If algae or other green life were established, it would also contribute a small amount of oxygen to the atmosphere, though not enough to allow humans to breathe. The conversion process to produce oxygen is highly reliant upon water, without which the is mostly converted to carbohydrates. In addition, because on Mars atmospheric oxygen is lost into space (unlike Earth where there is an Oxygen cycle), this would represent a permanent loss from the planet. For both of these reasons it would be necessary to cultivate such life inside a closed system. This would decrease the albedo of the closed system (assuming the growth had a lower albedo than the Martian soil), but would not affect the albedo of the planet as a whole.