estimating relative contribution of autotrophic respiration to soil respiration … ·...

Estimating Relative Contribution of Autotrophic Respiration to Soil Respiration in Permafrost Region of Alaska,

Using 13C Pulse Labeling Method

Akira L. Yoshikawa, Masako Dannora, Koh Yasue, Tetsuou Shirota, Kenshi Takahashi, Tomoaki Morishita, Tomohiro Saito, Ryohei Yamamoto, Yojiro Matsuura,Kyotaro Noguchi, Christian Hossann, Roger W. Ruess

“For the past 20 years, temperatures above freezing in February have only been recorded three times -- first in 2011, then in 2017 and now, [2018].”

On Greenland and Central Arctic

“Alaska, for first time in modern records, had a spring average temperature of 0°C.”

On temperature of March-May 2016

Climate Change in Circumpolar Region

• Changing climate is likely to dramatically change the below ground environment in permafrost region (Schuur et al. 2015).

• This is expected to influence tree phenology, plant below ground C allocation pattern, as well as activities of soil microbial community (Hicks Pries et al. 2013).

• These activities determine CO2 efflux from boreal forest floor which is crucial for climate modeling. Thus, properly understanding how soil respiration and its components respond to the environment is important.

Cl imate Change in Circumpolar Region

Soil Respiration

Soil Respiration: Rs Pump CO2 analyzer Gas sampler

Soil collar

CO2

Soil Respiration: Rs

Soil collar

• Plant derived Autotrophic respiration: Ra

• Microorganism derived Heterotrophic respiration: Rh

Ra RhRh

Rs = Ra + Rh

Pump CO2 analyzer Gas sampler

Soil Respiration

CO2




Ra RhRh

Rs = Ra + Rh

Partit ioning Soil Respiration

Our Objective

Calculate proportional contribution of autotrophic respiration to soil respiration (Ra/Rs).

Compare seasonal differences between respiration rate and Ra/Rs.




Ra RhRh

Rs = Ra + Rh

Separating Ra & Rh using 13C pulse labeling method




Ra RhRh

𝛿13C (‰)

-10 -20 -30

010

Rs = Ra + Rh



δsδhδa

13C: Stable carbon isotope (approx. 1% of all carbon on earth)

• Atmosphere 𝛿13C = approx. -8 ‰

• C3 plant 𝛿13C = approx. -28 ‰



Ra RhRh

𝛿13C (‰)

-10 -20 -30

010

Rs = Ra + Rh


Ra/Rs =δs − δh

δa − δh


δsδhδa

δs =Ra

Rsδa +

Rh

Rsδh


Ra RhRh

𝛿13C (‰)

-10 -20 -30

010

Rs = Ra + Rh


Ra/Rs =δs − δh

δa − δh


99% 13CO2

δsδhδa

13C Pulse Labeling

δs =Ra

Rsδa +

Rh

Rsδh


Ra RhRh

𝛿13C (‰)

-10 -20 -30

010


Ra/Rs =δs − δh

δa − δh


99% 13CO2

13C Pulse Labeling

δsδhδa

𝛿13C from soil chamber efflux

𝛿13C from isolated root chamber efflux

𝛿13C from soil chamber prior to labeling

𝛿s:

𝛿a:

𝛿h:


Ra RhRh

𝛿13C (‰)

-10 -20 -30

010


Ra/Rs =δs − δh

δa − δh


99% 13CO2

13C Pulse Labeling

δsδhδa

* Calculated by Keeling plot method

𝛿13C from soil chamber efflux

𝛿13C from isolated root chamber efflux

𝛿13C from soil chamber prior to labeling

𝛿s:

𝛿a:

𝛿h:

(Keeling 1961)

Rh/Rs = 1 − Ra/Rs

Caribou-Poker Creek Research Watersheds Fairbanks / ALASKA

65.271˚ N, -147.268˚ W

Long-term ecological research site (LTER)

Boreal forest with discontinuous permafrost

Monthly average temperature & precipitation from 2016 (excludes. snowfall) Map: UAF Institute of Arctic Biology, Bonzana Creek LTER

Caribou-Poker Creek Research Watersheds

Boreal Forest

• Black Spruce forest (Picea mariana)

• Sampling season July 2015 (3 trees labeled) May 2016 (3 trees labeled) Sept 2017 (3 trees labeled)

Study Plot

Isolated root chamber Soil chamber

Before and after labeling 3 chambers 3 chambers

Final day 3 chambers16 chambers

(additional chambers measured in 2015)

Respiration sampled from:

Isolated root chamberSoil Chamber

Example of 4m x 4m plot with P. mariana root distribution

13C Pulse Labeling and Gas Sampling

IRMS

Gas samples

Calculate source 𝛿13C using

keeling plot method (Keeling 1961)

Instantaneous Rate of Daytime Respiration Soil Respiration (Rs) & Isolated Root Respiration

• Significantly higher respiration in July

• May and Sept showed similar respiration pattern

May July Sept

Median Rs

(µmol m-2 s-1) 1.48 4.94 1.64

Median isolated root respiration

(µmol L-1 s-1)0.14 2.57 0.15

A A

B

Isolated root respiration by root volume

Soil respiration

aa

b

Average temperature during sampling

Organic moss layer 2.3˚C 7.6˚C 3.0˚C

Mineral Layer 11.5cm depth

0.2˚C 3.6˚C 2.9˚C

13C Label Recovery: Isolated Root Chamber• Peak 𝛿13C from root chamber:

May: 6-9 days after labeling July: 4-8 days after labeling Sept: 9 days or more after labeling (has not reached a peak)

13C Label Recovery: Soi l Chamber (Rs)

Days after labeling

• 13C label increased with time, and spread further

• 𝛿13C from Rs showed large variation between chambers

Labeled photosynthetic assimilates are transported further with time

Spatial heterogeneity in distribution of roots from labeled tree

Relative Contribution of Autotrophic Respiration to Soil Respiration Ra/Rs

𝛿s : 𝛿13C of soil Rs

𝛿a : Average 𝛿13C from 3 isolated root chamber

𝛿h : Average 𝛿13C of Rs prior to labeling

Ra/Rs of each chamber with average value denoted by large circles

Relative Contribution of Autotrophic Respiration to Soil Respiration Ra/Rs

Within 1m from tree May July Sept

Median Ra/Rs. (%) 2.5% 21.6% 6.8%

Max Ra/Rs (%) 16.0% ≥100% 46.9%

Average temperature during samplingOrganic moss

layer2.3˚C 7.6˚C 3.0˚C

Mineral Layer 11.5cm depth

0.2˚C 3.6˚C 2.9˚C

Summary of Results

• July had the highest Rs and the highest Ra/Rs.

• Ra/Rs was higher in September than in May, even though Rs and organic layer temperature were similar.

• This may be due to near 0˚C temperature in May at mineral layer affecting root physiological conditions and metabolism.

• There was a large spatial heterogeneity among sampled chambers for Ra/Rs and 13C label recovery.

Conclusion

• We observed changes in the proportion of Ra and Rh in soil respiration between three seasons.

• Strong spatial heterogeneity was observed in the estimated Ra/Rs, which needs to be addressed in future studies.

• By using 13C pulse labeling method, we can partition Ra and Rh, and observe seasonal differences among them.

• Because Ra and Rh is dictated by separate biological processes and can be affected differently by phenology, it is important to consider seasonal changes in order to understand CO2 efflux from boreal forest floor.

Acknowledgements

The research in this presentation was made possible with funding from Exploratory Research on Humanosphere Science and

KAKENHI: Grant-inAid for Scientific Research.

We wish to express our gratitude to Jamie Hollingsworth, Daniel Epron, Nicolas Angeli, Caroline Plain, Tomoko Tanabe,

Yudong Shen, Satoko Otake and Jay Jones for their support on this research

estimating relative contribution of autotrophic respiration to soil respiration … ·...

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