Effect of light on macrophyte sprouting and assessment of viable seedbank to predict community composition

The role of the aquatic macrophyte seedbank in sustaining macrophyte communities in lakes is understudied. Therefore, a controlled laboratory experiment was conducted using sediment from two Minnesota lakes. Lake Ann had historically good water clarity and a high diversity of native macrophytes, whereas Lake Riley had historically poor water clarity, few natives, and abundant invasive macrophytes because of a common carp (Cyprinus carpio L.) infestation. The experiment was designed 1) to assess the germination response under different light treatments including a treatment representative of a lake with good water clarity, a treatment representative of a lake with poor water clarity, and a maximum germination treatment (treated with gibberellic acid), and 2) to compare the taxa observed sprouting to the taxa growing in the lakes. There was no significant difference in germination among light treatments, but germination was higher in the maximum germination treatment. The most frequent species observed in the seedbanks were chara (Chara spp. L.), curlyleaf pondweed (Potamogeton crispus L.), and wild celery (Vallisneria americana Michx.). Seventeen species were observed sprouting in Lake Riley and 16 in Lake Ann. Under maximum germination conditions, Lake Riley had a viable seed density of 2,916 +/- 1,828 seeds per square meter and a viable chara spore density of 1,033 +/- 698 spores per square meter . Lake Ann had a viable seed density of 1,100 +/- 440 seeds per square meter and viable chara spore density of 13,833 +/- 2,825 spores per square meter. The observed viable seedbanks reflected the macrophyte community growing in the lakes. In Lake Ann, every species observed in the seedbank experiment was growing in the lake. In Lake Riley, all but two species observed in the seedbank were also growing in the lake. Overall, the study demonstrated that by germinating propagules from a lake seedbank, managers can evaluate the viable macrophyte taxa present and the potential for recruitment from the seedbank.