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Root uptake under mismatched distributions of water and nutrients in the root zone

Citation

Yan, Jing; Bogie, Nathaniel; Ghezzehei, Teamrat (2021), Root uptake under mismatched distributions of water and nutrients in the root zone, Dryad, Dataset, https://doi.org/10.6071/M39M2T

Abstract

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.

Methods

The data was collected from laboratory experiments conducted using laterally split root systems of tomato plants with the mismatched distribution of water and nutrients. 

  1. Plant physiological characteristics were determined across the plant canopy and soil profile, including fruit, shoot, and root characteristics. 
  2. Soil water content as volumetric water content was monitored continuously through the five-month experiments. 
  3. Soil water potential in dry soil patches was monitored continuously using precalibrated psychrometers. 
  4. Rhizosphere water content and magnitude of hydraulic redistribution was calculated by using an independently determined soil water retention curve.

Usage Notes

 

The repository includes data sets and codes that process and visualize the data sets.

The data sets include:

  1. shoot nitrogen content and NDVI across the canopy
  2. root and rhizosheath mass distribution across the soil profile
  3. irrigation and nutrient application pattern 
  4. soil water retention characteristics
  5. temporal variations in volumetric water content 
  6. temporal variations in soil water potential
  7. temporal variations in hydraulic redistribution

      More details can be found in README along with the datasets.

The code includes:

  1. visualization of datasets mentioned above
  2. statistical tests of physiological indicators across treatments
  3. parameterization of a water retention curve
  4. Calculation of the magnitude of hydraulic redistribution

 

Funding

U.S. Department of Agriculture, Award: 2016-67019-25283