendrometer data and NDVI measurements were taken to compare the above-with the belowground season.
Results/Conclusions
Synchrony in the timing of above- and belowground phenology was found dependent on ecosystem. Onset of root growth, as compared to shoot growth, was delayed in all three peatlands. Contrasting to this asynchrony, onset of root growth started similar to the aboveground season in the beech forest. The growing season ended earlier belowground than aboveground in the two forested ecosystems, while no difference was detected for the phragmites reed. In all ecosystems, fine root production increased over the growing season as soil temperature increased and, in the peatlands, water level decreased. Root production in the alder carr was not correlated with water level in spring but decreased significantly with water levels rising in autumn. In the beech forest, abiotic factors were less correlated with leaf activity or root production in either spring or autumn, implying that internal drivers are stronger controls of beech phenology.
Even under the same macroclimatic conditions, ecosystems differ in the start and end of their growing season. Thus, results from other ecosystems or climate regions are likely not transferable and measuring root phenology is indispensable and a distinction between above-and belowground phenology is indispensable, since overall plant phenology cannot be drawn from aboveground phenology alone.