Moshe Shenker

Phosphorus (P) nanoparticles (NPs) have been proposed as a promising alternative to conventional water‐soluble inorganic P (WSP) fertilizers, based on the hypothesized advantages of higher mobility and bioavailability in soils. However, systematic quantification of the mobility and bioavailability of P NPs in soils remains lacking. The transport (saturated and unsaturated), diffusion, and plant response of spherical polyacrylic acid‐coated nano‐hydroxyapatite (PAA‐nHAP) and WSP were evaluated in two low‐P soils: an alkaline sand (Alk) and an acidic sandy clay loam (Ac), targeting scenarios where P is surface‐applied without incorporation into the root zone. After systematically comparing 36 one‐site or two‐site kinetic models in HYDRUS‐1D, a model selection process was established for the first time. The results showed that two‐site kinetic models can capture the transport pattern, with distinct retention mechanisms across soils: reversible and time‐dependent at both sites for the Alk soil; reversible and depth‐dependent at one site and irreversible and time‐dependent at the other for the Ac soil. Because of the air‐water‐solid or air‐water interface, greater retention of the PAA‐nHAP was observed in the unsaturated transport than in the saturated transport. The diffusion capacity of the PAA‐nHAP was lower than that of the WSP in both soils, primarily due to NPs aggregation. Tomato bioassays further demonstrated that the bioavailability of PAA‐nHAP was not superior to, and in most cases, lower than that of conventional P fertilizers. The limited fertilization efficacy of the PAA‐nHAP was attributed to the low solubility of hydroxyapatite and the restricted diffusion of aggregated NPs, which prevented the macroscale transport advantage from translating into sustained plant‐available P supply. The framework of this study can be used to assess the agronomic benefits of nanofertilizers and the environmental risks posed by NPs in surface soils.

Waterlogging constrains terrestrial plants by limiting oxygen diffusion in the rhizosphere and altering root-zone physical and chemical properties. However, the extent to which whole-plant responses to waterlogging can be reproduced by oxygen deficiency alone remains unresolved. In tomato ( Solanum lycopersicum ), waterlogging is commonly associated with adventitious-root formation, yet the functional contribution of these roots to whole-plant water relations has rarely been quantified. Here, we experimentally separated root-zone hypoxia from waterlogging and quantified the contribution of surface-associated adventitious roots to whole-plant transpiration. Using high-resolution gravimetric lysimeters, we monitored transpiration dynamics under two conditions: (i) N ₂ -driven displacement of root-zone O ₂ under near-field-capacity conditions and (ii) root-zone waterlogging. These measurements were complemented by analyses of soil redox potential and pH, mineral composition, stem anatomy, and genotypic variation among M82, IL11-4, and IL8-1. N ₂ -driven oxygen depletion rapidly reduced rhizosphere O ₂ concentration and induced a moderate decline in redox potential, accompanied by changes in rhizosphere chemistry and mineral relations. Whole-plant transpiration, however, declined only progressively over several days. Under waterlogging, transpiration declined rapidly in all genotypes, with strong genotype dependence. A transient partial recovery coincided with the appearance of adventitious roots at the soil surface and was followed by renewed decline after drainage. Quantitative analysis indicated that adventitious roots contributed only a limited fraction of daily water uptake, approximately 15% to 20%, which was insufficient to restore pre-waterlogging transpiration or growth. Together, these results show that waterlogging responses were not reproduced by rapid oxygen deprivation alone and that adventitious roots provide limited hydraulic compensation.

Phosphorus (P) nanoparticles were hypothesized to exhibit greater mobility in soils than water-soluble P (WSP) and were therefore proposed to be used as a P fertilizer. Unsaturated transport is the main pathway from the application site to plant roots. Though its importance to fertilizer efficacy, quantitative evaluation of unsaturated transport of P nanoparticles has been overlooked to date. Mobility of spherical nano-hydroxyapatite particles coated with polyacrylic acid (PAA-nHAP) suspension and WSP (a mixture of KH₂PO₄ and K₂HPO₄) was evaluated in breakthrough column experiments under unsaturated states using three soils: alkaline sand (sandy-alk), acidic sandy clay loam (sandy-ac) and clayey soils. Next, P retention was determined by total P extraction layer-by-layer from the disassembled soil columns. In all soils, PAA-nHAP exhibited faster transport compared to WSP. In the sandy-alk soil, earlier breakthrough but lower plateau of the final relative P concentration of PAA-nHAP (64.0% vs. 100% of the input P concentration) and consistent low P retention with depth after washing with 10 mM KBr solution for the two sources were observed. In the other two soils, PAA-nHAP displayed greater retention near the inlet and decreased retention with depth. In the sandy-ac soil, no WSP and low final relative concentrations of PAA-nHAP (11.6%) were transported through the soil column. The retention of PAA-nHAP was much lower than that of WSP with depth. In the clayey soil, the breakthrough (relative P concentration >1%) occurred earlier (~35 pore volumes vs. ~45 pore volumes) and the eluted P concentration increased more rapidly (~2.6 times) for PAA-nHAP compared to WSP. The difference between the two sources mainly occurred at the soil surface with higher retention of WSP. Soil properties affected the P retention capacity of the two P sources, but for all soils, P mobility was increased by changing from the common soluble fertilizers to nanoparticles. Adsorption and size exclusion effect are suggested as the major factors affecting nHAP mobility. We suggest that the nHAP transport can be improved by modifying its coating with more negative zeta-potential to decrease coagulation and adopting drip flows with short hydraulic retention time. The design of the nanoparticles needs to take into account soil properties.

The exposure of plants to pharmaceuticals via treated wastewater irrigation and biosolid application presents an important route of chronic exposure of crops to a wide variety of bioactive pollutants. This paper presents a novel approach which aims to improve our understanding of the interactions of bioactive pollutants with plants through the concept of plant pharmacology and two main sub-divisions: (i) plant pharmacokinetics which describes the fate of exogenous xenobiotics in the plant based on the processes of absorption, distribution, metabolism and accumulation (ADMA), processes that are analogous to pharmacokinetics in animals; and (ii) plant pharmacodynamics that proposes that exogenous xenobiotics interact with plant enzymes and biochemical pathways, establishing a relationship with pharmacological concepts and emphasizing the importance of exposure-response interactions. The concept of plant pharmacology and its two subdivisions provide a foundation for the development of in-depth knowledge regarding the fate of xenobiotics in plants and establishing plant pharmacokinetic-pharmacodynamic models that include both the ADMA processes and time-dependent response of the plant to these compounds. This concept provides a new perspective on pharmacovigilance, focusing on plant-xenobiotic compound interactions, and a conceptual framework for understanding the fate and interactions of these bioactive molecules in agricultural systems, to enable more accurate risks assessments of environmental and human health. Graphical Abstract

Soil oxygen has been recognized as a potential limiting factor in plant production second only to water and nutrients. While it is widely accepted that soil gaseous oxygen levels below 10% V/V are detrimental to plant production, there are currently no accepted indices to quantify the effect of different agricultural practices on soil oxygen supply and availability. To address this challenge, a new approach is introduced, whereby indices describing the soil oxygen dynamics are determined using data from continuous in-situ soil oxygen measurements. To give the measurements a mechanistic interpretation, we developed a conceptual model describing the soil oxygen dynamics as a simplified mass balance between oxygen supply rate and oxygen consumption rate. The approach was applied to analyze field measurements of soil oxygen and water tension at 35 cm depth in avocado orchards irrigated with either Fresh Water (FW) or Treated Wastewater (TWW) in clay soil (~60% clay). The reliability of the method was shown, as soil respiration rates equivalent to 1-2 g O2m-2 d-1 were established, in line with previous reports for evergreen trees. The model defines the soil water tension at which oxygen supply to the measurement depth after irrigation surpasses the oxygen consumption rate as the critical soil water tension, and a value of ~50 mbar was established for the experiment site, again within the range described in the literature for soils with similar properties using other methodologies. Using the new approach, it was established that more hypoxic conditions occur in TWW irrigated plots as compared to FW irrigated plots due to a difference in the time required to reach the critical soil water tension – TWW irrigated plots took nearly 50% longer to reach a soil water tension of 50 mbar after each irrigation in the height of the irrigation season. This delay in TWW irrigated plots was directly related to the soil drying rate, which was lower in the TWW irrigated soils in both night and day periods, indicating both a hindering of drainage and of plant water uptake. In a second study site, the values describing the soil oxygen dynamics were found to relate to the soil stone content (particles>2mm), a known effector of soil aeration. By utilizing in-situmeasurements, the method aims to represent the intricate interrelations occurring in the field which may be missed using methods focusing on the individual factors affecting soil oxygen. The insights gained can provide the basis for designing management techniques to resolve unfavorable low oxygen levels in agriculture, as well as in natural environments where hypoxia affects soil carbon turnover, the evolution of greenhouse-gasses, and the fate of toxic elements in soils.