Water-level fluctuations as a driver of Phragmites australis primary productivity, litter decomposition, and fungal root colonisation in an intermittent wetland

The hypothesis of this study is that the variable hydrological regime of intermittent lakes and wetlands affects the primary productivity, decomposition and root fungal colonisation of Phragmites australis, with effects on the whole ecosystem metabolism. The above-ground biomass of reed stands was monitored in littoral and riparian stands of Lake Cerknica, under different water levels. Leaf and culm litter decomposition was also studied at three locations, from predominantly dry to permanently submerged. Root colonisation by fungi was monitored across two seasons in the littoral reed stand. The primary productivity of the littoral stands was related to a variable degree with water levels and air temperature in July in the current year. In the riparian reeds, only monthly temperatures in October of the previous year were important. The submersion duration of the litter enhanced the decomposition rates. The frequency of fungal colonisation of reed roots was decreasing with the submersion time length. Overall, roots were colonised by arbuscules, hyphae, vesicles, hyphal coils and microsclerotia. The main outcomes of this study deals with the role of intermittent hydrological conditions in determining the structure and functioning of reed-dominated lacustrine wetlands, which are exposed to climate threats.