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Predicting the response of fine roots to increased atmospheric CO₂concentration has important implications for carbon (C) and nutrient cycling in forest ecosystems. Root architecture is known to play an important role in how trees acquire soil resources in changing environments. However, the effects of elevated CO₂on the fine‐root architecture of trees remain unclear. We investigated the architectural response of fine roots exposed to 14 yr of CO₂enrichment and 6 yr of nitrogen (N) fertilization in a Pinus taeda (loblolly pine) forest. Root traits reflecting geometry, topology and uptake function were measured on intact fine‐root branches removed from soil monoliths and the litter layer. CO₂enrichment resulted in the development of a fine‐root pool that was less dichotomous and more exploratory under N‐limited conditions. The per cent mycorrhizal colonization did not differ among treatments, suggesting that root growth and acclimation to elevated CO₂were quantitatively more important than increased mycorrhizal associations. Our findings emphasize the importance of architectural plasticity in response to environmental change and suggest that changes in root architecture may allow trees to effectively exploit larger volumes of soil, thereby pre‐empting progressive nutrient limitations.

Three-dimensional models of root growth, architecture and function are becoming important tools that aid the design of agricultural management schemes and the selection of beneficial root traits. However, while benchmarking is common in many disciplines that use numerical models, such as natural and engineering sciences, functional-structural root architecture models have never been systematically compared. The following reasons might induce disagreement between the simulation results of different models: different representation of root growth, sink term of root water and solute uptake and representation of the rhizosphere. Presently, the extent of discrepancies is unknown, and a framework for quantitatively comparing functional-structural root architecture models is required. We propose, in a first step, to define benchmarking scenarios that test individual components of complex models: root architecture, water flow in soil and water flow in roots. While the latter two will focus mainly on comparing numerical aspects, the root architectural models have to be compared at a conceptual level as they generally differ in process representation. Therefore, defining common inputs that allow recreating reference root systems in all models will be a key challenge. In a second step, benchmarking scenarios for the coupled problems are defined. We expect that the results of step 1 will enable us to better interpret differences found in step 2. This benchmarking will result in a better understanding of the different models and contribute toward improving them. Improved models will allow us to simulate various scenarios with greater confidence and avoid bugs, numerical errors or conceptual misunderstandings. This work will set a standard for future model development.

Aims The objective of this research was to develop a three-dimensional (3D) rhizosphere modeling capability for plant-soil interactions by integrating plant biophysics, water and ion uptake and release from individual roots, variably saturated flow, and multicomponent reactive transport in soil. Methods We combined open source software for simulating plant and soil interactions with parallel computing technology to address highly-resolved root system architecture (RSA) and coupled hydrobiogeochemical processes in soil. The new simulation capability was demonstrated on a model grass, Brachypodium distachyon . Results In our simulation, the availability of water and nutrients for root uptake is controlled by the interplay between 1) transpiration-driven cycles of water uptake, root zone saturation and desaturation; 2) hydraulic redistribution; 3) multicomponent competitive ion exchange; 4) buildup of ions not taken up during kinetic nutrient uptake; and 5) advection, dispersion, and diffusion of ions in the soil. The uptake of water and ions by individual roots leads to dynamic, local gradients in ion concentrations. Conclusion By integrating the processes that control the fluxes of water and nutrients in the rhizosphere, the modeling capability we developed will enable exploration of alternative RSAs and function to advance the understanding of the coupled hydro-biogeochemical processes within the rhizosphere.

• This study aims to link three-dimensional coarse root architecture to tree stability in mature timber trees with an average of 1-m rooting depth. • Undamaged and uprooted trees were sampled in a stand damaged by a storm. Root architecture was measured by three-dimensional (3-D) digitizing. The distribution of root volume by root type and in wind-oriented sectors was analysed. • Mature Pinus pinaster root systems were organized in a rigid 'cage' composed of a taproot, the zone of rapid taper of horizontal surface roots and numerous sinkers and deep roots, imprisoning a large mass of soil and guyed by long horizontal surface roots. Key compartments for stability exhibited strong selective leeward or windward reinforcement. Uprooted trees showed a lower cage volume, a larger proportion of oblique and intermediate depth horizontal roots and less wind-oriented root reinforcement. • Pinus pinaster stability on moderately deep soils is optimized through a typical rooting pattern and a considerable structural adaptation to the prevailing wind and soil profile.

As one of the largest genera of the Lamiaceae family, Salvia has a wide distribution worldwide. Despite their great importance and medicinal use, most Salvia species are collected from their natural habitats, and some of them are endangered and vulnerable. This study aimed to evaluate the domestication process of eight Iranian native Salvia species. The studied species were cultivated and adapted to the cultivation area after two years, and then some of their important biochemical properties were investigated. According to some significant results, the root architecture was closely correlated with the climatic conditions of the species origins. The distribution of total dry matter varied widely among species; accordingly, S. sclarea and S. officinalis had 65.6% and 55.9% dry weights in their leaves, respectively. Moreover, S. nemorosa had a 24.3% dry weight in its flowers, while S. frigida (Jahrom), S. frigida (Targavar), S. virgata (Eghled), and S. macrosiphon had 44.6%, 43.3%, 46.0%, and 44.3% dry weights in their roots. The most potent antioxidant activity (IC50) was observed in the roots of S. macrosiphon (10.9 μg/mL) and S. sclarea (14.9 μg/mL), the stem of S. nemorosa (14.3 μg/mL), and the leaves of S. atropatana (14.0 μg/mL). Rosmarinic acid, a key phenolic substance in Salvia species, was present in the range of 0.24–0.47 mg/g dry weight. The essential oil content ranged from 0.35% in S. atropatana to 1.45% (w/w) in S. officinalis. β-caryophyllene, caryophyllene oxide, and germacrene D were the major ingredients of the essential oils. The cluster analysis based on the essential oil data revealed the most similarities between S. sclarea and S. macrosiphon, and a clear separation of S. virgate, S. syriaca, and S. officinalis from other species. Salvia spp. contain a wide variety of compounds of interest under cultivation, with S. sclarea having the greatest potential to profit from the production of medicinal compounds, such as phenolic compounds, flavonoids, and essential oils. Furthermore, S. officinalis, S. nemorosa, and S. sclarea are the best species for producing raw medicinal materials.

This paper reviews recent research on the processes involved in the yield advantage in wheat (Triticum aestivum L.)/maize (Zea mays L.), wheat/soybean [Glycine max (L.) Merr.], faba bean (Vicia faba L.)/maize, peanut (Arachis hypogaea L.)/maize and water convolvulus (Ipomoea aquatica Forsk.)/maize intercropping. In wheat/maize and wheat/soybean intercropping systems, a significant yield increase of intercropped wheat over sole wheat was observed, which resulted from positive effects of the border row and inner rows of intercropped wheat. The border row effect was due to interspecific competition for nutrients as wheat had a higher competitive ability than either maize or soybean had. There was also compensatory growth, or a recovery process, of subordinate species such as maize and soybean, offsetting the impairment of early growth of the subordinate species. Finally, both dominant and subordinate species in intercropping obtain higher yields than that in corresponding sole wheat, maize or soybean. We summarized these processes as the 'competition-recovery production principle'. We observed interspecific facilitation, where maize improves iron nutrition in intercropped peanut, faba bean enhances nitrogen and phosphorus uptake by intercropped maize, and chickpea facilitates P uptake by associated wheat from phytate-P. Furthermore, intercropping reduced the nitrate content in the soil profile as intercropping uses soil nutrients more efficiently than sole cropping.

Root system architecture (RSA) - the spatial configuration of a root system - is an important developmental and agronomic trait, with implications for overall plant architecture, growth rate and yield, abiotic stress resistance, nutrient uptake, and developmental plasticity in response to environmental changes. Root architecture is modulated by intrinsic, hormone-mediated pathways, intersecting with pathways that perceive and respond to external, environmental signals. The recent development of several non-invasive 2D and 3D root imaging systems has enhanced our ability to accurately observe and quantify architectural traits on complex whole-root systems. Coupled with the powerful marker-based genotyping and sequencing platforms currently available, these root phenotyping technologies lend themselves to large-scale genome-wide association studies, and can speed the identification and characterization of the genes and pathways involved in root system development. This capability provides the foundation for examining the contribution of root architectural traits to the performance of crop varieties in diverse environments. This review focuses on our current understanding of the genes and pathways involved in determining RSA in response to both intrinsic and extrinsic (environmental) response pathways, and provides a brief overview of the latest root system phenotyping technologies and their potential impact on elucidating the genetic control of root development in plants.

The aim of the present study was to analyze the effects of two arbuscular mycorrhizal fungi (AMF), Funneliformis mosseae and Paraglomus occultum, on leaf water status, root morphology, root sugar accumulation, root abscisic acid (ABA) levels, root malondialdehyde (MDA) content, and root antioxidant enzyme activities in white clover (Trifolium repens L.) exposed to well-watered (WW) and drought stress (DS) conditions. The results showed that root colonization by F. mosseae and P. occultum was significantly decreased by 7-week soil drought treatment. Under drought stress conditions, mycorrhizal fungal treatment considerably stimulated root total length, surface area and volume, as compared with non-mycorrhizal controls. In addition, inoculation with arbuscular mycorrhizal fungi also increased leaf relative water content and accelerated the accumulation of root glucose and fructose under drought stress. Mycorrhizal plants under drought stress registered higher activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) and ABA levels in roots, while lower MDA contents, relative to non-mycorrhizal plants. As a result, mycorrhiza-inoculated plants represented better physiological activities (e.g. antioxidant defense systems, root morphology, and sugar accumulation) than non-inoculated plants in response to soil drought, whilst P. occultum had superior effects than F. mosseae.

Nutrient-efficient crops are a solution to the two grand challenges of modern agriculture: improving food security while reducing environmental impacts. The primary challenges are (1) nitrogen (N) and phosphorus (P) efficiency; (2) potassium (K), calcium (Ca), and magnesium (Mg) efficiency for acid soils; and (3) iron (Fe) and zinc (Zn) efficiency for alkaline soils. Root phenotypes are promising breeding targets for each of these. The Topsoil Foraging ideotype is beneficial for P capture and should also be useful for capture of K, Ca, and Mg in acid soils. The Steep, Cheap, and Deep ideotype for subsoil foraging is beneficial for N and water capture. Fe and Zn capture can be improved by targeting mechanisms of metal mobilization in the rhizosphere. Root hairs and phenes that reduce the metabolic cost of soil exploration should be prioritized in breeding programs. Nutrient-efficient crops should provide benefits at all input levels. Although our current understanding is sufficient to deploy root phenotypes for improved nutrient capture in crop breeding, this complex topic does not receive the resources it merits in either applied or basic plant biology. Renewed emphasis on these topics is needed in order to develop the nutrient-efficient crops urgently needed in global agriculture.

Parsimonious root phenotypes may benefit water capture under drought. Abstract I propose that reduced root development would be advantageous for drought resistance in high-input agroecosystems. Selection regimes for crop ancestors and landraces include multiple stresses, intense competition, and variable resource distribution, which favored prolific root production, developmental plasticity in response to resource availability, and maintenance of unspecialized root tissues. High-input agroecosystems have removed many of these constraints to root function. Therefore, root phenotypes that focus on water capture at the expense of ancestral adaptations would be better suited to high-input agroecosystems. Parsimonious architectural phenotypes include fewer axial roots, reduced density of lateral roots, reduced growth responsiveness to local resource availability, and greater loss of roots that do not contribute to water capture. Parsimonious anatomical phenotypes include a reduced number of cortical cell files, greater loss of cortical parenchyma to aerenchyma and senescence, and larger cortical cell size. Parsimonious root phenotypes may be less useful in low-input agroecosystems, which are characterized by multiple challenges and trade-offs for root function in addition to water capture. Analysis of the fitness landscape of root phenotypes is a complex challenge that will be aided by the development of robust functional-structural models capable of simulating the dynamics of root-soil interactions.