Seasonal shift of dominance in a submerged rooted macrophyte community of Lake Balaton

Abiotic heterogeneity of the littoral zone of Lake Balaton influences both horizontal and vertical distribution of macrophytes, but biotic differences could shape the nature of a community. Vertical and tem- poral (small timescale) biomass distributions of Potamogeton perfoliatus and Myriophyllum spicatum were analysed in relation to their photosynthetic capacities to understand their coexistence, general presence over the northern shore of the lake seasonal shift of dominance within the community. Our results indicated the adaptation of these macrophytes to the rapidly changing and mostly low irradiance of the Lake Balaton originated from its high turbidity: both P. perfoliatus and M. spicatum had high photosynthetic activity (20 to 50 mg O2.g drw x1 .h x1 ), low dark respiration (around 12-14% of maximal photosynthetic capacity) and high shade tolerance (Ic of plants were 29 i 18 and 26 i 18 mmol.m x2 .s x1 , re- spectively). The majority of photosynthetic parameters had no (or little) seasonal changes. On the other hand, in Lake Balaton P. perfoliatus and M. spicatum differed in vertical distribution of biomass: Myriophyllum concentrated its biomass in the upper, well-lit region of the water more strongly than the Potamogeton. Results suggest that the autogenic shift of dominance from Potamogeton to Myriophyllum in Lake Balaton can't be explained only by seasonal patterns of photophysiological changes, but supported by constitutive differences in plants architecture could led to the described phenomena.