Patterns and Controls of COq Fluxes in Wet Tundra Types of the Taimyr Peninsula, Siberia - the Contribution of Soils and Mosses

Muster und Steuerung von COo-Flüsse in nassen Tundraformen der Taimyr Halbinsel, Sibirien - der Beitrag von Böde und Moosen

Martin Sommerkorn

Ber. Polarforsch. 298 (1 998) ISSN 01 76 - 5027

Martin Sommerkom

Institut fü Polarökologi

Wischhofstr. 1-3, Geh. 12

D-24148 Kiel

Deutschland

Die vorliegende Arbeit ist die inhaltlich unverändert Fassung einer Dissertation, die 1998 der

Mathematisch-Naturwissenschaftlichen Fakultä der Christian-Albrecht-Universitä zu Kiel

vorgelegt wurde.

Contents

LIST OF ABBREVIATIONS

1 SUMMARY AND CONCLUSIONS

I . I ZUSAMMENFASSUNG UND SCHLU~FOLGERUNGEN

2 INTRODUCTION

2.1 CO, FLUXES, WHAT CAN THEY TELL?

2.2 TUNDRA ECOSYSTEMS: A CRITICAL FELD FOR CO2 FLUX~NVESTIGATIONS

2.3 OBJECTTVE OF THE STUDY

2.4 APPROACH

3 TAIMYR PENINSULA AND THE STUDY AREAS

3.1 TAIMYR PENINSULA, AN OVERVIEW

3.1.1 The Area of Lake Labaz

3.1.2 The Area o f Lake Levinson-Lessing

4 METHODS

4.1 C o 2 EXCHANGE

4.1.1Instrumentation Design

4.1.2 The Set-up in the Field

4.1.2.1 Soil Respiration Measurements

4.1.2.2 Soil-Moss System Measurements

4. 1.2.3 Whole System Measurements

4.1.3 The Set-up in the Laboratoiy: Water Table Experiments

4.1.4 Data Handling

4.1.5 Modelling

4.1.6 Statistics

4.2 MESO- AND MICROCLIMATOLOGICAL MEASUREMENTS

4.3 VEGETATION ANALYSIS AND SAMPLING FOR VASCULAR PLANT BIOMASS

5 RESULTS

5 RESULTS

5 . 1 . 1 L a k e Labaz

5.1.1.1 Mesoclimate of the Field-Season

5.1.1.2 Characteristics of the Experimental Sites

5.1.1.2.1 Tussock Tundra

5.1.1.2.1.1 Vegetation and Vascular Plant Biomass

5.1.1.2.1.2 Soils

5.1.1.2.1.3 Soil Microdimate

5.1.1.2.1.4 Bacterial Biomass

5.1.1.2.2 Wet Sedge Tundra

5.1.1.2.2.1 Vegetation and Vascular Plant Biomass

5.1.1.2.2.2 Soils

5.1.1.2.2.3 Soil Microciimate

5.1.1.2.2.4 Bacterial Biomass

5.1.2 Lake Levinson-Lessing

5.1.2.1 Mesoclimate of the Field Season

5.1.2.2 Characteristics of the Experimental Sites

5. 1.2.2. l Low-Centre Polygonal Tundra

5.1.2.2.1.1 Vegetation and Vascular Plant Biomass

5.1.2.2.1.2 Soils

5.1.2.2.1.3 Soil Microclimate

5.1.2.2.1.4 Bacterial Biomass

5.2 EXPERIMENTAL WSULTS

5.2. l Soil Respiration Studies

5.2.1. l Experiments in the Field

5.2.1.1.1 Lake Labaz

5.2.1.1.2 Lake Levinson-Lessing

5.2. 1.2 Experiments in the Lahoratory

5.2.1.3 Modelling of Soil Respiration in Tundra Systems

5.2.1.3,l Balancing the C02 Efflux of Soil Respiration

5.2.1.3.2 Performance of the Soil Respiration Process

5.2.1.3.2.1 Temperature Response

5.2.1.3.2.2 Relative Temperature Sensitivity

5.2.1.3.2.3 Response to Depth to Water Tahle

5.2.1.3.2.4 Identifying Patterns

5.2. 1.3.3 Simulating Scenarios for Soil Respiration

5.2.2 Studies on CO; Fluxes of the Soil-Moss System Considering Moss Photosynthesis

5.2.2.1 Experiments in the Field

5.2.2.1.1 Lake Labaz

5.2.2.1.2 Lake Levinson-Lessing

5.2.2.2 Moss Photosynthetic Performance

5.2.2.3 Balancing the C02 Fluxes of the Soil-Moss System

5.2.3 Studies on CO; Fluxes of the Whole System

5.2.4 Connecting the Subsystems

6 DISCUSSION

6. 1 CONTROL OF SOIL RESPIRATION IN TUNDRA SYSTEMS

6.1.1 Microsite und Efflux Patterns

6.1.2 The Factor Water Table

6.1.3 The Factor Temperature

6.1.4 Microsite und Soil Respiration Potential

6.2 THE ROLE OF MOSS ASSIMILATION AS A BUFFER FOR C02 EFFLUXES FROM TUNDRA

6.2. I Microsite und Moss Photosynthesis

6.2.2 Microsite und Quantitative Aspects of Buffering

6.3 TUNDRASYSTEM Coi FLUXES: CONTRIBUTIONS OFTHE SUBSYSTEMS

6.4 TUNDRA CARBON BUDGETS: A MATTER OF SCALING

7 REFERENCES

8 ACKNOWLEDGEMENTS

9 APPENDIX

IV

List of abbreviations

CO2

DW

GMP

LAI

max,

rnin .

NSF

PD

PH

PL

PPFD

Qio

SMR

ST2

TD

temp.

TH

TT

WS

WT

ww

carbon dioxide

dry weight

g o s s photosynthesis of mosses

leaf area index

rnaximum value

r mimum value

net System flux

depression microsite in the low-centre polygonal tundra

high apex microsite in the low-centre polygonal tundra

low apex microsite in the low-centre polygonal tundra

photosynthetic photon flux density

temperature quotient

respiration of the soil-moss system

soil temperature at 2 cm depth

depression microsite in the tussock tundra

temperature

moss hummock microsite in the tussock tundra

tussock microsite in the tussock tundra

wet sedge tundra

soil water table

wet weight

Summary 1

1 Summary and Conclusions

The goal of this study was to gain an understanding of the small-scale variability of CO2

fluxes in wet tundra types. The investigation aimed at showing the spatial variability of the

magnitude of CO2 fluxes and at explaining differences in the mode of operation of their

driving forces. Due to the fine-grained heterogeneity of the tundra, an understanding of the

small-scale Patterns can increase the insight into functional interrelations of the ecosystem.

The study focused On the CO2 fluxes from soils and the soil-covering moss layer. The CO2

efflux from the soil to the atmosphere (soil respiration) describes the mobilization of carbon

from the soil organic matter, the largest carbon store of the tundra. Mosses form the extensive

interface between soil and atmosphere in tundra. Via their photosynthesis, they hnction as a

filter for the COz efflux originating from soil respiration.

To accomplish the overall goal, an existing measuring-technique was refined and a new

method was developed: The application of C02 gas-exchange in dynamic differential mode

resulted in the high-resolution capture of the CO2 fluxes both in time and space. Continuous

in situ measurements of the soil-moss system were accomplished by means of a transparent

and conditioned chamber. The model used for describing the temperature response of soil

respiration (Lloyd and Taylor 1994) allowed for a changing temperature sensitivity of the

process across the temperature range. This provided an additional Parameter for the

description of CO2 flux control. Individually fitted models describing the CO2 fluxes of each

investigaied microsite permitted the identification of spatial differences with respect to the

mode of operation of the controlling factors. Correlating the obtained model Parameters with

biotic and abiotic site characteristics of the microsites allowed to describe the control of CO2

fluxes on a higher level.

Field experiments were carried out at seven microsites in three tundra types of the Taimyr

Peninsula, North Siberia, during July and August of 1995 and 1996. At the intensive study site

"Lake Labaz" within the belt of the "Southern Arctic Tundra", a tussock tundra and a wet

sedge tundra were investigated. Within the belt of the "Typical Arctic Tundra", measurements

were carried out in a low-centre polygonal tundra at Lake Levinsson-Lessing.

The diurnal Course of soil respiration of all microsites was determined by depth to water table

and soil temperature at two centimetres depth. The position of the water table controlled the

total level of soil respiration by determining the soil volume available for aerobic processes.

2 Summary

The soil temperature modified this signal level. The high correlation of soil respiration with a

temperature close to the soil surface indicates the source for the bulk of the respired CO2 to be

in the upperrnost horizon. An individually fitted soil respiration model on the basis of the

position of the water table and soil temperature at two centimetres depth was capable to

explain more than 90 % of the variations of soil respiration. Differences in the magnitude of

the CO; fluxes were much greater between directly adjacent microsites than between the

different study areas. The highest daily means of soil respiration of 10.9 g c ~ ^ m ^ d " were

obtained at the comparatively dry microsites in the tussock tundra (tussock, moss hummock).

These microsites also showed the lowest positions of the water table and the highest soil

temperatures. The lowest daily means of soil respiration were measured at the wet and cold

depressions of the tussock tundra and the polygonal tundra, as well as in the wet sedge tundra.

When focusing on the relative potential of soil respiration instead of on the absolute

magnitude of fluxes, a contrasting pattem was found. The wet an