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Characterizing rhizosphere size and composition under distinct plant water use strategies

EMSL Project ID


Plant roots exude water and metabolites into the rhizosphere, to condition their environment and to foster symbiotic relationships with soil microorganisms which, in exchange, provide essential nutrients otherwise inaccessible to the plant. Plants can alter exudate composition and rate in response to stress, such as water limitation. This can alter rhizosphere water retention, hydraulic conductivity, and hydrophobicity, and considering the control of water over biotic activity in the soil, can impact rhizosphere carbon dynamics. Our objective is to delineate the relationship between water availability and root exudate spatial patterns and chemical composition.
We will pursue our objectives using maize (Zea mays L). Maize is a robust crop with well-characterized and diverse lines that vary in their root traits, and large diameter roots for ease of observation using visual imaging and X-ray computed tomography. Specifically, we will utilize the SLAC1 maize mutant to decouple stomatal closure (and hence carbon fixation) from plant water stress. The slow-activating anion channel 1 (SLAC1) gene has been identified as a key player in regulating stomatal closure, which controls carbon fixation rate and water loss, thereby affecting plant productivity and water use efficiency. SLAC1 maize mutants result in an extreme phenotype where stomata remain constitutively open, hence we expect that exudation will continue even under water limitation. We propose to utilize the extreme phenotypes of SLAC1 vs wild type (wt) to study the impact of limited water availability, a key stressor associated with global warming, on rhizosphere spatial patterns and composition.
Our approach consists of a 13CO2 labeling experiment to study the allocation of recent photoassimilates to roots and rhizosphere in SLAC1 and wt maize grown in a defined water deficit treatment and sampled at a critical vegetative stage (v3-4). We will use XCT and visual imaging to characterize root structure and volume, and LA-IRMS measurements to characterize rhizosphere spatial patterns. Combined, we aim to derive initial estimates of rhizosphere volumes under different water availability scenarios. We will apply spatially resolved mass spectrometry imaging and bulk 13C-NMR to characterize rhizosphere chemical composition and correlate it with its spatial patterns. We hypothesize that maize with overexpressed stomatal opening (SLAC1 mutants) will (1) exude a greater quantity of root exudates and (2) influence a larger volume of soil, i.e., have a larger rhizosphere. Based on the literature we also expect (3) greater concentrations of organic acids, secondary metabolites, and osmolytes in the rhizospheres of droughted vs. control plants.

Project Details

Project type
Exploratory Research
Start Date
End Date


Principal Investigator

Itamar Shabtai
Connecticut Agricultural Experiment Station


Taryn Bauerle
Cornell University

Team Members

Andrea Sanchez
Cornell University