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Here, we aimed to understand the effects of nitrogen (N) -fixing and non-N-fixing tree species on the stoichiometric characteristics of soil carbon (C), N, phosphorus (P), and soil readily oxidized carbon (ROC) in south China. We determined the levels of soil total organic C (TOC), total N (TN), total P (TP), and ROC in 13-year-old Acacia crassicaipa and Eucalyptus urophylla plantations in Heshan, Guangdong Province, to analyze their characteristics and correlation of N-fixing and non-N-fixing tree species after afforestation. The results showed that soil ROC and TOC contents in N-fixing tree stands were significantly higher than those in non-N-fixing tree stands (P＜0.05), and ROC/TOC values were lower in the N-fixing than the non-N-fixing tree stand soils, indicating that soil C stability was improved in the N-fixing tree stand soils compared to the non-N-fixing tree stand soils. The soil TN content and C: N value were significantly higher in the N-fixing stands than in the non-N-fixing stands (P＜0.05). Soil C: P, N: P, and C: N: P were higher in the N-fixing stands, but the differences were not statistically significant. Soil TOC and TN were positively correlated in both stands (P＜0.01). In N-fixing stands, soil TOC and TN were negatively correlated with ROC/TOC (P＜0.05), and soil water content (SWC), C: P, and N: P were significantly positively correlated with TOC (P＜0.05). In south China, where SWC is high, afforestation with N-fixing trees increased soil TN and TOC contents and soil stoichiometric ratio, which helped improve soil C stability. [ABSTRACT FROM AUTHOR]

To understand the soil′s physical and chemical properties as well as soil readily oxidizable organic carbon (ROC) content under different stand types, the physico-chemical properties, cation exchange capacity (CEC), ROC content, and other top soil indicators were studied in Schima superba and Eucalyptus urophylla plantations of 30 years old in Changgangshan Natural Reserve of Guangzhou, Guangdong Province. The results revealed that the contents of total soil organic carbon (TOC) and total nitrogen (TN) in Eucalyptus urophylla were significantly higher than those in S. superba. The C/N ratio in S.superba was significantly higher than that in Eucalyptus urophylla, whereas the C/P and N/P ratios in Eucalyptus urophylla were higher than those in S. superba. The soil CECs were not significantly different between the two stands. The total exchangeable base cations and base saturation percentage in Eucalyptus urophylla plantations were significantly higher than those in S. superba plantations. The contents of exchangeable base ions showed a trend of Ca2+＞Mg2+＞K+＞Na+. The ROC contents and ROC/TOC ratio in Eucalyptus urophylla were higher than those in S. superba, with significant differences in ROC between the two stands. The correlation analysis showed that the ROC content in Eucalyptus urophylla plantation had a significant positive correlation with AP (P＜0.05), where as the ROC/TOC was significantly positively correlated with TP (P＜0.05). ROC had a significant positive correlation with CEC in S. superba plantation (P＜0.05), and ROC had an extremely significant positive correlation with ROC/TOC (P＜0.01). We found that the ROC contents were significantly different between the two stand types, and ROC/TOC in S. superba was lower than that in Eucalyptus urophylla plantation, indicating that the soil carbon stability in S. superba plantation is stronger than that in Eucalyptus urophylla plantation thus resulting in higher carbon sequestration. [ABSTRACT FROM AUTHOR]