The study of soil ecological stoichiometry has mainly focused on surface soils. Exploring the nutrient content and stoichiometric characteristics of deep soils in karst areas helps us to understand the intrinsic relation mechanism and provides scientific evidence for making full use of fractured soil. We analyzed soil nutrient content, nutrient supply intensity, stoichiometric ratios, and their interrelations at different soil depths in a karst plateau mountain area of China. Soil nutrient supply capacity was relatively low in the study area. The nitrogen and potassium supply capacity was highest in the surface layer, while phosphorus supply capacity was highest in deep soil. Carbon, nitrogen, phosphorus and potassium made varying contributions to the ecological stoichiometric ratios. Soil nitrogen and phosphorus were found to be deficient in the karst plateau mountain area of China. There was certain coordination between nutrient supply intensity and ecological stoichiometric ratios.
Understanding the relationships between carbon; nitrogen, their stable isotopes δ13C and δ15N, and soil stoichiometry may further our understanding of the regulatory mechanisms of the soil quality index on the equilibrium on isotopic fractionation. Four plantations of Zanthoxylum planispinum var. dintanensis (5–7, 10–12, 20–22 and 30–32 years) in the karst plateau gorge area, Guizhou Province, China, were selected to determine the variation characteristics and interactions between leaves, leaf litter, soil carbon (C), soil nitrogen (N) and their isotopes with plantation age, and to explore the relationship between soil stoichiometry and the isotopes δ13C and δ15N. The results were as follows: (1) the δ13C in leaves, litter, and soil were −28.04‰ ± 0.59‰, −26.85‰ ± 0.67‰, and −19.39‰ ± 1.37‰, respectively. The contents of δ15N were 2.01‰ ± 0.99‰, 2.91‰ ± 1.32‰, and 3.29‰ ± 0.69‰, respectively. The contents of δ13C and δ15N were ranked in the order, soil > litter > leaf. (2) With increasing plantation age, the soil 13C decreased; the leaf and the litter δ15N increased first then decreased, and the litter δ13C and the soil δ15N did not vary significantly. (3) The litter layer was positively correlated with soil δ13C and negatively correlated to δ15N. (4) Redundancy analysis showed that the soil microbial biomass carbon (MBC) and the bacteria/fungi (BAC/FUN) were the dominant factors affecting the natural abundance of C and N isotopes
The present study clarified the forest‐age associated change in the pericarp quality of Zanthoxylum planispinum ‘dintanensis’ (ZPD) and aimed to provide a theoretical foundation for formulating management strategies. The studied forest age groups consisted of 5‐to‐7‐, 10‐to‐12‐, 20‐to‐22‐, and 28‐to‐32‐yr‐old ZPD plants growing in rocky desertified areas of karst dry‐hot valleys in Guizhou, China. By measuring the pericarp quality indices of the plants present in the stands, the changes in pericarp quality were determined. The quality traits were optimal when the forest age was 28–32 yr, and the quality did not degrade with increased forest age. The sensitivity levels of ash contents and vitamins to the forest age were weak, whereas the levels of amino acids and trace elements were more affected by forest age. The latter two compounds were, therefore, more suitable for quality grading. The comprehensive quality index of the 28‐to‐32‐yr‐old plant group was the highest, followed by the 10‐to‐12‐yr‐old, 5‐to‐7‐, and 20‐to‐22‐yr‐old plants.
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