Jiapeng Zhang

Stoichiometric homeostasis is an important mechanism in maintaining ecosystem structure, function, and stability. Phyllostachys edulis (moso bamboo) is a typical clone plant, forming pure bamboo forests or bamboo–wood mixed forests by expanding rhizomes around. Studying the stoichiometric homeostasis characteristics of moso bamboo at different ages after expansion contributes to a deeper understanding of the stability of bamboo forest ecosystems, and is of great significance for expanding the research scope of ecological stoichiometry. Based on the stoichiometric internal stability theory, the nitrogen (N) and phosphorus (P) elements in the soil and plants of typical moso bamboo forests in Tianbaoyan National Nature Reserve of Fujian Province were determined, and the internal stability index (H) of bamboo leaves of different ages (I-du, II-du, III-du, and IV-du bamboos) was calculated. The results showed that the dependence of moso bamboo on soil nutrients and the ability of moso bamboo to regulate nutrient elements were both significantly affected by the plant’s age. Under the condition of the same soil nutrients (N, P), the content of N and P in bamboo leaves decreased significantly with the increase in bamboo age. The limiting effect of phosphorus on the growth and development of moso bamboo was greater than that of nitrogen, and the limiting effect of phosphorus on aged bamboo was greater than that of young bamboo. The stoichiometric internal stability index of N and P in bamboo leaves is H_N:P > H_N > H_P, which means that the internal stability of moso bamboo is closely related to the limiting elements. Therefore, the regulation ability of the internal stability of moso bamboo of different ages makes it grow well in the changeable environment, has stronger adaptability and competitiveness, and the leaf internal stability of I-du bamboo was higher than that of other ages, which may be one of the reasons for its successful expansion to form a stable bamboo stand structure.

There is a dearth of research regarding the windbreak and sand stabilization functions of Caragana liouana shelter forests in the Gonghe Basin of the Qinghai-Tibet Plateau. Therefore, the aim is to elucidate the patterns of near-surface wind–sand activity in artificial Caragana liouana forests of varying ages and mixed forests of different configurations in alpine sandy areas. Additionally, this research seeks to clarify the windbreak and sand fixation effects of these forests. To this end, we have selected artificial forests of Caragana liouana of varying ages (10-year-old pure Caragana liouana forest (10aZJ-C), 17-year-old pure Caragana liouana forest (17aZJ-C), 37-year-old pure Caragana liouana forest (3aZJ-C)) and shrub mixed forests of different mixing modes (10-year-old Caragana liouana and Caragana korshinskii mixed forest (10aNZ-HJ), 10-year-old Caragana liouana and Artemisia desertorum mixed forest (10aSZ-HJ), an 10-year-old Caragana liouana and Salix cheilophila mixed forest (10aWZ-HJ)) within the Sand Control Station of Shazhuyu Village in the Gonghe Basin of the Qinghai-Tibet Plateau as the research subjects. Naked sand dunes were used as the control plot (CK), and through field observations of the wind speed profile, sand transport rate, and micro-topographic changes of each stand plot, we analyzed the wind–sand flow structure characteristics and sand transport process of Caragana liouana of different ages and their mixed forests, eventually proposing suitable afforestation configuration modes for the alpine sand area of the Gonghe Basin in Qinghai. The findings indicate that the wind speed profile within each stand plot follows a linear distribution pattern. Compared to naked dune land, the windbreak effect of each plot decreases as the height from the ground increases. Among them, the 10aWZ-HJ plot significantly alters the wind speed profile and has a substantial windbreak effect; at a height of 200 cm, the windbreak effect can still reach 41.27%. The sand transport rate of each plot fits into an exponential function relationship, with the correlation coefficients (R²) of the fitting equations for each plot all exceeding 0.95 and significantly lower than the control plot, suggesting vegetation can effectively reduce near-surface sand transport. The sand-fixing effects at the height of 0–45 cm from the ground in each plot are as follows: 37aZJ-C > 17aZJ-C > 10aWZ-HJ > 10aNZ-HJ > 10aZJ-C > 10aSZ-HJ. Overall, all plots indicate a state of accumulation. The 10aWZ-HJ plot has the largest relative accumulation area at 88.00%, and the highest average intensity of wind erosion and accumulation at 1.11. Taking into account the stability of the stand and the total protection time, this study suggests that it is suitable to mainly use mixed forests of Salix cheilophila and Caragana liouana in the alpine sand area of the Qinghai-Tibet Plateau. The results of this study can provide a theoretical basis for the construction of windbreak and sand-fixing forests in alpine sand areas.

Grazing impacts soil enzyme activities by changing soil conditions and microbial functions. Yet, the specific effects of grazing on soil enzymes in different northeastern China forest-steppe vegetation types remain poorly understood. To examine this, catalase (CA), urease (UA), and cellulase (CEA) activities were measured in different vegetation types (NS, MF, CP, GL) under both grazing and non-grazing conditions. Soil microbial biomass carbon and nitrogen (MBC and MBN) and other soil factors were also studied to gauge their impact on enzyme activities. The results indicated that enzyme activities were influenced by grazing, soil nutrient levels, mineralization, and microbial biomass carbon and nitrogen content. Grazing exerted the most significant influence on UA. CEA was predominantly affected by the content of biomass nitrogen and soil mineralization. CA, on the other hand, was primarily influenced by soil nutrient levels. Grazing influenced enzyme activities differently based on vegetation type. Under grazing, CA showed higher values in NS, MF, CP, and GL (4.09, 2.42, 3.26, and 3.90 mL 0.1 mol L⁻¹ KMnO₄ g⁻¹ soil 20 min⁻¹, respectively) with increases ranging from 32.52% to 505.00% (p < 0.05). Additionally, UA values were significantly higher in MF and CP (0.24 and 0.59 mg NH₄⁺-N g⁻¹ soil d⁻¹, respectively) with increases of 66.67% and 156.00%, while UA and CEA were lower in GL, showing reductions of 78.79% and 166.67% (p < 0.05) (0.33 NH₄⁺-N g⁻¹ soil d⁻¹ and 0.06 mg glucose g⁻¹ soil 72 h⁻¹, respectively) under grazing conditions. These findings underscore the importance of vegetation types in the grazing effects on soil enzymes at the forest-steppe ecotone and suggest that further efforts should be made to strengthen grassland grazing management to mitigate negative impacts on soil environmental health.

This study was conducted in a Pinus sylvestris var. Mongolia plantation within the Xiaotaojiagou watershed of the Winter Olympic venues (Chongli competition area) to explore the influence of forest growth factors, soil physical properties, soil nutrients, and other factors on the competition index (CI) of dominant trees in the plantation. A 20 m × 20 m sample square was established every 300 m, and a total of 20 plots were set. The Hegyi single-tree competition index model and structural equation model (SEM) were used to analyze the dominant tree CI and its association with the forest growth factor, soil nutrient content, and soil physical properties. The CI of Pinus sylvestris var. Mongolia showed a decreasing trend with increases in the forest growth factor, the soil nutrient content, and the soil physical properties. Soil physical properties had the greatest influence on the CI, with a significant negative correlation (p < 0.05) and a total effect of −0.91. The results indicate that the competition index of dominant trees is sensitive to changes in soil physical and chemical properties as well as growth indicators such as diameter at breast height, tree height, and crown width of Pinus sylvestris var. mongolica.

This study was carried out to clarify the response of photosynthesis physiology of Caragana intermedia, an excellent tree species for wind protection and sand fixation, to soil water content (SWC) and to determine the relevant threshold ranges in the sandy lands of Qinghai-Tibet Plateau. In this study, based on the three-year forest experiment from 2017a to 2019a, C. intermedia in different afforestation years (2013a, 2011a, 2008a, 2006a, 2001a and 1986a) were selected for experimental analysis, the response process of leaf photosynthesis of C. intermedia to SWC changes was studied, and the physiological mechanism and growth suitability of C. intermedia to adapt to an alpine desert environment were clarified. The results showed that SWC played a critical role in the photosynthesis of C. intermedia in the sandy lands of Qinghai-Tibet Plateau. Afforestation years are negatively correlated with Pn, gs and Tr, but positively correlated with WUE; the longer the afforestation years, the higher demand for soil moisture. Regarding the relative roles of SWC and photosynthetic parameters, we demonstrated that this showed a significant square relationship (p < 0.001), while stomatal closure induced by the photosynthesis decline was important under dryness stress. The no-productivity and no-efficiency water (NPNEW) for the photosynthesis physiology of trees in different afforestation years were 3.31–3.64%; 3.33–4.06%; 3.08–3.63%; 3.36–3.85%; 1.45–4.02% and 3.39–5.50%, and the highest productivity with the highest availability of water (HPHAW) were 6.65–7.19%; 6.74–7.36%; 7.36–7.91%; 6.10–7.51%; 6.57–8.19% and 6.52–8.35%. Plantations in different afforestation years could survive safely in the sandy lands of Qinghai-Tibet Plateau. However, the productivity of trees decreased with the increase length of afforestation years; thus, we should pay attention to their growth status and make timely management adjustments in the future. These results provide important information for theoretical support for the diagnosis of ecological adaptability and field water management of C. intermedia in the sandy lands of Qinghai-Tibet Plateau and provide a reference for the adaptability evaluation and water–carbon cycle simulation of plantations in the sandy lands of Qinghai-Tibet Plateau against the background of global climate change.