When two different plant species compete for the same requirements in an ecosystem, the most likely outcome is competitive exclusion. This is a process where one species outcompetes the other for resources, eventually leading to the decline and possible extinction of the less competitive species.

Competitive exclusion occurs when the requirements of two species overlap significantly and they cannot coexist in the same habitat. The species that is better adapted to the environment and utilizes resources more efficiently will have a competitive advantage. Over time, this advantage will lead to an increase in the population of the more competitive species, while the population of the less competitive species will decline.

The specific outcome of competitive exclusion depends on various factors, including the degree of overlap in resource requirements, the availability of alternative resources, and the presence of other competitors. In some cases, competitive exclusion may lead to the extinction of one species. However, in other cases, the two species may coexist if they are able to adapt and differentiate their niches to reduce resource competition.