Differential Effects of Exogenous Glomalin-Related Soil Proteins on Plant Growth of Trifoliate Orange Through Regulating Auxin Changes

Effects of AMF inoculation on the growth, photosynthesis and root physiological morphology of root-pruned Robinia pseudoacacia seedlings

Root pruning hinders the absorption and utilization of nutrients and water by seedlings in the short term. Arbuscular mycorrhizal fungi (AMF) are an important source of nutrient and water for seedlings except for the root system. However, the mechanism by which AMF affect the physiological growth of seedlings after root pruning has rarely been studied. In this study, a pot experiment was conducted through a three-compartment partition system to clarify the effects of Funneliformis mosseae (F. mosseae) strain BGC XJ07A on the physiological growth of root-pruned Robinia pseudoacacia seedlings. Five root pruning treatments (zero, one-fifth, one-fourth, one-third and one-half of the taproot length were removed) were applied to noninoculated seedlings and those inoculated with F. mosseae. The results showed that the presence of F. mosseae significantly increased the shoot and root biomasses, leaf photosynthetic rate, stomatal conductance and transpiration rate. The root projected area, root surface area, average root diameter, root density, root volume and number of root tips of the inoculated seedlings were higher than those without inoculation in all root pruning treatments. The root cytokinin, gibberellins and indole-3-acetic acid concentrations, but root abscisic acid concentration, were higher than those measured in the absence of inoculation in all root pruning treatments. Moreover, the changes in the root endogenous hormone concentrations of the seedlings were closely related to the root morphological development and seedling biomass. The AMF increased the soil available nitrogen, soil available phosphorus, soil available potassium and soil organic matter concentrations compared with the noninoculated treatment. These results indicate that AMF can alleviate the adverse effects of root pruning on the physiological growth of R. pseudoacacia and soil properties, and can provide a basis for AMF application to forest cultivation and the sustainable development of forest ecosystems.

Exogenous Easily Extractable Glomalin-Related Soil Protein Stimulates Plant Growth by Regulating Tonoplast Intrinsic Protein Expression in Lemon

Arbuscular mycorrhizal fungi (AMF) have the function of promoting water absorption for the host plant, whereas the role of easily extractable glomalin-related soil protein (GRSP), an N-linked glycoprotein secreted by AMF hyphae and spores, is unexplored for citrus plants. In this study, the effects on plant growth performance, root system characteristics, and leaf water status, along with the changes of mineral element content and relative expressions of tonoplast intrinsic protein (TIP) genes in lemon (Citrus limon L.) seedlings, were investigated under varying strengths of exogenous EE-GRSP application under potted conditions. The results showed that 1/2, 3/4, and full-strength exogenous EE-GRSP significantly promoted plant growth performance, as well as increased the biomass and root system architecture traits including root surface area, volume, taproot length, and lateral root numbers of lemon seedlings. The four different strengths of exogenous GRSP displayed differential effects on mineral element content: notably increased the content of phosphorus (P) and iron (Fe) in both leaves and roots, as well as magnesium (Mg) and zinc (Zn) content in the roots, but dramatically decreased the content of calcium (Ca) and manganese (Mn) in the roots, as well as Zn and Mn in the leaves. Exogenous EE-GRSP improved leaf water status, manifesting as decreases in leaf water potential, which was associated with the upregulated expressions of tonoplast intrinsic proteins (TIPs), including ClTIP1;1, ClTIP1;2, ClTIP1;3, ClTIP2;1, ClTIP2;2, ClTIP4;1, and ClTIP5;1 both in leaves and roots, and TIPs expressions exhibited diverse responses to EE-GRSP application. It was concluded that exogenous EE-GRSP exhibited differential responses on plant growth performance, which was related to its strength, and the effects were associated with nutrient concentration and root morphology, especially in the improvement in water status related to TIPs expressions. Therefore, EE-GRSP can be used as a biological promoter in plant cultivation, especially in citrus.

The visualized knowledge map and hot topic analysis of glomalin-related soil proteins in the carbon field based on Citespace

Arbuscular mycorrhizal fungi (AMF) in the soil have many positive effects on growth, nutrient acquisition, and stress tolerance of host plants, as well as soil fertility, soil structure, and soil ecology. Glomalin-related soil proteins (GRSP) are a mixture of humic substances and heat-stable glycoproteins, primarily of AMF origin. GRSP are as an important component of soil organic carbon (C) pools, which can stabilize and sequestrate C, thus reducing soil C emissions for slowing down global warming. Based on the CiteSpace software and the core collection of Web of Science as the database, this study made a visual analysis of GRSP’s literature in the C field published from 1999 to 2022, including the number of publications, countries, institutions, co-cited literature, keywords, top cited papers, etc. The study regarding the GRSP in the C field could be divided into the initial stage (1999–2009), the steady stage (2010–2018), and the explosive stage (2019–2022). The Chinese Academy of Sciences is the organization with the most publications, and the United States, China, and India are the three leading nations in the C field of GRSP. However, there was little collaboration among the participating countries and the study’s institutions. The focus of the research has shifted from the composition and content of GRSP in C to the question of whether C in GRSP affects soil properties. Future research was also prospected.

Graphical Abstract

Serendipita indica promotes P acquisition and growth in tea seedlings under P deficit conditions by increasing cytokinins and indoleacetic acid and phosphate transporter gene expression

The culturable endophytic fungus Serendipita indica has many beneficial effects on plants, but whether and how it affects physiological activities and phosphorus (P) acquisition of tea seedlings at low P levels is unclear. The objective of this study was to analyze the effects of inoculation with S. indica on growth, gas exchange, chlorophyll fluorescence, auxins, cytokinins, P levels, and expressions of two phosphate transporter (PT) genes in leaves of tea (Camellia sinensis L. cv. Fudingdabaicha) seedlings grown at 0.5 μM (P_0.5) and 50 μM (P₅₀) P levels. Sixteen weeks after the inoculation, S. indica colonized roots of tea seedlings, with root fungal colonization rates reaching 62.18% and 81.34% at P_0.5 and P₅₀ levels, respectively. Although plant growth behavior, leaf gas exchange, chlorophyll values, nitrogen balance index, and chlorophyll fluorescence parameters of tea seedlings were suppressed at P_0.5 versus P₅₀ levels, inoculation of S. indica mitigated the negative effects to some extent, along with more prominent promotion at P_0.5 levels. S. indica inoculation significantly increased leaf P and indoleacetic acid concentrations at P_0.5 and P₅₀ levels and leaf isopentenyladenine, dihydrozeatin, and transzeatin concentrations at P_0.5 levels, coupled with the reduction of indolebutyric acid at P₅₀ levels. Inoculation of S. indica up-regulated the relative expression of leaf CsPT1 at P_0.5 and P₅₀ levels and CsPT4 at P_0.5 levels. It is concluded that S. indica promoted P acquisition and growth in tea seedlings under P deficit conditions by increasing cytokinins and indoleacetic acid and CsPT1 and CsPT4 expression.

Extraradical Mycorrhizal Hyphae Promote Soil Carbon Sequestration through Difficultly Extractable Glomalin-Related Soil Protein in Response to Soil Water Stress

Soil water stress (WS) affects the decomposition of soil organic carbon (SOC) and carbon (C) emissions. Glomalin, released by arbuscular mycorrhizal fungi into soil that has been defined as glomalin-related soil protein (GRSP), is an important pool of SOC, with hydrophobic characteristics. We hypothesized that mycorrhizal fungi have a positive effect on SOC pools under soil WS for C sequestration in GRSP secreted by extraradical mycorrhizal hyphae. A microsystem was used to establish a root chamber (co-existence of roots and extraradical mycorrhizal hyphae) and a hyphal chamber (the presence of extraradical mycorrhizal hyphae) to study changes in plant growth, leaf water potential, soil aggregate stability, SOC, GRSP, C concentrations in GRSP (C_GRSP), and the contribution of C_GRSP to SOC after inoculating Rhizophagus intraradices with trifoliate orange (Poncirus trifoliata) in the root chamber under adequate water (AW) and WS. Inoculation with R. intraradices alleviated negative effects on leaf water potential and plant growth after 7 weeks of WS. Soil WS decreased SOC and mean weight diameter (MWD), while AMF inoculation led to an increase in SOC and MWD in both chambers, with the most prominent increase in the hyphal chamber under WS. The C concentration in easily extractable GRSP (EE-GRSP) and difficultly extractable GRSP (DE-GRSP) was 7.32 - 12.57 and 24.90 - 32.60 mg C/g GRSP, respectively. WS reduced C_GRSP, while AMF mitigated the reduction. Extraradical mycorrhizal hyphae increased GRSP production and C_GRSP, along with a more prominent increase in DE-GRSP under WS than under AW. Extraradical mycorrhizal hyphae increased the contribution of C_DE-GRSP to SOC only under WS. C_EE-GRSP and C_DE-GRSP were significantly positively correlated with SOC and MWD. It is concluded that extraradical mycorrhizal hyphae prominently promoted C sequestration of recalcitrant DE-GRSP under soil WS, thus contributing more organic C accumulation and preservation in aggregates and soil C pool.

Symbiotic Fungi Alter the Acquisition of Phosphorus in Camellia oleifera through Regulating Root Architecture, Plant Phosphate Transporter Gene Expressions and Soil Phosphatase Activities

Plant roots can be colonized by many symbiotic fungi, whereas it is unclear whether and how symbiotic fungi including arbuscular mycorrhizal fungi and endophytic fungi promote phosphorus (P) uptake in Camellia oleifera plants. The objective of the present study was to analyze the effect of inoculation with a culturable endophytic fungus (Piriformospora indica), three arbuscular mycorrhizal fungi (Funneliformis mosseae, Diversispora versiformis, and Rhizophagus intraradices), and mixture of F. mosseae, D. versiformis and R. intraradices on plant growth, root architecture, soil Olsen-P, soil phosphatase activities, leaf and root P concentrations, and phosphate transporter gene expressions, in order to explore the potential and mechanism of these symbiotic fungi on P acquisition. All the symbiotic fungi colonized roots of C. oleifera after 16 weeks, with P. indica showing the best effect on fungal colonization. All the symbiotic fungi significantly increased acid, neutral, and total phosphatase activities in the soil, accompanied with an elevation of soil Olsen-P, of which P. indica presented the best effect. All symbiotic fungal treatments, except D. versiformis, significantly promoted plant growth, coupled with an increase in root total length, area, and volume. Symbiotic fungi almost up-regulated root CoPHO1-3 expressions as well as leaf CoPHO1-1, CoPHO1-3, and CoPHT1;4 expressions. Correlation analysis showed that P concentrations in leaves and roots were significantly positively correlated with root morphological variables (length, volume, and surface area) and soil acid, neutral and total phosphatase activities. It is concluded that symbiotic fungi, especially P. indica, played an important role in P uptake of C. oleifera plants through regulating root architecture, part plant phosphate transporter gene expressions and soil phosphatase activities.