Environmental science - Nitrogen impacts on forest carbon
(Impact Factor: 41.46).
07/2007; 447(7146):781-2. DOI: 10.1038/447781a
Does the extra nitrogen input from anthropogenic sources mean that more carbon from the atmosphere is being locked up in boreal and temperate forests? 'Yes' is the answer to emerge from the latest analysis.
Available from: Ji-Hyung Park
- "N availability has been proposed as a major constraint on plant biomass accumulation in response to rising atmospheric CO2 (Hungate et al. 2003, Reich et al. 2006) or climatic warming (Shaver et al. 2000), although the response of plant C accumulation to environmental changes is determined by a suite of controlling factors other than N, including plant species and soil nutritional status. As depicted in pathway I of Fig. 1, increased inputs of N to forests with limited natural supply can initially enhance tree biomass accumulation per unit area through increased activity of the photosynthesizing enzyme RUBISCO (Högberg 2007). The terrestrial C sink represents 15～30% of annual global emission of C from anthropogenic sources and evidence for biomass C accumulation in boreal and temperate forests has lately been provided by satellite observations or plot-level measurements of ecosystem C exchange (Myneni et al. 2001, Magnani et al. 2007). "
Available from: Scott X. Chang
- "Although soil microbial biomass has been reported to decline by an average of 15% globally under N addition, the impact of elevated N input on soil microbial biomass is inconsistent among studies and site-specific (Treseder 2008). Nitrogen addition can increase aboveground litter production and improve litter quality in N-limited forests (Högberg 2007) and may therefore alleviate microbial N limitation and lead to an increase in soil microbial biomass (Gallardo and Schlesinger 1994). However, when N saturation occurred in forest soils, "
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ABSTRACT: Chronic nitrogen (N) and (or) sulfur (S) deposition to boreal forests in the Athabasca oil sands region (AOSR) in Alberta, Canada, has been caused by oil sands mining and extraction/upgrading activities. It is important that we understand the response of microbial community function to chronic N and S deposition as microbial populations mediate soil carbon (C) and N cycles and affect ecosystem resilience. To evaluate the impact of N and (or) S deposition on soil microbial community functions, we conducted a simulated N and S deposition experiment in a boreal mixedwood forest with the following four treatments: control (CK), N addition (+N, 30 kg N·ha−1 as NH4NO3), S addition (+S, 30 kg S·ha−1 as NaSO4), and N plus S addition (+NS, 30 kg N·ha−1 + 30 kg S·ha−1), from 2006 to 2010. Nitrogen and (or) S deposition did not change soil organic carbon, total N, dissolved organic C and N, or soil microbial biomass C and N. Soil microbial community-level physiological profiles, however, were strongly affected by 5 years of N and (or) S addition. Soil β-glucosidase activity in the +NS treatment was greater than that in the +S treatment, and S addition decreased soil arylsulfatase; however, urease and dehydrogenase activities were not affected by the simulated N and (or) S deposition. Our data suggested that N and (or) S deposition strongly affected soil microbial community functions and enzymatic activities without changing soil microbial biomass in the studied boreal forest.
Available from: Xueming Yang
- "Overall, it is most likely that atmospheric N deposition promotes C sequestration (Janssens et al., 2010). However, the efficiency of estimated C sequestration in terrestrial ecosystems caused by N deposition varies, ranging from 60 to 200 kg C kg −1 N (Högberg, 2007; Magnani et al., 2007). It is apparent that there is considerable uncertainty about how C dynamics and C sequestration in terrestrial ecosystems respond to increased N deposition. "
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ABSTRACT: The effects of atmospheric nitrogen (N) deposition on carbon (C) sequestration in terrestrial ecosystems are controversial. Therefore, it is important to evaluate accurately the effects of applied N levels and forms on the amount and stability of soil organic carbon (SOC) in terrestrial ecosystems. In this study, a multi-form, small-input N addition experiment was conducted at the Haibei Alpine Meadow Ecosystem Research Station from 2007 to 2011. Three N fertilizers, NH 4 Cl, (NH 4) 2 SO 4 and KNO 3 , were applied at four rates: 0, 10, 20 and 40 kg N ha −1 year −1 . One hundred and eight soil samples were collected at 10-cm intervals to a depth of 30 cm in 2011. Contents and íµí»¿ 13 C values of bulk SOC were measured, as well as three particle-size fractions: macroparticulate organic C (MacroPOC, > 250 μm), microparticulate organic C (MicroPOC, 53–250 μm) and mineral-associated organic C (MAOC, < 53 μm). The results show that 5 years of N addition changed SOC contents, íµí»¿ 13 C values of the bulk soils and various particle-size fractions in the surface 10-cm layer, and that they were dependent on the amounts and forms of N application. Ammonium-N addition had more significant effects on SOC content than nitrate-N addition. For the entire soil profile, small additions of N increased SOC stock by 4.5% (0.43 kg C m −2), while medium and large inputs of N decreased SOC stock by 5.4% (0.52 kg C m −2) and 8.8% (0.85 kg C m −2), respectively. The critical load of N deposition appears to be about 20 kg N ha −1 year −1 . The newly formed C in the small-input N treatment remained mostly in the > 250 μm soil MacroPOC, and the C lost in the medium or large N treatments was from the > 53 μm POC fraction. Five years of ammonium-N addition increased significantly the surface soil POC:MAOC ratio and increased the instability of soil organic matter (SOM). These results suggest that exogenous N input within the critical load level will benefit C sequestration in the alpine meadow soils on the Qinghai–Tibetan Plateau over the short term.
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