Stable nitrogen and carbon isotope compositions in plant-soil systems under different land-use types in a red soil region, Southeast China

BACKGROUND: Stable N isotope compositions in plant-soil systems have been widely used to indicate soil N transformation and translocation processes in ecosystems. However, soil N processes and nitrate ([Image: see text] ) loss potential under different land-use types are short of systematic comparison in the red soil region of Southeast China. METHODS: In the present study, the stable N and C isotope compositions (δ(15)N and δ(13)C) of soil and leaf were analyzed to indicate soil N transformation processes, and the soil to plant (15)N enrichment factor (EF) was used to compare soil [Image: see text] loss potential under different land-use types, including an abandoned agricultural land, a natural pure forest without understory, and a natural pure forest with a simple understory. RESULTS: The foliar δ(15)N value (−0.8‰) in the abandoned agricultural land was greater than those of the forest lands (ranged from −2.2‰ to −10.8‰). In the abandoned agricultural land, δ(15)N values of soil organic nitrogen (SON) increased from 0.8‰ to 5.7‰ and δ(13)C values of soil organic carbon (SOC) decreased from −22.7‰ to −25.9‰ with increasing soil depth from 0–70 cm, mainly resulting from SON mineralization, soil organic matter (SOM) decomposition, and C(4) plant input. In the soils below 70 cm depth, δ(15)N values of SON (mean 4.9‰) were likely affected by microbial assimilation of (15)N-depleted [Image: see text] . The variations in δ(15)N values of soil profiles under the two forests were similar, but the EF values were significant different between the pure forest with a simple understory (−10.0‰) and the forest without understory (−5.5‰). CONCLUSIONS: These results suggest that soil to plant (15)N enrichment factor have a great promise to compare soil [Image: see text] loss potential among different ecosystems.