This study investigates the role of arbuscular mycorrhizal (AM) fungi, particularly Rhizophagus irregularis, in enhancing the lead (Pb) stress tolerance of poplar trees (Populus simonii × P. nigra ‘1307’). Under Pb stress conditions (0, 250, and 750 mg/kg), AM fungi significantly improved poplar growth, evidenced by increases in plant height (25.4%–31.2%), shoot biomass (21.6%–37.8%), and root biomass (28.9%–41.7%). Photosynthetic parameters, including net photosynthetic rate (P_n), stomatal conductance (G_s), and transpiration rate (T_r), were substantially enhanced by AM inoculation. For instance, at 750 mg/kg Pb, Pn increased by 46.8% compared to non-inoculated controls. AM fungi facilitated Pb sequestration primarily in the roots, leading to 53.7% lower Pb concentrations in leaves and 47.3% lower concentrations in stems under 750 mg/kg Pb stress. This was attributed to root barrier effects and reduced Pb translocation. AM fungi also mitigated oxidative stress by increasing antioxidant enzyme activities, including superoxide dismutase (SOD, +45.6%), catalase (CAT, +38.2%), and peroxidase (POD, +32.5%). Concurrently, hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) levels decreased significantly, indicating enhanced membrane stability. These findings reveal that AM fungi improve Pb stress resistance in poplar by promoting Pb immobilization in roots, enhancing photosynthetic performance, and fortifying antioxidant defense systems. This study provides both theoretical insights and practical implications for utilizing AM fungi in phytoremediation of Pb-contaminated soils.

Globally, 14–20% of peatlands are affected by agricultural activities, which account for about one-third of global greenhouse gas emissions from farmlands. However, how agricultural activities such as nitrogen fertilization affect peatlands’ CH₄, CO₂ and N₂O emission patterns and their resulting warming effects needs to be improved and complemented. Here, we elucidate the characterization of CH₄, CO₂ and N₂O emissions from the soil surface and different depths of the soil profile during the growing season of agricultural peatlands for over 50 years and the mechanisms of their resulting global warming potential (GWP) impact through field monitoring and molecular techniques. The 100-year GWP of peatlands increased by 1200% with N fertilization of 260 kg N ha⁻¹ yr⁻¹. At the soil surface, N fertilization increased CO₂ and N₂O emissions by 111% and 2600%, respectively, although CH₄ emissions decreased by 87%. In the soil profile, N fertilization had a significant effect on CO₂ from 0 to 60 cm, resulting in an increase in CO₂ concentrations of 14–132%, whereas the top 30 cm of soil was the zone of significant N fertilization effects, with CH₄ concentrations decreasing by 49–95% and N₂O concentrations increasing by 22–26%. Elevated soil pH and NH₄⁺ were the key environmental factors influencing CH₄, CO₂ and N₂O emissions and their resulting increase in GWP. These results suggest that agricultural N fertilization led to a change in the contributor to the GWP of peatlands from CH₄ to N₂O, especially in the top 30 cm of soil. This study helps to provide theoretical support for the development of effective peatland management strategies.

The sharp increase in atmospheric nitrogen deposition has had profound effects on nitrogen availability and the photosynthetic capacity of terrestrial plants. Consequently, understanding the intricate trade-off between nitrogen sources and their allocation within leaves is essential for unraveling the photosynthetic responses of grassland ecosystems to nitrogen deposition. In a series of field experiments, the effects of different nitrogen forms (ammonium and nitrate nitrogen) on nitrogen assimilation and allocation in the C₄ plant Hemarthria altissima were thoroughly investigated. Towards the end of the growing season, H. altissima was observed to exhibit high photosynthetic efficiency. Ammonium nitrogen treatment notably enhanced photosynthetic nitrogen use efficiency (PNUE) by modifying the nitrogen allocation within the leaf’s photosynthetic apparatus and leaf area, leading to a significant improvement in photosynthetic efficiency and biomass accumulation. Under ammonium nitrogen treatment, H. altissima directed more nitrogen toward its carboxylation process and other protein-related functions to increase carboxylation efficiency, thereby facilitating the accumulation of photosynthetic products. In contrast, under nitrate nitrogen treatment, the plant balanced growth and light absorption by allocating nitrogen to leaf light-capturing proteins. The application of both ammonium and nitrate nitrogen resulted in increased nitrogen content in the soil, as ammonium nitrogen is converted to nitrate nitrogen through nitrification. The net photosynthetic rate (A_n), nitrogen allocation to photosynthetic components (N_psn), and chlorophyll content per unit area (Chl_area) were all significantly and positively correlated with photosynthetic nitrogen use efficiency (PNUE). Notably, under the sole NH₄⁺ treatment, nitrogen allocation to the photosynthetic components increased, which enhanced the NPQ and ETR in H. altissima leaves. These findings suggest that H. altissima preferentially utilizes ammonium nitrogen from the soil, optimizing its PNUE and biomass accumulation through a strategic allocation of nitrogen within its leaves. Further investigation is needed to explore how these nitrogen allocation strategies may vary under different environmental conditions and how they influence ecosystem-level productivity.

Low temperature combined with fluctuating irradiance frequently co-occurs and suppresses photosynthesis, with irreversible injury to photosystem I (PSI) recognized as a key constraint on growth and yield. To test whether exogenous hydrogen sulfide (H₂S) mitigates this “cold–fluctuating light” stress in mulberry, we established six treatment combinations (room temperature controls, sodium hydrosulfide, and hypotaurine, each with or without low temperature plus fluctuating light). We quantified PSI/PSII photochemical properties, gas exchange, reactive oxygen species (ROS), and antioxidant enzyme activities. Under cold with fluctuating light, PSI was strongly inhibited: Y_NA increased, whereas Y_I and ΔI/I_o decreased, and the P700 re-reduction half-time (t½) was prolonged (ANOVA, Tukey’s HSD, p < 0.05), indicating pronounced acceptor-side over-reduction and impaired electron transport. PSII performance also declined (lower F_v/F_m and PI_ABS, higher ΔV_J; p < 0.05). NaHS pretreatment significantly alleviated these effects relative to the stressed control: PSI/PSII metrics partly recovered, net photosynthetic rate (P_n) and water-use efficiency (WUE) increased, H₂O₂ and MDA decreased, and SOD/POD/CAT activities rose (p < 0.05). Notably, NPQ_high correlated negatively with Y_NA (Pearson r < 0, p < 0.001), consistent with the notion that enhanced energy dissipation relieves PSI acceptor-side limitation. We propose that exogenous H₂S stabilizes electron transport and supports carbon assimilation via a dual strategy—faster engagement of energy dissipation and activation of antioxidant defenses—highlighting its potential utility for managing stress in fruit crops under erratic early-season weather.

Atmospheric nitrogen deposition is increasing worldwide, with profound implications for plant nitrogen acquisition and ecosystem nutrient cycling, particularly in nitrogen-limited systems. In this study, we investigated how inorganic nitrogen form regulates nitrogen uptake in H. altissima through pot experiments by applying ammonium nitrogen, nitrate nitrogen, mixed nitrogen, and a nitrogen-free control in Songnen grassland ecosystems at the eastern end of Eurasia. Soil abiotic properties, root morphological traits, and nitrogen uptake dynamics were jointly quantified using integrative modeling in combination with ¹⁵N stable isotope tracing. Relative to the no-nitrogen control, both ammonium and nitrate nitrogen significantly altered soil physicochemical conditions and stimulated root development, with ammonium consistently exhibiting stronger effects. Ammonium and nitrate applications reduced soil pH by 4.83% and 6.25%, increased electrical conductivity by 2.01% and 1.17%, and enhanced inorganic nitrogen pools by 115.84% and 45.69%, respectively. Root morphological traits were significantly enhanced under ammonium, nitrate, and mixed nitrogen treatments. ¹⁵N tracing further demonstrated that ammonium nitrogen significantly increased root ¹⁵N uptake compared with the no-nitrogen control (p < 0.05) and promoted a 20.10% greater allocation of absorbed nitrogen to aboveground biomass than nitrate nitrogen. Collectively, these findings highlight nitrogen form as a key regulator of soil–plant nitrogen coupling, with ammonium nitrogen more effectively enhancing nitrogen acquisition and internal translocation than nitrate.

(1) Background: Seasonal breeding constraints represent a long-standing barrier to efficient sheep production worldwide. Small Tail Han sheep, a Chinese indigenous breed that exhibits year-round estrus independent of photoperiod, offers a unique natural model for investigating the regulatory mechanisms underlying estrus cyclicity—yet the molecular basis of this remarkable trait remains largely unexplored. This study therefore aimed to compare ovarian whole-transcriptome profiles between Small Tail Han sheep (year-round estrus) and Ujumqin sheep (seasonal estrus) during estrus and diestrus. Specifically, we sought to characterize breed-specific transcriptional response strategies, identify key miRNAs associated with continuous estrus, and construct ceRNA networks that mediate ovarian estrous cycle regulation. (2) Methods: To address these objectives, we profiled ovarian transcriptomes of Small Tail Han sheep (year-round estrus) and Ujumqin sheep (seasonal estrus) during both estrus and diestrus (12 samples total) using whole-transcriptome sequencing, systematically characterizing the expression landscapes of mRNAs, miRNAs, lncRNAs and circRNAs. Through differential expression analysis, GO/KEGG functional enrichment, multi-tiered miRNA screening, and ceRNA network construction, we compared the transcriptional response strategies between the two breeds. (3) Results: Our findings revealed two unexpected and divergent patterns. Small Tail Han sheep showed 1881 differentially expressed mRNAs between estrus and diestrus, 82-fold more than the 23 in Ujumqin sheep, suggesting a broader mRNA-level transcriptional response in the year-round estrus breed. circRNAs were predominantly up-regulated (80–85%) in both breeds, while mRNAs and lncRNAs were predominantly down-regulated, uncovering a conserved “circRNA-up, mRNA-down” regulatory logic across breeds. Multi-tiered screening identified 38 “brake-releaser” miRNAs (high in diestrus, down-regulated in estrus) and 21 “accelerator” miRNAs (low in diestrus, up-regulated in estrus), which together constitute a “de-repression–activation” dual regulatory mode. ceRNA network analysis further revealed a clear functional stratification: conserved core miRNAs targeted “sensor” pathways (cAMP, PI3K-Akt, MAPK), whereas accelerator miRNAs specifically targeted “executor” pathways (estrogen signaling, progesterone-mediated oocyte maturation, Hippo signaling). Network topology analysis pinpointed miR-199a-5p, miR-204-3p and miR-199b as the core hubs bridging the two regulatory modules. (4) Conclusions: Taken together, our findings redefine the molecular basis of year-round estrus—moving beyond single-gene mutations or overexpression to an enhanced global transcriptomic responsiveness of the ovary. This work provides a fresh conceptual framework for understanding the divergence of reproductive strategies in sheep and offers actionable candidate targets for genetic improvement of continuous estrus traits.