Role of mycorrhizas and root exudates in plant uptake of soil nutrients (calcium, iron, magnesium, and potassium): has the puzzle been completely solved?

Mitigating secondary salinization in grapes: long-term benefits of biochar and cow dung

Secondary salinization of soil seriously hinders the healthy cultivation of facility grapes. Biochar has been shown to mitigate the negative effects of saline stress on plants. However, the long-term response mechanism between the soil's key physicochemical properties, ion concentration, and enzyme activity and the physiological resistance of facility grape plants to biochar combined with cow dung application to alleviate the soil secondary salinization stress remains unclear. In this study, a field experiment was set up once in September 2021 with five different treatments, including no amendments. which was used as the blank control (CK), and application of biochar (10 t·ha-1, T1), cow dung (30 t·ha-1, T2), biochar mixed with cow dung (5 t·ha-1+15 t·ha-1, T3), and biochar mixed with cow dung (10 t·ha-1+30 t·ha-1, T4), respectively. The results showed that compared with the CK treatment, application treatments significantly reduced soil total salt(TS) content and the electrical conductivity(EC) value; increased soil water-stable aggregates and nutrient content; stimulated an increase in soil urease (S-UE), sucrose (S-SC) and phosphatase(S-ALP)activities; and changed soil exchangeable calcium and magnesium ion concentrations. Among the treatments, the T4 treatment reduced TS and EC by 73.03% and 61.11%, respectively. Biochar combined with cow dung significantly increased chlorophyll content and reduced malondialdehyde content (MDA), the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) in grape leaves. The T4 treatment decreased MDA, SOD, POD, and CAT by 54.59%, 40.14%, 44.28%, and 70.17% compared with the CK treatment, respectively. Correlation analysis showed that the balance of soil exchangeable calcium and magnesium ions and the stability of soil aggregate structure were the key factors in alleviating soil secondary salinization stress. In conclusion, biochar combined with cow dung application can alleviate the oxidative stress response of grape plants and improve the quality of grapes by improving the structure of soil water-stable aggregates, coordinating the concentration of soil exchangeable calcium and magnesium ions, and stimulating soil enzyme activity.

Significant Enrichment of Potential Pathogenic Fungi in Soil Mediated by Flavonoids, Phenolic Acids, and Organic Acids

It is well established that root exudates play a crucial role in shaping the assembly of plant rhizosphere microbial communities. Nonetheless, our understanding of how different types of exudates influence the abundance of potential pathogens in soil remains insufficient. Investigating the effects of root exudates on soil-dwelling pathogenic fungi is imperative for a comprehensive understanding of plant-fungal interactions within soil ecosystems and for maintaining soil health. This study aimed to elucidate the effects of the principal components of root exudates-flavonoids (FLA), phenolic acids (PA), and organic acids (OA)-on soil microbial communities and soil properties, as well as to investigate their mechanisms of action on soil potential pathogenic fungi. The results demonstrated that the addition of these components significantly modified the composition and diversity of soil microbial communities, with OA treatment notably altering the composition of dominant microbial taxa. Furthermore, the introduction of these substances facilitated the proliferation of saprophytic fungi. Additionally, the incorporation of flavonoids, phenolic acids, and organic acids led to an increased abundance of potential pathogenic fungi in the soil, particularly in the FLA and PA treatments. It was observed that the addition of these substances enhanced soil fertility, pH, and antioxidant enzyme activity. Specifically, FLA and PA treatments reduced the abundance of dominant microbial taxa, whereas OA treatment altered the composition of these taxa. These findings suggest that the inclusion of flavonoids, phenolic acids, and organic acids could potentially augment the enrichment of soil potential pathogenic fungi by modulating soil properties and enzymatic activities. These results offer valuable insights into the interactions between plants and fungal communities in soil ecosystems and provide a scientific foundation for the management and maintenance of soil health.

Root Exudates in Soilless Culture Conditions

Root metabolite secretion plays a critical role in increasing nutrient acquisition, allelopathy, and shaping the root-associated microbiome. While much research has explored the ecological functions of root exudates, their relevance to horticultural practices, particularly soilless cultivation, remains underexplored. Steering root exudation could help growers enhance the effectiveness of plant growth-promoting bacteria. This review summarizes current knowledge on root exudation in soilless systems, examining its process and discussing environmental influences in the context of soilless cultivation. Plants in soilless systems exhibit higher total carbon exudation rates compared to those in natural soils, with exudation profiles varying across systems and species. Root exudation decreases with plant age, with most environmental adaptations occurring during early growth stages. Several environmental factors unique to soilless systems affect root exudation. For instance, nutrient availability has a major impact on root exudation. Light intensity reduces exudation rates, and light quality influences exudation profiles in a species- and environment-dependent manner. Elevated CO2 and temperature increase exudation. Factors related to the hydroponic nutrient solution and growing media composition remain insufficiently understood, necessitating further research.

Light and substrate composition control root exudation rates at the initial stages of soilless lettuce cultivation

Plant root exudation is an inherent metabolic process that enhances various functions of the root system like the mobilization of nutrients and interactions with surrounding microbial communities. In soilless crop production, roots are temporally submerged in a nutrient solution affecting the root exudation process. In this study, we asked whether root exudation in soilless cultures is affected by culturing method and substrate composition, important factors determining the root microbial ecosystem. Exploration of different growth conditions revealed that the effect of light quality depended on the substrate used. The impact of light quality and substrate was assessed by growing soilless lettuce in 100 % red light (660 nm), 100 % blue light (450 nm), and white light (full-light spectrum) in deep flow culture, or in 100 % perlite, 100 % potting soil, or mixtures of both growing media. Root exudates were collected at different time points after transplanting. The root exudation rate declined with plant age in all culturing conditions, underscoring its importance during the early stages of development. The total carbon root exudation rate was influenced by light conditions and substrate composition at the earliest timepoint of the culture but not at later growth stages. The total carbohydrate exudation rate was significantly higher under pure blue and red light compared to white light. The impact of light depended on the presence of perlite in the substrate. The total phenolic compound exudation rate was most strongly influenced by the substrate composition and reached the highest level in either pure potting soil or pure perlite. Light and growing media influence the exudation rate at the early stage, suggesting that exudation is an adaptive process of the soilless lettuce culture.

Phytoremediation: Sustainable Approach for Heavy Metal Pollution

Rapid industrialization, mining, and other anthropogenic activities have poisoned our environment with heavy metals, negatively impacting all forms of life. Heavy metal pollution causes physiological and neurological disorders, as heavy metals are endocrine disrupters, carcinogenic, and teratogenic. Therefore, it becomes mandatory to address the challenge of heavy metal contamination on a global scale. Physical and chemical approaches have been employed for pollutant removal and detoxification, but these methods cannot be adopted universally due to high cost, labor intensiveness, and possible negative impact on natural microflora. Phytoremediation is one of the preferred and safest approaches for environmental management due to its high efficiency and low cost of investment. The plant can uptake the pollutants and heavy metals from water and soil through an intense root network via rhizofiltration and process via phytostabilization, phytovolatilization, and accumulation. At a cellular level, the phytoremediation process relies on natural mechanisms of plant cells, e.g., absorption, transpiration, intracellular storage, and accumulation to counter the detrimental effects of pollutants. It is widely accepted because of its novelty, low cost, and high efficiency; however, the process is comparatively slower. In addition, plants can store pollutants for a long time but again become a challenge at the end of the life cycle. The current review summarizes phytoremediation as a potential cure for heavy metal pollutants, released from natural as well as anthropogenic sources. It will provide insight into the advancement and evolution of advanced techniques like nanoremediation that can improve the rate of phytoremediation, along with making it sustainable, cost-effective, and economically viable.

Phosphatases: Decoding the Role of Mycorrhizal Fungi in Plant Disease Resistance

Mycorrhizal fungi, a category of fungi that form symbiotic relationships with plant roots, can participate in the induction of plant disease resistance by secreting phosphatase enzymes. While extensive research exists on the mechanisms by which mycorrhizal fungi induce resistance, the specific contributions of phosphatases to these processes require further elucidation. This article reviews the spectrum of mycorrhizal fungi-induced resistance mechanisms and synthesizes a current understanding of how phosphatases mediate these effects, such as the induction of defense structures in plants, the negative regulation of plant immune responses, and the limitation of pathogen invasion and spread. It explores the role of phosphatases in the resistance induced by mycorrhizal fungi and provides prospective future research directions in this field.

Not only phosphorus: dauciform roots can also influence aboveground biomass through root morphological traits and metal cation concentrations

Background

Phosphorus in the soil is mostly too insoluble for plants to utilize, resulting in inhibited aboveground biomass, while Carex can maintain their aboveground biomass through the presence of dauciform roots. However, dauciform roots lead to both morphological and physiological changes in the root system, making their primary mechanism unclear.

Methods

A greenhouse experiment was conducted on three Carex species, in which Al-P, Ca-P, Fe-P, and K-P were employed as sole phosphorus sources. The plants were harvested and assessed after 30, 60 and 90 days.

Results

(1) The density of dauciform roots was positively correlated with root length and specific root length, positively influencing aboveground biomass at all three stages. (2) The aboveground phosphorus concentration showed a negative correlation with both dauciform root density and aboveground biomass in the first two stages, which became positive in the third stage. (3) Aboveground biomass correlated negatively with the aboveground Al concentration, and positively with Ca and Fe concentration (except Al-P). (4) Root morphological traits emerged as critical factors in dauciform roots' promotion of aboveground biomass accumulation.

Conclusion

Despite the difference among insoluble phosphorus, dauciform roots have a contributing effect on aboveground growth status over time, mainly by regulating root morphological traits. This study contributes to our understanding of short-term variation in dauciform roots and their regulatory mechanisms that enhance Carex aboveground biomass under low available phosphorus conditions.

Phylogenetic diversity drives soil multifunctionality in arid montane forest-grassland transition zone

Exploring plant diversity and ecosystem functioning in different dimensions is crucial to preserve ecological balance and advance ecosystem conservation efforts. Ecosystem transition zones serve as vital connectors linking two distinct ecosystems, yet the impact of various aspects of plant diversity (including taxonomic, functional, and phylogenetic diversity) on soil multifunctionality in these zones remains to be clarified. This study focuses on the forest-grassland transition zone in the mountains on the northern slopes of the Tianshan Mountains, and investigates vegetation and soil characteristics from forest ecosystems to grassland ecosystems to characterize plant diversity and soil functioning, as well as the driving role of plant diversity in different dimensions. In the montane forest-grassland transition zone, urease (URE) and total nitrogen (TN) play a major role in regulating plant diversity by affecting the soil nutrient cycle. Phylogenetic diversity was found to be the strongest driver of soil multifunctionality, followed by functional diversity, while taxonomic diversity was the least important driver. Diverse species were shown to play an important role in maintaining soil multifunctionality in the transition zone, especially distantly related species with high phylogeny. The study of multidimensional plant diversity and soil multifunctionality in the montane forest-grassland transition zone can help to balance the relationship between these two elements, which is crucial in areas where the ecosystem overlaps, and the application of the findings can support sustainable development in these regions.

Modulation of potassium transport to increase abiotic stress tolerance in plants

Potassium is the major cation responsible for the maintenance of the ionic environment in plant cells. Stable potassium homeostasis is indispensable for virtually all cellular functions, and, concomitantly, viability. Plants must cope with environmental changes such as salt or drought that can alter ionic homeostasis. Potassium fluxes are required to regulate the essential process of transpiration, so a constraint on potassium transport may also affect the plant's response to heat, cold, or oxidative stress. Sequencing data and functional analyses have defined the potassium channels and transporters present in the genomes of different species, so we know most of the proteins directly participating in potassium homeostasis. The still unanswered questions are how these proteins are regulated and the nature of potential cross-talk with other signaling pathways controlling growth, development, and stress responses. As we gain knowledge regarding the molecular mechanisms underlying regulation of potassium homeostasis in plants, we can take advantage of this information to increase the efficiency of potassium transport and generate plants with enhanced tolerance to abiotic stress through genetic engineering or new breeding techniques. Here, we review current knowledge of how modifying genes related to potassium homeostasis in plants affect abiotic stress tolerance at the whole plant level.

Continued Organic Fertigation after Basal Manure Application Does Not Impact Soil Fungal Communities, Tomato Yield or Soil Fertility

There is currently a limited understanding of the complex response of fungal microbiota diversity to organic fertigation. In this work, a 2-year field trial with organic tomato crops in a soil previously amended with fresh sheep manure was conducted. Two hypotheses were compared: (i) fertigation with organic liquid fertilizers versus (ii) irrigation with water. At the end of both years, soils were analyzed for physical-chemical parameters and mycobiome variables. Plate culture and DNA metabarcoding methods were performed in order to obtain a detailed understanding of soil fungal communities. Fertigation did not increase any of the physical-chemical parameters. Concerning soil fungal communities, differences were only found regarding the identification of biomarkers. The class Leotiomycetes and the family Myxotrichaceae were identified as biomarkers in the soil fungal community analyzed by means of DNA metabarcoding of the "fertigation" treatment at the end of Year 1. The Mortierella genus was detected as a biomarker in the "water" treatment, and Mucor was identified in the "fertigation" treatment in the cultivable soil fungi at the end of Year 2. In both years, tomato yield and fruit quality did not consistently differ between treatments, despite the high cost of the fertilizers added through fertigation.