Mucilage Facilitates Nutrient Diffusion in the Drying Rhizosphere

Abstract

Core Ideas Our aim was to test whether mucilage promotes diffusion of nutrients in dry soil. Mucilage favors transport of nutrients in drying soil and their uptake by plant. Mucilage increases the soil moisture in the rhizosphere as soil dries. Mucilage maintains the connectivity of liquid phase in the rhizosphere as soil dries. Despite detailed investigations of its distinct biochemical properties and their effects on the availability of nutrients for plants, the biophysical aspects of the rhizosphere, particularly the effect of mucilage on the transport of water and nutrients, are poorly understood. The aim of this study was to investigate the effect of mucilage on the diffusion of nutrients and consequently their transport through the rhizosphere into the plant roots. Phosphor imaging technique determined the temporospatial distribution of 137Cs in a model rhizosphere (a sandy soil mixed with chia seed (Salvia hispanica L) mucilage. The observed profiles of activities were used to estimate the diffusion coefficient of K in soils. A diffusion–convection equation was numerically solved to predict the transport of K and its uptake by a single plant root in drying soil. The results suggest that mucilage (i) keeps the rhizosphere wet and (ii) maintains the connectivity of the liquid phase in drying soil. In these ways, mucilage moderates the drop in diffusive transport. The modeling results showed that the presence of mucilage in the rhizosphere (i) prevents depletion of nutrients in soils with a low nutrient concentration in the soil solution and (ii) delays the risk of nutrient and/or salt accumulation in the vicinity of the root in soils with a high concentration nutrient and/or salt the soil solution. In conclusion, mucilage appears to mitigate the risk of nutrient deficiency and salinity stress as it enhances the diffusive transport in drying soil. In this way, mucilage may favor the transport of nutrients within the rhizosphere and their uptake by plant roots in drying soil.

Root Exudates Alters Nutrient Transport in Soil

“…For example, after extraction of 1.3 mL, the water flow rate in the 0.1% mucilage treatment was 0.06 mL min −1 , a 25‐fold decrease from the 1.5 mL min −1 flow rate in the control soil (Figure 4c). Such a difference in water flow rate is in agreement with previous reports of lower saturated hydraulic conductivity of soil containing exudates (Ahmed et al., 2014; Benard et al., 2019; Carminati et al., 2011; Zarebanadkouki et al., 2019); specifically, for the same 0.1% concentration of chia‐nutlet mucilage, Kroener et al., (2018) have reported up to 10‐fold decrease of soil saturated hydraulic conductivity, depending on soil particle size. Previous reports show that as the soil containing exudates continues to dry, the decline in hydraulic conductivity is attenuated compared to the decline in soil with no exudates (Ahmed et al., 2014; Benard et al., 2019; Carminati et al., 2011; Zarebanadkouki et al., 2019) which is in line with the trend observed in our loamy sand soil mixed with mucilage (Figure 4c).…”

An extended root phenotype: the rhizosphere, its formation and impacts on plant fitness

“…Furthermore, this technique in combination with experimental systems using chia seed mucilage combined with diverse soil mixtures aid to reproduce rhizosphere analogues where the dynamics of biophysical processes in response to changes in water content can be assessed at a smaller scale. In this regard, recent work suggests that the increased water retention associated with mucilage secretion sustains higher soil enzymatic activity and the diffusion of the rhizospheric solutes in dry soils (Zarebanadkouki et al , 2019). Importantly, the mucilage life‐span extends significantly in response to low water availability, ensuring a source of carbon that preserves the necessary microbial activity in the rhizosphere (Ahmed et al , 2018; Benard et al , 2019b).…”

Rhizosphere modelling reveals spatiotemporal distribution of daidzein shaping soybean rhizosphere bacterial community

“…Analyses of carbon and nitrogen with autoradiography or Positron Emitting Tracer Imaging System revealed the presence of the rhizodeposits within a few millimetres from root surface as well (Holz, Zarebanadkouki, Kaestner, Kuzyakov, & Carminati, ; Kuzyakov & Razavi, ). In addition, advection–diffusion (dispersion) equation has been used to simulate the distribution of mineral ions and water contents in soil surrounding roots (Duncan, Daly, Sweeney, & Roose, ; Vereecken et al, ; Zarebanadkouki, Fink, Benard, & Banfield, ; Zarebanadkouki, Kroener, Kaestner, & Carminati, ). Although the simulation of the distribution of metabolites could provide valuable insights in the rhizosphere interactions, it has not been employed to analyse the distribution of metabolites in soil, at least partly because of the instability of root‐secreted metabolites and the difficulty of the measurement in rhizosphere.…”