DOI: 10.6071/m39m2t
title: Root uptake under mismatched distributions of water and nutrients in the root zone

description: Most plants derive their water and nutrient needs from soils, where the
 resources are often scarce, patchy, and ephemeral. It is not uncommon for
 plant roots to encounter mismatched patches of water-rich and
 nutrient-rich regions in natural environments. Such an uneven distribution
 of resources necessitates plants to rely on strategies to explore and
 acquire nutrients from relatively dry patches. We conducted a laboratory
 study that elucidates the biophysical mechanisms that enable this
 adaptation. The roots of tomato (Solanum lycopersicum) seedlings were
 laterally split and grown in two adjacent, hydraulically-disconnected
 pots, which permitted precise control of water and nutrient applications
 to each compartment. We observed that physical separation of water-rich
 and nutrient-rich compartments (one received 90% water + 0% nutrients and
 the other received 10% water + 100% nutrients) does not significantly
 stunt plant growth and productivity compared to two control treatments
 (control 1: 90% water + 100% nutrients versus 10% water + 0% nutrients;
 and control 2: 50% water + 50% nutrients in each compartment).
 Specifically, we showed that soil dryness does not reduce nutrient uptake,
 vegetative growth, flowering, and fruiting compared to control treatments.
 We identified localized root proliferation in nutrient-rich dry soil
 patches as a critical strategy that enabled nutrient capture. We observed
 nocturnal rewetting of the nutrient-rich but dry soil zone (10% water +
 100% nutrients) but not in the nutrient-free and dry zone of the control
 experiment (90% water + 100% nutrients). We interpreted the rewetting as
 the transfer of water from the wet to dry zones through roots, a process
 commonly known as hydraulic redistribution (HR). The occurrence of HR
 likely prevents the nutrient-rich soil from drying to permanent wilting
 and subsequent decline of root functions. Sustaining rhizosphere wetness
 is also likely to increase nutrient mobility and uptake. Lack of HR in the
 absence of nutrients suggests that HR is not entirely passive,
 water-potential gradient driven flow. The density and size of root-hairs
 appeared to be higher (qualitative observation) in the nutrient-rich and
 dry compartments than the nutrient-free and dry compartments. We also
 observed organic coating on sand grains in the rhizosphere of the
 nutrient-rich and dry compartments. The observations are consistent with
 prior observations that root hairs and rhizodeposition aid rhizosphere
 wetting. These findings were synthesized in a conceptual model that
 explains how plants of dry regions may be adapted to mismatched resources.
 This study also suggests that separating the bulk of applied nutrients
 from the frequently irrigated soil region can increase nutrient use
 efficiency and curtail water pollution from intensive agricultural
 systems.
description: The data was collected from laboratory experiments conducted
 using laterally split root systems of tomato plants with the mismatched
 distribution of water and nutrients.  Plant
 physiological characteristics were determined across the plant canopy and
 soil profile, including fruit, shoot, and root
 characteristics.  Soil water content as volumetric
 water content was monitored continuously through the five-month
 experiments.  Soil water potential in dry soil
 patches was monitored continuously using precalibrated
 psychrometers.  Rhizosphere water content and
 magnitude of hydraulic redistribution was calculated by using an
 independently determined soil water retention curve.
description:   The repository includes data sets and codes
 that process and visualize the data sets. The data sets
 include: shoot nitrogen content and NDVI
 across the canopy root and rhizosheath mass
 distribution across the soil profile irrigation and
 nutrient application pattern  soil water retention
 characteristics temporal variations in volumetric
 water content  temporal variations in soil water
 potential temporal variations in hydraulic
 redistribution       More details can be
 found in README along with the datasets. The code
 includes: visualization of datasets
 mentioned above statistical tests of physiological
 indicators across treatments parameterization of a
 water retention curve Calculation of the magnitude of
 hydraulic redistribution