The effects of long-term Free Air CO_1tn2 Enrichment (FACE) on soil aggregation, soil carbon input, and ecosystem CO_1tn2 dynamics in a temperate grassland ecosystem [Elektronische Ressource] / vorgelegt von Katharina Lenhart
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The effects of long-term Free Air CO_1tn2 Enrichment (FACE) on soil aggregation, soil carbon input, and ecosystem CO_1tn2 dynamics in a temperate grassland ecosystem [Elektronische Ressource] / vorgelegt von Katharina Lenhart

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134 pages
Deutsch

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Publié le 01 janvier 2009
Nombre de lectures 19
Langue Deutsch
Poids de l'ouvrage 2 Mo

Exrait


The effects of long-term Free Air CO 2
Enrichment (FACE) on soil aggregation, soil
carbon input, and ecosystem CO dynamics in 2
a temperate grassland ecosystem






Inauguraldissertation

zur Erlangung des akademischen Grades doctor rerum naturalium
(Dr. rer. nat.)

der naturwissenschaftlichen Fachbereiche der
Justus-Liebig-Universität Gießen

vorgelegt von
Katharina Lenhart

Gießen, im September 2008


Dekan: Prof. Dr. Peter R. Schreiner

Erster Gutachter: Prof. Dr. Dr. h.c. Hans-Jürgen Jäger

Zweiter Gutachter: Prof. Dr. Christoph Müller

Tag der mündlichen Prüfung:

22. Dezember 2008 Erklärung

Hiermit erkläre ich, dass ich die vorgelegte Dissertation selbstständig und ohne unerlaubte
fremde Hilfe und nur mit den Hilfen angefertigt habe, die ich in der Dissertation angegeben
habe.
Alle Textstellen, die wörtlich oder sinngemäß aus veröffentlichten Schriften entnommen sind,
und alle Angaben, die auf mündlichen Auskünften beruhen, sind als solche kenntlich
gemacht.
Bei den von mir durchgeführten und in der Dissertation erwähnten Untersuchungen habe ich
die Grundsätze guter wissenschaftlicher Praxis, wie sie in der „Satzung der Justus-Liebig-
Universität Gießen zur Sicherung guter wissenschaftlicher Praxis“ niedergelegt sind,
eingehalten.


Gießen, den 26. September 2008 Table of contents I
Table of contents
List of tables……………………………………………………………..………………… III
List of figures……………………………………………………………………...…..……IV
Abbreviations…………………………………….……………………………….……… VI
Abstract………………...……………………………………………………………….….XII
Kurzfassung…………………………………………………………………………….…..IX

1 Introduction _________________________________________ 1
1.1 Climate change and grassland ecosystems ........................................... 1
1.2 Effects of elevated CO on ecosystem C dynamics ............................... 2 2
1.2.1 Grassland FACE experiments................................................................ 2
1.2.2 Ecosystem C balance ............................................................................ 3
1.2.3 Soil aggregate structure......................................................................... 4
1.2.4 Soil and ecosystem respiration and its components............................... 6
1.3 Objectives of this study............................................................................ 8
2 Materials and methods ________________________________ 9
2.1 Site description......................................................................................... 9
2.2 Air temperature, precipitation, and soil data .........................................10
2.2.1 Air temperature and precipitation ..........................................................10
2.2.2 Soil texture............................................................................................12
2.2.3 Bulk density ..........................................................................................12
2.2.4 Soil moisture.........................................................................................13
2.3 Soil and plant biomass sampling and analysis .....................................14
2.3.1 Soil sampling ........................................................................................14
2.3.2 Soil aggregate fractionation ..................................................................14
2.3.3 Plant biomass .......................................................................................16
132.3.4 Analysis of C signature and SOC content...........................................17
2.3.5 Calculations ..........................................................................................17
2.4 Gas sampling and analysis .....................................................................19
2.4.1 Gas sampling........................................................................................19
132.4.2 Analysis of δ C signature and CO concentration.................................20 2
2.4.3 Separation of soil and ecosystem respiration into its components.........20
2.5 Statistical analysis...................................................................................25
3 Results ____________________________________________ 27
3.1 Air temperature, precipitation, and soil moisture..................................27
3.2 Plant biomass ..........................................................................................30
133.2.1 δ C signature of above and belowground biomass ..............................30
3.2.2 Root biomass yield................................................................................32
3.3 Soil aggregate structure..........................................................................34
3.3.1 Distribution of aggregates in the soil profile...........................................34
3.3.2 Soil aggregation changes between 1998 and 2007...............................35 Table of contents II
3.3.3 Effect of elevated CO on soil aggregation ...........................................36 2
133.4 Soil organic carbon content and δ C signature under ambient and
elevated CO ............................................................................................38 2
3.4.1 SOC content.........................................................................................38
3.4.2 Effects of elevated CO on SOC content ..............................................44 2
133.4.3 δ C signature of SOC in bulk soil and the soil aggregate fractions.......45
3.5 Soil C input in the CO enriched plots ...................................................49 2
3.5.1 Fraction of new C .................................................................................49
3.5.2 Input of new C ......................................................................................50
3.5.3 Input of new C into free and macroaggregate-associated
microaggregates...................................................................................53
3.6 Soil air CO and ecosystem respiration.................................................55 2
133.6.1 Annual dynamics of ecosystem respiration and δ C and CO 2
concentration in soil air.........................................................................55
3.6.2 Partitioning of R into autotrophic and heterotrophic components.......65 soil
3.6.3 Partitioning of R ................................................................................69 eco
4 Discussion_________________________________________ 73
4.1 Effects of elevated CO on the soil aggregate structure.......................73 2
4.2 Effects of elevated CO on the soil C content .......................................77 2
4.3 Soil C input under elevated CO .............................................................83 2
4.4 Effects of elevated CO on the autotrophic and heterotrophic 2
components of soil and ecosystem respiration....................................91
5 Conclusions and outlook _____________________________ 99
6 References________________________________________ 101
7 Appendix _________________________________________ 116
7.1 Date of aboveground biomass clipping...............................................116
7.2 Drying-Wetting Cycles between 1997 and 2004 ..................................116
7.3 List of gas samples ...............................................................................116
7.4 Bulk density...........................................................................................121

List of tables III
List of Tables

13Tab. 2.1 δ CO of tank-CO and atmospheric CO in the CO -enriched plots ........10 2 2 2 2
Tab. 2.2 Soil texture and pH in the soil profile ........................................................12
Tab. 3.1 Mean air temperatures (T ) and temperature changes.............................27 air
13Tab. 3.2 Predicted and measured δ C signature of plants .....................................30
13Tab. 3.3: δ C signature of aboveground plant biomass..........................................31
13Tab. 3.4 Effect of depth on δ C signature of root biomass .....................................32
Tab. 3.5 Differences in root biomass between the CO treatments .........................33 2
Tab. 3.6 Relative changes in soil aggregation.........................................................36
Tab. 3.7 Average changes in SOC content between April 1998 and 2004..............39
Tab. 3.8 Changes in total SOC under ambient atmospheric CO conditions ...........39 2
Tab. 3.9 Area-related changes in SOC of several soil fractions ..............................41
Tab. 3.10 Fraction of new C in several soil aggregate fractions after 8 years of
elevated [CO ] +20%................................................................................49 2
Tab. 3.11 Fraction of new C in several soil aggregate fractions after 8 years of
elevated [CO ] +30%................................................................................50 2
Tab. 3.12 Rate of C input per year under [CO ] +20% ............................................51 2
Tab. 3.13 Rate of C input per year under [CO ] +30% ............................................52 2
Tab. 3.14 Fraction of new C in June 2004 in free and macroaggregate-
associated microaggregates.....................................................................53
13Tab. 3.15 δ C signature of soil air CO in the ring pairs 1-3 ...................................56 2
13Tab. 3.16 δ C signature of soil air CO in ring pair 4 ..............................................63 2
Tab. 3.17 Contribution of R on R [%] ...............................................................66 root soil
13Tab. 3.18 The mean δ C signature of the CO source of R . ...............................69 2 eco
Tab. 3.19 Relative contribution of autotrophic respiration on R ...........................71 eco
Tab. 4.1 Reported effects of elevated CO on soil C stocks of in-situ CO 2 2
enrichment experiments on grassland ecosystems ..................................77
Tab. 4.2 Components of R in the Giessen-FACE, an annual grassland, and a eco
Californian redwood forest ecosystem......................................................98
Tab. 7.1 Dates of aboveground biomass clipping..................................................116
Tab. 7.2 List of gas samples .................................................................................117
Tab. 7.3 Bulk density values. ................................................................................121 List of figures IV
List of Figures

Fig. 1.1 Components of ecosystem C budget...........................................................3
Fig. 1.2 Sources of soil respiration............................................................................7
Fig. 2.1 Aboveground biomass yield in the Giessen-FACE.......................................9
13Fig. 2.2 δ C signature of enrichment-CO ..............................................................10 2
Fig. 2.3 Temperature function (fT) according to Jarvis-Stewart...............................11
Fig. 2.5 Soil fractions obtained from wet sieving and microaggregate isolation.......15
Fig. 3.1 Precipitation...............................................................................................28
Fig. 3.2 Soil moisture..............................................................................................29
13Fig. 3.3 δ C signature of root biomass...................................................................31
13Fig. 3.4 Coherency between root δ C signature and depth....................................32
Fig. 3.5 Mean root biomass after 9 years of CO enrichment..................................33 2
Fig. 3.6 Distribution of soil aggregates in the soil profile .........................................34
Fig. 3.7 Soil aggregate structure of plots. ...............................................................35
Fig. 3.8 LM content differences between E- and A-plots.........................................37
Fig. 3.9 SOC content of several soil fractions in the soil profile...............................38
Fig. 3.10 Average changes in SOC content............................................................40
Fig. 3.11 SOC content stored in each aggregate fraction.. .....................................42
Fig. 3.12 SOC loss between April 1998 and 2004 and magnitude of LM loss.........43
Fig. 3.13 SOC content in 1998 and after 9 years of elevated CO ..........................44 2
Fig. 3.14 Changes in SOC since 1998....................................................................44
13Fig. 3.15 δ C signature of SOC in the soil profile...................................................46
13Fig. 3.16 Shift in δ C signature of SOC in several soil aggregate fractions ...47
13Fig. 3.17 The δ C signature of aggregate fractions in E and A-plots......................48
Fig. 3.18 Input of new C into free and macroaggregate-associated
microaggregates......................................................................................54
13Fig. 3.19 Ecosystem respiration, soil air CO concentration and δ C signature 2
of soil air CO in ring pair 1. .....................................................................57 2
13Fig. 3.20 Ecosystem respiration, soil air CO concentration and δ C signature 2
of soil air CO in ring pair 2.. ....................................................................58 2
13Fig. 3.21 Ecosystem respiration, soil air CO concentration and δ C signature 2
of soil air CO in ring pair 3. .....................................................................59 2
Fig. 3.22 Mean values of the ring pairs 1-3.............................................................60
13Fig. 3.23 δ C signature of soil air CO in the soil profile.........................................62 2List of figures V
13Fig. 3.24 Correlation of soil depth and decrease in δ CO ......................................64 2
Fig. 3.25 Contribution of R on R over time ([CO ] +20%).................................65 root soil 2
Fig. 3.26 Correlation of root-derived CO and depth ([CO ] +30%). ........................67 2 2
Fig. 3.27 Contribution of R on R in the soil profile ([CO ] +30%)......................68 root soil 2
13Fig. 3.28 δ C signature of the CO source of R and soil air CO .........................70 2 eco 2
Fig. 3.29 Contribution of leaf respiration to R ......................................................71 eco
Fig. 3.30 Contributions of R , R and R to R ...............................................72 leaf root bulk eco
Fig. 4.1 Theoretical periodic changes on decadal scale..........................................82
Fig. 7.1 Drying-wetting events of the upper 15 cm of soil......................................116 Abbreviations VI
Abbreviations

f C Fraction of new C new
f Fraction of SOM-derived CO on R bulk 2 soil
f Fraction of leaf derived CO on R leaf 2 eco
f Fraction of plant derived CO on R plant 2 eco
f Fraction of root derived CO on R root 2 soil
f Fraction of soil derived CO on R soil 2 eco
LM Large macroaggregates (> 2000 µm)
Mic Microaggregates (53-250 µm)
Mic-LM Microaggregates within large macroaggreates
Mic-SM Microaggregates within small macroaggregates
R Ecosystem respiration eco
R Leaf respiration leaf
R Plant respiration (roots + leaves) plant
R Root respiration root
R Soil respiration soil
SC Silt and clay particles (< 53 µm)
SM Small macroaggregates (250-2000 µm)
SOC Soil organic carbon
SOM Soil organic matter
T Air temperature air
VWC Volumetric water content

Abstract VII
Abstract
Elevated atmospheric CO concentrations enhance photosynthesis, however, they 2
also increase respiratory carbon (C) losses from ecosystems. The changes of both
will have a yet unknown effect on ecosystem C dynamics and balances. The aim of
this study was to investigate the effects of a moderate long-term CO enrichment on 2
ecosystem C dynamics of a temperate grassland ecosystem. To address this
subject the effects of elevated CO on the soil aggregate structure were 2
investigated, and the soil C content and the input of new C to several soil aggregate
13fractions were determined. Furthermore, the C isotope signature of soil air CO 2
13and ecosystem respiration was measured. The C signature was used to separate
soil and ecosystem respiration into its autotrophic (plant-derived) and heterotrophic
(old soil organic carbon) components. The study was conducted at the Free-Air CO 2
Enrichment (FACE) site near Giessen, Germany. The CO enrichment started in 2
13 13May 1998 using C depleted CO with a signature of -25‰. In July 2004 the δ C 2
signature of the enrichment-CO was switched from -25 to -48‰ without altering the 2
CO concentration. This experimental setup provided the unique opportunity to trace 2
ecosystem C fluxes without concomitant priming effects of a CO step increase. 2
In the Giessen-FACE study no CO -induced increase in soil aggregation occurred 2
after nine years of elevated CO . Root biomass increased under [CO ] +30% but 2 2
remained mainly unaltered in the [CO ] +20% treatment. The CO enrichment 2 2
enhanced ecosystem respiration (R ) by 13%. However, elevated CO did not eco 2
result in increased soil C sequestration after 9 years of elevated CO in any soil 2
aggregate fraction, nor did it prevent the loss of soil C observed between 1998 and
2004 at the site. This C loss coincided with a breakup of large macroaggregates. In
the [CO ] +20% enriched plots the input of C to the soil corresponded to 109 ±43.5 g 2
-2 -1m yr in the first observation period between 1998 and June 2004, and to 44.4
-2 -1±32.5 g m yr in the second observation period between June 2004 and June
-2 -12006. Under elevated [CO ] +30%, C inputs were 82.1 and 76.2 g m yr for both 2
periods, respectively, indicating no higher C input with increasing [CO ] in both 2
investigation periods.
Under elevated [CO ] +20%, the overall contribution of root-derived soil respiration 2
13was 55% in the top 15 cm of the soil. The C signature of R and soil air CO eco 2
showed the strongest depleted values during the growth period, indicating a higher
contribution of plant-derived CO at that time. The mean contributions of root, leaf 2
and soil respiration to R were 29 ±18%, 32 ±23% and 38 ±20%, respectively. A eco
13significant decrease in soil air δ CO with soil depth indicated a relatively higher 2
13contribution of root-derived CO in the deeper soil layers. The δ CO gradient 2 2
showed distinct annual dynamics with a significant impact of soil temperature. The
13steepest δ CO gradients occurred during winter but became less distinctive during 2
the summer month.
Overall, the data gave evidence for an accelerated C-turnover with increasing CO 2
concentration but without a net C sequestration under elevated CO . Therefore, we 2