Environmental science - Nitrogen impacts on forest carbon
ABSTRACT 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.
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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.Canadian Journal of Forest Research 09/2014; 43(9). DOI:10.1139/cjfr-2013-0049 · 1.66 Impact Factor
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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.European Journal of Soil Science 06/2014; 65:510-519. DOI:10.1111/ejss.12154 · 2.39 Impact Factor
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ABSTRACT: Increasing accumulation of CO2 in the atmosphere has led to calls for terrestrial mechanisms for CO2 abatement and given that soils represent the largest terrestrial body of C on Earth, there is a great deal of interest in soils as a sink for atmospheric C. This emphasis on sequestration in boreal forest soils is understandable given the sheer mass of this C reservoir (∼1700 Pg of C) but diverts our attention from the importance of soil C in soil physical, chemical and biotic functions, and importantly, it ignores the possibility that soils may also represent a source of C. In this review, we address these issues through a discussion of the size and character of boreal forest soil C pool, its role in ecosystem function, the potential impacts of climate change on soil C, efforts to model these processes and the role of soil C in boreal resilience to the impacts of climate change. Soil C is fundamental to ecosystem function in terms of improving soil physical properties, increasing soil biotic activity anForestry 04/2012; 85(2). DOI:10.1093/forestry/cps003 · 1.87 Impact Factor