Souls don't exist.
There is no scientific evidence for the existence of souls. Claiming that something doesn't exist, however, would be like saying that the earth is flat back when no one really knew any better.
Now I don't necessarily believe in right other than the ones we grant ourselves and others. However, through realism
Putting beliefs to paper--the Bible, the Quran, even the US Constitution--doesn't make them any more "real". The only thing "real" about them are humans reacting in ways that support them.
Could we stop suffering animals caused by other animals? Perhaps.
Of course we could. Probably wouldn't be advantageous for the animals involved, but it is certainly possible.
But as of the moment, it simply isn't feasible. There will be too much research and money needed.
Bullets are pretty cheap. If you kill them, you end suffering, ufortunately the propagation of the species as well.
Humans can stop suffering of animals by getting rid of factory farming, eating more plants, and spreading the word out.
You'd limit specific instances of abuse, yes, but you would not significantly impact suffering one way or the other.
And even though plants may be able to have negative stimuli, you still need to show that they are self aware.
Actually, the burden of proof is on you to demonstrate that higher vertebrate stimulus response deserves increased attention.