Impact of long-term nitrogen addition on carbon stocks in trees and soils in northern Europe |
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Authors: | Email author" target="_blank">Riitta?Hyv?nenEmail author Tryggve?Persson Stefan?Andersson Bengt?Olsson G?ran?I??gren Sune?Linder |
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Institution: | (1) Department of Ecology, Swedish University of Agricultural Sciences, Box 7072, 750 07 Uppsala, Sweden;(2) Department of Soil Sciences, Swedish University of Agricultural Sciences, Box 7014, 750 07 Uppsala, Sweden;(3) Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences, Box 49, 230 53 Alnarp, Sweden |
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Abstract: | The aim of this study was to quantify the effects of fertiliser N on C stocks in trees (stems, stumps, branches, needles,
and coarse roots) and soils (organic layer +0–10 cm mineral soil) by analysing data from 15 long-term (14–30 years) experiments
in Picea abies and Pinus sylvestris stands in Sweden and Finland. Low application rates (30–50 kg N ha−1 year−1) were always more efficient per unit of N than high application rates (50–200 kg N ha−1 year−1). Addition of a cumulative amount of N of 600–1800 kg N ha−1 resulted in a mean increase in tree and soil C stock of 25 and 11 kg (C sequestered) kg−1 (N added) (“N-use efficiency”), respectively. The corresponding estimates for NPK addition were 38 and 11 kg (C) kg−1 (N). N-use efficiency for C sequestration in trees strongly depended on soil N status and increased from close to zero at
C/N 25 in the humus layer up to 40 kg (C) kg−1 (N) at C/N 35 and decreased again to about 20 kg (C) kg−1 (N) at C/N 50 when N only was added. In contrast, addition of NPK resulted in high (40–50 kg (C) kg−1 (N)) N-use efficiency also at N-rich (C/N 25) sites. The great difference in N-use efficiency between addition of NPK and
N at N-rich sites reflects a limitation of P and K for tree growth at these sites. N-use efficiency for soil organic carbon
(SOC) sequestration was, on average, 3–4 times lower than for tree C sequestration. However, SOC sequestration was about twice
as high at P. abies as at P. sylvestris sites and averaged 13 and 7 kg (C) kg−1 (N), respectively. The strong relation between N-use efficiency and humus C/N ratio was used to evaluate the impact of N
deposition on C sequestration. The data imply that the 10 kg N ha−1 year−1 higher deposition in southern Sweden than in northern Sweden for a whole century should have resulted in 2.0 ± 1.0 (95% confidence
interval) kg m−2 more tree C and 1.3 ± 0.5 kg m−2 more SOC at P. abies sites in the south than in the north for a 100-year period. These estimates are consistent with differences between south
and north in tree C and SOC found by other studies, and 70–80% of the difference in SOC can be explained by different N deposition. |
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Keywords: | N-use efficiency C sequestration C/N ratio C stock in trees and soil |
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