Determining Plant Water Relations

As for all living organisms, water is fundamental for plants, not only because water is the origin of life (Daniel et al. 2006), but because plants use water loss by transpiration as a mechanisms of heat dissipation and cooling of leaves (Curtis 1936; Pallas et al. 1967), and furthermore, water is essential to maintain plant cell turgor and favor plant growth. Thus, the percentage of water in plant tissues (the term plant in this chapter will be referred only to higher plants) may range from 30 to 50% in woody trunks (Borchert 1994) to around 90% in leaves and roots of several plant species. However, since plants are sessile organisms they have need to develop mechanisms to get water homeostasis mostly when water availability is scare. The main mechanisms that plants have to regulate their water content are the regulation of stomatal aperture and of root water uptake properties (Vaadia et al. 1961; Aroca et al. 2012). Thus, this chapter will start describing the methods for measuring root water uptake capacity, followed by methods determining xylem sap flow, tissue water status and stomatal aperture.