Background and aims Alterations in root growth and rhizosphere processes in maize (Zea mays L.) occur under phosphorus (P) deficiency, but the dynamics of root morphological and physiological ...modifications with increasing shoot P concentration remain unclear. This study investigated root responses to a wide gradient in shoot P status. Methods A range of maize shoot P concentrations (1.0–4.0 mg g−1) was established using controlled pot experiment with eleven rates of P supply from 0 to 1200 mg P kg−1 soil. Root morphology and rhizosphere processes were characterized 28 days after planting. Results Maize reached maximum biomass at shoot P concentration of 2.7 mg g−1. Root morphological responses (i.e. total root length, specific root length and proportion of fine roots) showed a strong increasing trend with decreasing shoot P concentration (1.1–1.3 mg g−1), but they decreased when shoot P concentration was extremely low (below 1.1 mg g−1). In contrast, with increasing shoot P concentration, root morphological responses decreased, but root physiological responses (rhizosphere acidification, acid phosphatase activity and carboxylate exudation in the rhizosphere) were enhanced, and no decrease was noted even at high shoot P concentration (4.0 mg g−1) corresponding to excess P supply. Conclusions Increasing maize shoot P concentration induced a decrease in root morphological responses and an enhancement in root exudation, with maize response to P deficiency being dependent on root morphological rather than physiological traits.
Iron and phosphorus availability is low in many soils; hence, microorganisms and plants have evolved mechanisms to acquire these nutrients by altering the chemical conditions that affect their ...solubility. In plants, this includes exudation of organic acid anions and acidification of the rhizosphere by release of protons in response to iron and phosphorus deficiency. Grasses (family
Poaceae) and microorganisms further respond to Fe deficiency by production and release of specific chelators (phytosiderophores and siderophores, respectively) that complex Fe to enhance its diffusion to the cell surface. In the rhizosphere, the mutual demand for Fe and P results in competition between plants and microorganisms with the latter being more competitive due to their ability to decompose plant-derived chelators and their proximity to the root surface; however microbial competitiveness is strongly affected by carbon availability. On the other hand, plants are able to avoid direct competition with microorganisms due to the spatial and temporal variability in the amount and composition of exudates they release into the rhizosphere. In this review, we present a model of the interactions that occur between microorganisms and roots along the root axis, and discuss advantages and limitations of methods that can be used to study these interactions at nanometre to centimetre scales. Our analysis suggests mechanisms such as increasing turnover of microbial biomass or enhanced nutrient uptake capacity of mature root zones that may enhance plant competitiveness could be used to develop plant genotypes with enhanced efficiency in nutrient acquisition. Our model of interactions between plants and microorganisms in the rhizosphere will be useful for understanding the biogeochemistry of P and Fe and for enhancing the effectiveness of fertilization.
► In the rhizosphere, plants and microorganisms compete for Fe and P. ► A model of these interactions along the root axis is presented. ► Advantages and limitations of methods to study these interactions are discussed. ► Mechanisms by which the plant’s competiveness could be enhanced are presented.
Reactive oxygen species (ROS) – the byproducts of aerobic metabolism – influence numerous aspects of the plant life cycle and environmental response mechanisms. In plants, ROS act like a double-edged ...sword; they play multiple beneficial roles at low concentrations, whereas at high concentrations ROS and related redox-active compounds cause cellular damage through oxidative stress. To examine the dual role of ROS as harmful oxidants and/or crucial cellular signals, this review elaborates that (i) how plants sense and respond to ROS in various subcellular organelles and (ii) the dynamics of subsequent ROS-induced signaling processes. The recent understanding of crosstalk between various cellular compartments in mediating their redox state spatially and temporally is discussed. Emphasis on the beneficial effects of ROS in maintaining cellular energy homeostasis, regulating diverse cellular functions, and activating acclimation responses in plants exposed to abiotic and biotic stresses are described. The comprehensive view of cellular ROS dynamics covering the breadth and versatility of ROS will contribute to understanding the complexity of apparently contradictory ROS roles in plant physiological responses in less than optimum environments.
•The evolution of ROS as harmful oxidants and/or universal signaling metabolites in eukaryotic cells is critically appraised.•A comprehensive view of cellular ROS dynamics, with particular emphasis on crosstalk between cellular compartments in mediating their redox state spatially and temporally is discussed.•The beneficial roles of ROS to regulate a diverse array of plant cellular responses under stress conditions are highlighted.
Despite numerous reports implicating salicylic acid (SA) in plant salinity responses, the specific ionic mechanisms of SA-mediated adaptation to salt stress remain elusive. To address this issue, a ...non-invasive microelectrode ion flux estimation technique was used to study kinetics of NaCl-induced net ion fluxes in Arabidopsis thaliana in response to various SA concentrations and incubation times. NaCl-induced K+ efflux and H+ influx from the mature root zone were both significantly decreased in roots pretreated with 10–500 μM SA, with strongest effect being observed in the 10–50 μM SA range. Considering temporal dynamics (0–8-h SA pretreatment), the 1-h pretreatment was most effective in enhancing K+ retention in the cytosol. The pharmacological, membrane potential, and shoot K+ and Na+ accumulation data were all consistent with the model in which the SA pretreatment enhanced activity of H+-ATPase, decreased NaCl-induced membrane depolarization, and minimized NaCl-induced K+ leakage from the cell within the first hour of salt stress. In long-term treatments, SA increased shoot K+ and decreased shoot Na+ accumulation. The short-term NaCl-induced K+ efflux was smallest in the gork1-1 mutant, followed by the rbohD mutant, and was highest in the wild type. Most significantly, the SA pretreatment decreased the NaCl-induced K+ efflux from rbohD and the wild type to the level of gork1-1, whereas no effect was observed in gork1-1. These data provide the first direct evidence that the SA pretreatment ameliorates salinity stress by counteracting NaCl-induced membrane depolarization and by decreasing K+ efflux via GORK channels.
Cadmium (Cd) is a toxic heavy metal occurring in the environment naturally and is also generated through various anthropogenic sources and acts as a pollutant. Human health is affected by Cd ...pollution in farmland soils because food is the main source of Cd intake in the non-smoking population. For crops, Cd toxicity may result from a disturbance in uptake and translocation of mineral nutrients and disturbance in plant metabolism, inhibiting plant growth and development. However, plants have Cd tolerance mechanisms, including restricted Cd uptake, decreased Cd root-to-shoot translocation, enhanced antioxidant enzyme activities, and increased production of phytochelatins. Furthermore, optimal supply of mineral nutrients is one of the strategies to alleviate the damaging effects of Cd on plants and to avoid its entry into the food chain. The emerging molecular knowledge contributes to understanding Cd uptake, translocation, and remobilization in plants. In this review, Cd toxicity and tolerance mechanisms, agricultural practices to minimize Cd accumulation, Cd competition with essential elements (calcium, copper, iron, zinc, and manganese), and genes associated with Cd uptake are discussed in detail, especially regarding how these mineral nutrients and genes play a role in decreasing Cd uptake and accumulation in crop plants.
Biochar is beneficial for improving soil quality and crop productivity. However, the long‐term effects of biochar addition on temporal dynamics of plant shoot and root growth, and the changes in soil ...properties and nitrogen (N) leaching are still obscure. Here, based on a long‐term (7 years) biochar field experiment with rice in northwest China, we investigated the effects of two biochar rates (0 and 9 t ha−1 year−1) and two N fertilizer rates (0 and 300 kg N ha−1 year−1) on shoot and root growth, root morphology, N leaching, and soil physicochemical properties. The results showed that both biochar and N fertilizer significantly promoted rice growth, with their interaction significant only in some cases. Both fertilizers enhanced rice shoot biomass and N accumulation in various growth stages as well as increased grain yield. Nitrogen fertilizer significantly promoted root growth regardless of biochar application. However, biochar application without N fertilizer increased root biomass and length during the whole growth period, except in the booting stage; biochar with N application promoted root growth at tillering, reduced root biomass but maintained root length with low root diameter and high specific root length during the jointing and booting stages, and then delayed root senescence in the grain filling stage. Long‐term applications of biochar and N fertilizer reduced 10%–12% bulk density of topsoil compared to the control treatment with no N fertilizer and no biochar. Long‐term biochar application also improved soil total organic carbon and concentrations of available N, phosphorus, and potassium. In addition, biochar and N fertilizer applied together significantly reduced nitrate and ammonium concentration in leachate at different soil depths. In conclusion, biochar could regulate root growth, root morphology, soil properties, and N leaching to increase rice N fertilizer‐use efficiency.
The long‐term effects of biochar addition on temporal dynamics of plant shoot and root growth, and the changes in soil properties and nitrogen (N) leaching are still obscure. Based on a long‐term (7 years) biochar field experiment with rice in northwest China, we investigated the effects of two biochar rates (0 and 9 t ha−1 year−1) and two N fertilizer rates (0 and 300 kg N ha−1 year−1) on shoot and root growth, root morphology, N leaching, and soil physicochemical properties. Our findings suggested biochar could regulate root growth, root morphology, soil properties, and N leaching to increase rice N fertilizer‐use efficiency.
Planting rice is one of the effective ways to improve saline soils, but the underlying mechanisms are unknown. We studied basic soil properties (including pH, salt content, total nitrogen, etc.) and ...microbial diversity of the bare soil (salt content >4 g/kg, CK), the Suaeda (Suaeda glauca (Bunge) Bunge) soil (JP), and the soil in which rice (cv. Huaidao 5) grew for one (1Y) and three (3Y) years. The results showed that the soil salinity decreased in the order: CK > JP > 1Y > 3Y. The contents of soil organic matter, total nitrogen, dissolved organic carbon, readily oxidizable carbon, microbial biomass carbon, and particulate organic carbon were higher in 1Y and 3Y compared with CK. The Chao 1 index of soil microbiome diversity was about 1.20 times and 1.49 times higher in the soils after rice compared with JP and CK, respectively. Among the soil microorganisms, the top four abundant phyla were Proteobacteria, Chloroflexi, Bacteriodetes, and Firmicutes. In summary, planting rice decreased soil salinity, and increased the content of nutrients and diversity of microorganisms, thereby improving the saline soil.
Display omitted
•Planting rice decreased soil salinity, increased the content of nutrients•Planting rice increased diversity of microorganisms.•The contents of SOM, TN, DOC, ROC, MBC, and POC were higher for planting rice.•Planting rice is one of the effective ways to improve saline-alkali soils.
Cultivars with increased efficiency of uptake and utilization of soil nutrients are likely to have positive environmental effects through reduced usage of chemicals in agriculture. This review ...assesses the available literature on differential uptake and utilization efficiency of K in farming systems. Large areas of agricultural land in the world are deficient in K (e.g. 3/4 of paddy soils in China, 2/3 of the wheatbelt in Southern Australia), with export in agricultural produce (especially hay) and leaching (especially in sandy soils) contributing to lowering of K content in the soil. The capacity of a genotype to grow and yield well in soils low in available K is K efficiency. Genotypic differences in efficiency of K uptake and utilization have been reported for all major economically important plants. The K-efficient phenotype is a complex one comprising a mixture of uptake and utilization efficiency mechanisms. Differential exudation of organic compounds to facilitate release of non-exchangeable K is one of the mechanisms of differential K uptake efficiency. Genotypes efficient in K uptake may have a larger surface area of contact between roots and soil and increased uptake at the root-soil interface to maintain a larger diffusive gradient towards roots. Better translocation of K into different organs, greater capacity to maintain cytosolic K⁺ concentration within optimal ranges and increased capacity to substitute Na⁺ for K⁺ are the main mechanisms underlying K utilization efficiency. Further breeding for increased K efficiency will be dependent on identification of suitable markers and compounding of efficiency mechanisms into locally adapted germplasm.
Aims
Arbuscular mycorrhizal fungi play important roles in plant phosphorus (P) accumulation. The aim of this study was to uncover how and to what extent soil plant-available P levels and maize ...genotypes influence the contribution of mycorrhizal P uptake pathway to plant P nutrition.
Methods
We selected an old genotype HMY and a modern genotype XY335, combined with
32
P labeling and qPCR to quantify P uptake efficiency of the direct pathway (DP) and the mycorrhizal pathway (MP) at three Olsen-P levels: 4.5 (low), 8 (medium) and 50 (high) mg kg
−1
.
Results
The P uptake efficiency ratio PAE-MP/PAE-DP was highest in the treatment with medium Olsen-P, and was correlated positively with MP contribution. The traits of arbuscular mycorrhizal fungi, such as percent colonization, hyphal length density, P uptake per unit hyphae length, and the expression of the mycorrhiza-specific P transporter
ZmPT1;6
were higher in XY335 than HMY in high-P soil, which was in accordance with the importance of the MP contribution.
Conclusions
Greater mycorrhizal responsiveness in the modern maize genotype than the old genotype under high P soil condition is related to higher P uptake efficiency of MP than DP; the inherent potential of MP can be maximized by managing soil plant P availability to achieve optimal P supply in intensive farming.
Growing rice on arsenic (As)-contaminated soil or irrigating with As-contaminated water leads to significant accumulation of As in grains. Moreover, rice accumulates more As into grains than other ...cereal crops. Thus, rice consumption has been identified as a major route of human exposure to As in many countries. Inorganic As species are carcinogenic and could pose a considerable health risk to humans even at low dietary concentration. Genotypic variation and concentration of nutrients such as iron, manganese, phosphate, sulfur and silicon are the two main factors that affect As accumulation in rice grains. Therefore, in addition to better growth and yield of plants, application of specific nutrients in optimum quantities offers an added benefit of decreasing As content in rice grains. These nutrient elements influence speciation of As in rhizosphere, compete with As for root uptake and interfere with As translocations to the shoot and ultimately accumulation in grains. This papers critically appraises the methods, forms and rate of application, mechanisms and extent of efficiency of different mineral nutrients in decreasing As accumulation in rice grains.
•Factors affecting arsenic uptake and accumulation in rice grains are discussed.•Nutrients effect speciation of arsenic in soil and thereby uptake by rice.•Iron, manganese and sulfur effectively reduce As accumulation in rice.•Excessive application of phosphorus may lead to higher grain arsenic.•Nutrient optimization is a cost-effective strategy to lower arsenic in rice grain.
PDF
