Black carbon (BC) from incomplete combustion of biomass and fossil fuel is widespread in sediments and soils because of its high stability in nature and is considered an important component of the global carbon sink. However, knowledge of BC stocks and influencing factors in forest ecosystems is currently limited. We investigated soil BC contents in burned boreal forests of the Great Khingan Mountains, northeast China. We collected soil samples from 14 sites with different fire severities, slope positions and aspects. The samples were analyzed by the chemo-thermal oxidation method to obtain their BC concentrations. The BC concentrations of the studied soils ranged from 0.03 to 36.91 mg C g −1 , with a mean of 1.44 ± 0.11 mg C g −1 . BC concentrations gradually decline with depth, and that was significantly less in the 20-30 cm layer compared to all shallower layers. Forests burned by moderate-severity fires had the highest soil BC, the shady aspect had higher soil BC than the sunny aspect. Our results provide some basic data for evaluating the soil BC sink in boreal forests, which is a useful amendment to current carbon budget and carbon cycle in boreal forest ecosystems.
Measuring the nitrogen isotope compositions (δ 15 N) of nitric oxide (NO) from different sources helps to quantify the relative contributions of atmospheric NO x. Soil is one of the most important sources of atmospheric NO x , but only limited measurements on the δ 15 N of soil-emitted NO exist, hampering our ability to partition sources to air pollution. Here we conducted soil incubations to measure the δ 15 N-NO under defined aerobic or anaerobic conditions, favoring either nitrification or denitrification. Soils were collected from seven sites spanning three ecosystems in northern China (two agricultural, two forest, and three grassland sites). We found that the δ 15 N-NO and their associated N isotope fractionations were significantly different between anaerobic and aerobic conditions in seven soils. Under aerobic condition, the δ 15 N-NO ranged from −62‰ to −50‰ (averaged −56 ± 4‰), being significantly more negative (by 23‰) than those under anaerobic condition (−45‰ to −23‰, averaged −33 ± 7‰). The apparent N isotope fractionation for NO production under aerobic condition (15 ε aerobic ¼ 61 ± 3‰) was significantly higher (by 26‰) than under anaerobic condition (15 ε anaerobic ¼ 35 ± 6‰), with a small variability among ecosystem types. Our study demonstrates that the δ 15 N-NO from different soils are very different from fuel combustions (mainly from 0‰ to +20‰), supporting that measuring 15 N is a useful tool to partition the contributions of soil NO to atmospheric NO x. Our results also imply δ 15 N-NO produced by nitrification and denitrification distinctly different, as these two processes are dominant processes producing NO under aerobic and anaerobic conditions, respectively. Plain Language Summary Nitric oxide (NO) affects the atmosphere chemistry and NO itself a key component of air pollution and a precursor to other air pollutants like particulate matter and ozone. To reduce the air pollution, it is crucial to identify the atmospheric NO sources. Measuring 15 N natural abundance has been considered as a promising tool to identify different sources, but the measurement on δ 15 N for soil-emitted NO is limited, adding to the large uncertainties on NO partitioning. Here we measured the δ 15 N-NO emitted from three ecosystem types across seven sites (two agriculture, two forest, and three grassland sites) under defined anaerobic or aerobic conditions. We found that soil-emitted NO was 15 N-depleted (−62‰ to −23‰) related to the source from fossil fuel combustion (0-20‰), suggesting that δ 15 N can be used to separate these two sources. We also found that the δ 15 N-NO under aerobic condition (nitrification prevailing, −62‰ to −50‰) was much lower than under anaerobic condition (denitrification prevailing, −45‰ to −23‰), which provide a useful tool to better understand the relative contributions of different sources of NO. In sum, soil-emitted NO has their own different isotope fingerprint, depending on the soil oxygen conditions, and can be used to partition sources.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2025 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.