Results
Over all concentrations and compositions, we found that L. turionifera had the highest total growth rate, followed by L. minor , and L. gibba (Figure S3). However, initial growth rate was greatest for L. minor (Figure S3). All three species showed an overall high tolerance to Zn. L. turionifera was not influenced by Zn pollution. In contrast, addition of ZnSO4 to the experimental cultures significantly influenced L. gibba and L. minor but only at the beginning of the experiment (Table 1, Figure 2). L. gibba profited from intermediate levels of ZnSO4 (Figure 2). Similarly,L. minor grew best at the second-highest level of Zn concentration (1.82 mg /L), but in contrast to L. gibba , the second-lowest level (0.45 mg / L) did not increase growth (Figure 2).
The setting (isolated vs. mixed) only significantly influenced L. gibba growth rates (Table 1), specifically, L. gibba profited from growing alone and showed significantly lower growth rates (initial and total) when paired with either L. minor or L. turionifera (also mirrored in significant effects of composition, Table 1). For L. minor it depended on the pairing (significant effects of composition on the individual species’ growth rate, Table 1, Figure 4). L. minor performed better when paired with L. turionifera and worse when paired with L. gibba . L. turionifera showed no difference in growth rate when paired with eitherL. gibba or L. minor (Table 1, Figure 4).