Abstract
Nitrogen (N) inputs from atmospheric deposition can increase soil organic carbon (SOC) storage in temperate and boreal forests, thereby mitigating the adverse effects of anthropogenic CO2 emissions on global climate. However, direct evidence of N-induced SOC sequestration from low-dose, long-term N addition experiments (that is, addition of < 50 kg N ha−1 y−1 for > 10 years) is scarce worldwide and virtually absent for European temperate forests. Here, we examine how tree growth, fine roots, physicochemical soil properties as well as pools of SOC and soil total N responded to 20 years of regular, low-dose N addition in two European coniferous forests in Switzerland and Denmark. At the Swiss site, the addition of 22 kg N ha−1 y−1 (or 1.3 times throughfall deposition) stimulated tree growth, but decreased soil pH and exchangeable calcium. At the Danish site, the addition of 35 kg N ha−1 y−1 (1.5 times throughfall deposition) impaired tree growth, increased fine root biomass and led to an accumulation of N in several belowground pools. At both sites, elevated N inputs increased SOC pools in the moderately decomposed organic horizons, but decreased them in the mineral topsoil. Hence, long-term N addition led to a vertical redistribution of SOC pools, whereas overall SOC storage within 30 cm depth was unaffected. Our results imply that an N-induced shift of SOC from older, mineral-associated pools to younger, unprotected pools might foster the vulnerability of SOC in temperate coniferous forest soils.
Highlights
Reactive nitrogen (NR) inputs from atmospheric deposition to terrestrial ecosystems have more than doubled since the onset of the industrial revolution, mainly due to agricultural intensification and fossil fuel burning (Galloway and others 2008)
Extractable organic carbon (EOC) concentrations were marginally lower in N addition plots by 38% on average across all horizons (P = 0.089, Figure 1B, Table S1.1)
In the soil N addition resulted in vertical shift of soil organic carbon (SOC) pools within the profile that was consistent across sites
Summary
Reactive nitrogen (NR) inputs from atmospheric deposition to terrestrial ecosystems have more than doubled since the onset of the industrial revolution, mainly due to agricultural intensification and fossil fuel burning (Galloway and others 2008). These forests were a net sink for atmospheric CO2 of up to 0.8 Pg of carbon (C) per year during the early 2000s (Pan and others 2011) corresponding to about 1/3 of the ‘residual land sink’ (Ciais and others 2014). The vegetation contains only 40% of C stored in temperate forest ecosystems, while soils down to 1 m depth account for the remaining 60%, mainly in the form of soil organic carbon (SOC; Dixon and others 1994; Lal 2005). It is vital to quantify N-induced changes in SOC in order to assess the overall effects of NR deposition on temperate forest C (De Vries and others 2006, 2014)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.