Sammanfattning

High delta N-15 of tree foliage in forests subject to high N supply has been attributed to N-15 enrichment of plant available soil N pools after losses of N through processes involving N isotope fractionation (ammonia volatilization, nitrification followed by leaching and denitrification, and denitrification in itself). However, in a long-term experiment with high annual additions of NH4NO3, we found no change in the weighted average delta N-15 of the soil, but attributed the high delta N-15 of trees to loss of ectomycorrhizal fungi and their function in tree N uptake, which involves redistribution of N isotopes in the ecosystem (Hogberg et al. New Phytol 189:515-525, 2011), rather than a loss of isotopically light N. Here, we compare the effects of additions of urea and NH4NO3 on the delta N-15 of trees and the soil profile, because we have previously found higher delta N-15 in tree foliage in trees in the urea plots. Doing this, we found no differences between the NH4NO3 and urea treatments in the concentration of N in the foliage, or the amounts of N in the organic mor-layer of the soil. However, the foliage of trees receiving the highest N loads in the urea treatment were more enriched in N-15 than the corresponding NH4NO3 plots, and, importantly, the weighted average delta N-15 of the soil showed that N losses had been associated with fractionation against N-15 in the urea plots. Thus, our results in combination with those of Hogberg et al. (New Phytol 189:515-525, 2011) show that high delta N-15 of the vegetation after high N load may be caused by both an internal redistribution of the N isotopes (as a result of change of the function of ectomycorrhiza) and by losses of isotopically light N through processes fractionating against N-15 (in case of urea ammonia volatilization, nitrification followed by leaching and denitrification).

Nyckelord

Ectomycorrhiza; Forest soils; Nitrogen deposition; N-15 natural abundance

Publicerad i

Biogeochemistry
2014, Volym: 117, nummer: 2-3, sidor: 351-358

SLU författare

• Högberg, Peter

  • Institutionen för skogens ekologi och skötsel, Sveriges lantbruksuniversitet
    

• Högberg, Mona N

  • Institutionen för skogens ekologi och skötsel, Sveriges lantbruksuniversitet
    

Globala målen

SDG15 Ekosystem och biologisk mångfald


UKÄ forskningsämne

Miljövetenskap


Publikationens identifierare

DOI: https://doi.org/10.1007/s10533-013-9873-x

Permanent länk till denna sida (URI)

https://res.slu.se/id/publ/51988