How would a drastic reduction in plant life on earth affect the atmosphere?
levels of oxygen and carbon dioxide would remain approximately the same.
levels of oxygen would decrease and levels of carbon dioxide would increase.
levels of oxygen would increase and levels of carbon dioxide would decrease.

Levels of oxygen would decrease and levels of carbon dioxide would increase.

Explanation:

The rate of photosynthesis will reduce on drastic reduction of the plants. The plants are the carbon sinks they absorb the carbon dioxide from the atmosphere in the absence of plants the carbon dioxide gas will raise in the atmosphere. The oxygen levels in the atmosphere will reduce as photosynthesis will not occur and the oxygen will not be produced as a byproduct of photosynthesis. Also the oxygen is the main requirement for the respiration of living beings except anaerobic bacteria. Thus the oxygen concentration will deplete in the atmosphere.

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