Understanding the composition and diversity of soil microorganisms that typically mediate the soil biogeochemical cycle is crucial for estimating greenhouse gas flux and mitigating global changes in plantation forests. Therefore, the objectives of this study were to investigate changes in diversity and relative abundance of bacteria and archaea with soil profiles and the potential factors influencing the vertical differentiation of microbial communities in a poplar plantation. We investigated soil bacterial and archaeal community compositions and diversities by 16S rRNA gene Illumina MiSeq sequencing at different depths of a poplar plantation forest in Chenwei forest farm, Sihong County, Jiangsu, China. More than 882,422 quality-filtered 16S rRNA gene sequences were obtained from 15 samples, corresponding to 34 classified phyla and 68 known classes. Ten major bacterial phyla and two archaeal phyla were found. The diversity of bacterial and archaeal communities decreased with depth of the plantation soil. Analysis of variance (ANOVA) of relative abundance of microbial communities exhibited that Nitrospirae, Verrucomicrobia, Latescibacteria, GAL15, SBR1093, and Euryarchaeota had significant differences at different depths. The transition zone of the community composition between the surface and subsurface occurred at 10–20 cm. Overall, our findings highlighted the importance of depth with regard to the complexity and diversity of microbial community composition in plantation forest soils.

Root biomass and length growth, functional traits, and their responses to soil nutrient availability are crucial for resource acquisition under environmental change. Previous studies have focused on the response of root morphological, architectural, and chemical traits to fertilization, while less attention has been given to root biomass and length growth, as well as mycorrhizal symbiosis, impeding a full understanding of root resource acquisition strategies. Here, using a nutrient addition experiment (control, inorganic, and organic nutrients), we explored the responses of function-based root (absorptive fine roots [AFRs] versus transport fine roots [TFRs]) growth, functional traits (morphological, architectural, and chemical traits), and mycorrhizal colonization of C. lanceolat and Q. acutissim, which are the dominant tree species in subtropical China. The results showed that the fine root biomass and total root length of AFRs for both tree species basically decreased significantly after nutrient addition, but TFRs responded less sensitively than AFRs. Nutrient addition significantly increased the mycorrhizal colonization rate in C. lanceolata but decreased it in Q. acutissima. The diameter of AFRs for C. lanceolata increased significantly, while the branch ratio and branch intensity decreased significantly in both inorganic nutrients (NPK) and organic nutrients (F); however, the opposite response pattern occurred for Q. acutissima. Fine root biomass, total root length, and root nutrient concentration exhibited the most plastic responses to changes in nutrient availability. The magnitude of the plastic response of fine root traits was slightly higher in the NPK treatment than in the F treatment. Our findings suggest that the responses of fine root traits and mycorrhizal fungi to nutrient addition were species-specific: C. lanceolata depended on mycorrhizal fungi for resource acquisition, while Q. acutissima could acquire soil nutrient resources by increasing root branching. The contrasting nutrient acquisition strategies between tree species may facilitate plant species coexistence and distribution under soil nutrient change. Fine root biomass and total root length emerged as more pivotal indicators for nutrient acquisition strategies compared to morphological traits.

The mechanisms through which forest thinning influences the fine root foraging strategies of coexisting tree species in mixed forests remain unclear, limiting our ability to manage mixed forests for long-term productivity. We employed a space-for-time substitution approach in a Qinling pine-oak forest, in which fine roots of Pinus tabuliformis (Pt) and Quercus aliena var. acuteserrata (Qa) were sampled from unthinned plots and plots thinned 6 years (transient phase) and 14 years (persistent phase) prior, respectively. We analyzed the morphological and chemical traits of both absorptive and transport fine roots (0–20 cm depth) to decipher their distinct adaptation strategies. The results showed that Pt enhanced morphological plasticity in both absorptive and transport roots at T₂₀₁₀ (e.g., specific root length: +44% and 37%, p < 0.05). In contrast, Qa showed minimal changes in absorptive root morphology and chemistry (p > 0.05). Redundancy analysis indicated that thinning intensified functional divergence in root strategies between the two tree species and between the two root functional types (i.e., absorptive vs. transport fine roots). Hierarchical variance partitioning analysis indicated that root functional type was the primary driver (51.9%), with tree species identity (Pt vs. Qa) and thinning practices being secondary. Critically, soil properties significantly shaped absorptive root traits (explaining 10.4% of the variance) but did not affect transport root traits, whereas thinning was a dominant factor for transport roots (21.6%). This insight enables the tailoring of silvicultural interventions to tree species-specific foraging strategies, optimizing belowground resource acquisition in mixed forests.

Forest phenology directly reacts to global climate change, potentially regulating greenhouse gas fluxes between ecosystems and the atmosphere. To explore this phenomenon in two plain poplar (Populus spp.) forests in eastern China, we measured CO₂ fluxes and phenology at the canopy scale based on the eddy covariance and PhenoCam technology. From 2019 to 2022, poplars in a high-speed wind site (HWS) experienced shorter maturity durations (108 ± 4.9 days vs. 152 ± 1.2 days) and an earlier date of foliar senescence (day of year: 223.8 ± 2.5 vs. 259.5 ± 0.9) than those in the low-speed wind site (LWS). The annual net CO₂ uptake in the HWS (689.65 ± 105.15 g C·m⁻²·year⁻¹) was approximately 2.4 times higher than that in the LWS (285.65 ± 81.37 g C·m⁻²·year⁻¹). Our results indicate that environmental changes like wind stress alter forest phenology that can dynamically regulate ecosystem respiration and gross primary production.

The root economics spectrum predicts coordinated trait shifts to a heterogeneous soil environment, yet how roots strategically respond to litter-driven nutrient patches is not fully understood. We conducted a litter addition experiment (CK: 0, Low: 30, Medium: 60, High: 120 g) in a Qinling mixed forest, quantifying root responses of Pinus tabuliformis (Pt) and Quercus aliena var. acuteserrata (Qa). Soil inorganic nitrogen (NH₄⁺-N and NO₃⁻-N) increased significantly only under high litter inputs (by 138% and 130%, respectively; p < 0.001), indicating a threshold effect. Root carbon and nitrogen concentration generally increased under the Medium and High litter addition treatments compared to the Low treatments (p < 0.05), while morphological traits remained conservative (p > 0.05). Species identity showed no significant effect in the multivariate root trait syndrome (redundance analysis, p = 0.716), though species-specific responses were observed in the root carbon concentration (Pt: p < 0.05; Qa: n.s.). These results demonstrate a hierarchical foraging strategy where physiological plasticity dominates over morphological change, challenging the root economics spectrum and providing a multidimensional framework for predicting root function in heterogeneous environments.