Your question is a little confusing to me? Are you asking A) or B)
A) Do different plant species have different # of guard cells per stoma?
B) Do different plant species have different # of stoma?
I believe B) might be what you are asking, because A) doesn't offer much in the way of discussion. In the case of B), think of the theories for the purpose of the stoma. Why would there be a need to have a different number of stoma in different species of plants? Do plants of different climates or biomes, have different needs? By answering those questions, you will answer your question.