I have a question on multiple plant invasion, co-occurrung invasion plant species.

There are two types of impacts causes by co-occuring invasive plants.

1. Additive impact- no interaction. Causes individual impacts

2. Non additive impact- the two species are interacting with each other. Type of interaction can be competition, faciliation, and neutral

My question is:

If there is a competition interaction, the diversity of the native species is increased. What happens to the soil properties. Is it increasing or decreasing.

Any explanation