Nitrogen addition and mowing had only weak interactive effects on macronutrients in plant-soil systems of a typical steppe in Inner Mongolia.

Effective management of macronutrients is pivotal in the optimization and provisioning of ecosystem services in grassland areas, particularly in degraded grasslands. In such instances where mowing and nitrogen (N) fertilization have emerged as predominant management strategies, nutrient management is especially important. However, the precise effects of these concurrent practices on the distribution of macronutrients in plant-soil systems remain unclear. Here we evaluated the effects of 12 years of N addition (2, 10, and 50 g N m-2 year-1) and mowing on the concentrations and pools of six macronutrients (i.e., N; phosphorus P; sulfur S, calcium Ca, magnesium Mg, and potassium K) in three plant components (aboveground plants, litter, and belowground roots) at the community level and in the soil in a typical steppe in Inner Mongolia. Our results revealed that N addition generally raised the N concentration in the entire plant-soil system, regardless of whether plots were mowed. Higher N addition (10 and 50 g N m-2 year-1) also led to higher concentrations of P (+22%, averaging two N addition rates), S (+16%), K (+22%), Ca (+22%), and Mg (+24%) in plants but lower concentrations of these nutrients in the litter. Similar decreases in K (-9%), Ca (-46%), and Mg (-8%) were observed in the roots. In light of the observed increases in vegetation biomass and the lack of pronounced changes in soil bulk density, we found that the ecosystem N enrichment resulted in increased pools of all measured macronutrients in plants, litter, and roots (with the exception of Ca in the roots) while concurrently decreased the pools of P (-20%, averaging two higher N addition rates), S (-12%), K (-10%), Ca (-37%), and Mg (-19%) in the soil, with no obvious effect of the mowing practice. Overall, mowing exhibited a very limited capacity to alleviate the effects of long-term N addition on macronutrients in the plant-soil system. These findings highlight the importance of considering the distribution of macronutrients across distinct plant organs and the dynamic nutrient interplay between plants and soil, particularly in the context of long-term fertilization and mowing practices, when formulating effective grassland management strategies.

Enhanced foliar 15 N enrichment with increasing nitrogen addition rates: Role of plant species and nitrogen compounds.

Determining the abundance of N isotope (δ15 N) in natural environments is a simple but powerful method for providing integrated information on the N cycling dynamics and status in an ecosystem under exogenous N inputs. However, whether the input of different N compounds could differently impact plant growth and their 15 N signatures remains unclear. Here, the response of 15 N signatures and growth of three dominant plants (Leymus chinensis, Carex duriuscula, and Thermopsis lanceolata) to the addition of three N compounds (NH4 HCO3 , urea, and NH4 NO3 ) at multiple N addition rates were assessed in a meadow steppe in Inner Mongolia. The three plants showed different initial foliar δ15 N values because of differences in their N acquisition strategies. Particularly, T. lanceolata (N2 -fixing species) showed significantly lower 15 N signatures than L. chinensis (associated with arbuscular mycorrhizal fungi [AMF]) and C. duriuscula (associated with AMF). Moreover, the foliar δ15 N of all three species increased with increasing N addition rates, with a sharp increase above an N addition rate of ~10 g N m-2  year-1 . Foliar δ15 N values were significantly higher when NH4 HCO3 and urea were added than when NH4 NO3 was added, suggesting that adding weakly acidifying N compounds could result in a more open N cycle. Overall, our results imply that assessing the N transformation processes in the context of increasing global N deposition necessitates the consideration of N deposition rates, forms of the deposited N compounds, and N utilization strategies of the co-existing plant species in the ecosystem.

Effects of 12-Year Nitrogen Addition and Mowing on Plant-Soil Micronutrients in a Typical Steppe.

Changes in soil micronutrient availability may have adverse consequences on grassland productivity, yet it's still largely unclear how concurrent human practices, such as fertilization and mowing, affect micronutrient cycling in the plant-soil systems. Here, we measured six essential micronutrient (Fe, Mn, Cu, Zn, Co and Mo) contents in both plant pool (separated as aboveground plant parts, litter, and belowground roots) at the community level and soil pool (0−10 cm depth) after 12-year consecutive nitrogen (N) addition (0, 2, 10, and 50 g N m−2 year−1) and mowing in a typical steppe of the Mongolian Plateau. The results show that (i) medium-N (10 g m−2 year−1) and high-N (50 g m−2 year−1) addition rates significantly increased contents of soil-available Fe (+310.0%, averaging across the two N addition rates), Mn (+149.2%), Co (+123.6%) and Mo (+73.9%) irrespective of mowing treatment, whereas these addition treatments usually decreased contents of soil total Fe (−8.9%), Mn (−21.6%), Cu (−15.9%), Zn (−19.5%), Co (−16.4%) and Mo (−34.7%). (ii) Contents of Fe in aboveground plant parts, litter, and roots significantly decreased, whereas plant Mn increased with N addition. Contents of above ground plant Cu, Zn, Co, and Mo significantly decreased at high-N addition rate, whereas contents of micronutrients in roots and litters, except for Fe, generally increased with N addition. Moreover, the total amount of micronutrients in the plant pool (contents × biomass) significantly increased at the medium-N addition rate but decreased at the high-N addition rate. All N addition rates significantly enlarged the pool of litter micronutrients, and roots could hold more micronutrients under N addition, especially combined with mowing treatment. Importantly, although mowing could regulate the effects of N addition on variables (i) and (ii), the effects were weaker overall than those of N addition. (iii) Changes in root micronutrients, except for Mn, could explain corresponding changes in plant micronutrients (R2: 0.19−0.56, all p < 0.01), and significant linear correlations were also observed between soil-available Fe and Fe in plant and roots. Aboveground plant Mn was significantly correlated with soil-available Mn, while Co and Mo in roots were also significantly correlated with soil-available Co and Mo. These results indicate that soil micronutrient supply capacity may decrease due to a decrease in total micronutrient contents after long-term N addition and mowing. They also suggest that different magnitude responses of soil micronutrients in plants (i.e., litters, roots) and soil should be considered when comprehensively examining nutrient cycling in grassland ecosystems.

CircSLC16A12 Absence Inhibits High Glucose-Induced Dysfunction in Retinal Microvascular Endothelial Cells through Mediating miR-140-3p/FGF2 Axis in Diabetic Retinopathy.

PURPOSE: Diabetic retinopathy (DR) is a common microvascular complication of diabetes mellitus which can cause irreversible visual impairment and blindness. We intended to investigate the function of circular RNA (circRNA) solute carrier family 16 member 12 (SLC16A12) in DR progression. METHODS: Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and Western blot assay were applied to measure RNA and protein expression. Cell apoptosis was analyzed by flow cytometry (FCM) analysis. The angiogenesis ability was assessed by tube formation assay. Enzyme-linked immunosorbent assay (ELISA) was performed to analyze the release of inflammatory cytokines. Cell oxidative stress status was evaluated using commercial kits. Dual-luciferase reporter assay, RNA immunoprecipitation (RIP) assay, and RNA-pull down assay were conducted to confirm the intermolecular interactions. RESULTS: CircSLC16A12 level was enhanced in the serum samples of DR patients and high glucose (HG)-treated HRECs. CircSLC16A12 absence protected HRECs from HG-induced apoptosis, blood-retinal barrier (BRB) injury, tube formation, inflammatory response, and oxidative stress. CircSLC16A12 acted as a sponge for microRNA-140-3p (miR-140-3p), and circSLC16A12 knockdown-mediated effects were largely reversed by the absence of miR-140-3p in HRECs under HG condition. miR-140-3p interacted with the 3' untranslated region (3'UTR) of fibroblast growth factor 2 (FGF2), and the overexpression of FGF2 largely overturned miR-140-3p overexpression-mediated effects in HRECs. CircSLC16A12 interference reduced the expression of FGF2 by up-regulating miR-140-3p in HRECs. CONCLUSION: CircSLC16A12 silencing suppressed HG-induced dysfunction in HRECs partly by targeting miR-140-3p/FGF2 axis.

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Increasing atmospheric nitrogen (N) deposition greatly affects species diversity, productivity, and stability of ecosystems. It is thus of the great importance to understand how grassland N pools respond to the increased atmospheric N deposition. This study was conducted in a meadow steppe in Erguna, Inner Mongolia, China. There were six levels of N addition (i.e., 0, 2, 5, 10, 20 and 50 g·m-2·a-1) and two levels of mowing (i.e., mowing and unmown). Samples of aboveground tissues of dominant plant, root, aboveground litter, and soil to the depth of 100 cm were collected in the seventh year after treatments. The N content was measured and the N pool was calculated. The results showed that N addition significantly increased the N content of aboveground plant tissues and litter, as well as N pools of Leymus chinensis, plant community, litter and ecosystem. Mowing significantly increased the N content of L. chinensis leaf and litter, but reduced N pools of L. chinensis, plant community and litter, and did not affect their responses to N addition. There was a significant interactive effect between mowing and N addition on plant community N pool. High levels of N addition in the unmown treatment led to more N stored in the litter pool, with the saturation threshold for the plant community N pool occurred at 10 g·m-2·a-1. Under mowing treatment, the plant community N pool increased with the increasing N addition, and more N stored in plant community N pool after mowing. Mowing could alleviate the negative impacts of increasing N deposition on biodiversity and ecosystem stability, and extended postponing the occurrence of ecosystem N saturation induced by increasing N deposition.