XVI International Botanical Congess

We have carried out a research of indexes of water relations complexity at 73 species of grassy plants in 14 natural communities (about 43 thousand measurements). This research allows to state the organization of water relations of grassy plants naturally varies on a gradient of soil humidity from desert to meadow communities. The complexity of organization of plant water relations in a humid part of a gradient is minimum, in arid - is maximum. More com-plex organization can be connected to a modification of thermodynamic characteristics of water within plants. At an amplification of water stress the depression of a chemical potential of water goes deep, and its activity is reduced. Despite of that coefficient of water activity is increased at the expense of faster drop of water concentration in comparison with its activity in a plant