Without more information specifically about how you envision "landscape" or "night" photography, no one can really give you a specific recommendation without relying on assumptions or their own personal preferences in these matters.

For landscape, it really depends on what/how you plan to shoot. Some folks use telephotos, others use ultrawides, others do just find with middling widish-to-normal 35e and 50e lenses. Landscape may not be about the lens as much as about what's in front of the lens. :)

With night photography, you probably want a fast lens which opens up to a wider aperture, but again, it depends on what type of night photography you plan to do. Northern lights vs. light trails from car headlights have very different requirements. Milky way vs. night-time street shooting similarly have very different requirements.

I will say, however, that the one thing you could buy that would benefit both of those types of photography, possibly more than a lens, would be a tripod to support your camera. Tripods allow you to use very slow shutter speeds without introducing blur from camera shake into the image. With landscape this means you can use a low iso and stop the lens down for depth of field, and not have to worry about handholding the camera steady. For night-time photography, it can open up entire new areas of long-exposure photography you can't possibly accomplish with handholding.