Nutrient deficiency effects on root architecture and root-to-shoot ratio in arable crops

Measuring leaf and root functional traits uncovers multidimensionality of plant responses to arbuscular mycorrhizal fungi

PREMISE

While many studies have measured the aboveground responses of plants to mycorrhizal fungi at a single time point, little is known about how plants respond belowground or across time to mycorrhizal symbiosis. By measuring belowground responses and growth over time in many plant species, we create a more complete picture of how mycorrhizal fungi benefit their hosts.

METHODS

We grew 26 prairie plant species with and without mycorrhizal fungi and measured 14 functional traits to assess above- and belowground tissue quality and quantity responses and changes in resource allocation. We used function-valued trait (FVT) modeling to characterize changes in species growth rate when colonized.

RESULTS

While aboveground biomass responses were positive, the response of traits belowground were much more variable. Changes in aboveground biomass accounted for 60.8% of the variation in mycorrhizal responses, supporting the use of aboveground biomass response as the primary response trait. Responses belowground were not associated with aboveground responses and accounted for 18.3% of the variation. Growth responses over time were highly variable across species. Interestingly, none of the measured responses were phylogenetically conserved.

CONCLUSIONS

Mycorrhizal fungi increase plant growth in most scenarios, but the effects of these fungi belowground and across time are more complicated. This study highlights how differences in plant allocation priorities might affect how they utilize the benefits from mycorrhizal fungi. Identifying and characterizing these differences is a key step to understanding the effects of mycorrhizal mutualisms on whole plant physiology.

Trichoderma viride improves phosphorus uptake and the growth of Chloris virgata under phosphorus-deficient conditions

Introduction

Phosphorus (P) readily forms insoluble complexes in soil, thereby inhibiting the absorption and utilization of this essential nutrient by plants. Phosphorus deficiency can significantly impede the growth of forage grass. While Trichoderma viride (T. viride) has been recognized for promoting the assimilation of otherwise unobtainable nutrients, its impact on P uptake remains understudied. Consequently, it is imperative to gain a more comprehensive insight into the role of T. viride in facilitating the uptake and utilization of insoluble P in forage grass.

Methods

This research explored the influence of T. viride inoculation on P absorption and the growth of Chloris virgata (C. virgata) across various P sources. We treated plants with control P (P), tricalcium phosphate (TCP), calcium phytate (PHY), and low P (LP), with and without T. viride inoculation (P+T, TCP+T, PHY+T, LP+T). We analyzed photosynthesis parameters, growth indices, pigment accumulation, P content, leaf acid phosphatase activity.

Results

Results demonstrated that T. viride inoculation alleviated inhibition of photosynthesis, reduced leaf acid phosphatase activity, and enhanced growth of C. virgata in the presence of insoluble P sources. Additionally, T. viride inoculation enabled the plants to extract more available P from insoluble P sources, as evidenced by a substantial increase in P content: shoot P content surged by 58.23 to 59.08%, and root P content rose by 55.13 to 55.2%. Biomass P-use efficiency (PUE) declined by 38% upon inoculation with T. viride compared to the non-inoculated insoluble P sources, paralleled by a reduction in photosynthetic P-use efficiency (PPUE) by 26 to 29%. Inoculation under insoluble P sources further triggered a lower allocation to root biomass (25 to 26%) and a higher investment in shoot biomass (74 to 75%). However, its application under low P condition curtailed the growth of C. virgata.

Discussion

Our results suggest that T. viride inoculation represents an innovative approach for plants to acquire available P from insoluble P sources, thereby promoting growth amid environmental P limitations. This insight is crucial for comprehending the synergy among forage grass, P, and T. viride.

Benefits and limits of biological nitrification inhibitors for plant nitrogen uptake and the environment

Plant growth and high yields are secured by intensive use of nitrogen (N) fertilizer, which, however, pollutes the environment, especially when N is in the form of nitrate. Ammonium is oxidized to nitrate by nitrifiers, but roots can release biological nitrification inhibitors (BNIs). Under what conditions does root-exudation of BNIs facilitate nitrogen N uptake and reduce pollution by N loss to the environment? We modeled the spatial-temporal dynamics of nitrifiers, ammonium, nitrate, and BNIs around a root and simulated root N uptake and net rhizosphere N loss over the plant's life cycle. We determined the sensitivity of N uptake and loss to variations in the parameter values, testing a broad range of soil-plant-microbial conditions, including concentrations, diffusion, sorption, nitrification, population growth, and uptake kinetics. An increase in BNI exudation reduces net N loss and, under most conditions, increases plant N uptake. BNIs decrease uptake in the case of (1) low ammonium concentrations, (2) high ammonium adsorption to the soil, (3) rapid nitrate- or slow ammonium uptake by the plant, and (4) a slowly growing or (5) fast-declining nitrifier population. Bactericidal inhibitors facilitate uptake more than bacteriostatic ones. Some nitrification, however, is necessary to maximize uptake by both ammonium and nitrate transporter systems. An increase in BNI exudation should be co-selected with improved ammonium uptake. BNIs can reduce N uptake, which may explain why not all species exude BNIs but have a generally positive effect on the environment by increasing rhizosphere N retention.

Tryptophan regulates sorghum root growth and enhances low nitrogen tolerance

Over evolutionary time, plants have developed sophisticated regulatory mechanisms to adapt to fluctuating nitrogen (N) environments, ensuring that their growth is balanced with their responses to N stress. This study explored the potential of L-tryptophan (Trp) in regulating sorghum root growth under conditions of N limitation. Here, two distinct sorghum genotypes (low-N tolerance 398B and low-N sensitive CS3541) were utilized for investigating effect of low-N stress on root morphology and conducting a comparative transcriptomics analysis. Our foundings indicated that 398B exhibited longer roots, greater root dry weights, and a higher Trp content compared to CS3541 under low-N conditions. Furthermore, transcriptome analysis revealed substantial differences in gene expression profiles related to Trp pathway and carbon (C) and N metabolism pathways between the two genotypes. Additional experiments were conducted to assess the effects of exogenous Trp treatment on the interplay between sorghum root growth and low-N tolerance. Our observations showed that Trp-treated plants developed longer root and had elevated levels of Trp and IAA under low-N conditons. Concurrently, these plants demonstrated stronger physiological activities in C and N metabolism when subjected to low-N stress. These results underscored the pivotal role of Trp on root growth and low-N stress responses by balancing IAA levels and C and N metabolism. This study not only deepens our understanding of how plants maintain growth plasticity during environmental stress but also provides valuable insights into the availability of amino acid in crops, which could be instrumental in developing strategies for promoting crop resilience to N deficiency.

Rejuvenating potato growth and yield in challenging semiarid and saline sandy Cholistan: harnessing PGPB-coated N and P application strategies

BACKGROUND

Potato serves as a major non-cereal food crop and income source for small-scale growers in Punjab, Pakistan. Unfortunately, improper fertilization practices have led to low crop yields, worsened by challenging environmental conditions and poor groundwater quality in the Cholistan region. To address this, we conducted an experiment to assess the impact of two fertilizer application approaches on potato cv. Barna using plant growth-promoting bacteria (PGPB) coated biofertilizers. The first approach, termed conventional fertilizer application (CFA), involved four split applications of PGPB-coated fertilizers at a rate of 100:75 kg acre-1 (N and P). The second, modified fertilizer application (MFA), employed nine split applications at a rate of 80:40 kg acre-1.

RESULTS

The MFA approach significantly improved various plant attributes compared to the CFA. This included increased plant height (28%), stem number (45%), leaf count (46%), leaf area index (36%), leaf thickness (three-folds), chlorophyll content (53%), quantum yield of photosystem II (45%), photosynthetically active radiations (56%), electrochromic shift (5.6%), proton flux (24.6%), proton conductivity (71%), linear electron flow (72%), photosynthetic rate (35%), water use efficiency (76%), and substomatal CO2 (two-folds), and lowered non-photochemical quenching (56%), non-regulatory energy dissipation (33%), transpiration rate (59%), and stomatal conductance (70%). Additionally, the MFA approach resulted in higher tuber production per plant (21%), average tuber weight (21.9%), tuber diameter (24.5%), total tuber yield (29.1%), marketable yield (22.7%), seed-grade yield (9%), specific gravity (9.6%), and soluble solids (7.1%). It also reduced undesirable factors like goli and downgrade yields by 57.6% and 98.8%, respectively. Furthermore, plants under the MFA approach exhibited enhanced nitrogen (27.8%) and phosphorus uptake (40.6%), with improved N (26.1%) and P uptake efficiency (43.7%) compared to the CFA approach.

CONCLUSION

The use of PGPB-coated N and P fertilizers with a higher number of splits at a lower rate significantly boosts potato production in the alkaline sandy soils of Cholistan.

Role of calcium nutrition in plant Physiology: Advances in research and insights into acidic soil conditions - A comprehensive review

Plant mineral nutrition has immense significance for crop productivity and human well-being. Soil acidity plays a major role in determining the nutrient availability that influences plant growth. The importance of calcium (Ca) in biological processes, such as signaling, metabolism, and cell growth, underlines its critical role in plant growth and development. This review focuses on soil acidification, a gradual process resulting from cation leaching, fertilizer utilization, and drainage issues. Soil acidification significantly hampers global crop production by modifying nutrient accessibility. In acidic soils, essential nutrients, such as nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), and Ca become less accessible, establishing a correlation between soil pH and plant nutrition. Cutting-edge Ca nutrition technologies, including nanotechnology, genetic engineering, and genome sequencing, offer the potential to deliver Ca and reduce the reliance on conventional soluble fertilizers. These fertilizers not only contribute to environmental contamination but also impose economic burdens on farmers. Nanotechnology can enhance nutrient uptake, and Ca nanoparticles improve nutrient absorption and release. Genetic engineering enables the cultivation of acid-tolerant crop varieties by manipulating Ca-related genes. High-throughput technologies such as next-generation sequencing and microarrays aid in identifying the microbial structures, functions, and biosynthetic pathways involved in managing plant nutritional stress. The ultimate goal is to shed light on the importance of Ca, problems associated with soil acidity, and potential of emerging technologies to enhance crop production while minimizing the environmental impact and economic burden on farmers.

Rhizospheric Precipitation of Manganese by Phosphate: A Novel Strategy to Enhance Mn Tolerance in the Hyperaccumulator Phytolacca americana

Manganese (Mn) exclusion in the Mn hyperaccumulator pokeweed (Phytolacca americana L.) was investigated. Hydroponic experiments were carried out to observe the responses of pokeweeds continually exposed to high levels of Mn. In this study, crystals were observed to appear firstly on the root hair, and soon after, more crystals appeared on the root surface, and crystals of Mn phosphate were observed to appear on the root surface in a time sequence negatively correlated with the number of leaves treated with 5 mM Mn. Crystals were identified via phase analysis of X-ray diffraction and element analysis, and these white insoluble crystals were identified using XRD to be Mn phosphate, with the molecular formula (Mn,Fe)3(PO4)2·4H2O. The nutrient solution pH increased from 4.5 to about 5.6 before the crystals appeared. Mn phosphate crystals appeared in all solutions except those without phosphate and emerged earlier in the solutions containing no Fe. Compared with control group, pokeweed accumulated much more Mn in the leaves when treated without phosphate or Fe. The present study suggests that pokeweed can exclude Mn by means of rhizosphere precipitation by phosphate to form Mn phosphate crystals that accumulate on the root surface. Although the detailed mechanism requires further investigation, this study provides the first direct evidence of a novel strategy to inhibit Mn uptake in the roots of a hyperaccumulator in a P-enriched environment.

The Growth-Inhibitory Effect of Increased Planting Density Can Be Reduced by Abscisic Acid-Degrading Bacteria

High-density planting can increase crop productivity per unit area of cultivated land. However, the application of this technology is limited by the inhibition of plant growth in the presence of neighbors, which is not only due to their competition for resources but is also caused by growth regulators. Specifically, the abscisic acid (ABA) accumulated in plants under increased density of planting has been shown to inhibit their growth. The goal of the present study was to test the hypothesis that bacteria capable of degrading ABA can reduce the growth inhibitory effect of competition among plants by reducing concentration of this hormone in plants and their environment. Lettuce plants were grown both individually and three per pot; the rhizosphere was inoculated with a strain of Pseudomonas plecoglossicida 2.4-D capable of degrading ABA. Plant growth was recorded in parallel with immunoassaying ABA concentration in the pots and plants. The presence of neighbors indeed inhibited the growth of non-inoculated lettuce plants. Bacterial inoculation positively affected the growth of grouped plants, reducing the negative effects of competition. The bacteria-induced increase in the mass of competing plants was greater than that in the single ones. ABA concentration was increased by the presence of neighbors both in soil and plant shoots associated with the inhibition of plant growth, but accumulation of this hormone as well as inhibition of the growth of grouped plants was prevented by bacteria. The results confirm the role of ABA in the response of plants to the presence of competitors as well as the possibility of reducing the negative effect of competition on plant productivity with the help of bacteria capable of degrading this hormone.

Phosphorus deficiency alters root length, acid phosphatase activity, organic acids, and metabolites in root exudates of soybean cultivars

Phosphorus (P) deficiency alters the root morphological and physiological traits of plants. This study investigates how soybean cultivars with varying low-P tolerance values respond to different P levels in hydroponic culture by assessing alterations in root length, acid phosphatase activity, organic acid exudation, and metabolites in root exudates. Three low-P-tolerant cultivars ('Maetsue,' 'Kurotome,' and 'Fukuyutaka') and three low-P-sensitive cultivars ('Ihhon,' 'Chizuka,' and 'Komuta') were grown under 0 (P0) and 258 μM P (P8) for 7 and 14 days after transplantation (DAT). Low-P-tolerant cultivars increased root length by 31% and 119%, which was lower than the 62% and 144% increases in sensitive cultivars under P0 compared to P8 at 7 and 14 DAT, respectively. Acid phosphatase activity in low-P-tolerant cultivars exceeded that in sensitive cultivars by 5.2-fold and 2.0-fold at 7 and 14 DAT. Root exudates from each cultivar revealed 177 metabolites, with higher organic acid exudation in low-P-tolerant than sensitive cultivars under P0. Low-P-tolerant cultivars increased concentrations of specific metabolites (oxalate, GABA, quinate, citrate, AMP, 4-pyridoxate, and CMP), distinguishing them from low-P-sensitive cultivars under P0. The top five metabolomic pathways (purine metabolism, arginine and proline metabolism, TCA cycle, glyoxylate and dicarboxylate metabolism, alanine, aspartate, and glutamate metabolism) were more pronounced in low-P-tolerant cultivars at 14 DAT. These findings indicate that increasing root length was not an adaptation strategy under P deficiency; instead, tolerant cultivars exhibit enhanced root physiological traits, including increased acid phosphatase activity, organic acid exudation, specific metabolite release, and accelerated metabolic pathways under P deficiency.

Nitrogen Journey in Plants: From Uptake to Metabolism, Stress Response, and Microbe Interaction

Plants uptake and assimilate nitrogen from the soil in the form of nitrate, ammonium ions, and available amino acids from organic sources. Plant nitrate and ammonium transporters are responsible for nitrate and ammonium translocation from the soil into the roots. The unique structure of these transporters determines the specificity of each transporter, and structural analyses reveal the mechanisms by which these transporters function. Following absorption, the nitrogen metabolism pathway incorporates the nitrogen into organic compounds via glutamine synthetase and glutamate synthase that convert ammonium ions into glutamine and glutamate. Different isoforms of glutamine synthetase and glutamate synthase exist, enabling plants to fine-tune nitrogen metabolism based on environmental cues. Under stressful conditions, nitric oxide has been found to enhance plant survival under drought stress. Furthermore, the interaction between salinity stress and nitrogen availability in plants has been studied, with nitric oxide identified as a potential mediator of responses to salt stress. Conversely, excessive use of nitrate fertilizers can lead to health and environmental issues. Therefore, alternative strategies, such as establishing nitrogen fixation in plants through diazotrophic microbiota, have been explored to reduce reliance on synthetic fertilizers. Ultimately, genomics can identify new genes related to nitrogen fixation, which could be harnessed to improve plant productivity.

Influence of management practices on water-related grain yield determinants

Adequate management of N supply, plant density, row spacing, and soil cover has proved useful for increasing grain yields and/or grain yield stability of rainfed crops over the years. We review the impact of these management practices on grain yield water-related determinants: seasonal crop evapotranspiration (ET) and water use efficiency for grain production per unit of evapotranspired water during the growing season (WUEG,ET,s). We highlight a large number of conflicting results for the impact of management on ET and expose the complexity of the ET response to environmental factors. We analyse the influence of management practices on WUEG,ET,s in terms of the three main processes controlling it: (i) the proportion of transpiration in ET (T/ET), (ii) transpiration efficiency for shoot biomass production (TEB), and (iii) the harvest index. We directly relate the impact of management practices on T/ET to their effect on crop light interception and provide evidence that management practices significantly influence TEB. To optimize WUEG,ET,s, management practices should favor soil water availability during critical periods for seed set, thereby improving the harvest index. The need to improve the performance of existing crop growth models for the prediction of water-related grain yield determinants under different management practices is also discussed.

Phosphorus Plays Key Roles in Regulating Plants' Physiological Responses to Abiotic Stresses

Phosphorus (P), an essential macronutrient, plays a pivotal role in the growth and development of plants. However, the limited availability of phosphorus in soil presents significant challenges for crop productivity, especially when plants are subjected to abiotic stresses such as drought, salinity and extreme temperatures. Unraveling the intricate mechanisms through which phosphorus participates in the physiological responses of plants to abiotic stresses is essential to ensure the sustainability of agricultural production systems. This review aims to analyze the influence of phosphorus supply on various aspects of plant growth and plant development under hostile environmental conditions, with a special emphasis on stomatal development and operation. Furthermore, we discuss recently discovered genes associated with P-dependent stress regulation and evaluate the feasibility of implementing P-based agricultural practices to mitigate the adverse effects of abiotic stress. Our objective is to provide molecular and physiological insights into the role of P in regulating plants' tolerance to abiotic stresses, underscoring the significance of efficient P use strategies for agricultural sustainability. The potential benefits and limitations of P-based strategies and future research directions are also discussed.

Silicon, by promoting a homeostatic balance of C:N:P and nutrient use efficiency, attenuates K deficiency, favoring sustainable bean cultivation

BACKGROUND

In many regions of the world, K is being depleted from soils due to agricultural intensification a lack of accessibility, and the high cost of K. Thus, there is an urgent need for a sustainable strategy for crops in this environment. Si is an option for mitigating stress due to nutritional deficiency. However, the underlying effects of Si in mitigating K deficiency C:N:P homeostasis still remains unknown for bean plants. This is a species of great worldwide importance. Thus, this study aims to evaluate whether i) K deficiency modifies the homeostatic balance of C, N and P, and, if so, ii) Si supply can reduce damage caused to nutritional stoichiometry, nutrient use efficiency, and production of dry mass in bean plants.

RESULTS

K deficiency caused a reduction in the stoichiometric ratios C:N, C:P, and P:Si in shoots and C:N, C:P, C:Si, N:Si, and P:Si in roots, resulting in a decrease in K content and use efficiency and reducing biomass production. The application of Si in K-deficient plants modified the ratios C:N, C:Si, N:P, N:Si, and P:Si in shoots and C:N, C:P, C:Si, N:Si, N:P, and P:Si in roots, increasing the K content and efficiency, reducing the loss of biomass. In bean plants with K sufficiency, Si also changed the stoichiometric ratios C:N, C:P, C:Si, N:P, N:Si, and P:Si in shoots and C:N, C:Si, N:Si, and P:Si in roots, increasing K content only in roots and the use efficiency of C and P in shoots and C, N, and P in roots, increasing the biomass production only in roots.

CONCLUSION

K deficiency causes damage to the C:N:P homeostatic balance, reducing the efficiency of nutrient use and biomass production. However, Si is a viable alternative to attenuate these nutritional damages, favoring bean growth. The future perspective is that the use of Si in agriculture in underdeveloped economies with restrictions on the use of K will constitute a sustainable strategy to increase food security.