Simulating the effects of water limitation on plant biomass using a 3D functional-structural plant model of shoot and root driven by soil hydraulics.

BACKGROUND AND AIMS: Improved modelling of carbon assimilation and plant growth to low soil moisture requires evaluation of underlying mechanisms in the soil, roots, and shoots. The feedback between plants and their local environment throughout the whole spectrum soil-root-shoot-environment is crucial to accurately describe and evaluate the impact of environmental changes on plant development. This study presents a 3D functional structural plant model, in which shoot and root growth are driven by radiative transfer, photosynthesis, and soil hydrodynamics through different parameterisation schemes relating soil water deficit and carbon assimilation. The new coupled model is used to evaluate the impact of soil moisture availability on plant productivity for two different groups of flowering plants under different spatial configurations. METHODS: In order to address different aspects of plant development due to limited soil water availability, a 3D FSP model including root, shoot, and soil was constructed by linking three different well-stablished models of airborne plant, root architecture, and reactive transport in the soil. Different parameterisation schemes were used in order to integrate photosynthetic rate with root water uptake within the coupled model. The behaviour of the model was assessed on how the growth of two different types of plants, i.e. monocot and dicot, is impacted by soil water deficit under different competitive conditions: isolated (no competition), intra, and interspecific competition. KEY RESULTS: The model proved to be capable of simulating carbon assimilation and plant development under different growing settings including isolated monocots and dicots, intra, and interspecific competition. The model predicted that (1) soil water availability has a larger impact on photosynthesis than on carbon allocation; (2) soil water deficit has an impact on root and shoot biomass production by up to 90 % for monocots and 50 % for dicots; and (3) the improved dicot biomass production in interspecific competition was highly related to root depth and plant transpiration. CONCLUSIONS: An integrated model of 3D shoot architecture and biomass development with a 3D root system representation, including light limitation and water uptake considering soil hydraulics, was presented. Plant-plant competition and regulation on stomatal conductance to drought were able to be predicted by the model. In the cases evaluated here, water limitation impacted plant growth almost 10 times more than the light environment.

Growing on calcareous soils and facing climate change.

Soil calcium carbonate (CaCO3) impacts plant mineral nutrition far beyond Fe metabolism, imposing constraints for crop growth and quality in calcareous agrosystems. Our knowledge on plant strategies to tolerate CaCO3 effects mainly refers to Fe acquisition. This review provides an update on plant cellular and molecular mechanisms recently described to counteract the negative effects of CaCO3 in soils, as well as recent efforts to identify genetic bases involved in CaCO3 tolerance from natural populations, that could be exploited to breed CaCO3-tolerant crops. Finally, we review the impact of environmental factors (soil water content, air CO2, and temperature) affecting soil CaCO3 equilibrium and plant tolerance to calcareous soils, and we propose strategies for improvement in the context of climate change.

Two-dimensional modeling of CO2 mineral trapping through the oxalate­carbonate pathway: Influence of the root system model.

Two-dimensional reactive transport models, one with a simplified root system and the other accounting for dynamically evolving root architecture, were constructed to examine the influence of model complexity on capturing the effect of soil-root dynamics relating to the Oxalate Carbonate Pathway (OCP) of the Iroko tree over 170 years. Oxidation of oxalate from fallen tree tissue by soil bacteria enables local soil pH increase, leading to the sequestration of atmospheric carbon in carbonate minerals (calcite) in the shallow soil surrounding the tree. Simulations of both root models corroborate previous one-dimensional models of the OCP focused on Ca and C mass balance, where high weathering rates of Ca-containing silicate minerals in bedrock, along with contributions from groundwater, provided sufficient Ca for precipitation of observed quantities of calcite. Both simulations demonstrate the development of a distinct high pH zone where oxalate is oxidized, Ca accumulates, and calcite precipitates (OCP zone); and a low pH zone where roots collect Ca, later returned to the top soil as calcium oxalate (Total Root Extent/TRE zone) via litterfall. While the extent of OCP zone development near the ground surface was very similar between simulations, differences in localized root water uptake between the two approaches resulted in variation in water and solute transport and influenced the geometry of the OCP zone at depth, with implications for calcite precipitation in the soil. Trends in CO2 and O2 partial pressures in the OCP zone were mirrored in the TRE zone, suggesting linkage between the two zones with regard to gas transport. Near the end of the tree's lifespan, results indicate that soil permeability decreases due to calcite precipitation may limit O2 ingress and availability in the shallow soil, while trapping CO2 released from the oxidation of organics in the shallow soil, with implications for the long-term sustainability of the OCP itself.

A mechanistic model for understanding root-induced chemical changes controlling phosphorus availability.

BACKGROUND AND AIMS: Plant nutrition models do not properly account for the effects of root-induced chemical changes in the rhizosphere, e.g. pH changes, on the availability of nutrients such as phosphorus (P). As a result, they underestimate the actual P uptake, i.e. P bioavailability to the plant, in low-P soils. The present study aims at simulating root-induced chemical mechanisms controlling P nutrition in a P-limited soil. METHODS: In this work a mechanistic description for the adsorption of cations and anions by soil constituents (1pK-Triple Plane Model, ion-exchange and Nica-Donnan) was used to simulate changes induced by durum wheat (Triticum durum turgidum) in the P availability of the soil, as measured by water and CaCl2 extraction. Calcium (Ca) availability was also measured and simulated. KEY RESULTS: The simulations were found to be in close agreement with experimental data. In the rhizosphere, the goodness-of-fit required to account for the measured uptake of Ca by plants, in addition to the measured uptake of P and root-induced alkalization, were satisfactory. Calcium uptake significantly increased P availability, as assessed through water extraction, by decreasing the promoting effect of Ca adsorption on P adsorption. The study thus enabled P and Ca availability to be related to their bioavailability for durum wheat under experimental conditions. It was also shown that P was primarily adsorbed onto Fe oxides and clay minerals (kaolinite and illite) depending on soil pH. The major source of P for durum wheat nutrition was P desorbed from goethite and kaolinite. CONCLUSIONS: In addition to confirming the validity of our approach to model P availability, the present investigation suggested that in the studied soil, a novel root-induced chemical process was controlling P nutrition under P-deficient conditions, namely the uptake of Ca.

ANCA-associated vasculitis in patients with primary Sjögren's syndrome: detailed analysis of 7 new cases and systematic literature review.

OBJECTIVES: To describe the clinical presentation, management and prognosis of patients diagnosed with both primary Sjögren's syndrome (pSS) and anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV). METHODS: French nation-wide survey completed by a systematic literature review. RESULTS: This work identified 7 new cases of coexisting pSS and AAV: 2 microscopic polyangiitis (MPA), 2 granulomatosis with polyangiitis (GPA), 2 anti-myeloperoxidase (MPO)-ANCA renal-limited AAV, and 1 eosinophilic granulomatosis with polyangiitis (EGPA). The systematic literature search identified 15 previously published cases. Among the 22 patients, 19 were females. Mean age at diagnosis of AAV was 63.9±9.8years. All individuals with available information experienced at least one extra-glandular manifestation attributable to pSS. p-ANCA with anti-MPO specificity were found in 76.2% (16/21), c-ANCA with anti-PR3 specificity in 14.3% (3/21) and isolated c-ANCA in 13.6% (3/22). Vasculitis involved kidneys (n=13), lungs (n=8), skin (n=6), peripheral nerves (n=5), central nervous system (n=2), small bowel (n=1), muscle (n=1), ear chondritis (n=1) and sinuses (n=1). The mean AAV follow-up was 73.5 (±120.0) months. While on treatment, disease remission occurred in 77.3% of cases, and one death was reported in the first 6months after diagnosis. CONCLUSION: This work shows that AAV may occur in patients with pSS. These are most commonly p-ANCA associated vasculitis with anti-MPO specificity. AAV may reveal an underlying pSS or arise during its evolution, but did not precede pSS in any of these cases. AAV occurrence appears to be correlated with extra-glandular manifestations of pSS.

The use of root growth and modelling data to investigate amelioration of aluminium toxicity by silicon in Picea abies seedlings.

Three-week-old Picea abies seedlings were grown for 7 days in 100 microM aluminium (Al), combined with 1000 or 2000 microM silicon (Si). Solution pH was adjusted to 4.00, 4.25, 4.50, 4.75, or 5.00. In the absence of Si, solution pH had no effect on the decrease in root growth caused by 100 microM Al. Silicon did not ameliorate toxic effects of Al on root growth at pH 4.00, 4.25 and 4.50, whereas significant, and apparently complete, amelioration was found at pH 4.75 and 5.00. An equilibrium speciation model (EQ3NR), with a current thermodynamic database, was used to predict the behaviour of Al and Si in growth solutions. When Si was not present in the 100 microM Al solutions, Al(3+) declined from 92.4% of total Al at pH 4.00 to 54.6% at pH 5.00, and there was a concomitant increase in hydroxyaluminium species as pH increased. The addition of 1000 microM Si to the 100 microM Al solutions caused a reduction in Al(3+) content over the whole pH range: at pH 4.00 Al(3+) fell from 92.4 to 83.3% in the presence of Si; and at pH 5.00 the fall was from 54.6 to 17.7%. These falls were attributed to the formation of hydroxyaluminosilicate (HAS) species. Similar, but somewhat greater, changes were observed in solutions containing 2000 microM Si. The match between root growth observations and the modelling data was not very good. Modelling predicted that change in Al(3+) content with pH in the presence of Si was gradual, but root growth was markedly increased between pH 4.50 and 4.75. Differences between root growth and modelling data may be due to the model not correctly predicting solution chemistry or to in planta effects which override the influence of solution chemistry.

Effects of spatial structure and diffusion on the performances of the chemostat.

Given hydric capacity and nutrient flow of a chemostat-like system, we analyse the influence of a spatial structure on the output concentrations at steady-state. Three configurations are compared: perfectly-mixed, serial and parallel with diffusion rate. We show the existence of a threshold on the input concentration of nutrient for which the benefits of the serial and parallel configurations over the perfectly-mixed one are reversed. In addition, we show that the dependency of the output concentrations on the diffusion rate can be non-monotonic, and give precise conditions for the diffusion effect to be advantageous. The study encompasses dead-zone models.