Soil salinization threatens soil organic carbon (SOC) sequestration. Although microbial necromass carbon (MNC) is crucial for SOC formation and stability, how biochar affects MNC in saline–alkaline soils remains unclear. This study assessed the impact of biochar amendment (0, 10, 20, and 30 t ha⁻¹) on SOC and MNC dynamics in saline–alkaline soils cultivated with Arundo donax cv. Lvzhou No. 1 across tillering, jointing, and maturity stages. Biochar amendment significantly enhanced SOC and the soil C/N ratio, with the highest dose (30 t ha⁻¹) raising SOC by 47.21% at jointing and 34.64% at maturity. Biochar significantly increased MNC at all growth stages, with increases ranging from 22.74% to 30.81%. From the jointing to the maturity stage, SOC exhibited a decline (20.03 to 27.77%), in contrast to the minimal change in MNC (–6.37% to 9.80%). This divergent trend consequently led to a peak in the MNC/SOC ratio at maturity. It directly demonstrates the relative stability of MNC and indicates its role as a persistent carbon reservoir within the topsoil. Biochar also elevated soil pH and nutrient availability, which reshaped microbial community structure and enhanced bacterial diversity. Partial least squares path modeling revealed that biochar facilitates MNC accumulation directly and indirectly by modifying soil chemical properties and thereby enhancing microbial diversity. These findings show that biochar enhances stable SOC storage in saline–alkaline soils primarily through the formation and stabilization of microbial necromass, thus revealing its potential for climate change mitigation.

The factors driving plant species diversity in different forest types and layers are still insufficiently understood. Therefore, we investigated the limiting factors of nutrient and water use efficiency in three forest layers (arbor, shrub and herb layers) and two forest types (plantation forest and natural forest), as well as their potential relationship with plant species diversity. The study area is located in mid-latitude evergreen broad-leaved forest ecosystems in southern Anhui province. The nitrogen content in the soil (2.90 g kg⁻¹) exceeded the national average for forest ecosystems (1.06 g kg⁻¹), whereas the phosphorus content (0.43 g kg⁻¹) was below the national average for such ecosystems (0.65 g kg⁻¹). The plant species diversity in the arbor layer was comparatively low, and nitrogen exerted a more substantial influence on it. In contrast, phosphorus had the most significant impact on the shrub and herb layers. In conclusion, nitrogen has little effect on plant growth patterns in this area, while there is a potential role for phosphorus in regulating plant succession rates. There are phenomenon of excessive nitrogen deposition and phosphorus loss in this forest ecosystem. Despite the fact that the plant species diversity indices (the Pielou Evenness Index, Gleason Richness Index, Shannon–Wiener Diversity Index and Simpson Dominance Index) in natural forests were higher than that in plantation forests, the disparity between them was not significant (p > 0.05). This may be due to similar water use efficiency and climate. The findings of this research hold substantial significance for forecasting the alterations in plant species diversity, functionality, and their influencing factors within mid-latitude evergreen broad-leaved forests.

Poplar (Populus L. species), a fast-growing temperate species, forms plantations with high productivity and biomass, with its litter sustaining key functions in nutrient cycling, microbial diversity, and carbon storage. Litter microbial communities drive decomposition, particularly in early stages, this initial phase is characterized by the leaching of water-soluble carbon and nutrients from the litter, which creates a readily available resource pulse that facilitates rapid microbial colonization and activation. This process is followed by the activation of microbial enzymes and the immobilization of nutrients, collectively initiating the breakdown of more recalcitrant litter materials. Under rising global nitrogen deposition, we conducted a field randomized block experiment in 13-year-old pure poplar (Populus deltoides L. ‘35’) stands, with three nitrogen addition treatments: N0 (0 g N·m⁻²·yr⁻¹), N2 (10 g N·m⁻²·yr⁻¹), and N4 (30 g N·m⁻²·yr⁻¹). In the initial phase of litter decomposition, we measured the soil properties and litter traits, the litter microbial community composition, and its taxonomic and phylogenetic diversity indices. The results indicate that nitrogen addition altered microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), soil NO₃⁻-N, and accelerated litter decomposition rates. The microbial community in leaf litter responded to nitrogen addition with increased phylogenetic clustering (higher OTU richness and NRI), which suggests that environmental filtering exerted a homogenizing selective pressure linked to both soil and litter properties, whereas the microbial community in branch litter responded to nitrogen addition with increased taxonomic diversity (higher OTU richness, Shannon, ACE, and Chao1), a pattern associated with litter properties that likely alleviated nitrogen limitation and created opportunities for more taxa to coexist. The observed differences in response stem from distinct substrate properties of the litter. This study elucidates microbial taxonomic and phylogenetic diversity responses to nitrogen addition during litter decomposition, offering a scientific foundation for precise microbial community regulation and sustainable litter management.

Accelerated urbanization has intensified nitrogen deposition and fine particulate matter (PM_2.5) pollution. While urban landscape plants play a vital role in atmospheric remediation, systematic exploration of their adaptation strategies to these dual stressors remains limited. This study investigated the dynamic responses of antioxidant defense systems and nitrogen/weight ratios of Iris germanica L. and Portulaca grandiflora Hook. under four nitrogen deposition scenarios (N0, N1, N2, and N4 with nitrogen concentrations of 0, 15, 30, and 60 kg N·hm⁻²·a⁻¹, respectively) combined with constant PM_2.5 exposure (50 μg/m³). Through fumigation experiments, we demonstrated that Iris germanica L. showed higher sensitivity to inorganic nitrogen-laden PM_2.5 stress than Portulaca grandiflora Hook. Both species exhibited stronger antioxidant enzyme (SOD, CAT, POD) activities in the high-growth season compared to the low-growth season. Nitrogen allocation analysis revealed that Portulaca grandiflora Hook. maintained stable nitrogen content across treatments, while Iris germanica L. showed progressive nitrogen loss under high nitrogen-laden PM_2.5 exposure. These findings establish Portulaca grandiflora Hook.’s superior resilience through two synergistic mechanisms: modulated antioxidant systems and efficient nitrogen remobilization. This comparative study provides actionable insights for selecting pollution-tolerant species in urban green infrastructure planning.