The right answer is Biosphere.
Terrestrial plants face a hostile environment, especially in terms of their water balance.
They draw water from the ground but it is more or less wet depending on its nature (sand, clay, etc.) and depending on the amount of precipitation. The latter are discontinuous and their importance varies according to the different climates.
On the other hand, they are confronted with a more or less dry atmosphere which favors the loss of water by transpiration.
The transit of water in the plant takes place according to the water potential of the various territories in presence. In a temperate climate wetland, the soil water concentration is very low and the soil water potential is close to zero (water potential). The potential of the atmosphere, even on a humid day, is very negative. Water passes from one territory to another in the direction of decreasing potentials. It, therefore, passes from the soil to the atmosphere in a purely physical manner and thus causes a continual flow of water into the plant. This is called the Soil / Plant / Atmosphere Continuum.