Spatio-temporal distribution dynamics of diverse soil nitrogen pools and patterns of nitrogen and carbon sequestration after slope farmland conversion to Zanthoxylum bungeanum plantations

Abstract Aims Plant-soil interactions, and regulatory roles of soil nitrogen (N) fractions in availability and the magnitudes of N sequestration, therein the interplay of soil C-N in cold arid regions is poorly characterized. Methods Post-afforestation and land-abandonment dynamics of C and N sequestration, and total inorganic N (TIN) availability were identified by quantifying changes in diverse N fraction, and their distributions patterns in 0–100 cm soil profile across a chronosequence of Zanthoxylum bungeanum (28-year (H28), 20-year (H20), 15-year (H15), and 8-year (H8) old) plantations, and abandoned-land (GL), originally converted from former farmland (FL) in cold-arid valley in Southwest China. Results Afforestation and GL favored gains in labile and non-labile (LON and NLON) N fractions and total N stocks. Concentrations of LON fractions and TIN was comparatively higher at 0–40 cm. Gains in NLON fractions and total organic N (TON) was significantly higher in the deep soil, as confirmed by correlation and redundancy analysis. N and C sequestration was synchronous (r = 0.948), with cumulative (0–100 cm) increase of 1.149–1.277 folds in H28 compared to H8, at an average sequestration rate of 1.336 − 0.121 Mg ha − 1 yr − 1, respectively. N pool management index (NPMI) correlated positively with soil TON, TIN, available phosphorus, potassium, and organic N fractions. NPMI improved significantly (P < 0.05) with the plantations age. Conclusion Plantations age and soil depths significantly influence ecosystems N dynamics. Furthermore, TON, NPMI, N fractions, and TIN can be useful indicators to gain comprehensive insights on ecosystems N restoration patterns.