Root Activity and its Dependence on Soil Water Availability

A Continuous measurement of soil-water depletion, transpiration rate and atmospheric water demand using a newly developed lysimeter system was used to determine the relationship between the latter two processes and the spatial and temporal distribution of soil water uptake rate - Root Activity. The lysimeter system monitors simultaneously the variation in plant weight, soil water content in the rhizosphere, and atmospheric demand at high-frequency for a large number of plants. The temporal and spatial variation of soil water flux to the roots was determined by a high-frequency measurement of soil water content variation at different locations in the root zone. The measured data are analyzed to provide the momentary transpiration rate, temporal and spatial variation of soil water flux to roots, and the effect of the balance between these fluxes on plant physiological traits. The daily pattern of relative water content (RWC), under normal conditions and a gradual soil dehydration was calculated as well. The plant`s response, and in particular the root response, to a gradually-developed soil dehydration at different VPD values was investigated. A replacement of the commonly used description of transpiration rate vs. time by transpiration rate vs. soil-water content, yielding a piecewise linear curve, was used to determine the soil water content at which the soil hydraulic conductivity turns to be a limiting factor that causes plants to reduce transpiration by closing the stomata under different environmental conditions. The application of these results to plant phenotyping, screening, water use efficiency characterization, and water management (e.g. irrigation) will be further discussed.