Reed die-back in central Italy: plant traits, environmental features, and implications for the vegetation.

Common reed die-back, a well known phenomenon in Central Europe, was recently detected in the Mediterranean Basin at Lake Trasimeno, one of the largest freshwater ecosystems in Central Italy. The symptoms of decline were analysed by using a large set of parameters including morphologic, phenologic, anatomical, cyto-histological and histochemical traits; fungal endophytes in reed leaves and roots were investigated too. Stem height and diameter, node number, growth rate, lateral root diameter and amount, clumped habit resulted the most significant morphologic factors highlighting the declining condition. A correlation between the presence of starch in roots and rhizomes and the die-back syndrome was confirmed. With regards to fungal endophytes, one of the dominant taxa in the most declining reed stands appeared to belong to a species complex that produces mycotoxins affecting the host plant health. All the investigated traits contributed to point out the features of the reed decline in the study area. Some environmental characteristics of the reed stands were also taken into account; among them, the period of submersion and the presence of standing litter emerged as important features, related to the degree of decline in the population. Finally, floristic and vegetational traits of declining and healty reed stands have been taken into account and analysed from a phytosociological point of view. Results show that Phragmites australis tends to form monospecific stands in permanently flooded areas rich in organic deposits and autogenous standing litter, where the symptoms of reed decline seem to be more severe. Species rich stands develop in terrestrial areas, on nutrient-rich soils, where reed shows vigorous growth and healthy condition; however, the observed floristic richness is mostly due to invasive and nitrophylous species from the classes Stellarietea mediae Txen et al. ex von Rochow 1951 and Artemisietea vulgaris Lohmeyer et al. ex von Rochow 1951, which give rise to a pseudo-reed bed, lacking in typical palustrine species. The results draw attention to the risk of loss of an ecosystem which plays an important role in biodiversity conservation.