Which factors can modify geotropic responses in plants?

Geotropism is the growth or movement of an organism in response to gravity. 

The sensitivity of plant roots and shoots to gravity can be modified by various environmental factors. The growth and orientation of roots and shoots towards or away from gravity can be influenced by light, relative humidity, and temperature of the surrounding air, as well as the growth and developmental state of the plant's root and shoot apices. 

However, atmospheric carbon dioxide and phytochrome (a light-sensitive pigment) are not specifically related to geotropism.