Climate Change in Arid Lands: Effects on Soil Biota and Ecosystem Processes

Deborah A. NeherUniversity of Vermont

Jayne BelnapUSGS - Southwest Biological Research Center

Cheryl KuskeLos Alamos National Laboratory

Thank you to B. Darby, D. Housman, S. Johnson and DOE PER

Average increased soil warming: surface +2.9oC, 5cm +2.7oC, 15cm +2.5oC% of 24 hr period with additional warming of >0oC and <5oC: 78, 81, 93%% of nighttime hrs with additional warming of >0oC and <5oC: 92, 82, 93%

HypothesesBiological soil crusts (BSC’s):

• H1: Increased temperature and summer precipitation will alter species composition, abundance, activity times and physiological functioning of BSC’s. This will reduce C and N inputs into soils. Increasing both temperature and precipitation will have a greater effect than either factor alone.

Subsurface soil biota:• H2: Increased temperature and summer precipitation will alter

the species composition, abundance, activity times, and physiological functioning of subsurface soil biota due to their dependence on C and N inputs from BSC’s, as well as direct effects of altered temperature and precipitation on their physiological functioning. Increasing both temperature and precipitation will have a greater effect than either factor alone.

Soil processes & vascular plants:• H3: Alterations in the species composition, abundance, activity

times, and physiological functioning of soil biota will affect soil processes and vascular plant performance.

Field Measurements• Air & soil temp, humidity, precipitation, wind, & net radiation• Soil water at three depths• CO2 flux in warmed and control plots• Crust cover, composition & pigments• Photosynthesis & Fv/Fm• Nitrogen (total, fixation, mineralization, isotopes)• Soil bacteria biomass & metabolism• Photosynthetic and N cycling bacterial abundance/composition• Soil fauna composition & abundance• Soil chemistry (nutrients, texture, OM, decomposition)• Soil enzymes

Baseline:

No significant difference in photosynthesis, Fv/Fm, N fixation, bacterial biomass, or faunal abundance

Early Warming Results:

Time of day

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

CO

2 flu

x (

mol

m-2

s-1

)

-0.2

-0.1

0.0

0.1

0.2

0.3

Crust tem

perature ( C)

-10

-5

0

5

10

15

20

25Control flux IR flux Control temperature IR temperature

C lo

ssC

gai

n

Nematodes

2

4

6

8

10 Amoebae

2000

4000

6000

Flagellates

0

1000

2000

3000

Con

trol

Lam

p C

ontro

l

[Wat

er]

Hea

t

Ciliates

0

100

200

300

400

Hea

t [+

Wat

er]

Con

trol

Lam

p C

ontro

l

[Wat

er]

Hea

t

Hea

t [+

Wat

er]

Indi

vidu

als

per g

ram

dry

soi

l

Winter C loss greater in warmed vs. control plots

Abundance of late-winter soil fauna similar across treatments except for amoebae

Drydown Experiment• Single drying events of 10, 20, 30(typical), and 120 min.

• Soil faunal abundance similar across drying treatments, but < controls.• N - fixing ability (nifH mRNA) declined slowly in dried soils. • Total RNA content and ammonia-oxidizing ability similar across treatments. • Soil crust Fv/Fm and pigments similar across treatments.

0%

10%

20%

30 60 90 120

Collection Time (minutes)

Rel

. nifH

Tra

nscr

ipts

0%

10%

20%

30 60 90 120

Collection Time (minutes)

Rel

. nifH

Tra

nscr

ipts

`

Cont 120 30 20 100

2

4

6

8

10

2006 Drydown Experiment - Fauna

Cont 120 30 20 100

1000

2000

3000

4000

Indi

vidu

als

per g

soi

l

Cont 120 30 20 10

Treatment

0

1000

2000

Cont 120 30 20 10

Treatment

0

100

200

a

cbc

bbc

a

ab

ab

abb

a

bb

bb

a

bab

b b

Nematodes Amoebae

Flagellates Ciliates

Experimental field study of the interactive effects of extremes (temperature and precipitation) on ecosystem function and diversity (including genetic diversity) in drylands.