Soil bacterial community structure remains stable with rising temperature in Hawaiian montane wet forests

Paul C. Selmants, Karen L. Adair, Creighton M. Litton, Christian P. Giardina & Egbert Schwartz

Bacteria are the most abundant and diverse organisms on Earth

How will soil bacteria respond to climate warming?

How will soil bacteria respond to climate warming?

Climatic controls on bacterial distribution poorly resolved

How will soil bacteria respond to climate warming?

Climatic controls on bacterial distribution poorly resolved

Shift in diversity could alter biogeochemical cycling

Hawaii Mean Annual Temperature Gradient

800-1600 m (13-18.2 °C)

A model study system: - Constant plant spp. composition

- Constant disturbance histories

- Constant substrate age & type

- Constant soil water balance

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18.2 °C

17.3 °C16.7 °C

16.1 °C

16.1 °C15.5 °C

15.1 °C

13.8 °C13.0 °C

¯0 2 41 Kilometers

Forest Reserve

Natural Area Reserve

National Wildlife Refuge

Island of Hawaii

Hawaii Mean Annual Temperature Gradient

800-1600 m (13-18.2 °C)

A model study system: - Constant plant spp. composition

- Constant disturbance histories

- Constant substrate age & type

- Constant soil water balance

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18.2 °C

17.3 °C16.7 °C

16.1 °C

16.1 °C15.5 °C

15.1 °C

13.8 °C13.0 °C

¯0 2 41 Kilometers

Forest Reserve

Natural Area Reserve

National Wildlife Refuge

Island of Hawaii

Long-term, whole-ecosystem response to rising MAT

Workflow

DNA extraction(8 samples/MAT plot)

16S rDNA amplification

454 Pyrosequencing

Workflow

DNA extraction(8 samples/MAT plot)

16S rDNA amplification

454 Pyrosequencing

Sequence processing(QIIME pipeline)

Rarefaction(2200 seq./sample)

Data analysis(Diversity, composition)

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0

500

1000

1500

2000

13 14 15 16 17 18Mean annual temperature (°C)

Estim

ated

OTU

rich

ness

No effect of rising MAT on OTU richness

No effect of rising MAT on phylogenetic diversity

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0

20

40

60

80

13 14 15 16 17 18Mean annual temperature (°C)

Phyl

ogen

etic

dive

rsity

No effect of rising MAT on composition at phylum level

0

25

50

75

100

13 13.8 15.1 15.5 16.1a 16.1b 16.7 17.3 18.2Mean annual temperature (°C)

Rel

ative

abu

ndan

ce (%

) PhylumProteobacteriaAcidobacteriaActinobacteriaChloroflexiCandidate WPS−2PlanctomycetesOther

Weak effect of rising MAT on OTU composition

R2 = 0.03, p = 0.07 (PERMANOVA)

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NMDS Axis 1

NM

DS

Axis

2

131415161718

MAT (°C)

Why do soil bacterial communities remain stable with rising MAT?

Increase in abundance

Increase in activity

Decrease in dormancy

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18.2 °C

17.3 °C16.7 °C

16.1 °C

16.1 °C15.5 °C

15.1 °C

13.8 °C13.0 °C

¯0 2 41 Kilometers

Forest Reserve

Natural Area Reserve

National Wildlife Refuge

Island of Hawaii

Conclusions

“Rising tide lifts all boats”

Warming alone may be insufficient to alter community structure

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18.2 °C

17.3 °C16.7 °C

16.1 °C

16.1 °C15.5 °C

15.1 °C

13.8 °C13.0 °C

¯0 2 41 Kilometers

Forest Reserve

Natural Area Reserve

National Wildlife Refuge

Island of Hawaii

@biogeocycle