关键词: 黄土高原, 植被恢复, 生态化学计量, 内稳态, 干旱度

Abstract:

Objective: This study analyzed the leaf-soil ecological stoichiometric characteristics and plant homeostasis differences of typical revegetation in different arid areas of the Loess Hilly Region. From the perspective of plant nutrient utilization strategies and homeostasis maintenance ability, it aimed to identify suitable revegetation types for different arid levels. By analyzing the nutrient cycling processes driven by the ecological stoichiometric characteristics and plant homeostasis differences of typical revegetation in different arid areas, it provided a scientific basis for vegetation optimization and soil nutrient management in the Loess Hilly Region of China. Method: Along the aridity gradient from south to north of the Loess Plateau, 17-year-old Robinia pseudoacacia (RP) plantations, shrublands, and abandoned land were selected in Fuxian County (aridity level 0.641), Baota District (aridity level 0.718), and Mizhi County (aridity level 0.764) for the purpose of examining the carbon (C), nitrogen (N), and phosphorus (P) content and stoichiometric properties of both leaves and soils. The interrelationships between these components and the homeostatic characteristics within the leaves were further analyzed. Result: 1) The leaf carbon and nitrogen contents of RP plantations were respectively lower and higher than those of other vegetation restoration types. The leaf phosphorus content and soil carbon to nitrogen ratio of abandoned land were the highest, while the leaf soil carbon to phosphorus ratio and soil nitrogen to phosphorus ratio of shrubland were the highest. In terms of soil characteristics, soil carbon to nitrogen ratio, and soil carbon to phosphorus ratio of abandoned land were generally higher than those of other vegetation restoration types. Soil nitrogen content and soil nitrogen to phosphorus ratio were lowest in RP plantations. However, soil phosphorus content in RP plantations was significantly higher than that in shrublands and abandoned land. 2) With increasing aridity, the carbon and nitrogen contents of leaves in Baota District were respectively 8.77% and 6.64% lower than those in Fuxian County, while the phosphorus content was 34.25% higher. In Mizhi County, the carbon and nitrogen contents of leaves were respectively 1.01% and 44.53% lower than those in Fuxian County, while the phosphorus content was 16.02% higher. As aridity increases, the trends in the soil carbon to phosphorus and soil nitrogen to phosphorus ratio of leaves were similar to those of carbon and nitrogen, showing initial decreases followed by increases and overall declines, respectively. In contrast, the soil carbon to nitrogen ratio showed an increasing trend. 3) Soil carbon content (7.47, 3.44, and 2.67 g·kg^?1on average in Fuxian County, Baota District, and Mizhi County, sane blow), nitrogen content (averaging 0.66, 0.36, and 0.37 g·kg^?1), and the soil carbon to nitrogen ratio (averaging 11.62, 9.62, and 7.59), soil carbon to phosphorus ratio (averaging 14.89, 9.25, and 6.64), and soil nitrogen to phosphorus ratio (averaging 1.37, 0.99, and 0.92) all tended to decrease with increasing aridity. In contrast, soil phosphorus content (averaging 0.501, 0.36, and 0.40 g·kg^?1) first decreased and then increased. 4) An increase in aridity intensifies nitrogen limitation on vegetation growth, while the shift from abandoned land to forest land increases phosphorus limitation. Mantel analysis shows significant correlations between leaf and soil carbon, nitrogen, and phosphorus contents and their stoichiometric ratios at different levels. Aridity has a greater impact on leaf and soil indicators than vegetation type and soil depth. 5) Different revegetation types show distinct abilities to maintain foliar chemical stoichiometric homeostasis. Leaf carbon in all vegetation types exhibits absolute homeostasis. Leaf nitrogen and phosphorus in abandoned land and shrubland show weak homeostasis or sensitive characteristics. The soil carbon to phosphorus ratio of abandoned land leaves is sensitive or weakly homeostatic, while the soil carbon to nitrogen and soil nitrogen to phosphorus ratios of RP and shrub leaves are sensitive. Conclusion: Aridity is a key environmental factor regulating the leaf-soil carbon, nitrogen, and phosphorus stoichiometric characteristics of revegetation. RP plantations can more effectively maintain foliar homeostasis under different aridity levels in the Loess Hilly Region, showing stronger adaptability than shrublands and abandoned land, and can be the main tree species for vegetation restoration and reconstruction in this area. In areas with higher aridity and in abandoned land, nitrogen fertilizer should be applied, while in relatively humid shrublands and forests, nitrogen and phosphorus fertilizers should be added.

Key words: Loess Plateau, revegetation, ecological stoichiometry, homeostasis, aridity level