Growth, Rhizosphere Carboxylate Exudation, and Arbuscular Mycorrhizal Colonisation in Temperate Perennial Pasture Grasses Varied with Phosphorus Application

Phosphorus Application Enhances Root Traits, Root Exudation, Phosphorus Use Efficiency, and Seed Yield of Soybean Genotypes

Phosphorus (P) is a vital macronutrient required for soybean growth and development but is a finite resource in agriculture worldwide. Low inorganic P availability in soil is often a significant constraint for soybean production. However, little is known about the response of P supply on agronomic, root morphology, and physiological mechanisms of contrasting soybean genotypes at various growth stages and the possible effects of different P on soybean yield and yield components. Therefore, we conducted two concurrent experiments using the soil-filled pots with six genotypes (deep-root system: PI 647960, PI 398595, PI 561271, PI 654356; and shallow-root system: PI 595362, PI 597387) and two P levels [0 (P0) and 60 (P60) mg P kg-1 dry soil] and deep PVC columns with two genotypes (PI 561271 and PI 595362) and three P levels [0 (P0), 60 (P60), and 120 (P120) mg P kg-1 dry soil] in a temperature-controlled glasshouse. The genotype × P level interaction showed that increased higher P supply increased leaf area, shoot and root dry weights, total root length, shoot, root, and seed P concentrations and contents, P use efficiency (PUE), root exudation, and seed yield at different growth stages in both experiments. At the vegetative stage (Experiment 1), shallow-rooted genotypes with shorter life cycles had more root dry weight (39%) and total root length (38%) than deep-rooted genotypes with longer life cycles under different P levels. Genotype PI 654356 produced significantly higher (22% more) total carboxylates than PI 647960 and PI 597387 under P60 but not at P0. Total carboxylates positively correlated with root dry weight, total root length, shoot and root P contents, and physiological PUE. The deep-rooted genotypes (PI 398595, PI 647960, PI 654356, and PI 561271) had the highest PUE and root P contents. In Experiment 2, at the flowering stage, genotype PI 561271 had the greatest leaf area (202%), shoot dry weight (113%), root dry weight (143%), and root length (83%) relative to the short-duration, shallow-rooted genotype PI 595362 with external P applied (P60 and P120), with similar trends at maturity. PI 595362 had a greater proportion of carboxylates as malonate (248%), malate (58%), and total carboxylates (82%) than PI 561271 under P60 and P120 but no differences at P0. At maturity, the deep-rooted genotype PI 561271 had greater shoot, root, and seed P contents and PUE than the shallow-rooted genotype PI 595362 under increased P rates but no differences at P0. Further, the genotype PI 561271 had higher shoot (53%), root (165%), and seed yield (47%) than PI 595362 with P60 and P120 than P0. Therefore, inorganic P application enhances plant resistance to the soil P pool and maintains high soybean biomass production and seed yield.

Microbial consortium inoculant increases pasture grasses yield in low-phosphorus soil by influencing root morphology, rhizosphere carboxylate exudation and mycorrhizal colonisation

BACKGROUND

Pasture farming in south-western Australia is challenged by nutrient-poor soils. We assessed the impact of microbial consortium inoculant (MI) and rock mineral fertiliser (MF) on growth, nutrient uptake, root morphology, rhizosphere carboxylate exudation and mycorrhizal colonisation in three pasture grasses - tall fescue (Festuca arundinacea L.), veldt grass (Ehrharta calycina Sm.) and tall wheatgrass (Thinopyrum ponticum L.) grown in low-phosphorus (P) sandy soil in a glasshouse for 30 and 60 days after sowing (DAS).

RESULTS

Veldt grass produced the highest specific root length and smallest average root diameter in both growth periods, and had similar shoot weight, root surface area and fine root length (except at 30 DAS) to tall fescue. Compared with the control, MI alone or combined with MF significantly increased shoot and root biomass (except root biomass at 30 DAS), likely due to the significant increases in root surface area and fine root length. Plants supplied with MI + MF had higher shoot N and P contents than those in the MI and the control treatments at 60 DAS. Malate, citrate and trans-aconitate were the major rhizosphere carboxylates exuded at both 30 and 60 DAS. Malate exudation varied among species and treatments in both growth periods, but citrate exudation was consistently higher in the low-P treatments (control and MI) than the MF and MI + MF treatments.

CONCLUSION

Microbial consortium inoculant can positively influence pasture production in low-P soil by increasing root surface area and fine root length, whereas exudation of nutrient-mobilising carboxylates (citrate) is dependent more on soil P supply than microbial consortium inoculant. © 2021 Society of Chemical Industry.

In situ Root Phenotypes of Cotton Seedlings Under Phosphorus Stress Revealed Through RhizoPot

Phosphorus (P) deficiency is a common challenge in crop production because of its poor mobility through the soil. The root system plays a significant role in P absorption from the soil and is the initial indicator of low P levels. However, the phenotypic dynamics and longevity of cotton roots under P stress remain unknown. In this study, RhizoPot, an improvised in situ root observation device, was used to monitor the dynamics of root phenotypes of cotton seedlings under P-deficient (PD) and P-replete (PR) conditions. Low P stress reduced P absorption and accumulation in the roots, leading to low dry weight accumulation. Cotton seedlings responded to low P stress by increasing the number of lateral roots, specific root length, branch density, root length density, and length of root hairs. Additionally, the life span of root hairs was prolonged. Low P stress also reduced the average diameter of roots, promoted root extension, expanded the root coverage area, and increased the range of P acquisition. Principal component analysis revealed that the net root growth rate, root length density, root dry weight, P absorption efficiency, average root hair length, and taproot daily growth significantly influenced the cotton root architecture. Collectively, these results show that low P stress reduces the net growth rate of cotton seedling roots and restricts plant growth. Plants respond to P deficiency by extending the life span of root hairs and increasing specific root length and lateral root branch density. This change in root system architecture improves the adaptability of plants to low P conditions. The findings of this study may guide the selection of cotton varieties with efficient P utilization.

Metabolic Alterations in Pisum sativum Roots during Plant Growth and Arbuscular Mycorrhiza Development

Intensive exchange of nutrients is a crucial part of the complex interaction between a host plant and fungi within arbuscular mycorrhizal (AM) symbiosis. For the first time, the present study demonstrates how inoculation with AMF Rhizophagus irregularis affects the pea (Pisum sativum L.) root metabolism at key stages of plant development. These correspond to days 21 (vegetation), 42 (flowering initiation), and 56 (fruiting-green pod). Metabolome profiling was carried out by means of a state-of-the-art GC-MS technique. The content shifts revealed include lipophilic compounds, sugars, carboxylates, and amino acids. The metabolic alterations were principally dependent on the stage of plant development but were also affected by the development of AM fungi, a fact which highlights interaction between symbiotic partners. The comparison of the present data with the results of leaf metabolome profiling earlier obtained did not reveal common signatures of metabolic response to mycorrhization in leaves and roots. We supposed that the feedback for the development and symbiotic interaction on the part of the supraorganismic system (root + AM fungi) was the cause of the difference between the metabolic profile shift in leaf and root cells that our examination revealed. New investigations are required to expand our knowledge of metabolome plasticity of the whole organism and/or system of organisms, and such results might be put to use for the intensification of sustainable agriculture.