HN Treatment Research Articles

Melatonin mitigates root growth inhibition and carbon-nitrogen metabolism imbalance in apple rootstock M9T337 under high nitrogen stress.

Nitrogen (N) is an essential element for plant growth, development, and metabolism. In apple production, the excessive use of N fertilizer may cause high N stress. Whether high N stress can be alleviated by regulating melatonin supply is unclear. The effects of melatonin on root morphology, antioxidant enzyme activity and 13C and 15N accumulation in apple rootstock M9T337 treated with high N were studied by soil culture. The results showed that correctly raising the melatonin supply level is helpful to root development of M9T337 rootstock under severe N stress. Compared with HN treatment, HN+MT treatment increased root and leaf growth by 11.38%, and 28.01%, respectively. Under high N conditions, appropriately increasing melatonin level can activate antioxidant enzyme activity, reduce lipid peroxidation in roots, protect root structural integrity, promote the transport of sorbitol and sucrose to roots, and promote further degradation and utilization of sorbitol and sucrose in roots, which is conducive to the accumulation of photosynthetic products, thereby reducing the inhibitory effect of high N treatment on root growth. Based on the above research results, we found that under high N stress, melatonin significantly promotes nitrate absorption, enhances N metabolism enzyme activity, and upregulates related gene expression, and regulate N uptake and utilization in the M9T337 rootstock. These results presented a fresh notion for improving N application and preserving carbon-nitrogen balance.

Exogenous N Supply on N Transportation and Reuse during the Rice Grain-Filling Stage and Its Relationship with Leaf Color-Changing Parameters

During the later reproductive period of rice growth, the chlorophyll in the leaves degraded, accompanied by the nitrogen (N) transportation from leaves to panicle, resulting in a change in leaf color from green to yellow. This study aimed to investigate the effects of exogenous N supply on leaf color-changing, N accumulation, N transportation, and N loss of indica-japonica hybrid rice during the grain-filling stage. Two indica-japonica hybrid rice cultivars, Chunyou 167 (CY167) and Chunyou 927 (CY927), which exhibited significant differences in leaf color-changing during the grain-filling stage, were selected as materials for field experiment and hydroponic experiment with low, medium, and high N treatments (LN, MN, and HN). The dynamic changes in SPAD value from heading to maturity were measured and fitted with quadratic function to extract leaf color-changing parameters; labeled 15N was used as N source after heading to trace the source of N in the panicle and the remobilization of vegetative organ N. The results showed that 67.37–72.38% of the panicle N was transported from vegetative organs, the N transport efficiency was the upper three leaves > lower leaves > stem, and about 3.1–35.0% of the transported N was lost via volatilization. The effects of exogenous N concentration on N harvest index, N dry matter/grain production efficiency, N reuse efficiency, and N loss were closely related to leaf color-changing parameters. In MN and HN treatment, the N loss was negatively correlated with the onset time of leaf color-changing (T0) and the final leaf color index (CIf), but positively correlated with the leaf color-changing rate (Rmean). Increasing the supply of exogenous N increased T0 and CIf, but decreased Rmean, N transport/reuse efficiency, N harvest index, and N dry matter/grain production efficiency. Compared to the cultivar CY167 with normal leaf color-changing, the “stay-green” cultivar CY927 had higher T0, CIf, and lower Rmean, resulting in less N volatilization loss, lower N harvest index and N transport efficiency, while higher N reuse efficiency. In conclusion, the exogenous N supply affects leaf color by influencing the transportation and reuse of leaf N during the grain-filling stage.

Effects of short-term nitrogen addition on the recovery of alpine grassland in the Tianshan Mountains of Xinjiang, China.

The restoration of alpine grasslands has garnered significant attention across various sectors. Historically, natural restoration has been the primary approach for grassland recovery, characterized by its prolonged duration. To expedite the recovery of degraded grasslands, it is essential to identify the limiting factors of restoration, enabling efficient and rapid recovery. Appropriate nitrogen (N) addition levels have been considered a potential strategy to enhance the recovery of grassland ecosystems and augment their ecological benefits. However, the effectiveness of N addition in alpine grassland restoration remains debated. This study investigated the impact of five N addition levels (CK: control [0 g/m2]; LN: low N [5 g/m2]; MN: medium N [10 g/m2]; HN: high N [15 g/m2]; SN: severe N [20 g/m2]) and two experimental approaches (N addition once per year [NPY] and three times per year [NTY] at the same dosages) on plant and soil properties and the maximum restoration capacity of alpine meadows. Our findings reveal three key insights: The level of N addition was the primary factor influencing aboveground plant biomass and coverage. Plant diversity decreased under the NTY regime and increased with NPY in the Bayinbruck grassland. N addition significantly altered soil properties, including pH, salinity, soil organic carbon (SOC), soil-available phosphorus (AP), and soil total phosphorus (TP). Notably, soil TP, total nitrogen (TN), and AP substantially impacted plant community structure and diversity. Based on structural equation model (SEM) and analysis of variance (ANOVA), optimal grassland restoration was achieved with the HN (15 g/m2) treatment under NPY and the MN and HN (10 and 15 g/m2) treatments under NTY. Overall, our study offers crucial insights into the conservation, management, and restoration of grassland ecosystems on the Bayinbruck Plateau. It underscores the significance of N addition effects on plant communities, vegetation restoration, and soil properties.

Soil solution chemistry weak response to long-term N addition points towards a strong resilience of northeastern American forests to past and future N deposition

Northern temperate and boreal forests are large biomes playing crucial ecological and environmental roles, such as carbon sequestration. Despite being generally remote, these forests were exposed to anthropogenic nitrogen (N) deposition over the last two centuries and may still experience elevated N deposition as human activities expand towards high latitudes. However, the impacts of long-term high N deposition on these N-limited forest ecosystems remain unclear. For 18 years, we simulated N deposition by chronically adding ammonium nitrate at rates of 3 (LN treatment) and 10 (HN treatment) times the ambient N deposition estimated at the beginning of the experiment at a temperate sugar maple and a boreal balsam fir forest site, both located in northeastern America. LN and HN treatments corresponded respectively to addition of 26 kgN·ha−1·yr−1 and 85 kgN·ha−1·yr−1 at the temperate site and 17 kgN·ha−1·yr−1 and 57 kgN·ha−1·yr−1 at the boreal site. Between 2002 and 2018, soil solution was collected weekly during summer and concentrations of NO3−, NH4+, Ca2+ and pH were measured, totalling ~12,700–13,500 observations per variable on the study period. N treatments caused soil solution NO3−, NH4+ and Ca2+ concentrations to increase while reducing its pH. However, ion responses manifested through punctual high concentration events (predominantly on the HN plots) that were very rare and leached N quantity was extremely low at both sites. Therefore, N addition corresponding to 54 years (LN treatment) and 180 years (HN treatment) of accelerated ambient N deposition had overall small impacts on soil solution chemistry. Our results indicate an important N retention of northeastern American forests and an unexpected strong resilience of their soil solution chemistry to long-term simulated N deposition, potentially explained by the widespread N-limitation in high latitude ecosystems. This finding can help predict the future productivity of N-limited forests and improve forest management strategies in northeastern America.

Nitrogen Application Timing and Levels Affect the Fate and Budget of Fertilizer Nitrogen in the Apple-Soil System.

This study aimed to determine the effects of the nitrogen (N) application period and level on the fate of fertilizer N and the contribution of N absorption and translocation to apple organ N. Two N application periods (labeled by the 15N tracer technique in spring and summer, represented by SP and SU, respectively) and three N levels (N0, MN, and HN) were used to determine the physiological indexes and aboveground, root, and soil 15N content of 4-year-old dwarf ('Red Fuji'/M9T337) and arborized ('Red Fuji'/Malus hupehensis Rehd.) apple trees. The results showed that HN led to shoot overgrowth, which was not conducive to the growth of the apple root system (root length, root tips, root surface area, and root volume) or the improvement of root activity. The contribution of soil N to apple organ N accounted for more than 50%, and the contribution of N application in summer to fruit N was higher than that in spring. Under HN treatment, the proportion of soil N absorbed by trees decreased, while that of fertilizer N increased; however, the highest proportion was still less than 50%, so apple trees were highly dependent on soil N. Under MN treatment, fertilizer N residue was similar to soil N consumption, and soil N fertility maintained a basic balance. Under HN treatment, fertilizer N residue was significantly higher than soil N consumption, indicating that excessive N application increased fertilizer N residue in the soil. Overall, the 15N utilization rate of arborized trees (17.33-22.38%) was higher than that of dwarf trees (12.89-16.91%). A total of 12.89-22.38% of fertilizer 15N was absorbed by trees, 30.37-35.41% of fertilizer 15N remained in the soil, and 44.65-54.46% of fertilizer 15N was lost. The 15N utilization rate and 15N residual rate of summer N application were higher than those of spring N application, and the 15N loss rate was lower than that of spring N application. High microbial biomass N (MBN) may be one of the reasons for the high N utilization rate and the low loss rate of N application in summer.

Decomposition and Carbon and Nitrogen Releases of Twig and Leaf Litter Were Inhibited by Increased Level of Nitrogen Deposition in a Subtropical Evergreen Broad-Leaved Forest in Southwest China

Atmospheric nitrogen (N) deposition has rapidly increased due to anthropogenic activities, which can exert a crucial effect on biochemical cycling process such as litter decomposition in the subtropical forests. However, the is still uncertainty about the knowledge of N deposition in regulating nutrient release from the leaf and twig litter. For this study, a 2 yr litterbag decomposition experiment was conducted under three levels of N addition treatments in a subtropical evergreen broad-leaved forest, in southwest China. This study aimed to identify the effects of low (LN: 10 g·N·m−2·y−1), medium (MN: 20 g·N·m−2·y−1), and high N addition (HN: 25 g·N·m−2·y−1) on litter decomposition and nutrient release from leaves and twigs. We observed that there was significantly lower litter decomposition (8.13%–13.86%) and nutrient release (7.24%–36.08%) in the HN treatment compared to the LN treatment. The decay of mass, lignin, and cellulose and the nutrient release were faster in leaf litter than in twig litter after N addition (p < 0.05). The ratios of C/phosphorus (P), C/N, and N/P were also significantly greater in twig litter than in leaf litter. Furthermore, the N addition treatments resulted in higher contents of the mass, lignin, and cellulgapose remaining in leaf and twig litter compared to the control (CK). The amount of C, N, and P remaining in leaf (51.4%–59.1%) and twig (44.1%–64.8%) debris was significantly higher in the N treatment compared to CK treatment (p < 0.05). In addition, the litter C/N and C/P were smaller and the litter N/P was larger for each N treatment compared to CK (p < 0.05). The results suggest that N inputs restrain lignin and cellulose degradation and C and N release, and increase the N/P ratio that limits P release in litter. These effects vary with the level of N treatments.

Eastern Canadian boreal forest soil and foliar chemistry show evidence of resilience to long-term nitrogen addition.

The boreal forest is one of the world's largest terrestrial biome and plays crucial roles in global biogeochemical cycles, such as carbon (C) sequestration in vegetation and soil. However, the impacts of decades of N deposition on N-limited ecosystems, like the eastern Canadian boreal forest, remain unclear. For 13 years, N deposition was simulated by periodically adding ammonium nitrate on soils of two boreal coniferous forests (i.e., balsam fir and black spruce) of eastern Canada, at low (LN) and high (HN) rates, corresponding to 3 and 10 times the ambient N deposition, respectively. We show that more than a decade of N addition had no strong effects on mineral soil C, N, P, and cation concentrations and on foliar total Ca, K, Mg, and Mn concentrations. In organic soil, C stock was not affected by N addition while N stock increased, and exchangeable Ca2+ and Mg2+ decreased at the balsam fir site under HN treatment. At both sites, LN treatment had nearly no impact on foliage and soil chemistry but foliar N and N:P significantly increased under HN treatment, potentially leading to foliar nutrient imbalance. Overall, our work indicates that, in the eastern Canadian boreal forest, soil and foliar nutrient concentrations and stocks are resilient to increasing N deposition potentially because, in the context of N limitation, extra N would be rapidly immobilized by soil micro-organisms and vegetation. These findings could improve modeling future boreal forest soil C stocks and biomass growth and could help in planning forest management strategies in eastern Canada.

Interaction of Biochar Addition and Nitrogen Fertilizers on Wheat Production and Nutrient Status in Soil Profiles.

To investigate the responses of crop production and soil profile nutrient status to biochar (BC) application, we conducted a soil column experiment considering two BC addition rates (0.5 and 1.5 wt% of the weight of 0-20 cm topsoil) combined with two nitrogen (N) input levels (low N: 144 kg ha-1, LN; high N: 240 kg ha-1, HN). The results showed that BC application increased the soil pH. The soil pH of the 0-10 cm profile under LN and the 20-40 cm profile under HN were both significantly increased by 0.1-0.2 units after BC addition. Under LN, BC addition significantly increased NH4+-N (17.8-46.9%), total N (15.4-38.4%), and soil organic carbon (19.9-24.0%) in the 0-10 cm profile, but decreased NH4+-N in the 20-30 cm soil profile and NO3--N in the 10-30 cm profile by 13.8-28.5% and 13.0-34.9%, respectively. BC had an increasing effect on the available phosphorus, the contents of which in the 10-20 and 30-40 cm soil profiles under LN and 20-30 cm profile under HN were significantly elevated by 14.1%, 24.0%, and 23.27%, respectively. However, BC exerted no effect on the available potassium in the soil profile. BC had a strong improving effect (15.3%) on the wheat yield, especially the N144 + BC0.5% treatment, which could be compared to the HN treatment, but there was no yield-increasing effect when high N fertilizer was supplied. In summary, BC improved the fertility of agriculture soil (0-20 cm) with wheat. In particular, low N inputs together with an appropriate rate of BC (0.5 wt%) could not only achieve the low inputs but also the high outputs in wheat production. In future study, we will compare the effects of multiple doses of N and BC on soil fertility and crop production.

Soil bacterial communities are more sensitive to short-term nitrogen deposition than fungal communities in subtropical Chinese fir forests

The increasing rate of atmospheric nitrogen (N) deposition seriously affects the structure and function of ecosystems. Although soil microorganisms play a crucial role in ecosystem carbon (C) and nutrient cycling, the impact of N deposition on soil microbial communities in subtropical forest ecosystems is unclear. Here, we selected the subtropical Chinese fir (Cunninghamia lanceolata) forest as the research object and conducted simulated N deposition experiments with different levels of N deposition (0 kg N ha−1 yr−1,50 kg N ha−1 yr−1, 100 kg N ha−1 yr−1, and 200 kg N ha−1 yr−1, respectively) to explore the response of soil nutrients, soil microbial community structure, and potential ecological functions to short-term N deposition. We found that the bacterial richness Chao1 index and phylogenetic diversity PD_whole_tree decreased with the N deposition level approximately 13 % −16 % under MN and HN treatment. N deposition significantly altered the composition of soil bacterial communities (P < 0.05), but the responses of different taxa to N deposition were inconsistent at different stages of growing season. N deposition treatment significantly increased the relative abundance of Actinobacteria at both beginning of growing season (BGS) and end of growing season (EGS), decreased the relative abundances of Planctomycetes at BGS, and decreased the relative abundances of Elusimicrobia and Cyanobacteria at both BGS and EGS. Non-metric multidimensional scaling (NMDS) and Anosim (Analysis of similarities) analyses showed that the bacterial communities were clearly distinguished among treatments at both BGS and EGS. However, N deposition had a relatively small impact on fungal communities, only altering the fungal community structure at BGS. The impact of N deposition on soil microbial communities was mainly induced by the alteration in soil water content (SWC), pH, NO3–-N, and available nitrogen (AN). Both bacterial and fungal communities exhibit seasonal community dynamics, while the interaction of N deposition and season was mainly reflected in the impact on bacterial communities. Our research not only provides research ideas for the potential impact of nitrogen deposition on subtropical forest ecosystems in the short term, but also provides a theoretical basis for future scientific management and regulation of forestry, microorganisms, and sustainable management of Chinese fir plantations.

Simulated nitrogen deposition alters the ectomycorrhizal fungal community structure in northern Korean pine plantations

Northern temperate forests are sensitive to nitrogen deposition. Korean pines are the zonal dominant vegetation in these forest ecosystems and a typical obligate ectomycorrhizal (ECM) tree. However, the impact of varying nitrogen additions on the ectomycorrhizal fungal (ECMF) community structure in Korean pine plantations remains unclear. In this experiment, nitrogen deposition was simulated (CK = 0 kg N ha−1 yr−1, LN = 20 kg N ha−1 yr−1, MN = 40 kg N ha−1 yr−1, HN = 80 kg N ha−1 yr−1), and soil biochemical indicators, ECMF community composition, and diversity were measured. The results showed that high nitrogen addition led to increased ECMF colonization, decreased ECMF community diversity and richness, and altered the occurrence of biomarkers. The MN treatment significantly increased the Simpson index compared to the LN treatment (P < 0.05), with Amphinema sp, Tuber sp, and Tylospora asterophora identified as biomarkers in the CK, LN, and HN treatments, respectively. The HN treatment significantly reduced the Chao1 index (P < 0.05), with Inocybe quietiodor, Tarzetta catinus, Inocybe giacomi, and Russula viscida serving as biomarkers in the CK, LN, MN, and HN treatments, respectively. Nitrogen addition led to decreased soil pH and available phosphorus content, increased ammonium nitrogen content, and affected ectomycorrhiza colonization by altering the soil ECMF community structure. Among these factors, ammonium nitrogen was the most influential in changing the ECMF community structure. This research offers valuable data to help predict changes in ECMF community structure in Korean pine plantations as nitrogen additions increase.

Enzyme activities of rhizosphere soil with different root diameters had varied responses to N deposition in Pinus tabuliformis forest

Root system exhibits hierarchical traits in physiology and exudation, and responds variably to environmental changes. However, it remains unclear if these phenomena result in corresponding alterations in the microbial characteristics of rhizosphere soil and diverse responses to nitrogen (N) deposition. This study evaluated microbial biomass, gas flow, and enzyme activity in rhizosphere soil of three root diameter classes (R1, <0.5 mm; R2, 0.5–1.0 mm; R3, 1.0–2.0 mm) of P. tabuliformis, and their responses to N application (0, 3, 6, 9 g N m−2 y−1, corresponding to CN, LN, MN, and HN) in a P. tabuliformis forest. Rhizosphere soil of R1 exhibited significantly higher microbial biomass N (MBN) content, enzyme activities, CO2 and N2O flow rates than those of R2 and R3 (P < 0.05). Soil microbial biomass carbon (MBC) and phosphorus (MBP) contents, N2O and CH4 flow rates significantly increased with N applications. While soil MBN content increased with the LN treatment and decreased with the HN treatment, the largest value was observed in the LN treatment (84.89 mg kg−1). N application promoted Alkaline phosphatase (ALP) and Alanine transaminase (ALT) activities in R1 rhizosphere soil while decreasing their activities in R2 and R3 rhizosphere soils. Moreover, β-glucosidase (BG), N-acetyl-β-Glucosaminidase (NAG), β-xylosidase (XYL), and β-D-cellulosidase (CBH) activities in R1 rhizosphere soil were inhibited, while their activities in R2 and R3 rhizosphere soils were promoted by N application. N application directly promoted microbial biomass then inhibited enzyme activity. Besides, nutrient content of rhizosphere soil decreased with root diameters, which indirectly reducing enzyme activity and microbial biomass. N application directly affected soil CH4 flow rate, while N2O flow rate was indirectly promoted by N application through increasing microbial biomass. CO2 and CH4 flow rates were inhibited by N application through decreasing enzyme activity. Root diameter slowed down the CO2 and CH4 flow rates by reducing soil nutrient content and enzyme activity. In conclusion, N deposition has varied effects on microbial characteristics in rhizosphere soil of different diameter roots, which are relevant to the corresponding changes in root system and soil properties.

Resource-acquisitive species have greater plasticity in leaf functional traits than resource-conservative species in response to nitrogen addition in subtropical China

The evergreen broad-leaf forest is subtropical zonal vegetation in China, and its species diversity and stability are crucial for maintaining forest ecosystem functions. The region is generally affected by global changes such as high levels of nitrogen deposition. Therefore, it is critical to determine the adaptation strategies of subtropical dominant species under nitrogen addition. Here, we conducted two-year field experiments with nitrogen addition levels as 0 kg N ha−1 yr−1 (CK), 50 kg N ha−1 yr−1 (LN) and 100 kg N ha−1 yr−1 (HN). We investigated the effects of nitrogen addition on leaf functional traits (including nutrition, structural and physiological characteristics) of five dominant species in subtropical evergreen broad-leaf forest. Results suggested that the effect of nitrogen addition on leaf functional traits was species-specific. Contrary to Rhododendron delavayi and Eurya muricata, Quercus glauca, Schima superba and Castanopsis eyrei all responded more to the HN treatment than LN treatment. Compared to other leaf functional traits, leaf anatomical structure traits had the highest average plasticity (0.246), and the relative effect of leaf photosynthetic property was highest (7.785) under N addition. Among the five species, S. superba was highest in terms of the index of plasticity for leaf functional traits under nitrogen addition, followed by Q. glauca, E. muricata, C. eyrei and R. delavayi. The major leaf functional traits representing the economic spectrum of leaves (LES) showed resource acquisitive strategy (high SLA, LNC, LPC, Pn) and conservative strategy (high LTD, LDMC, C/N) clustering on the opposite ends of the PCA axis. The PCA analysis indicated that species with high leaf plasticity adopt resource acquisitive strategy (S. superba and Q. glauca), whereas species with low leaf plasticity adopt resource conservative strategy (E. muricata, C. eyrei and R. delavayi). In aggregate, resource-acquisitive species benefit from nitrogen addition more than resource-conservative species, suggesting that S. superba and Q. glauca will occupy the dominant position in community succession under persistently elevated nitrogen deposition.

Soil phosphorus drives variation in diazotrophic communities in a subtropical nitrogen-rich forest

Although nitrogen (N)-fixing bacteria (diazotrophs) play a vital role in the biosphere's N cycle. However, large uncertainty exists regarding how atmospheric N deposition regulates biological N fixation (BNF) in soils and which diazotrophic taxa are responsible for this process. We targeted the nifH gene to investigate the effects of long-term N addition on the abundance and composition of diazotrophic communities in subtropical N-rich forests, using real-time quantitative polymerase chain reaction (q-PCR) and MiSeq sequencing. We conducted a field trial for seven years and included three N treatment levels (+0, +50, +150 kg N ha−1 yr−1; CK, LN, HN). With increasing N addition, the average total P concentration in the whole soil profile and the topsoil P availability decreased significantly, further reducing nitrogenase activity and nifH abundance significantly, while increasing the diversity of the diazotrophic community. After seven years of N addition, the relative abundance of uncultured Cyanobacteria significantly decreased, while those of Rhizobiales and Desulfobulbaceae significantly increased. The diazotrophic communities transitioned from free-living N fixers (uncultured Cyanobacteria-dominated) to symbiotic N fixers (Rhizobiales-dominated; HN treatment). The relative abundance of heterotrophic diazotrophic bacteria and the occasional diazotrophic species increased, resulting in diazotrophic bacteria still maintaining high competitiveness in the N-rich and/or P-limited soils. Proteobacteria (e.g., Rhizobiales) had the highest potential to participate in microbial mechanisms triggered by P scarcity. Variation partitioning analyses showed that diazotrophic community composition and diversity were mainly correlated with the soil P availability, with soil AP having the highest individual effect. Overall, this study will broaden our understanding of N fixation mechanisms and the diazotrophic community variation in N-rich forests, while also highlighting soil P as a key factor driving changes in diazotrophic communities.

Effects of Simulated Nitrogen Deposition on Soil Microbial Community Structure in Temperate Forest Based on PLFA Method

Soil microorganisms play a crucial role in the biogeochemical cycling of terrestrial ecosystems. However, previous studies on the effects of nitrogen deposition on microorganisms have primarily focused on nitrogen-sensitive tropical forest ecosystems. This study focused on soil in a temperate Korean pine plantation and conducted a field simulated nitrogen deposition experiment. The effects of different nitrogen application rates on the microbial community structure were analyzed using the phospholipid fatty acid (PLFA) method. The experiment included four nitrogen application rates: control (CK: 0 kg N ha−1 yr−1), low nitrogen treatment (LN: 20 kg N ha−1 yr−1), medium nitrogen treatment (MN: 40 kg N ha−1 yr−1), and high nitrogen treatment (HN: 80 kg N ha−1 yr−1). After seven years of continuous application of ammonium nitrate solution, the soil microbial community structure was determined using the PLFA method. The results showed that all nitrogen application rates significantly reduced the PLFA concentration of fungi and AM fungi (P &lt; 0.05), while bacterial biomass significantly decreased in the high nitrogen treatment group. The biomass of Gram-positive bacteria, Gram-negative bacteria (G-), and actinomycetes also significantly decreased in the HN treatment group. Furthermore, long-term application of high nitrogen concentration (80 kg N ha−1 yr−1) significantly reduced soil microbial biomass and changed the fungal to bacterial ratio, thus affecting the soil microbial community structure. Redundancy analysis (RDA) of soil microbial and soil chemical properties found that the long-term simulated nitrogen deposition experiment affected the soil microbial community structure by changing the content of soil N, P elements, and soil pH values. In summary, long-term simulated N deposition can negatively affect soil microbial biomass and its community structure, and the main reason for this analysis is related to long-term N application leading to soil acidification and changes in the conversion of soil N and P elements.

Inhibition of ferroptosis ameliorates hypertensive nephropathy through p53/Nrf2/p21 pathway by Taohongsiwu decoction: Based on network pharmacology and experimental validation

Ethnopharmacological relevanceHypertensive nephropathy (HN) is a complication of hypertension. Taohongsiwu decoction (THSWD) is used clinically but its application in the prevention and treatment of HN remains unelucidated. Aim of studyThis study aims to explore the potential targets and molecular mechanisms of THSWD in the treatment of HN. Materials and methodsA network pharmacology approach was used to predict the components and targets of THSWD for treating HN. Animal experiments were performed to verify the network pharmacology findings. Results205 targets were identified and regarded as potential targets of THSWD in HN treatment. Subsequently, we screened 17 hub genes and identified TP53 as the most critical one. KEGG enrichment analysis showed that p53 signaling pathway might play a significant role. In vivo experiments indicated that high-salt diets can lead to high blood pressure, kidney injury, inflammation, and fibrosis. Furthermore, the altered levels of biomarkers (Iron, malondialdehyde, catalase, ferritin, transferrin, Superoxide dismutase and Glutathione Peroxidase 4) provided evidence of ferroptosis. We found that the ferroptosis inhibitor ferrostatin-1 (Fer-1) and THSWD could significantly alleviate HN by suppressing ferroptosis. THSWD and Fer-1 treatment downregulated the protein and mRNA expression of p53, p21, RB, and CTNNB1, which were upregulated by high salt. Meanwhile, THSWD and Fer-1 reversed the downregulation of Nrf2 caused by high-salt diet. ConclusionsOur results suggested that THSWD attenuate HN induced by a high-salt diet through inhibiting ferroptosis via the p53/Nrf2/p21 pathway.

Chemistry of soil and foliage in declining sugar maple stands over 13 years of nitrogen addition

Cumulative effects of nitrogen (N) deposition are a matter of concern in temperate forests of northeastern North America. Increased N deposition may stimulate forest growth and carbon sequestration while also causing N saturation, which may lead to soil cation depletion, particularly in base-poor systems. We applied ammonium nitrate for 13 years in a sugar maple (Acer saccharum; SM) stand at the rates of 3 (Low N, LN) and 10 times (High N, HN) the ambient N deposition rate. N concentrations in soil layers were similar among treatments, except for a nitrate increase in the top B horizon in the HN treatment. Exchangeable Ca2+, Mg2+, and K+ were significantly lower than for the Control, at least in one of the top organic soil layers in the HN treatment. The temporal dynamics of foliar chemistry revealed that N:P ratio increased and both Ca and Mn decreased in the early years following treatment initiation, but that they did not change much thereafter. Foliar Ca values in the HN treatment are the lowest reported in the literature. This probably explains why the proportion of crown dieback steadily increased over time, reaching values as high as 80% in the HN treatment in 2017.

Phosphorus limitation induced by nitrogen addition changed soil microbial community structure in a subtropical Pinus taiwanensis forest.

Soil microorganisms play an important role in the biogeochemical cycles of terrestrial ecosystems. How-ever, it is still unclear how the amount and duration of nitrogen (N) addition affect soil microbial community structure and whether there is a correlation between the changes in microbial community structure and their nutrient limi-tation status. In this study, we conducted an N addition experiment in a subtropical Pinus taiwanensis forest to simulate N deposition with three treatments: control (CK, 0 kg N·hm-2·a-1), low N (LN, 40 kg N·hm-2·a-1), and high N (HN, 80 kg N·hm-2·a-1). Basic soil physicochemical properties, phospholipid fatty acids content, and carbon (C), N and phosphorus (P) acquisition enzyme activities were measured after one and three years of N addition. The relative nutrient limitation status of soil microorganisms was analyzed using ecological enzyme stoichiometry. The results showed that one-year N addition did not affect soil microbial community structure. Three-year LN treatment significantly increased the contents of Gram-positive bacteria (G+), Gram-negative bacteria (G-), actinomycetes (ACT), and total phospholipid fatty acids (TPLFA), whereas three-year HN treatment did not significantly affect soil microbial community, indicating that bacteria and ACT might be more sensitive to N addition. Nitrogen addition exacerbated soil C and P limitation. Phosphorus limitation was the optimal explanatory factor for the changes in soil microbial community structure. It suggested that P limitation induced by N addition might be more beneficial for the growth of certain oligotrophic bacteria (e.g. G+) and the microorganisms participating in the P cycling (e.g. ACT), with consequences on soil microbial community structure of subtropical Pinus taiwanensis forest.

Exogenous sucrose promotes the growth of apple rootstocks under high nitrate supply by modulating carbon and nitrogen metabolism

Excessive nitrogen (N) supply often leads to an imbalance of carbon (C) and N metabolism and inhibits plant growth. Sucrose, an important source and signaling substance of C in plants, is closely linked to N metabolism. However, it is not clear whether exogenous sucrose can mitigate the inhibitory effect of high N on plant growth by regulating C and N metabolism. In this study, we investigated the effects of exogenous sucrose on the growth, N metabolism, and C assimilation in the apple rootstock M26 seedlings under normal (5 mM NO3－, NN) and high (30 mM NO3－, HN) NO3－ concentrations. Our results showed that high NO3－ supply reduced plant growth, photosynthesis, and chlorophyll fluorescence, but spraying with 1% sucrose (HN + 1% Sucrose) significantly alleviated this inhibition. Application of 1% sucrose increased sucrose and sorbitol contents as well as sucrose-phosphate synthase and sucrose synthase activities in the plants under HN treatment and promoted the distribution of 13C photoassimilation products to the root. In addition, spraying with 1% sucrose alleviated the inhibition of N metabolizing enzyme activities by high NO3－ supply, reduced NO3－ accumulation and N content, increased free amino acid content, and promoted 15N distribution to the aboveground parts. However, spraying with 1% sucrose under the NN treatment negatively affected plant photosynthesis and carbon assimilation. In conclusion, exogenous sucrose increased the C level in plants in the presence of excess N, promoted the balance of C and N metabolism, and alleviated the inhibitory effect of high N on the apple plant growth.

Alleviation effects of niacin supplementation on beef cattle subjected to heat stress: A metagenomic insight.

The objective of this study was to investigate the alleviation effects of niacin supplementation on beef cattle subjected to heat stress and to provide a theoretical basis for exploring the alleviation methods of heat stress environmental factors on the rumen of beef cattle. In the experiment, 36 Jinjiang bull cattle with a body weight of about 400 ± 20.0 kg were randomly divided into three treatments, each treatment contains four replicates, with three cattle in each replicate. Treatments included thermoneutral treatment (TN; temperature: 24–25°C, humidity: 45–55%), heat stress treatment, exposure to environmental temperature (HS; average THI: 82.74), and heat stress supplemented with niacin treatment (HN; high temperature + 800 mg/kg NA). Measured indicators were body temperature, respiratory rate, production performances, rumen fermentations, and microbial diversity. Results showed that adding niacin reduced the body temperature and respiratory rate (P < 0.05) but had no significant effect on the production performances compared with heat-stressed beef cattle. HS treatment significantly increased body temperature and respiratory rate (P < 0.01), while decreasing the content of acetic acid, butyric acid, and total volatile fatty acids (P < 0.05) compared with the TN treatment. Supplement of niacin did not affect ruminal fermentation parameters (P > 0.05) but had a decreased tendency on A/P (P < 0.1). Microbial diversity results showed that, at the phylum level, the relative abundance of Desulfobacterota in the HS treatment was increased compared with TN and HN treatment (P < 0.05). At the genus level, the relative abundance of Succiniclasticum and Family_XIII_AD3011 group in the HN treatment significantly proliferated compared with the HS treatment (P < 0.05). In conclusion, niacin supplementation may alleviate heat stress by proliferating those bacteria belonging to the phylum Succiniclasticum, which may further contribute to the digestion of cellulose and the improvement of the metabolic function of Jinjiang cattle under heat-stress conditions.

Effects of rising VPD on the nutrient uptake, water status and photosynthetic system of tomato plants at different nitrogen applications under low temperature

In winter and spring, the low-temperature and high-humidity environment of greenhouses in China and some locations are not suited for the development of tomatoes, which is sensitive to cold. At low temperature circumstances, the plant growth is slow, and the water transpiration ability is weak. The study tried to increase the vapor pressure deficit (VPD) by decreasing the humidity to observe if it can promote plant transpiration, which in turn facilitates nutrient absorption conveyed by the water, or it directly influences plant development through the alteration of the plant morphological structure. Two VPD levels (high VPD, HVPD; low VPD, LVPD) and three N supply gradients (low N level, LN; normal N level, NN; high N level, HN) were set in a climate chamber for 30 days test. We observed the physiological alterations of plants. The results revealed that biomass of low nitrogen, normal nitrogen and high nitrogen of HVPD plants decreased by 22.54%, 40.75% and 10.31%, respectively, compared with LVPD-treated plants. The palisade/spongy tissue ratio in leaves of HVPD plants decreased at normal and high nitrogen levels. Under HVPD conditions, the stomatal length and width increased, but its density decreased; the electron transfer and photochemical efficiency of the photosystem reaction center reduced. At low, normal and high nitrogen concentration, the photosynthetic rate of HVPD plants was 17.29%, 30.18% and 15.15% lower than that of LVPD plants. For HVPD plants, compared with LVPD plants, K+ absorption under LN increases significantly; nutritional absorption with HN treatment reduced significantly; the absorption of trace elements was also lower than LVPD plants. It revealed that even within the theoretically suitable VPD range for plant growth, rising VPD cannot achieve the purpose of improving nutrient absorption and stimulating growth. It needed to be examined according to certain environmental circumstances. In addition, the promotion impact of increasing N fertilizer was restricted, and it may not be favorable to plant development. At low nitrogen, LVPD treated plants thrived nicely, compared with HVPD treated plants. The investigation revealed that the optimal growth treatment at low temperature was LVPD+NN treatment.