Dynamics and underlying processes of N_1tn2O and NO soil atmosphere exchange under extreme meteorological boundary conditions [Elektronische Ressource] / von Stefanie Goldberg

Stefanie Goldberg

Informations

• Publié par: universitat_bayreuth
• Publié le: 01 janvier 2009
• Nombre de lectures: 29
• Langue: Deutsch
• Poids de l'ouvrage: 5 Mo

Extrait

Dynamics and underlying processes of N O and 2
NO soil-atmosphere exchange under extreme
meteorological boundary conditions





DISSERTATION



zur Erlangung des akademischen Grades eines
Doktors der Naturwissenschaften
– Dr. rer. nat. –

vorgelegt der
Fakultät für Biologie / Chemie / Geowissenschaften
der Universität Bayreuth




von
Stefanie D. Goldberg
geb. am 24.11.1982 in Rodewisch


Bayreuth, Januar 2009

Die vorliegende Arbeit wurde in der Zeit von Januar 2006 bis Januar 2009 unter der Lei-
tung von Prof. Dr. Gerhard Gebauer am Labor für Isotopen-Biogeochemie angefertigt.

Die Untersuchungen fanden im Rahmen der Forschergruppe „Dynamik von Bodenpro-
zessen bei extremen meteorologischen Randbedingungen“ unter Leitung von Prof. Dr.
Egbert Matzner statt und wurden durch Mittel der Deutschen Forschungsgemeinschaft
gefördert (DFG FOR 562).






Vollständiger Abdruck der von der Fakultät für Biologie / Chemie / Geowissenschaften
der Universität Bayreuth genehmigten Dissertation zur Erlangung des Grades eines Dok-
tors der Naturwissenschaften (Dr. rer. nat.).



Tag der Einreichung: 07. Januar 2009
Tag des Kolloquiums: 19. Februar 2009



Erstgutachter: Prof. Dr. Gerhard Gebauer
Zweitgutachter: Prof. Dr. Egbert Matzner

Contents

SUMMARY ...........................................................................................................................5
ZUSAMMENFASSUNG ...........................................................................................................7
CHAPTER 1 On this thesis
Background..........................................................................................................................12
Objectives.......21
Synopsis...............................................................................................................................23
Record of contributions to this thesis ...................................................................................34
References......36

CHAPTER 2 N O concentrations and isotope signatures along soil profiles 2
Goldberg SD, Knorr K-H, Gebauer G (2008) N O concentration and isotope 2
signature along profiles provide deeper insight into the fate of N O in soils. 2
Isotopes in Environmental and Health Studies, 44, 377-391................................................48

CHAPTER 3 Forest soil N O and NO emissions as affected by drought/rewetting 2
PART A: Goldberg SD, Gebauer G (2009) Drought turns a Central European
Norway spruce forest soil from an N O source to a transient N O sink. Global 2 2
Change Biology, doi: 10.1111/j.1365-2486.2008.01752.x, in press. ....................................74

PART B: Goldberg SD, Gebauer G (2009) N O and NO fluxes between a 2
Norway spruce forest soil and atmosphere as affected by prolonged summer
drought. Soil Biology & Biochemistry (submitted).................................................................98

CHAPTER 4 Forest soil N O emissions as affected by freezing/thawing 2
Goldberg SD, Borken W, Gebauer G (2009) N O emission in a Norway spruce 2
forest due to soil frost – Concentration and isotope profiles shed a new light on
an old story. Biogeochemistry (submitted). ........................................................................124

CHAPTER 5 Fen soil N O and NO emissions as affected by water table 2
Goldberg SD, Knorr K-H, Blodau C, Lischeid G, Gebauer G (2009) Impact of
experimental drying and rewetting on N O and NO turnover and emissions from 2
a temperate acidic fen. Global Change Biology (submitted). .............................................144

APPENDIX ............................................................................................................................I
Acknowledgements ............................................................................................................... III
List of further publications ......................................................................................................V


3





4


SUMMARY


Climate models predict an increasing frequency and intensity of summer drought periods
with subsequent heavy rainfall or soil frost and thaw events in mountain regions of Cen-
tral Europe. These indirect effects of global warming may considerably influence soil mi-
crobial processes and in consequence emissions of climate-relevant trace gases. Re-
garding the nitrogen cycle, N O and NO emissions are of concern, since they are in-2
volved in climate warming and soils represent a main source for these two gases. In spite
of a growing number of studies on this subject, knowledge on effects of climate change
on soil N O and NO emissions is still scarce. This is mainly due to a hitherto poor mecha-2
nistic understanding of underlying processes within soil.
In this thesis, the impact of extreme meteorological boundary conditions on N O and 2
NO fluxes in a Norway spruce forest and an acidic fen in the Fichtelgebirge area was in-
vestigated. The summer drought period and precipitation were experimentally increased
in the forest and the fen over a 2-year span. Soil frost was induced in the forest by re-
moval of the natural snow cover. The experiments were run in three replicates each and
non-manipulated plots served as controls. Throughout the experiments, N O and NO 2
fluxes were recorded in weekly to monthly intervals. In addition, N O concentrations and 2
isotope signatures in soil air were measured along soil profiles to identify and localise the
underlying biogenic production and consumption processes.
Prolonged drought continuously reduced the N O emission from the forest soil and 2
even turned the soil temporarily into a sink for atmospheric N O. Soil freezing and thaw-2
ing caused a burst of N O release contributing 84 % of the annual emission. 2
Soil air N O concentration and stable isotope profiles provide a new mechanistic ex-2
planation tool for all of these findings. N O concentration in the soil air decreased in most 2
cases exponentially from the subsoil to the soil surface. This observation identifies micro-
bial activity in the subsoil (at ≥ 70 cm soil depth) as an additional source for N O and dif-2
fusion to the soil surface along a concentration gradient. Furthermore, isotope abundance
analysis identified simultaneous microbial N O consumption (reduction to N ). Drought 2 2
reduced the source strength of the organic layers for N O while simultaneously the sink 2
function of the mineral soil for N O remained active. This resulted in a net N O sink func-2 2
5
tion of the forest soil under severe drought. Frost in the topsoil was the only exception for
these trends in N O concentration and isotope signature along soil profiles. Under condi-2
tions of soil frost the topsoil served no longer as a sink for N O, thus leading to the ob-2
served burst in N O emission. 2
NO emissions from the forest soil exceeded the N O emissions by up to two orders of 2
magnitude. Prolonged drought in- or decreased NO emissions depending on the soil
moisture content of the organic layers. Wetting after long-lasting drought periods – which
turned out to be of less importance regarding N O fluxes – strongly increased biogenic 2
NO emissions and contributed 44 % to the annual loss. In contrast to the forest soil, NO
fluxes from the fen were always one to two orders of magnitude lower than the N O 2
fluxes. These results support earlier findings that this highly reactive gas is either only
marginally produced in the fen soil or undergoes chemical conversion before escaping
from the soil surface. Nevertheless, water table reduction resulted in significantly in-
creased net NO emission.
Regarding N O, this thesis suggests that summer drought periods may drastically in-2
crease emissions from minerotrophic fens depending on the reduction of water table
height. Furthermore, heavy rainfall following drought periods caused short lived, but
strong N O peaks having significant impact on the annual N O loss, that have not been 2 2
15 18reported so far. N and O isotope data provide evidence that these N O peaks are due 2
to newly produced N O in the upper soil. 2
This thesis documents the huge impact of extreme weather events on soil N O and 2
NO emissions and provides so far scarcely considered mechanistic explanations for
these observations. A major outcome of this work is the finding of a hitherto unconsidered
sink function of forest soils for atmospheric N O, when soil net N O production is com-2 2
pensated for by net consumption during long-lasting droughts. This work underlines the
importance of investigating the fate of N O within soil profiles next to flux measurements 2
to improve the current knowledge on the complex interactions between meteorological
boundary conditions and soil biogenic processes and thus help further upgrading global
N O balances. 2





6

ZUSAMMENFASSUNG


Klimamodelle prognostizie