Exudation Rate Research Articles

Root exudation patterns of contrasting rice (Oryza sativa L.) lines in response to P limitation

Main conclusionRice exudation patterns changed in response to P deficiency. Higher exudation rates were associated with lower biomass production. Total carboxylate exudation rates mostly decreased under P-limiting conditions.Within the rhizosphere, root exudates are believed to play an important role in plant phosphorus (P) acquisition. This could be particularly beneficial in upland rice production where P is often limited. However, knowledge gaps remain on how P deficiency shapes quality and quantity of root exudation in upland rice genotypes. We therefore investigated growth, plant P uptake, and root exudation patterns of two rice genotypes differing in P efficiency in semi-hydroponics at two P levels (low P = 1 µM, adequate P = 100 µM). Root exudates were collected hydroponically 28 and 40 days after germination to analyze total carbon (C), carbohydrates, amino acids, phenolic compounds spectrophotometrically and carboxylates using a targeted LC–MS approach. Despite their reported role in P solubilization, we observed that carboxylate exudation rates per unit root surface area were not increased under P deficiency. In contrast, exudation rates of total C, carbohydrates, amino acids and phenolics were mostly enhanced in response to low P supply. Overall, higher exudation rates were associated with lower biomass production in the P-inefficient genotype Nerica4, whereas the larger root system with lower C investment (per unit root surface area) in root exudates of the P-efficient DJ123 allowed for better plant growth under P deficiency. Our results reveal new insights into genotype-specific resource allocation in rice under P-limiting conditions that warrant follow-up research including more genotypes.

Differential Drought Responses of Soybean Genotypes in Relation to Photosynthesis and Growth-Yield Attributes.

Water scarcity leads to significant ecological challenges for global farming production. Sustainable agriculture depends on developing strategies to overcome the impacts of drought on important crops, including soybean. In this present study, seven promising soybean genotypes were evaluated for their drought tolerance potential by exposing them to water deficit conditions. The control group was maintained at 100% field capacity (FC), while the drought-treated group was maintained at 50% FC on a volume/weight basis. This treatment was applied at the second trifoliate leaf stage and continued until maturity. Our results demonstrated that water shortage exerted negative impacts on soybean phenotypic traits, physiological and biochemical mechanisms, and yield output in comparison with normal conditions. Our results showed that genotype G00001 exhibited the highest leaf area plant-1 (483.70 cm2), photosynthetic attributes like stomatal conductance (gs) (0.15 mol H2O m-2 s-1) and photosynthetic rate (Pn) (13.73 μmol CO2 m-2 s-1), and xylem exudation rate (0.25 g h-1) under drought conditions. The G00001 genotype showed greater leaf greenness by preserving photosynthetic pigments (total chlorophylls (Chls) and carotenoids; 4.23 and 7.34 mg g-1 FW, respectively) in response to drought conditions. Soybean plants accumulated high levels of stress indicators like proline and malondialdehyde when subjected to drought stress. However, genotype G00001 displayed lower levels of proline (4.49 μg g-1 FW) and malondialdehyde (3.70 μmol g-1 FW), indicating that this genotype suffered from less oxidative stress induced by drought stress compared to the other investigated soybean genotypes. Eventually, the G00001 genotype had a greater yield in terms of seeds pod-1 (SP) (1.90) and 100-seed weight (HSW) (14.60 g) under drought conditions. On the other hand, BD2333 exhibited the largest decrease in plant height (37.10%), pod number plant-1 (85.90%), SP (56.20%), HSW (54.20%), gs (90.50%), Pn (71.00%), transpiration rate (59.40%), relative water content (34.40%), Chl a (79.50%), total Chls (72.70%), and carotenoids (56.70%), along with the maximum increase in water saturation deficit (290.40%) and malondialdehyde content (280.30%) under drought compared to control conditions, indicating its higher sensitivity to drought stress. Our findings suggest that G00001 is a promising candidate to consider for field trials and further evaluation of its molecular signature may help breeding other elite cultivars to develop drought-tolerant, high-yielding soybean varieties.

Effects of fasting on golden pompano Trachinotus ovatus: Physiological and biochemical responses

In practice, golden pompano (Trachinotus ovatus) reared in offshore cages may experience short-term fasting during extreme weather conditions, yet their physiological and biochemical responses remain poorly understood. To investigate the responses of this species to fasting, golden pompano weighing 138.0 ± 2.1 g were deprived of food for 0, 7, 14, 21 and 28 days, followed by assessments of body mass, somatic parameters, proximate composition, muscle glycogen, intestinal digestive enzymes, muscle amino acid and fatty acid profiles, nutritional value, and muscle texture and water holding capacity. Lower condition factor, hepatosomatic index, viscerosomatic index, hepatic glycogen, and intestinal activities of amylase, lipase and trypsin were found in the fasted fish than in the non-fasted fish, while a sharp decline in these parameters occurred on the first week of fasting. Fresh mass, dry mass, whole body and muscle contents of crude protein and lipid tended to decrease with prolonged fasting, while no statistical differences were found in these parameters between fish fasted for 7 days and the non-fasted fish. Furthermore, the decline rate of whole body crude lipid was consistently higher than that of whole body crude protein throughout the different stages of the 28-day fasting period, with the exception of the second week of fasting. No statistical differences were found in the total essential amino acids (∑EAA), non-essential amino acids (∑NEAA), ratio of ∑EAA to∑NEAA, chemical score, amino acid score, and essential amino acid index in the fasted fish compared to the non-fasted fish of group 0d. Fasting altered the muscle profile of SFA, MUFA and PUFA, sometimes reducing muscle springiness (groups 7d and 14d) and hardness (group 21d). Compared to non-fasted fish, fish fasted for 7 and 14 days exhibited statistically lower or equal drip loss, water loss rate, storage losses, and frozen exudate rate, whereas higher cooked meat rate. The above results indicate that during the 28-day fasting period, the visceral fat and hepatic glycogen are initially metabolized, followed by body proteins and lipids, to maintain the normal metabolism in fasted fish. Fasting has beneficial effects on the nutritional value of amino acids and fatty acids in muscle, although it modifies the muscle SFA, MUFA and PUFA composition and sometimes has negative effects on muscle texture. Considering the balance between body weight loss and flesh quality improvement, the duration of fasting for cultured golden pompano prior to harvesting should not exceed 14 days.

Two grasses differ in their absorptive root physiological traits and rooting depth under drought in an alpine steppe.

Absorptive root traits play important roles in acquisition of water and nutrients from soil by plants. Despite numerous reports on the changes in species dominance under long-term drought in grassland community, few studies have specifically investigated absorptive root traits of these dominant species in grasslands, especially in the alpine grasslands. Here, two grass species (Leymus secalinus and Stipa purpurea) differing in their responses to drought were selected from an alpine steppe. A series of absorptive root traits were examined under drought in a 3-year glasshouse experiment. We found that drought had no effects on root morphological and architectural traits, whereas root physiological traits and rooting depth differed in their responses to drought. Specifically, drought significantly reduced root respiration and enhanced organ carbon (C) exudation rate, carboxylate exudation rate, acid phosphatase activity and rooting depth of L. secalinus. Particularly, L. secalinus released more citrate into the rhizosphere under drought than S. purpurea. In contrast, these root traits of S. purpurea remained relatively unchanged in response to the drought. These differential responses would render L. secalinus more competitive in acquisition of nutrients and water, thus contributing to its dominance in the community under drought. Moreover, root respiration was negatively correlated with organic C exudation rate, carboxylate exudation rate and acid phosphatase activity, indicating a tradeoff between root respiration and root exudates to acquire nutrients and water by optimizing C allocation under drought. Additionally, all root traits exhibited two independent dimensions in root economic space (RES) for both species under drought. These results indicate that the plant species with great capacity to acquire water and nutrients in soil by optimizing C allocation under drought will be dominant in the community of the alpine grasslands. These findings provide an important insight into species re-ordering under drought on the Tibetan Plateau.

Different patterns of fine-root exudation rates along soil depth of Pinus densiflora, Chamaecyparis obtusa, and Cryptomeria japonica in coniferous forests

Tree fine-root exudation and organic carbon compounds in the soil affect physiological functions through degradation by microorganisms around the roots and the enhancement of allelopathic effects on invasion attempts by other plant species. However, the underlying mechanism of fine-root action in vertically heterogeneous resource-distribution patterns along the soil profile is little known. Here, we quantified root exudation and its morphological and chemical traits in the soil layers down to 100-cm depth for three conifer species, Pinus densiflora (ectomycorrhiza), Chamaecyparis obtusa, and Cryptomeria japonica (arbuscular mycorrhiza), in a cool temperate Japanese forest. By using glass filter-trap method, root exudation rates in all three species varied with soil depth in a species dependent pattern. Specifically, the root exudation rate of P. densiflora was significantly higher in the middle soil layer, and lower in the topsoil layer, whereas the exudation rates significantly decreased in C. japonica and did not vary in C. obtusa along soil depth. Exudation strongly correlated with variation in root traits in C. obtusa and C. japonica but not in P. densiflora. These findings suggest that differences in exudation patterns among tree species are likely compensated for by structural modifications in fine roots in response to soil depth. In addition, the traits with mycorrhizal types might be related to adequate root exudation and enhanced soil-nutrient acquisition. Distinct differences among species in exudation, associated with vertical root distribution, will increase our understanding of root survival strategies for nutrient acquisition and carbon sequestration in forest tree species.

Nitrogen fertilization affected microbial carbon use efficiency and microbial resource limitations via root exudates

Root exudation and its mediated nutrient cycling process driven by nitrogen (N) fertilizer can stimulate the plant availability of various soil nutrients, which is essential for microbial nutrient acquisition. However, the response of soil microbial resource limitations to long-term N fertilizer application rates in greenhouse vegetable systems has rarely been investigated. Therefore, we selected a 15-year greenhouse vegetable system, and investigated how N fertilizer application amount impacts on root carbon and nitrogen exudation rates, microbial resource limitations and microbial carbon use efficiency (CUEST). Four N treatments were determined: high (N3), medium (N2), low (N1), and a control without N fertilization (N0). Compared to the control (N0), the results showed that the root C exudation rates decreased significantly by 42.9 %, 57.3 % and 33.6 %, and the root N exudation rates decreased significantly by 29.7 %, 42.6 %, and 24.1 % under N1, N2, and N3 treatments, respectively. Interactions between fertilizer and plant roots altered microbial C, N, P limitations and CUEST; Microbial C and N/P limitations were positively correlated with root C and N exudation rates, negatively correlated with microbial CUEST. Random Forest analysis revealed that the root C and N exudation rates were key factors for soil microbial resource limitations and microbial CUEST. Through the structural equation model (SEM) analysis, soil NH4+ content had significant direct effects on the root exudation rates after long-term N fertilizer application. An increase in root exudation rates led to enhanced microbial resource limitations in the rhizosphere soils, potentially due to increased competition. This enhancement may reduce microbial carbon use efficiency (CUE), that is, microbial C turnover, thereby reducing soil C sequestration. Overall, this study highlights the critical role of root exudation rates in microbial resource limitations and CUE changes in plant-soil systems, and further improves our understanding of plant-microbial interactions.

Role of phytoplankton composition on exudation of dissolved organic carbon in the Bay of Bengal

Phytoplankton in the marine environment exudates part of the primary production as dissolved organic carbon (DOC) into the surrounding waters. The rate of exudation of DOC is depended on the hydrographic condition, nutrient availability, phytoplankton composition, and their size structure. To examine this, samples were collected from the coastal and offshore regions where different hydrographic conditions exists in the Bay of Bengal. The coastal waters were relatively low saline, rich in inorganic nutrients, high phytoplankton biomass (Chl-a) and primary production in the coastal compared to offshore regions. The photic zone integrated Chl-a displayed insignificant difference between coastal and offshore regions whereas higher photic zone integrated primary production was observed in the former than latter region. Dominance of microplankton was observed in the coastal waters associating with high inorganic nitrogen concentrations, in contrast, picoplankton dominated in the offshore region associating with low inorganic nitrogen but high organic nitrogen concentrations. Due to high surface-to-volume ratio of picoplankton, ∼45% of the primary production exudated as DOC in the offshore compared to the coastal region (∼12%) due to dominance of microplankton. The sum of primary production and DOC exudation, called total primary production, was almost equal in the coastal and offshore regions. The mean phytoplankton biomass normalized primary production (pB) in the Bay of Bengal was low (17 ± 8 mgC mgChl-a−1 d−1) compared to Arabian Sea (37 ± 5 mgC mgChl-a−1 d−1). In contrast pB estimated based on total primary production is close (30 ± 16 mgC mgChla−1 d−1) to that of the Arabian Sea (37 ± 5 mgC mgChl-a−1 d−1) suggesting that the Bay of Bengal is equally productive compared to that of Arabian Sea than hitherto hypothesized due to strong stratification and less nutrients input in the former basin. The low sinking carbon flux observed below the photic zone is attributed to the release of primary production as DOC. The released DOC from the phytoplankton may support heterotrophic activity as evidenced by the existence of strong net heterotrophy in the Bay of Bengal. This may lead to the time lag between primary and export productions. None of these processes were incorporated into the numerical models resulting in inaccurate simulations of carbon cycling in the northern Indian Ocean. Modifications in the models by incorporating these processes may improve model simulations for a better understanding the modifications in biogeochemical processes due to climate change in the Bay of Bengal.

Adapting to climate change: responses of fine root traits and C exudation in five tree species with different light-use strategy.

Trees that are categorised by their light requirements have similarities in their growth strategies and adaptation mechanisms. We aimed to understand the complex responses of elevated air humidity on whole tree fine root carbon (C) exudation (ExC) and respiration rate, morphology, and functional distribution in species with different light requirements. Three light-demanding (LD) species, Populus × wettsteinii, Betula pendula, and Pinus sylvestris, and two shade-tolerant species, Picea abies and Tilia cordata saplings were grown in growth chambers under moderate and elevated air relative humidity (eRH) at two different inorganic nitrogen sources with constant air temperature and light availability. The proportion of assimilated carbon released by ExC, and respiration decreased at eRH; up to about 3 and 27%, respectively. There was an indication of a trade-off between fine root released C and biomass allocation. The elevated air humidity changed the tree biomass allocation and fine root morphology, and the responses were species-specific. The specific fine root area and absorptive root proportion were positively related to canopy net photosynthesis and leaf nitrogen concentration across tree species. The variation in ExC was explained by the trees' light-use strategy (p < 0.05), showing higher exudation rates in LD species. The LD species had a higher proportion of pioneer root tips, which related to the enhanced ExC. Our findings highlight the significant role of fine root functional distribution and morphological adaptation in determining rhizosphere C fluxes in changing environmental conditions such as the predicted increase of air humidity in higher latitudes.

Soil organic carbon under decadal elevated CO2: Pool size unchanged but stability reduced

Soil organic carbon (SOC) dynamics under elevated atmospheric CO2 concentration has been widely reported, however, in which the behaviors of active and passive fractions remain inadequately explored. Here we studied this issue using three pairs of active and passive fractions of SOC under a 10-year free-air CO2 enrichment experiment (550 ​± ​17 ​ppm) in a cropland in the North China Plain. We found that decadal elevated CO2 increased the root biomass, root exudation rate and microbial biomass, but had little effects on SOC pool size. Elevated CO2 increased the readily oxidizable organic carbon (ROOC) and particulate organic carbon (POC) due to the increments of root C input, but decreased their paired passive fractions possibly because of the carbon input-induced positive priming effect. Our results indicate the reduced stability of SOC pool under elevated CO2. This is significant for better predicting SOC feedback to future climate change.

Critical analysis of using recycled wax oils in asphalt binder considering exudation effects

The tendency of asphalt to exude oil under certain conditions is often overlooked as a form of aging in asphalt pavement. To better understand the issue of oil exudation in asphalt during long term cold storage, two different oil sources of asphalt binders with recycled wax oils were investigated using the extended bending beam rheometer test (Ex-BBR), double edge notched tension test (DENT), extended Hansen solubility model, and fluorescence and polarizing microscopy. The results of the Ex-BBR and DENT tests demonstrate that the addition of recycled wax oils significantly enhances the low-temperature performance of asphalt. However, the use of fluorescing markers in cooling media indicates that recycled wax oil exudation can lead to ethanol diffusion in the asphalt binder. To further elucidate the factors influencing exudation, a device for accelerating the exudation of asphalt was developed. The research results show that, in addition to the intrinsic properties of asphalt and recycled wax oils, pressure, time, and temperature significantly influence the acceleration of exudation. The primary changes in recycled wax oil exudation occur early on, with the exudation rate decreasing over time. The fluorescent microscope reveals the separation of recycled wax oils as a fluorescent ring. Recycled wax oils alter the internal stability of asphalt, as evidenced by an increase in polarity and hydrogen bonding. This change is expected to impact the compatibility of asphalt binders. The mechanism of these interactions varies significantly depending on the source of the asphalt binder. After accelerated exudation, the three interaction forces representing sensitivity to chemical environments are further reduced.

Estimating the global root exudate carbon flux

Root exudation, the export of low-molecular weight organic carbon (C) from living plant roots to soil, influences microbial activity, nutrient availability, and ecosystem feedbacks to climate change, but the magnitude of this C flux at ecosystem and global scales is largely unknown. Here, we synthesize in situ measurements of root exudation rates and couple those to estimates of fine root biomass to estimate global and biome-level root exudate C fluxes. We estimate a global root exudate flux of 13.4 (10.1–20.2) Pg C y−1, or about 9% (7–14%) of global annual gross primary productivity. We did not find differences in root mass-specific exudation rates among biomes, though total exudate fluxes are estimated to be greatest in grasslands owing to their high density of absorptive root biomass. Our synthesis highlights the global importance of root exudates in the terrestrial C cycle and identifies regions where more in situ measurements are needed to improve future estimates of root exudate C fluxes.

A model of time-dependent macromolecular and elemental composition of phytoplankton

Phytoplankton Chl:C:N:P ratios are important from both an ecological and a biogeochemical perspective. We show that these elemental ratios can be represented by a phytoplankton physiological model of low complexity that includes major cellular macromolecular pools. In particular, our model resolves time-dependent intracellular pools of chlorophyll, proteins, nucleic acids, carbohydrates/lipids, and N and P storage. Batch culture data for two diatom and two prasinophyte species are used to constrain parameters that represent specific allocation traits and strategies. A key novelty is the simultaneous estimation of physiological parameters for two phytoplankton groups of such different sizes. The number of free parameters is reduced by assuming (i) allometric scaling for maximum uptake rates, (ii) shared half-saturation constants for synthesis of functional macromolecules, (iii) shared exudation rates of functional macromolecules across the species. The rationale behind this assumption is that across the different species, the same or similar processes, enzymes, and metabolites play a role in key physiological processes. For the turnover numbers of macromolecular synthesis and storage exudation rates, differences between diatoms and prasinophytes need to be taken into account to obtain a good fit. Our model fits suggest that the parameters related to storage dynamics dominate the differences in the C:N:P ratios between the different phytoplankton groups. Since descriptions of storage dynamics are still incomplete and imprecise, predictions of C:N:P ratios by phytoplankton models likely have a large uncertainty.

Double-dose investigation of aflibercept in neovascular age-related macular degeneration (DIANA): a real-world study.

To investigate the clinical effects of double-dose (4mg) aflibercept treatment in neovascular age-related macular degeneration (nAMD), compared with the standard-dose (2mg) treatment. A total of 108 eyes from 97 patients with nAMD and received intravitreal aflibercept 2mg and/or 4mg treatment were retrospectively reviewed. The changes of central macular thickness (CMT)/ pigmental epithelium detachment height and the recurrence rate of exudation during the 12-month follow-up were compared between the 2mg group and the 4mg group. Self-control comparisons (2mg switch to 4mg) were also made between two regimens. Compared with the 2mg group, tendencies of lower intraretinal fluid incidence and more CMT reduction were observed in the 4mg group. The later one was also observed when eyes switching from 2mg to 4mg regimen. The median remission interval was 5 months in the 4mg group, 2 months longer than the 3 months in the 2mg group (P = 0.452). Injections needed in the 4mg group were 3.644 ± 1.670, less than the 4.286 ± 2.334 injections in the 2mg group within 12 months as well (P = 0.151). However, no associated vision benefits were gained from the double-douse regimen. No markedly increased-intraocular pressure events, or other adverse events were found in two groups. Compared to the aflibercept 2mg treatment in nAMD, tendencies of anatomic gains and relieving treatment burden were brought by the aflibercept 4mg treatment. This study may have additional importance, given the further application of high-dose aflibercept in real-world settings.

Distinct effects of canopy vs understory and organic vs inorganic N deposition on root resource acquisition strategies of subtropical Moso bamboo plants

Atmospheric nitrogen (N) deposition inevitably alters soil nutrient status, subsequently prompting plants to modify their root morphology (i.e., adopting a do-it-yourself strategy), mycorrhizal symbioses (i.e., outsourcing strategy), and root exudation (i.e., nutrient-mining strategy) linking with resource acquisition. However, how N deposition influences the integrated pattern of these resource-acquisition strategies remains unclear. Furthermore, most studies in forest ecosystems have focused on understory N and inorganic N deposition, neglecting canopy-associated processes (e.g., N interception and assimilation) and the impacts of organic N on root functional traits. In this study, we compared the effects of canopy vs understory, organic vs inorganic N deposition on eight root functional traits of Moso bamboo plants. Our results showed that N deposition significantly decreased arbuscular mycorrhizal fungi (AMF) colonization, altered root exudation rate and root foraging traits (branching intensity, specific root area, and length), but did not influence root tissue density and N concentration. Moreover, the impacts of N deposition on root functional traits varied significantly with deposition approach (canopy vs. understory), form (organic vs. inorganic), and their interaction, showing variations in both intensity and direction (positive/negative). Furthermore, specific root area and length were positively correlated with AMF colonization under canopy N deposition and root exudation rate in understory N deposition. Root trait variation under understory N deposition, but not under canopy N deposition, was classified into the collaboration gradient and the conservation gradient. These findings imply that coordination of nutrient-acquisition strategies dependent on N deposition approach. Overall, this study provides a holistic understanding of the impacts of N deposition on root resource-acquisition strategies. Our results indicate that the evaluation of N deposition on fine roots in forest ecosystems might be biased if N is added understory.

Characterization of SgALMT genes reveals the function of SgALMT2 in conferring aluminum tolerance in Stylosanthes guianensis through the mediation of malate exudation

Aluminum (Al) toxicity is the major constraint on plant growth and productivity in acidic soils. An adaptive mechanism to enhance Al tolerance in plants is mediated malate exudation from roots through the involvement of ALMT (Al-activated malate transporter) channels. The underlying Al tolerance mechanisms of stylo (Stylosanthes guianensis), an important tropical legume that exhibits superior Al tolerance, remain largely unknown, and knowledge of the potential contribution of ALMT genes to Al detoxification in stylo is limited. In this study, stylo root growth was inhibited by Al toxicity, accompanied by increases in malate and citrate exudation from roots. A total of 11 ALMT genes were subsequently identified in the stylo genome and named SgALMT1 to SgALMT11. Diverse responses to metal stresses were observed for these SgALMT genes in stylo roots. Among them, the expressions of 6 out of the 11 SgALMTs were upregulated by Al toxicity. SgALMT2, a root-specific and Al-activated gene, was selected for functional characterization. Subcellular localization analysis revealed that the SgALMT2 protein is localized to the plasma membrane. The function of SgALMT2 in mediating malate release was confirmed by analysis of the malate exudation rate from transgenic composite stylo plants overexpressing SgALMT2. Furthermore, overexpression of SgALMT2 led to increased root growth in transgenic stylo plants treated with Al through decreased Al accumulation in roots. Taken together, the results of this study suggest that malate secretion mediated by SgALMT2 contributes to the ability of stylo to cope with Al toxicity.

Effects of Exogenous Melatonin on the Growth and Physiological Characteristics of Ginkgo biloba L. under Salinity Stress Conditions

Ginkgo (Ginkgo biloba L.) is a cherished relic among plants, commonly planted as a street tree. However, it faces cultivation challenges due to escalating soil salinization and widespread snowmelt application. Therefore, this study used 4-year-old Ginkgo seedlings to investigate how exogenous melatonin at varying concentrations affects seedling growth and physiology under salinity stress. The results revealed that appropriate melatonin concentrations (0.02, 0.1 mmol·L−1) significantly mitigated leaf yellowing under different NaCl stress levels. Furthermore, they increased ground diameter, current-year branch growth, relative water concentration, free proline, and soluble sugars in leaves. Melatonin also reduced electrolyte exudation rates, flavonoids, and malonic dialdehyde concentration, while enhancing peroxidase and superoxide dismutase activities. This led to reduced chlorophyll content, photosynthetic rate, stomatal conductance, and transpiration rate, stabilizing intercellular CO2 concentration, preserving photosynthetic structures, and enhancing photosynthetic rates. Additionally, the decline in the photosynthetic electron transport rate, the effective photochemical quantum yield of PSII, and the potential efficiency of primary conversion of light energy of PSII was alleviated. Minimal fluorescence and the non-photochemical quenching coefficient also improved. However, high melatonin concentration (0.5 mmol·L−1) exacerbated salinity stress. After analyzing composite scores, the 0.02 mmol·L−1 melatonin treatment was most effective in alleviating NaCl stress, while the 0.5 mmol·L−1 treatment intensified physiological stress under 200 mmol·L−1 NaCl stress. Principal component analysis and correlation analysis identified seven physiological indicators (photosynthetic rate, transpiration rate, photosynthetic electron transport rate, minimal fluorescence, superoxide dismutase, free proline, and chlorophyll a) and three growth indicators (ground diameter, branch length, and current-year branch thickness) as key markers for rapid salinity stress assessment in Ginkgo. These findings are crucial for addressing challenges associated with snowmelt’s impact on roadside Ginkgo trees, expanding planting areas, and breeding exceptional salt-tolerant Ginkgo varieties.

The quantification of root exudation by an in-situ method based on root morphology over three incubation periods.

Investigating the quantity and spatiotemporal dynamics of metabolite release from plant roots is essential if we are to understand the ecological significance of root exudates in the rhizosphere; however, this is difficult to quantify. In the present study, we quantified in situ root exudation rates during three incubation periods (0-24, 24-48, and 48-72 h) and fine roots within four diameter ranges (<0.8, 0.8-1.0, 1.0-1.2, and 1.2-2.0 mm), and also measured nine morphological traits in the fine roots of Pinus massoniana. Higher root carbon (C) exudation rates were detected during the 0-24 h period. During the 0-24 h and 24-48 h periods, nitrogen (N) uptake rates were higher than N exudation rates, while during the 48-72 h period, N exudation rates exceeded uptake rates. As C exudation increased during 0-48h incubation period, the uptake of N tended to level out. We concluded that the 24-48 h incubation period was the most suitable for capturing root exudates from P. massoniana. The exudation of C from the roots was positively associated with root mass, length, surface area, volume, the number of root tips, and the root tissue density, when incubated for 0-24 h and 24-48 h. Furthermore, length-specific C exudation rates, along with N exudation and uptake rates, all increased as the diameter of the fine roots increased. The release of root exudates could be efficiently predicted by the fine root morphological traits, although the accuracy of prediction depended on the incubation period. Higher values for fine root morphological traits were generally indicative of higher nutrient requirements and tissue investment, as well as higher C exudation rates.

Divergent rhizosphere and non-rhizosphere soil microbial structure and function in long-term warmed steppe due to altered root exudation.

While there is an extensive body of research on the influence of climate warming on total soil microbial communities, our understanding of how rhizosphere and non-rhizosphere soil microorganisms respond to warming remains limited. To address this knowledge gap, we investigated the impact of 4 years of soil warming on the diversity and composition of microbial communities in the rhizosphere and non-rhizosphere soil of a temperate steppe, focusing on changes in root exudation rates and exudate compositions. We used open top chambers to simulate warming conditions, resulting in an average soil temperature increase of 1.1°C over a span of 4 years. Our results showed that, in the non-rhizosphere soil, warming had no significant impact on dissolved organic carbon concentrations, compositions, or the abundance of soil microbial functional genes related to carbon and nitrogen cycling. Moreover, soil microbial diversity and community composition remained largely unaffected, although warming resulted in increased complexity of soil bacteria and fungi in the non-rhizosphere soil. In contrast, warming resulted in a substantial decrease in root exudate carbon (by 19%) and nitrogen (by 12%) concentrations and induced changes in root exudate compositions, primarily characterized by a reduction in the abundance in alcohols, coenzymes and vitamins, and phenylpropanoids and polyketides. These changes in root exudation rates and exudate compositions resulted in significant shifts in rhizosphere soil microbial diversity and community composition, ultimately leading to a reduction in the complexity of rhizosphere bacterial and fungal community networks. Altered root exudation and rhizosphere microbial community composition therefore decreased the expression of functional genes related to soil carbon and nitrogen cycling. Interestingly, we found that changes in soil carbon-related genes were primarily driven by the fungal communities and their responses to warming, both in the rhizosphere and non-rhizosphere soil. The study of soil microbial structure and function in rhizosphere and non-rhizosphere soil provides an ideal setting for understanding mechanisms for governing rhizosphere and non-rhizosphere soil carbon and nitrogen cycles. Our results highlight the distinctly varied responses of soil microorganisms in the rhizosphere and non-rhizosphere soil to climate warming. This suggests the need for models to address these processes individually, enabling more accurate predictions of the impacts of climate change on terrestrial carbon cycling.

Plant growth and development of tropical seagrass determined rhizodeposition and its related microbial community

In the recent study, we investigated the seasonal variations in root exudation and microbial community structure in the rhizosphere of seagrass Enhalus acoroides in the South China Sea. We found that the quantity and quality of root exudates varied seasonally, with higher exudation rates and more bioavailable dissolved organic matter (DOM) during the seedling and vegetative stages in spring and summer. Using Illumina NovaSeq sequencing, we analyzed bacterial and fungal communities and discovered that microbial diversity and composition were influenced by root exudate characteristics s and seagrass biomass, which were strongly dependent on seagrass growth stages. Certain bacterial groups, such as Ruegeria, Sulfurovum, Photobacterium, and Ralstonia were closely associated with root exudation and may contribute to sulfur cycling, nitrogen fixation, and carbon remineralization, which were important for plant early development. Similarly, specific fungal taxa, including Astraeus, Alternaria, Rocella, and Tomentella, were enriched in spring and summer and showed growth-promoting abilities. Overall, our study suggests that seagrass secretes different compounds in its exudates at various developmental stages, shaping the rhizosphere microbial assemblages.

Phosphorus absorption kinetics and exudation strategies of roots developed by three lupin species to tackle P deficiency.

Different lupin species exhibited varied biomass, P allocation, and physiological responses to P-deprivation. White and yellow lupins had higher carboxylate exudation rates, while blue lupin showed the highest phosphatase activity. White lupin (Lupinus albus) can produce specialized root structures, called cluster roots, which are adapted to low-phosphorus (P) soil. Blue lupin (L. angustifolius) and yellow lupin (L. luteus), which are two close relatives of white lupin, do not produce cluster roots. This study characterized plant responses to nutrient limitation by analyzing biomass accumulation and P distribution, absorption kinetics and root exudation in white, blue, and yellow lupins. Plants were grown in hydroponic culture with (64µM NaH2PO4) or without P for 31days. Under P limitation, more biomass was allocated to roots to improve P absorption. Furthermore, the relative growth rate of blue lupin showed the strongest inhibition. Under + P conditions, the plant total-P contents of blue lupin and yellow lupin were higher than that of white lupin. To elucidate the responses of lupins via the perspective of absorption kinetics and secretion analysis, blue and yellow lupins were confirmed to have stronger affinity and absorption capacity for orthophosphate after P-deprivation cultivation, whereas white lupin and yellow lupin had greater ability to secrete organic acids. The exudation of blue lupin had higher acid phosphatase activity. This study elucidated that blue lupin was more sensitive to P-scarcity stress and yellow had the greater tolerance of P-deficient condition than either of the other two lupin species. The three lupin species have evolved different adaptation strategies to cope with P deficiency.