Maize Root Growth Research Articles

Maize root biomass and architecture depend on site but not on variety: Consequences for prediction of C inputs and spread in topsoil based on root-to-shoot ratios

Abstract Knowledge about the response of root biomass and root system architecture (RSA) to soil conditions would increase efficiency in selecting high performance crop varieties and predicting the impact of rotations on long-term soil organic matter (SOM) stock. We evaluated the effect of variety and site on maize (Zea mays L.) root growth. Two-dimensional (2D) and 3D techniques were used to quantify changes of RSA. Commercial maize varieties were grown in three sites with typical soil types for maize cultivation in Belgium. We observed that at Merelbeke, above- and belowground biomass and root-to-shoot ratios (R/S) were larger compared to those at Ravels. Both factors interactively influenced an index of biological stability (ISB) based on biochemical quality of the roots. There were also more fine roots at Merelbeke than at Bassevelde and Ravels. Together with a lower ISB value, this suggests that site had an inherent effect on root biochemical quality. We conclude that a strong impact of site exists on both above- and belowground biomass; however, they are not necessarily correlated. With a fixed R/S, predictions of root biomass were misestimated in one half of the cases. This complex response of root phenotyping to varying soil conditions should not be overlooked.

Influence of moisture stress management techniques on the root growth and yield stability of maize (Zea mays)

Influence of moisture stress management techniques on the root growth and yield stability of maize (Zea mays)

Maize yield and root morphological characteristics affected by controlled-release diammonium phosphate and Paecilomyces variotii extracts

Abstract Application of conventional phosphorus (P) fertilizer poses great concern due to its low P efficiency and potential eutrophication of P in sensitive waters. A novel biostimulant, Paecilomyces variotii extract (ZNC), with functionality of improving nutrient uptakes of crops, was integrated with diammonium phosphate coated with biobased polyurethane polymer in a three-year field trial. The objectives were to explore the effects and mechanisms of the controlled-release diammonium phosphate (CRP), ZNC and their combination on P use efficiency (PUE), economic benefit, soil P supply, and root growth and yield of maize (Zea mays L., Zhengdan ‘958’). The experiment consisted of five treatments: regular diammonium phosphate (DAP); CRP with release longevity of three months (CDAP); regular diammonium phosphate combined with ZNC (DAPZ); CRP combined with ZNC (CDAPZ); and no added P fertilizer (Control), each with three replicates. The results indicated that CDAP and DAPZ treatments significantly increased average yield by 9.65 % and 3.56 %, and PUE by 7.72 % and 3.32 %, respectively, when compared with DAP treatment. Similarly, the average soil available-P of CDAP and DAPZ treatments was increased by 10.0 % and 45.9 % at 0−40 cm soil depth. Furthermore, CDAP and DAPZ treatments significantly increased maize total root length by 178.2 % and 223.6 %, and bleeding sap rate by 23.3 % and 32.5 %, respectively, at the jointing stage. However, the average maize yield and net income of combined CDAPZ treatment had no significant difference relative to CDAP and DAPZ treatments. Moreover, the total root length of CDAPZ treatment was reduced by 16.0 % and 27.8 %, compared to CDAP and DAPZ treatments. Hence the application of CRP or ZNC could increase maize yield by improving soil P supply intensity to meet maize P demand and promoting root morphological characteristics and vitality. However, the combination of CRP and ZNC did not demonstrate significant synergies on yield improvement and root growth promotion. Further research is needed for the development and application of biostimulant enhanced fertilizer as a green environmental technology.

Tropical Bacillus Strains Inoculation Enhances Maize Root Surface Area, Dry Weight, Nutrient Uptake and Grain Yield

The rising demand for agricultural commodities in developing countries has put increasing pressure on land resources for higher yields, with associated growth in the demand for phosphate fertilizers. However, there are a number of adverse environmental impacts associated with the use of inorganic P fertilizers that is pushing global fertilizer prices up. In this context, phosphate solubilizing microorganisms, such as Bacillus, are the most eco-friendly and inexpensive option for enhancing P availability for plants, once they are capable of transforming insoluble P into soluble (plant accessible) forms and are regarded as plant growth-promoting microorganisms. This work aimed to understand the effect of tropical Bacillus strains on maize root morphology and growth using a hydroponic system and to evaluate their performance under two phosphorus fertilization conditions in the field. Maize root was inoculated separately with six Bacillus strains and grown in nutrient solution. Several root traits, dry weight and nutrient content were measured in maize seedlings. Moreover, we measured bacterial IAA-like molecules in vitro production and evaluated inoculated maize performance under field conditions with no P added (P0) and triple superphosphate (TSP) soil fertilization. All the Bacillus strains increased shoot and total dry weight and strains B2084, B119 and B32 had the greatest performance, producing the highest biomass, shoot nutrient content and root surface area compared to other strains in hydroponics. All strains that produced IAA-like molecules demonstrated a positive effect on plant growth by stimulating root elongation. In the field experiments, strain B116 inoculation increased maize yield and P grain accumulation by around 36% and 58%, respectively, and B119 increased P grain in 21% in soils with no P added. Even in soils fertilized with TSP, maize yield increase and P grain accumulation was around 20% after inoculation with these two strains comparing to non-inoculated control. Our results indicated that maize plants inoculated with Bacillus strains capable of producing IAA-like molecules and solubilizing phosphate, presented enhanced root system, dry matter and nutrient accumulation in hydroponics and higher yield and grain P content with and without addition of phosphate fertilizer under field conditions.

Biostimulant Potential of Acetic Acid Under Drought Stress Is Confounded by pH-Dependent Root Growth Inhibition.

Recent reports of acetic acid-induced drought tolerance and avoidance across a diverse range of plant species encourage consideration of this low-cost commodity organic acid as a biostimulant. These results are surprising as they contrast with earlier studies showing pH-dependent root growth inhibition at similar concentrations. We test the hypothesis that the concentration of the membrane permeable undissociated form of acetic acid (CH3COOH) selectively inhibits maize root growth, and subsequently evaluate its impact on seedling water use and growth under deficit irrigation. We demonstrate conclusively for the first time that when germinating maize on filter paper, low pH exacerbates, and high pH mitigates, this inhibition of root growth in a predictable manner based on the dissociation constant of acetic acid. The buffering capacity of potting media can reduce this root damage through keeping the acetic acid primarily in the membrane impermeable dissociated form (CH3COO–) at near neutral pH, but peat substrates appear to offer some protection, even at low pH. While both deficit irrigation and acetic acid reduced water use and growth of maize seedlings outdoors, there was no significant interaction between the treatments. Twenty nine millimolar total acetic acid (CH3COOH + CH3COO–) reduced transpiration, compared to lower and higher concentrations, but this did not specifically improve performance under reduced water availability, with parallel declines in shoot biomass leading to relatively consistent water use efficiency. Any acetic acid biostimulant claims under water stress should characterize its dissociation level, and exclude root damage as a primary cause.

High-resolution profile of transcriptomes reveals a role of alternative splicing for modulating response to nitrogen in maize

BackgroundThe fluctuation of nitrogen (N) contents profoundly affects the root growth and architecture in maize by altering the expression of thousands of genes. The differentially expressed genes (DEGs) in response to N have been extensively reported. However, information about the effects of N variation on the alternative splicing in genes is limited.ResultsTo reveal the effects of N on the transcriptome comprehensively, we studied the N-starved roots of B73 in response to nitrate treatment, using a combination of short-read sequencing (RNA-seq) and long-read sequencing (PacBio-sequencing) techniques. Samples were collected before and 30 min after nitrate supply. RNA-seq analysis revealed that the DEGs in response to N treatment were mainly associated with N metabolism and signal transduction. In addition, we developed a workflow that utilizes the RNA-seq data to improve the quality of long reads, increasing the number of high-quality long reads to about 2.5 times. Using this workflow, we identified thousands of novel isoforms; most of them encoded the known functional domains and were supported by the RNA-seq data. Moreover, we found more than 1000 genes that experienced AS events specifically in the N-treated samples, most of them were not differentially expressed after nitrate supply-these genes mainly related to immunity, molecular modification, and transportation. Notably, we found a transcription factor ZmNLP6, a homolog of AtNLP7-a well-known regulator for N-response and root growth-generates several isoforms varied in capacities of activating downstream targets specifically after nitrate supply. We found that one of its isoforms has an increased ability to activate downstream genes. Overlaying DEGs and DAP-seq results revealed that many putative targets of ZmNLP6 are involved in regulating N metabolism, suggesting the involvement of ZmNLP6 in the N-response.ConclusionsOur study shows that many genes, including the transcription factor ZmNLP6, are involved in modulating early N-responses in maize through the mechanism of AS rather than altering the transcriptional abundance. Thus, AS plays an important role in maize to adapt N fluctuation.

Growth and aluminum tolerance of maize roots mediated by auxin- and cytokinin-producing Bacillus toyonensis requires polar auxin transport

Plant Growth Promotion Rhizobacteria (PGPR) control plant development by modulation of their phytohormone activities. To probe how PGPR trigger plant growth and mitigate stress induced by aluminum (Al), the beneficial effect of Bacillus toyonensis strain Bt04 (Bt04), isolated from the Algerian Sahara rhizosphere, on maize roots was assessed. Our results revealed that the strain Bt04 is producing indole-3-acetic acid (IAA) both endogenously and from tryptophan (Trp). Surprisingly, the production of another endogenous auxin, a non-indole phenylacetic acid (PAA), was found at higher concentrations than IAA. Additionally, the production of cytokinins (CKs) by Bt04 has been demonstrated. Inoculation with Bt04 resulted in a promotion of maize growth and an enhancement of root development under aluminium (Al) toxicity condition. Importantly, Bt04 reduced Al accumulation in the young maize roots. Moreover, we could demonstrate that Bt04 itself exhibits tolerance to high concentrations of AlCl3. Bt04 might exert its growth promoting effect partially by increasing protection against oxidative stress since bacterial treatment reduced lipid peroxidation in maize seedlings under Al toxicity. To investigate a possible mechanism of this growth induction of maize seedlings we treated them under control and stress conditions with auxin transport inhibitors and demonstrated that the auxin transport pathway is needed for the Al induced stress response after inoculation with the PGPR.

Biochar retards Al toxicity to maize (Zea mays L.) during soil acidification: The effects and mechanisms

Biochar can effectively alleviate the Al phytotoxicity in acidic soils due to its alkaline nature. However, the longevity of this alleviation effect of biochar under re-acidification conditions is still unclear. In the present study, the maize root growth responding to the simulated re-acidification of two acidic soils amended by peanut straw biochar or Ca(OH)2 was investigated to evaluate the long-term effect of biochar on alleviating Al toxicity in acidic soils. Compared with Ca(OH)2 amendment, the application of biochar significantly retarded Al toxicity to plant during soil re-acidification. When 4.0 mM HNO3 was added, the maize seedling root elongation in an Oxisol with biochar was 99% higher than that in the Oxisol with Ca(OH)2. Also, the Evans blue uptake and Al content in the root tip in the biochar treatment were 60% and 51% lower than those in the Ca(OH)2 treatment. The retarding effect was mainly attributed to the slow decrease in soil pH during acidification and the release of dissolved organic carbon (DOC) in the soils amended by biochar. The slower decrease in soil pH resulting from the increased pH buffering capacity after biochar application inhibited the increase of soluble and exchangeable Al during re-acidification. The increased DOC after biochar application decreased the toxic soluble Al speciation at the same pH value and total Al concentration in soil solution. Therefore, given the re-acidification of soils, biochar presented a longer-term effect on alleviating Al toxicity of acidic soil than liming.

Influence of plastic film mulching and planting density on yield, leaf anatomy, and root characteristics of maize on the Loess Plateau

In rainfed areas of northwestern China, maize production is constrained mainly by low temperature during early growth and water limitation during the entire growth period. Plastic film mulching is commonly used to increase maize yield in this area, because it increases topsoil temperature and moisture content as well as water use efficiency. However, the physiological and anatomical bases of maize yield improvement with plastic film mulching are not well understood. The effects of plastic film mulching and planting density on maize yield, photosynthetic characteristics, respiration, leaf anatomy, and root growth were studied in a two-year field experiment conducted on the Loess Plateau of China in 2017 and 2018. The experiment used a split-split plot design with two mulching treatments (plastic film mulching and no mulching), two planting densities (7.5 × 104 and 10.5 × 104 plants ha−1), and two maize cultivars, Zhengdan 958 and Xianyu 335. Compared with no mulching, plastic film mulching increased maize yields by 31.1%–46.4% in 2017 and 3.6%–34.7% in 2018. Compared with low planting density, high planting density significantly increased and slightly reduced yields of both cultivars in the dry year 2017 and the rainy year 2018, respectively. Plastic film mulching increased photosynthesis and respiration as well as leaf stomatal density and aperture. Photosynthetic rate, dark respiration, and stomatal conductance and aperture were lower at high planting than at low planting density. Maize yield was positively correlated with photosynthesis, dark respiration, and stomatal aperture. Mulching increased root dry weight and length in the 0–20 cm soil layer and root activity at maturity. Overall, the changes in root growth and leaf anatomy resulted in increased photosynthesis and dark respiration, and the increased photosynthesis contributed to the increase in grain yield and biomass production under plastic film mulching conditions. Our results increase understanding of the physiological mechanisms by which plastic film mulching increases maize yield in water- and temperature-limited areas.

Transcriptome analysis of maize seedling roots in response to nitrogen-, phosphorus-, and potassium deficiency

Soil deficiencies with respect to the availability of macronutrients such as nitrogen, phosphorus, and potassium seriously affect the growth, yield, and grain quality of maize (Zea mays L.). To improve the utilization efficiency of mineral elements in maize, we wanted to find the key genes that regulate the growth of maize roots under nutrient-deficient conditions. Maize plants were subjected to nitrogen, phosphorus, and potassium deficiency stress and their roots were collected and analyzed using transcriptome sequencing. GO and KEGG analyses of the differentially expressed genes (DEGs) were performed, and qPCR was used to verify the reliability of the transcriptome data. When maize was subjected to any of the three nutrient-deficiencies mentioned in Methods, the growth and root vitality of its roots were inhibited. 1255, 1082, and 324 genes specifically expressed when the maize was subjected to N, P, and K deficiencies, respectively, and all three treatments shared 575 DEGs. Genes that are associated with nutrient utilization, hormones, and transcription factors differentially expressed under different types of nutrient-deficiency stress. We speculated that MRP2, bZIP77, and bZIP53 play a positive regulatory role in maize root growth in an environment suffering from nutrient deficiencies. The molecular mechanism by which maize root growth responds to nutrient stress is complicated. NPF7.3, GlpT4, HAK24, and HAK5, MRP2, bZIP77, and bZIP53 can be used as candidates’ genes that regulate maize root growth under nitrogen, phosphorus, and potassium deficiency stress.

Effect of conservation agriculture and nitrogen management on root architecture and soil properties in maize-wheat cropping system

A field experiment was conducted to evaluate the effect of conservation agricultural and nitrogen management practices on root architecture and soil physical, chemical and biological properties after 2years of continuous maize-wheat cropping system. The experiment was carried out in split plot design with six main plot treatments of tillage and crop establishment techniques, i.e. conventional tillage-flat bed (CT-F), CT-raised bed (CT-B), zero tillage-flat bed with crop residue (ZT-F+R) and without crop residue (ZT-F), ZT-raised bed with crop residue (ZT-B+R) and without crop residue (ZT-B) and four sub plot treatments of nitrogen (N), i.e. 0, 60, 120 and 180 kg N ha−1. Most of the soil physical, chemical and biological parameters were significantly improved with ZT-B+R as compared to other treatments. ZT-B+R recorded 7.7 and 9.1% higher organic carbon than CT-B and CT-F, respectively. Microbial biomass carbon, dehydrogenase activity and fluorescein diacetate hydrolysis were improved by 57.4, 47.0 and 55.4% with ZT-B+R over CT-F, respectively. ZT-B+R also registered significantly lower bulk density compared to ZT without residue and CT-F treatments. The same treatment also improved the aggregation, hydraulic conductivity, infiltration rate and available N, P and K in soil. Root length density (RLD), root surface area (RSA) and root volume density (RVD) of maize and wheat were also recorded higher with ZT-B+R which was at par with CT-B and ZT-B, but significantly higher than CT-F and ZT-F treatments. Nitrogen levels did not exert significant influence on most of the soil properties, however, organic carbon and biological activities in soil improved up to 60 kg N ha−1, while soil available N, RLD, RSA and RVD improved significantly up to 120 kg N ha−1. Thus, we concluded that permanent-bed with crop residue (ZT-B+R) and 120 kg N ha−1 was found to be beneficial for improving soil health and root growth of maize and wheat crops.

Effects of Phosphorus Supply on Root Morphology and Phosphorus Uptake in Maize Seedlings under Different Water Regimes

Water deficit and phosphorus (P) deficiency in soil have become the main limiting factors for the production of maize (<i>Zea mays</i> L.), but it still remains unclear how water and P regulate maize root morphology and P uptake. Through an experiment of potted soil culture, this study has set 4 water gradients [35% (W1), 55% (W2), 75% (W3) and 100% (W4)] of field capacity, and two P levels [high P: 205 mg (P)∙kg^-1; low P: 11 mg (P)∙kg^-1] to investigate the coupling effects of water and P on root growth and P uptake in maize seedlings. The results have shown that: (1) Regardless of soil P supply, the shoot dry weight, root dry weight, total root length, and root surface area of maize seedlings shows a trend of increasing first and then decreasing with increasing water supply intensity; the soil available P content also shows similar trend; the root mass ratio and mean root diameter shows a downward trend with the increase of water supply intensity; furthermore, the P content and P accumulation of plants shows a steady increase with the increase of water supply intensity; (2) Water deficit (W1) and excess water supply (W4) is not conducive to root growth and dry matter accumulation in maize. Water deficit (W1) inhibits the acquisition of soil P by maize, while excess water supply (W4) causes extravagant absorption of soil P (W4). Mild water stress (W2) can promote the growth and dry matter accumulation of maize roots and reduce the extravagant absorption of soil P, and adequate water supply (W3) can promote root growth, dry matter accumulation and the absorption of soil P; (3) Phosphorus supply significantly increases the dry weight, root dry weight (except W4), total root length, root surface area, plant P content (except W4) and P accumulation of maize seedlings, but reduces the root mass ratio of maize. It is thus evident that water is a key factor controlling the morphology and accumulation of dry matter in maize roots, and P is a key factor controlling P uptake and soil available P content in corn field. The better coupling between water and P can promote maize root growth and dry matter accumulation, as well as reduce the extravagant absorption of soil P.

Inoculation with the mycorrhizal fungus Rhizophagus irregularis modulates the relationship between root growth and nutrient content in maize (Zea mays ssp. mays L.).

Plant root systems play a fundamental role in nutrient and water acquisition. In resource‐limited soils, modification of root system architecture is an important strategy to optimize plant performance. Most terrestrial plants also form symbiotic associations with arbuscular mycorrhizal fungi to maximize nutrient uptake. In addition to direct delivery of nutrients, arbuscular mycorrhizal fungi benefit the plant host by promoting root growth. Here, we aimed to quantify the impact of arbuscular mycorrhizal symbiosis on root growth and nutrient uptake in maize. Inoculated plants showed an increase in both biomass and the total content of twenty quantified elements. In addition, image analysis showed mycorrhizal plants to have denser, more branched root systems. For most of the quantified elements, the increase in content in mycorrhizal plants was proportional to root and overall plant growth. However, the increase in boron, calcium, magnesium, phosphorus, sulfur, and strontium was greater than predicted by root system size alone, indicating fungal delivery to be supplementing root uptake.

Mechanical and Hydric Stress Effects on Maize Root System Development at Different Soil Compaction Levels.

Soil mechanical resistance, aeration, and water availability directly affect plant root growth. The objective of this work was to identify the contribution of mechanical and hydric stresses on maize root elongation, by modeling root growth while taking the dynamics of these stresses in an Oxisol into consideration. The maize crop was cultivated under four compaction levels (soil chiseling, no-tillage system, areas trafficked by a tractor, and trafficked by a harvester), and we present a new model, which allows to distinguish between mechanical and hydric stresses. Root length density profiles, soil bulk density, and soil water retention curves were determined for four compaction levels up to 50 cm in depth. Furthermore, grain yield and shoot biomass of maize were quantified. The new model described the mechanical and hydric stresses during maize growth with field data for the first time in maize crop. Simulations of root length density in 1D and 2D showed adequate agreement with the values measured under field conditions. Simulation makes it possible to identify the interaction between the soil physical conditions and maize root growth. Compared to the no-tillage system, grain yield was reduced due to compaction caused by harvester traffic and by soil chiseling. The root growth was reduced by the occurrence of mechanical and hydric stresses during the crop cycle, the principal stresses were mechanical in origin for areas with agricultural traffic, and water based in areas with soil chiseling. Including mechanical and hydric stresses in root growth models can help to predict future scenarios, and coupling soil biophysical models with weather, soil, and crop responses will help to improve agricultural management.

The root-layer regulation based on the depth of phosphate fertilizer application of summer maize improves soil nitrogen absorption and utilization

Favorable root phenotypes can promote crops to obtain soil nutrients efficiently. The root-layer regulation technology based on the depth of phosphate fertilizer application can optimize the spatial and temporal distribution of summer maize root system and promote its spatial matching with soil water and nutrients to supply, providing a theoretical and technical support for realizing fertilizer saving and efficiency improvement by tapping potential of maize root system. In the present study, there were five treatments including CK (no P applied), P5 (phosphorus placement depth of 5 cm), P10 (phosphorus placement depth of 10 cm), P15 (phosphorus placement depth of 15 cm), and P20 (phosphorus placement depth of 20 cm). The effect of phosphorus application depth on root distribution, plant growth and yield formation, as well as nitrogen uptake, accumulation and transport in summer maize was analyzed. The suitable application depths of phosphate fertilizer promoted the growth of summer maize roots and increased root dry weight, root length density, root surface area and root volume significantly totally showing a trend of P15 > P10 > P20 > P5 > CK. With the increase of phosphate fertilizer application depth, the deep corn roots increased significantly. The proportion of root dry weight in P15 and P20 treatments was 12.3% and 12.1% in the 20–40 cm soil layer, and 6.7% and 6.9% in the 40–60 cm soil layer, respectively. The increase of root distribution depth promoted the absorption of nitrogen in the soil, and the nitrogen content in each soil layer, especially below 20 cm, was reduced significantly by the deep application of phosphate fertilizer. The optimization of root distribution promoted the accumulation and transportation of nitrogen in plants. Compared with P5 treatment, the averaged nitrogen fertilizer absorption efficiency, accumulation amount, accumulation rate, partial factor productivity and the grain yield in two years of P15 treatment increased by 14.5 kg kg–1, 19.2%, 48.9%, 6.4 kg kg–1, and 16.4% respectively, showing that under the conditions of the present study, concentrated application of phosphate fertilizer in −15 cm treatment can significantly promote the growth of deep soil roots, expand the space of nutrient utilization for root system, increase the absorption of nitrogen in deep soil, promote the accumulation and transportation of plant nitrogen, improve the productivity and ultimately yield in summer maize.

Early priority effects of occupying a nutrient patch do not influence final maize growth in intensive cropping systems

Priority effects can be caused by an individual plant within a population that is the first to occupy and explore nutrient patches. However, the magnitude of priority effects of exploring a nutrient patch on plant growth during the ontogeny remains obscure. A 30-day rhizo-box experiment and a 2-year field trial with maize (Zea mays L) were conducted to examine the influence of priority effects arising from heterogeneous nutrient (nitrogen and phosphorus) supply on the root and shoot growth of maize under nutrient-limited and nutrient-rich environments. In the rhizo-box with limited soil resources, maize shoot biomass and nutrient content increased with the closeness to the nutrient patch, suggesting strong priority effects. In the field trial with high fertilizer input, priority effects arising from root proliferation within the nutrient patch also brought growth advantages for individual plants close to the patch in the first 45 days after sowing (DAS), but positive effects were weaker than in rhizo-box conditions. The growth advantage was not maintained after 60 DAS. The early priority effects did not promote grain yield. Our findings demonstrated that the growth advantage of early priority effects from exploring the nutrient patch was dependent on time and soil nutrient supply.

Comparative Proteomics Analysis of the Seedling Root Response of Drought-sensitive and Drought-tolerant Maize Varieties to Drought Stress.

The growth and development of maize roots are closely related to drought tolerance. In order to clarify the molecular mechanisms of drought tolerance between different maize (Zea mays L.) varieties at the protein level, the isobaric tags for relative and absolute quantitation (iTRAQ) quantitative proteomics were used for the comparative analysis of protein expression in the seedling roots of the drought-tolerant Chang 7-2 and drought-sensitive TS141 maize varieties under 20% polyethylene glycol 6000 (PEG 6000)-simulated drought stress. We identified a total of 7723 differentially expressed proteins (DEPs), 1243 were significantly differentially expressed in Chang 7-2 following drought stress, 572 of which were up-regulated and 671 were down-regulated; 419 DEPs were identified in TS141, 172 of which were up-regulated and 247 were down-regulated. In Chang 7-2, the DEPs were associated with ribosome pathway, glycolysis/gluconeogenesis pathway, and amino sugar and nucleotide sugar metabolism. In TS141, the DEPs were associated with metabolic pathway, phenylpropanoid biosynthesis pathway, and starch and sucrose metabolism. Compared with TS141, the higher drought tolerance of Chang 7-2 root system was attributed to a stronger water retention capacity; the synergistic effect of antioxidant enzymes; the strengthen cell wall; the osmotic stabilization of plasma membrane proteins; the effectiveness of recycling amino acid; and an improvement in the degree of lignification. The common mechanisms of the drought stress response between the two varieties included: The promotion of enzymes in the glycolysis/gluconeogenesis pathway; cross-protection against the toxicity of aldehydes and ammonia; maintenance of the cell membrane stability. Based on the proteome sequencing information, the coding region sequences of eight DEP-related genes were analyzed at the mRNA level by quantitative real-time PCR (qRT-PCR). The findings of this study can inform the future breeding of drought-tolerant maize varieties.

Effect of nitrogen supply method on root growth and grain yield of maize under alternate partial root-zone irrigation

A field experiment was carried out to investigate effect of nitrogen (N) supply method on root growth and its correlation with the above-ground parts in maize (Zea mays L.) under alternate partial root-zone irrigation (APRI) at Wuwei, northwest China in 2012 and 2014. The treatments included alternate N supply, conventional N supply and fixed N supply under APRI (designated AN, CN and FN, respectively), with an additional CN fertilizer treatment coupled with conventional irrigation (CK). Ridges were built in a west-east direction. Root weight density (RWD) in the 0–100 cm soil layer and shoot biomass at the V6, V12, VT, R2 and R6 stages, and grain yield and yield components at the R6 were determined. Results showed that RWD around the plant (i.e. under the plant, south and north of the plant) in the 0–40 cm soil layer varied among different treatments at the VT, R2 and R6 stages. The RWD north and south the plant were comparable during maize growth stages for AN, CN and CK, while FN significantly decreased the RWD of its no N supply side at the three stages and markedly decreased the RWD of its N supply side at the VT. AN and CN significantly increased the RWD, shoot biomass at the three stages, and grain yield compared with FN and CK. Grain yield was positively correlated with RWD in the 0–40 cm soil layer at the three stages. These results suggested that AN and CN produced a relatively uniform distribution of roots and a greater root biomass, which contributed to the enhanced shoot biomass and grain yield of maize under APRI.

Root Growth Responses of Maize (Zea mays L.) and Soybean (Glycine max L.) to Soil Compaction and Fertilization in a Ferric Acrisol

Mechanical impedance to root growth is one of the most important factors determining root elongation and proliferation within a soil profile. Two pot experiments were conducted at the Department of Horticulture, KNUST, Kumasi, Ghana, to determine the impact of subsurface compaction and different fertilizer amendments on the root growth of maize (Zea mays L.) and soybean (Glycine max L.). The experiments were arranged in a factorial Completely Randomized Design (CRD) with three replications. Maize and soybean varieties, “Obaatanpa” and “Anidaso” were sown in 72 plastic buckets (36 for each crop) of 12 L volume filled with a Ferric Acrisol. The treatments were different levels of compaction, using bulk density as proxy – 1.3, 1.5 and 1.7 Mg m-3, and fertilizer amendments of 100% poultry manure (15 g/pot), 100% NPK fertilizer (2.89 g/pot) and 50% each of poultry manure (7.5 g/pot) and NPK fertilizer (1.45 g/pot). The highest root growth occurred in the uncompacted soil and along the periphery of the soil core. The applied soil amendments significantly increased the root penetration ratio (RPR) of both crops in relation to the control. The shoot biomass of both crops decreased with increasing soil bulk density. All the applied soil amendments significantly increased the shoot biomass of maize and soybean over the control. The magnitude of response of the crops to the soil amendments was greater in soybean than in maize.

Soil Compaction and Soil Amendments on the Growth and Biomass Yield of Maize (Zea mays L.) and Soybean (Glycine max L.)

Two factorial pot experiments arranged in a Completely Randomised Design (CRD) with three replications were carried out to assess the impact of different levels of soil compaction and fertilizer amendments on root growth and biomass yield of maize (Zea mays L.) and soybean (Glycine max L.) plants. The treatments were different rates of bulk densities – 1.3, 1.5 and 1.7 Mg m-3 and fertilizer amendments comprising 100% poultry manure (applied at 15 g/plant), 100% 15:15:15 NPK fertilizer (applied at 2.89 g/plant) and 50% rate each of poultry manure and NPK fertilizer (applied at 7.5 g poultry manure + 1.45 g NPK/plant), and control (no fertilizer amendments). Soil compaction reduced the heights of maize and soybean plants. Increasing soil compaction resulted in the accumulation of most of the root biomass in the uncompacted soil above the compacted layer. Application of soil amendments increased the relative root biomass of maize plants in the uncompacted soil, while that in the compacted soil was reduced. In the case of soybean plants, although the relative root biomass in the uncompacted soil was relatively greater than that of maize plants, application of soil amendments tended to slightly decrease the relative root biomass to that of the control. The shoot biomass of both crops decreased with increasing soil bulk density. All the applied soil amendments significantly increased the shoot biomass of maize and soybean plants over the control. The magnitude of response of the crops to the soil amendments was greater in soybean than in maize plants. Soil compaction and amendments significantly influenced root/shoot ratio of both crops. The root/shoot ratio decreased with increasing compaction from 1.3 to 1.5 Mg m-3, however, at 1.7 Mg m-3, the root/shoot ratio increased. The fertilizer amendments significantly influenced the root/shoot ratio of maize but not soybean plants. The fertilizer amendments increased the biomass of both roots and shoots, being higher in the former than in the latter. The fertilizer amendments x compaction interactions showed that the root/shoot ratio was influenced by the type of crop, and the confounding effects of factor interactions on the relative increases/decreases in shoot and root growth. Overall, soil compaction accounted for 52 to 100% of the variations in the magnitude of the measured parameters of maize plants, and 62 to 98% for soybean plants. The ideal bulk density for shoot biomass production of both crops should, therefore, be within the range of 1.3 – 1.5 Mg m-3. At soil bulk density of 1.5 Mg m-3 and above, soil amendment should be added to ameliorate the negative impact of soil compaction.