There is only a single interaction estimated, and that is the -4.08 value. What is confusing you is just the fact that your Species variable is a CLASS (categorical) predictor and is represented in the model with two dummy-coded (0,1-coded) variables. However, since Species has two levels, it has only 1 degree of freedom and therefore only 1 estimable parameter. The second parameter is restricted to zero. Similarly, the interaction has only 1 degree of freedom (1 for log10root times 1 for Species equals 1). Again, the second is restricted to zero. The significant -4.08 interaction suggests that the effect of log10root differs between the two Species.
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