Large-scale Quercus variabilis natural secondary forests are protected under the Natural Forest Protection (NFP) program in China to improve the ecological environment. However, information about nutrient characteristics and carbon (C) storage is still lacking. Plant biomass and C, nitrogen (N) and phosphorus (P) stoichiometry of tree tissues, shrubs, herbs, litter, and soil were determined in young, middle-aged, near-mature and mature Quercus variabilis secondary forests in the Qinling Mountains, China. Tree leaf N and P concentrations indicated that the N-restricted situation worsened with forest age. The per hectare biomass of trees in decreasing order was near-mature, mature, middle-aged, then young stands. The majority of the biomass was in the stems (44.88–48.15%), followed by roots (24.54–28.68%), and branches (10.15–14.16%), and leaves made up the lowest proportion (2.86–3.55%) of trees. C storage at plant layer increased significantly with age, reaching maximum values in near-mature stand (100.4 Mg·ha⁻¹) and then decreasing in mature stands. Soil C storage at a depth of 0 to 100 cm was 82.8, 96.8, 85.8, 104.2 Mg·ha⁻¹, and C storage of forest ecosystem was 122.8, 163.0, 184.9, 178.3 Mg·ha⁻¹ in young, middle-aged, near-mature, mature stands, respectively. There were significant correlations between biomass and C, N, P stoichiometry in different layers, especially in young stands.

Introduction: Salinity and droughts are severe abiotic stress factors that limit plant growth and development. However, the differences and similarities of non-structural carbohydrates (NSCs) responses patterns of trees under the two stress conditions remain unclear.Methods: We determined and compared the growth, physiology, and NSCs response patterns and tested the relationships between growth and NSCs concentrations (or pool size) of Eucommia ulmoides seedlings planted in field under drought and salt stress with different intensities and durations.Results and discussion: We found that drought and salt stress can inhibit the growth of E. ulmoides, and E. ulmoides tended to enhance its stress resistance by increasing proline concentration and leaf thickness or density but decreasing investment in belowground biomass in short-term stress. During short-term drought and salt stress, the aboveground organs showed different NSCs response characteristics, while belowground organs showed similar change characteristics: the starch (ST) and NSCs concentrations in the coarse roots decreased, while the ST and soluble sugar (SS) concentrations in the fine roots increased to enhance stress resistance and maintain water absorption function. As salt and drought stress prolonged, the belowground organs represented different NSCs response patterns: the concentrations of ST and SS in fine roots decreased as salt stress prolonged; while ST in fine roots could still be converted into SS to maintain water absorption as drought prolonged, resulting in an increase of SS and a decrease of ST. Significant positive relationships were found between growth and the SS and total NSCs concentrations in leaves and branches, however, no significant correlations were found between growth and below-ground organs. Moreover, relationships between growth and NSCs pool size across organs could be contrast.Conclusion: Our results provide important insights into the mechanisms of carbon balance and carbon starvation and the relationship between tree growth and carbon storage under stress, which were of great significance in guiding for the management of artificial forest ecosystem under the context of global change.

Relative growth rate (RGR) has been a core demographic performance trait in community ecology because its species‐specific divergent responses to light often determine community structure and dynamics. Nevertheless, how divergent responses of plant species in RGR to water stress govern community assembly, alongside the mechanistic basis of inter‐ and intra‐specific variations in functional traits, remain elusive. We propose a theoretical framework for describing how the directional change of RGR across dry and wet patches drives community assembly in a landscape with frequent droughts. The framework was applied to a subtropical understory shrub community where rock fragment content, an important proxy for water stress, shows strong spatial variability. Our empirical evidence demonstrated that RGR directional change (RGR_{dir change}) was more robust than RGR in wet patches, RGR in dry patches and the mean RGR in predicting species' dominance hierarchy. Inter‐specific variation in functional traits contributed equally to inter‐specific variation in mediating shifts in species' RGR_{dir change}. Species with increasing RGR as substrate water availability decreased were dominant (with higher relative abundance and importance). Dominant species generally had acquisitive roots and hydraulically safe stems. In response to decreasing substrate water availability, dominant species further increased their leaf drought tolerance and optimized root specific length, which not only contributed to their faster radial stem growth but also likely contributed to their release from light competition. Our results highlight the roles of RGR directional change across contrasting water stress situations in driving community assembly in patchy landscapes with frequent droughts and may improve our understanding of how global climate change‐related droughts shape plant community assembly. Read the free Plain Language Summary for this article on the Journal blog.

The soil microbial community composition and Alpha diversity serve as key indicators of soil quality changes driven by forest development. We explored the variations in soil properties, root traits, microbial communities, and their interrelationships across forest age and soil depth in Populus tomentosa , Platycladus orientalis , and Styphnolobium japonicum plantations. The results showed that the Chao, Shannon, and Pielou_e indices of the soil microbial community increased with forest age. Soil properties and root traits had a stronger influence on the composition of soil bacteria (41.4%) compared to fungi (28.8%). In comparison to root traits (7%–10%), soil properties had a more significant influence (23%–26%) on microbial composition. Soil clay, water content, and conductivity showed positive effects on bacterial diversity and composition, while fungi were mainly affected by soil total phosphorus and soil pH. The influence of root traits on bacterial diversity declined with forest age, whereas the effect of soil properties increased. Fungal diversity was jointly shaped by soil properties and root traits in 13–19a plantations, but mainly by soil properties in 9–12a and 16–36a plantations. With increasing soil depth, the impact of roots on bacterial diversity grew while on fungal diversity diminished. The results highlight the need to account for forest age and soil depth when revealing the association among soil microbial diversity, environmental variation, and root traits.

Iron is one of the most important strategic materials in national production, and the demand for iron ore is huge in the world. High quality iron ore reserves have been almost exhausted, and it is necessary to develop a technology that utilizes low-grade iron ore. Limonite is a representative low-grade iron ore due to its complex mineral and elemental composition. In this paper, the union process was employed to separate the iron elements in low-grade limonite. Firstly, a rough iron concentrate was obtained under 1.0 T of magnetic field intensity and −0.074 mm > 94.84% of grinding fineness; then, the rough iron concentrate was magnetization roasted under a temperature of 700 °C, 60 min of retention time, 3 wt% of biochar consumption, and 0.15 T of magnetic field intensity. The grade of iron concentrate was 59.57% and the recovery of iron was 90.72%. Finally, the red iron pigment was produced via a high temperature hydrothermal method in order to increase the additional value of this ultra-low-grade limonite. The optimal parameters were 10.0 g/L of solution acidity, a 200 °C reaction temperature, 5 h of reaction time, and a 6:1 solid-to-liquid ratio. The reaction mechanism was also discussed.