AcknowledgmentsUniversity of Toledo, Maumee Valley Audubon Society, Daryl Moorhead, Tom Weicht, Alison Spongberg, Li Fafeng, Brian Marlow, Jayne Belnap.

MICROBIOTIC CRUST COMMUNITIES: NITROGEN FIXATION AND LEACHING WITHIN

A MESIC TEMPERATE OAK SAVANNA

Cladina cristatella Tuck.

by Roberta Veluci & Deborah A. Neher

ABSTRACT

Microbiotic crust is a biological soil crust composed of lichens, cyanobacteria, green algae, mosses, and fungi. Although crusts are a dominant source of nitrogen in arid ecosystems, this study is the first to examine their contribution to nitrogen (N) availability in xeric temperate habitats in Northwest Ohio. N fixation occurs in these crusts covering sandy, low N soil. Moss-crust surfaces are covered with cyanobacteria responsible for N fixation and cyanobacterial abundance was independent from days since last rainfall. Moreover, increases in temperature correspond with amount of N fixed. N leaching from the crust layer was quantified using ion exchange resin bags inserted at 2.5-cm depth from surface of intact cores. Leaching of NO3

- and NH4 +

were reduced in forest edge relative to shrub or grass vegetations, and did not vary significantly among months. Leaching of NO3

- is retarded with temperature rise and, thus, a function of temperature. Conversely, precipitation increased N leaching, and is expected to maximize during rain fall events. Furthermore, environmental parameters such as moisture and temperature fluctuations in soil are moderated under crust compared to bare soil without crust. We conclude that biological crusts in northwestern Ohio enhance N fixation, moderate soil microclimate and, impact N leaching.

STUDY SITE

Oak Openings Metropark

•4.0 to 5.4 pH• 91-94% sand •Low N soil

A) Well established crust, B) Intermediate crust and C) Bare Soil.

A C B

Moss

Lichen

Bare

Algae

Video Imaging Analysis: estimate crust type and extent

NITROGEN FIXATION

Acetylene Reduction Assay: confirmed N fixation in 50% of samples.

Eth

ylen

e p

rop

ortio

n (

10-4

)

0.00

0.05

Lichen

0.10

Extent Cover (proportion)

y = 0.021 + 0.044x R2 = 0.03 & p < 0.003

0.20 0.40 0.60 0.80 1.000.00

0.20 0.40 0.60 0.80 1.000.00

0.10

0.20

0.30

Mossy = 0.006 + 0.0043xR2 = 0.09 & p < 0.003

0.40

Fig. 6

0.20

0.15

0.00

Moss cover and lichen explained more N fixation than did cyanobacteria or bare soil

Result: Abundance of cyanobacteria decreased with crust depth

Method: Fluorescent microscopy to quantify cyanobacterial populations

3 6 9

Crust depth (mm)

0

1

2

3

4

5

6

7

8

Cya

noba

cter

ia (

105

ce

lls/g

of

dry

soil)

b

a

ab

Contrasting letters

(p = 0.0002)

Fig. 8

Moss surfaces are covered with cyanobacteria and its abundance was independent from days since last rainfall

0 7 14Days since rainfall

0

1

2

3

Cya

noba

cter

ia (

106 ,

tota

l cel

ls/g

of d

ry s

oil)

p = 0.70

Fig. 7

Fig. 2 Recovery efficiency of resin bags

Volume (ml)

0.0

0.2

0.4

0.6

0.8

1.0

P

ropo

rtio

n o

f io

n r

eco

very

(µ

g/g

)

150 300 600 900 15000.0

0.2

0.4

0.6

0.8

1.0

B

Recovery efficiency of

NO3- and NH4

+ from

resins were 33 and

70%, respectively.

NO3- = 1N KHSO4

-

NH4+ = 0.5 N K2SO4

+

NH4+ = 1N K2SO4

NITROGEN LEACHING

1) Method Development

Fig. 3 Relatively flow of N to resin bags flush with bottom of core

inside core around core below core

Nitrogen source

Mea

n r

eco

very

(µ

g/g

)

0

5

10

15

20

25

30

01020

304050

60

70NH4

+

0

2

4

6

8

10

0

10

20304050

6070

NO3-

% T

ota

l Rec

ove

ry

2) Method Development

Ion exchange resin bags placed

flush with the bottom surface of

an intact core collected most

NO3- or NH4

+ from outside the

core than from directly above or

underneath the resin bag inside

the core (p < 0.0067). Therefore,

resin bags were inserted at 2.5-

cm depth from surface of intact

cores in field experiments.

NITROGEN LEACHING

Time (weeks)

Fig. 4 Dynamic equilibrium of N on resins and in soil

= resins O = soil

0.0

0.1

0.2

0.3

0.4

0.5

1 3 5 7 10 18 220.0

0.1

0.2

0.3

0.4

0.5

Res

in a

nd s

oil n

itrog

en (

µg/

g) NO3-

NH4+

2) Field Measurements

Concentrations of NO3- (r2 = 0.33) and NH4

+ (r2 = 0.21) on resins were associated linearly

with soil concentrations. Concentrations of N on resins were typically greater than in

soil (p = 0.0001), although they were in equilibrium through time (p = 0.18).

49 80 98 1270

2

4

6

8

10

Nitr

oge

n le

ach

ing

(µ

g/g

)NO3

- p = 0.009

40 80 98 1270

2

4

6

8

10

Aug DecNovOctSept

NH4+ p = 0.03

Time (days)

▲= FOREST

■= SHRUB

●= GRASS

Fig. 5 N leaching among vegetation types

Concentration of NO3- (A, p = 0.0089) and NH4

+ (B, p = 0.0314) leaching

were less at forest edge than shrub or grass, and did not vary significantly

among months.

A

B

Fig 1. Soil A) water potential & B) temperature for bare ( ) or crust soils ( ) through time.

Soil crusts moderate soil climate

0 5 10 15 20 25

Time since deployment (weeks)

-7

-6

-5

-4

-3

-2

-1

0

Mo

istu

re (

MP

a)

0 5 10 15 20 250

10

20

30

40

Tem

per

atu

re (

°C)

A

B

MAY SEPT

CONCLUSIONS

This is the first study to:

• Confirm N fixation of microbiotic crusts in mesic temperate biome

•Employ IRN-77/78 resins in sandy soil, low in both N & organic matter