You can't simulate zero gravity on Earth because your experimental samples are still exposed to 1g. If you use a clinostat, what you are studying is the effect of clinorotation on plant physiology, which is different from zero gravity (or microgravity as experienced aboard the International Space Station).
Please refer to the following. KSC is the host institution for all space biology related ground based platforms for NASA. Additionally, they are the experts in plant physiology in space. Please contact Ye Zhang.