Abstract
AbstractPlant root systems are exposed to spatial and temporal heterogeneity regarding water availability. In the long‐term, compensation, increased uptake by roots in areas with favorable conditions in response to decreased uptake in areas under stress, is driven by root growth and distribution. In the short‐term (hours–days), compensative processes are less understood. We hypothesized hydraulic compensation where local lowered water availability is accompanied by increased uptake from areas where water remains available. Our objective was to quantify instantaneous hydraulic root uptake under conditions of differential water availability. Tomato (Solanum lycopersicum L.) plants were grown in split‐root weighing‐drainage lysimeters in which each half of the roots could alternatively be exposed to short‐term conditions of salinity. Uptake was quantified from each of the two root zone compartments. One‐sided exposure to salinity immediately led to less uptake from the salt‐affected compartment and increased uptake from the nontreated compartment. Compensation occurred at salinity, caused by NaCl solution of 4 dS m−1, that did not decrease uptake in plants with entire root systems exposed. At higher salinity, 6.44 dS m−1, transpiration decreased by ∼50% when the total root system was exposed. When only half of the roots were exposed, total uptake was maintained at levels of nonstressed plants with as much as 85% occurring from the nontreated compartment. The extent of compensation was not absolute and apparently a function of salinity, atmospheric demand, and duration of exposure. As long as there is no hydraulic restriction in other areas, temporary reduction in water availability in some parts of a tomato's root zone will not affect plant‐scale transpiration.
Highlights
Water plays an important role in plant functioning: in addition to the small number of water molecules needed in photosynthetic and sequestration processes, plants take up and evaporate large volumes of water
The only significant differences in container-scale uptake occurred on the treatment application days for both alternating partial salinization (APS) and constant partial salinization (CPS), where one compartment received salty irrigation water and the other compartment continued to receive water without salt
The extent of the compensative behavior increased with each subsequent treatment day and was largest on the fourth day, when irrigation water electrical conductivity (EC) was just over 6 dS m−1
Summary
Water plays an important role in plant functioning: in addition to the small number of water molecules needed in photosynthetic and sequestration processes, plants take up and evaporate large volumes of water (transpiration). Ment during the day from the soil to roots and from roots to transpiring organs is a physical process functioning passively, but which is dependent on soil and plant hydraulic conductivity. There is temporal variation in water availability in the different regions of the root zone due to nonuniform patterns of irrigation, evaporation, transpiration, and more. In contrast to the spatial variability of the soil, which is often relatively stable and only slowly, if at all, changing, the temporal variability is likely to occur quickly and often. Such changes are likely dynamic and irregular. In order to deal with these quick and temporary changes, a plant needs methods for regulating uptake between different parts of its root zone, such as to temporarily augment uptake from certain areas and simultaneously reduce uptake from others
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