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.
