Mohsen Zare

Technical University of Munich · Soil Biophysics and Environmental Systems

Background and Aims The optimal management of plant nutrition is an effective strategy for sustainable agriculture under various conditions. Soil drying is one of the main limiting factors for plant nutrient acquisition. Plants imposed to these limitations have evolved several strategies such as modifying root-to-shoot ratio, modifying their root a...

Deadwood is a key component of forest ecosystems, but there is limited information on how it influences forest soils. Moreover , studies on the effect of thinning-derived deadwood logs on forest soil properties are lacking. This study aimed to investigate the impact of thinning-derived deadwood logs on the soil chemical and microbial properties of...

Organic and synthetic fertilizers not only increase soil fertility and crop productivity but also enhance soil organic carbon (SOC). However, the priming effect (PE) leads to increased soil carbon (C) loss through native SOC mineralization. To date, the mechanisms by which long-term (>66 years) synthetic and/or organic fertilization alters net SOC...

Aims This study investigated the influence of climate and soil on the exudation rate and polysaccharide composition of aerial nodal root mucilage from drought-resistant and drought-susceptible maize varieties. Methods Two maize varieties were grown in two different soils (sandy-clay loam Acrisol and loam Luvisol) under simulated climatic conditio...

Purpose Although the coordination between stomatal closure and aboveground hydraulics has extensively been studied, our understanding of the impact of belowground hydraulics on stomatal regulation remains incomplete. Here, we investigated whether and how the water use of maize (Zea mays L.) varied under hydraulically contrasting soil textures. Our...

Climate scenarios predict more frequent and longer drought periods, potentially threatening agricultural yield. The water holding capacity of soils is crucial in controlling drought stress intensity for plants. Recently, amorphous silica was suggested to increase soil water holding capacity and availability. The objective of this study was to explo...

Soils are considered the largest sink of microplastic (MP) in terrestrial ecosystems. However, little is known about the implications of MP on soil physical properties. We hypothesize that low wettability of MP induces soil water repellency, depending on MP content and size of MP and soil particles. We quantified wettability of mixtures of MP and s...

Salinity and soil drying are expected to induce salt accumulation at the root-soil interface of transpiring plants. However, the consequences of this on the relationship between transpiration rate (E) and leaf xylem water potential (ψleaf-x) are yet to be quantified. Here, we used a non-invasive root pressure chamber to measure the E(ψleaf-x) relat...

This study investigated the effect of different salinity (EC≈6 and 9 dS/m) and Ca/Mg ratios (≈0.95,0.50, and 0.25) in irrigation water on the chemical composition of soil solution and growth of pistachio (Pistacia vera L.). The physiological, biochemical, and yield-related responses of pistachio seedlings were measured within ≈30 weeks in a greenho...

Soil compaction associated with mechanized wood harvesting can long-lastingly disturb forest soils, ecosystem function, and productivity. Sustainable forest management requires precise and deep knowledge of logging operation impacts on forest soils, which can be attained by meta-analysis studies covering representative forest datasets. We performed...

Plant roots and bacteria alter the soil physical properties by releasing polymeric blends into the soil pore space (e.g., extracellular polymeric substances and mucilage). The physical mechanisms by which these substances interact with the soil matrix and alter the spatial configuration of the liquid phase and the related hydraulic properties remai...

Biochar (BC) has been shown to positively impact soil hydraulic properties. However, its effect on water flow in unsaturated soil and root access to water have been poorly understood. This study was conducted to investigate the potential impact of BC application on soil water accessibility and plant responses under soil drying cycles. A grapevine w...

Background and aimsThere is little information about the role of fungal endophytes on plant performance under oxygen-limited conditions. This study aimed to investigate the effect of Epichloë endophyte symbiosis on tall fescue responses to oxygen stress in a greenhouse experiment.Methods The experiment was conducted with seven air-filled porosity l...

Background and aims There is little information about the effect of grass-fungal endophyte symbiota on plant performance under oxygen-limited conditions. This study aimed to investigate the effect of Epichloë endophyte symbiosis and tall fescue genotype on plant responses to oxygen stress in a greenhouse pot experiment. Methods A greenhouse pot exp...

Plants redistribute water from wet to dry soil layers through their roots, in the process called hydraulic redistribution. Although the relevance and occurrence of this process are well accepted, resolving the spatial distribution of hydraulic redistribution remains challenging. Here, we show how to use neutron radiography to quantify the rate of w...

The adsorption of arsenic (V), As(V), on two porous iron oxyhydroxide-based adsorbents, namely, micro-sized tetravalent manganese feroxyhyte (µTMF) and granular ferric hydroxide (µGFH), applied in a submerged microfiltration membrane hybrid system has been investigated and modeled. Batch adsorption tests were carried out to determine adsorption equ...

The objective of this study was to evaluate the potential effect of biochar (BC) and humic acid (HA) application on the improvement of plant growth and the acquisition of nutrients by plant roots of calendula (Calendula officinalis L.). A factorial experiment with a completely randomized design was conducted to investigate the HA and BC effects on...

Phosphatases in soil are of great importance for plant P acquisition. It is hypothesized that root hairs increase rhizosphere phosphatase activity as they release enzymes into soil and stimulate microbial activity. To test the effect of root hairs on soil phosphatase activity, we grew barley (Hordeum vulgare ‘Pallas’) wild type and its root-hairle...

More frequent and longer drought periods are predicted threatening agricultural yield. The capacity of soils to hold water is a highly important factor controlling drought stress intensity for plants. Biogenic amorphous silica (bASi) pools in soils are in the range of 0–6% and are suggested to help plants to resist drought. In agricultural soils, b...

Aims As soil dries, the loss of soil hydraulic conductivity limits water supply to the leaves, which is expected to generate a nonlinear relationship between leaf water potential (ψleaf) and transpiration (E). The effect of soil drying and root properties on ψleaf and E remains elusive. Methods We measured E and ψleaf of pearl millet for varying E...

In the original version of this article, equations 4 and 9 unfortunately contained errors

A common assumption in models of water flow from soil to root is that the soil can be described in terms of its representative or effective behavior. Microscale heterogeneity and structure are thereby replaced by effective descriptions, and their role in flow processes at the root‐soil interface is neglected. Here the aim was to explore whether a d...

The relationship between leaf water potential, soil water potential and transpiration depends on soil and plant hydraulics and stomata regulation. Recent concepts of stomatal response to soil drying relate stomatal regulation to plant hydraulics, neglecting the loss of soil hydraulic conductance around the roots. Our objective was to measure the ef...

Aims Rhizosheath is known as a layer of adhering soil particle to the root surface. Despite several speculations, the positive function of rhizosheath in acquisition of water and nutrients from drying soil has not yet been experimentally proven. The objective of this study was to experimentally show whether an enhanced rhizosheath formation could h...

Background and aims Soil drying negatively impacts several rhizosphere processes, but plant roots are capable of alleviating changes in rhizosphere water content by releasing mucilage. We propose that enhanced water retention in the rhizosphere due to mucilage and microbial extracellular polysaccharides allows for fast diffusion of enzymes and subs...

The pathways of water across root tissues and their relative contribution to plant water uptake remain debated. This is mainly due to technical challenges in measuring water flux non-invasively at the cellular scale under realistic conditions. We developed a new method to quantify water fluxes inside roots growing in soils. The method combines spat...

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 i...

Core Ideas Plant mucilage and bacterial extracellular polymeric substances (EPS) prevent the breakup of the soil liquid phase. Formation of continuous structures buffers soil hydraulic properties. The release of viscous polymeric substances represents a universal strategy. Plant roots and bacteria are capable of buffering erratic fluctuations of w...

Background and Aims: Root exudation is an important carbon (C) and energy source for soil microorganisms but quantifying its spatial distribution is challenging. We tested whether 14C imaging (analogue of previous autoradiography) can be used to quantitatively estimate the spatial distribution of root exudates in the rhizosphere. Methods: First, t...

The relationship between leaf water potential, transpiration rate and soil water potential is complex, particularly when the soil water potential in the root zone is not uniform, which is the rule rather than the exception in soils. Our objectives were: 1) to measure the effect of heterogeneous soil water potentials on the relation between leaf wat...

Lentil and lupine, having contrasting root morphologies, were chosen to investigate the effects of plant growth and root morphology on the spatial distribution of β-glucosidase, cellobiohydrolase, leucine aminopeptidase, and acid phosphomonoesterase activities. Lentil kept as vegetative growth and the rhizosphere extent was constant, while the enzy...

Background and AimsRecent experiments showed that rhizosphere of several plant species turns temporarily hydrophobic after severe drying and subsequent rewetting. Whether or not such hydrophobicity limits root water uptake is not known. MethodsA set of experiments was performed to test whether rhizosphere water repellency negatively affects root wa...

Recent studies proved that the rhizosphere of some plant species turn water repellant upon drying. The effects of rhizosphere water repellency on microbial biomass and enzyme activity are not known. We hypothesized that rhizosphere water repellency limits microbial biomass and enzyme activities and increasing rhizosphere wettability by application...

Take home messageMucilage secreted by roots and EPS produced by microorganisms alter the physical properties of the soil solution and impact the water dynamics in the rhizosphere. The high viscosity of mucilage and EPS is responsible for the formation of thin filaments and interconnected thin lamellae that span throughout the soil matrix maintainin...

Vast amounts of water flow through a thin layer of soil around the roots, the rhizosphere, where high microbial activity takes place—an important hydrological and biological hotspot. The rhizosphere was shown to turn water repellent upon drying, which has been interpreted as the effect of mucilage secreted by roots. The effects of such rhizosphere...

Nitrogen (N) fertilization is an indispensable agricultural practice worldwide, serving the survival of half of the global population. Nitrogen transformation (e.g. nitrification) in soil as well as plant N uptake releases protons and increases soil acidification. Neutralizing this acidity in carbonate‐containing soils (7.49 10⁹ ha; ca. 54% of the...

Aims Rhizodeposition is an important energy source for soil microorganisms. It is therefore crucial to estimate the distribution of root derived carbon (C) in soil and how it changes with soil water content. Methods We tested how drought affects exudate distribution in the rhizosphere by coupling ¹⁴CO2 labelling of plants and phosphor imaging to e...

Core Ideas We propose a model of mechanistic pore‐scale interactions of mucilage, water, and soil. Effect of mucilage on saturated hydraulic conductivity is stronger in coarse soils. Coarse soils require higher mucilage concentration to increase water content. Upscaling to macroscopic soil hydraulic properties remains challenging. The model was val...

Improving or maintaining crop productivity under conditions of long term change of soil water availability and atmosphere demand for water is one the big challenges of this century. It requires a deep understanding of crop water acquisition properties, i.e. root system architecture and root hydraulic properties among other characteristics of the so...

The importance of root hairs and root radius for exudation and nutrient acquisition by plants is known mainly from nutrient solution studies. The in situ effects of root hairs and root radius on the spatial distribution of enzyme activity in the rhizosphere of various plants are unknown. Four plants with contrasting root morphology (maize, wheat, l...

The Tibetan Plateau hosts the world's largest alpine pastoral ecosystems, dominated by the endemic sedges Ko-bresia pygmaea and Kobresia humilis. Owing to the very harsh environment and also to soil nitrogen (N) and phosphorus (P) limitations, these pastoral ecosystems are very sensitive to disturbances (e.g. anthropogenic activities and climate ch...

For experiments with low contrast between the relevant features it can be beneficial to add a second modality to reduce ambiguity. At Paul Scherrer Institut the two neutron imaging facilities NEUTRA (thermal neutrons) and ICON (cold neutrons) we have installed X-ray beamlines for on-site bimodal imaging with neutrons and X-rays. This allows us to l...

In 1978, Landsberg and Fowkes presented a solution of the water flow equation inside a root with uniform hydraulic properties. These properties are root radial conductivity and axial conductance, which control, respectively, the radial water flow between the root surface and xylem and the axial flow within the xylem. From the solution for the xylem...

Background and aims: Although it is commonly accepted that root exudation enhances plant-microbial interactions in the rhizosphere, experimental data on the spatial distribution of exudates are scarce. Our hypothesis was that root hairs exude organic substances to enlarge the rhizosphere farther from the root surface. Methods: Barley (Hordeum vu...

The ability of plants to take up water from the soil depends on both the root architecture and the distribution and evolution of the hydraulic conductivities among root types and along root length. Mature maize (Zea mays L.) root system is composed of primary, seminal and crown roots alongside with their respective laterals. Our understanding of ro...

Core Ideas During drying, mucilage is preferentially deposited in small pores. This microscopic heterogeneity critically affects macroscopic wettability. Infiltration is impeded when a critical fraction of pores is blocked by dry mucilage. Dry mucilage bridges are shaped like hollow cylinders connecting particles. The physical properties of the rh...

Background The role of the root-soil interface on soil-plant water relations is unclear. Despite many experimental studies proved that the soil close to the root surface, the rhizosphere, has different properties compared to the adjacent bulk soil, the mechanisms underlying such differences are poorly understood and the implications for plant-water...

Background and aims Biopores as microbial hotspots provide additional nutrients to crops – but only if their roots grow within the biopores. Such reuse has never been quantified as pre-crop-specific biopores are hardly differentiated from the multitude of pre-existing biopores. Quantification requires e.g. radionuclide labelling of pre-crops (¹³⁷Cs...

Do root hairs help roots take up water from the soil? Despite the well‐documented role of root hairs in phosphate uptake, their role in water extraction is controversial. We grew barley ( Hordeum vulgare cv Pallas) and its root‐hairless mutant brb in a root pressure chamber, whereby the transpiration rate could be varied whilst monitoring the sucti...

Manure is an important source of nutrients for plants and stimulates a wide range of enzyme-mediated microbial processes. Such stimulation, however, depends on manure distribution and the duration of its decomposition in soil. For the first time, we investigated the spatio-temporal patterns of enzyme activities as affected by manure application str...

The ability of roots to extract water and nutrients from soil depends on the biophysical properties of the rhizosphere, which are strongly influenced by mucilage secretion. The aim of this study was to introduce the concept of rhizoligands to engineer the biophysical properties of the rhizosphere. A rhizoligand is defined as an additive that increa...

Manure is an important source of nutrients for plants and stimulates a wide range of enzyme-mediated microbial processes. Such stimulation, however, depends on manure distribution and the duration of its decomposition in soil. For the first time, we investigated the spatio-temporal patterns of enzyme activities as affected by manure application str...

Developing new technologies to optimize the use of water in irrigated croplands is of increasing importance. Recent studies have drawn attention to the role of mucilage in shaping rhizosphere hydraulic properties and regulating root water uptake. During drying mucilage keeps the rhizosphere wet and conductive, but upon drying it turns hydrophobic l...

Background and Aims Although maize roots have been extensively studied, there is limited information on the effect of root exudates on the hydraulic properties of maize rhizosphere. Recent experiments suggested that the mucilaginous fraction of root exudates may cause water repellency of the rhizosphere. Our objectives were: 1) to investigate wheth...

Computed tomography has become a routine method for probing processes in porous media, and the use of neutron imaging is especially suited to the study of the dynamics of hydrogenous fluids, and of fluids in a high-density matrix. In this paper we give an overview of recent developments in both instrumentation and methodology at the neutron imaging...

Background and Aims Radial and axial hydraulic conductivities are key parameters for proper understanding and modelling of root water uptake. Despite their importance, there is limited experimental information on how the radial and axial hydraulic conductivities vary along roots growing in soil. Here, a new approach was introduced to estimate inver...