Soil biodiversity and nutrient cycling in rich fens

New prospects in Restoration ecology ?

Rolf Kemmers Bas van Delft, Miki Madaras, Ab Grootjans

Problem: Natural vegatations affected by drainage, acidification and

eutrophication Restoration efforts directed to amelioration of abiotic conditions Effects:

Some times manifest Frequently retarded, transient or ambiguous !

Questions: Did we tune the right buttons ? Why should soil organisms not suffer from env. stress as well ? Did we fuel the car leaving the batteries unloaded ?

Is plant biodiversity linked to diversity of soil organisms ?

Introduction

1. Acidification of a Dutch rich fen

Changed N-availability and plant productivity/biodiversity

Two cases:

2. Declined rich fens (NL) compared to calcareous fens (SLK)

Changed P-availability and plant productivity/biodiversity

Case 1 Reference of an ‘undisturbed’ rich fen Well buffered homogenized humus

profile: Mull

‘Optimal’ conditions•Acid-buffer supplied by seepage water (pH 5.5)•Active soil fauna (earthworms)•High microbial nutrient demand: N-immobilisation

•C/N: 16 Nr. of species/4m2 : 22

g/m2

Crop production: 375

N-yield: 4,3

N-min: 2,8

Ahg

ACg

Case 1 Acidification and decrease of acid buffering capacity development of a stratified humus profile

3

4

5

6

7

0 25 50 75 100

Ca-saturation

pH

-H2

O

lime

ion-exchange

aluminumCa-saturation = 60%pH-H2O = 6

Ca-saturation = 20%pH-H2O = 4.5

Case 1 Acidified and stratified humus profile:

Moder •Acid-buffer depleted (pH decreased)•Earth worm activity decreased•Accumulation of organic matter•Low microbial nutrient demand•Increased C/N ratio’s

Nr. of species/4m2 : 22 13g/m2

Crop production: 375

490N-yield: 4,3 6,2N-min 2,8 5,1

C/N

37

20

14

Conclusions case 1: A shift from N-immobilisation to net N-

mineralisation is associated with cessation of earth worm activity

A >> Hypothesis:

A healthy earth worm population supports microbial N-

immobilisation and supports mesotrophic conditions

1. (Pot)wormen

2. Microben

NH4+ min.1. (Pot)wormen

2. Microben

NH4+ min.

Case 2 Declined rich fens (NL) and calcareous fens (SLK)

Case 2 Phosphorus behaviour in calcareous fen

Theory: Inorganic P is bound to

Ca, Fe- or Al-oxides

However:• No correlations between inorganic P and Ca or Fe

•Despite high content CaCO3 and (Fe+Al)ox

hardly any inorganic P bound and

• P organically bound !

0

1

2

3

4

5

0 25 50 75 100

CaCO3 (%)

PH

Cl (

mm

ol/k

g)

0

2

4

6

8

10

0 200 400 600 800 1000

Fe+Al (mmol/kg)

Po

x (m

mo

l/kg

)

0

2

4

6

8

10

12

14

1 2 3 4 5 6 7 8 9 10 11

Sites

Pa

n/P

tot

(%)

Case 2 Phosphorus behaviourSlowak fens (SLK) compared to 10 (best preserved)

Dutch fens (NL)

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0 100 200 300 400

P-tot (mg/100g)

Pa

n/P

tot

NL

SLK

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0 500 1000 1500 2000

C/P

Pa

n/P

tot

0

500

1000

1500

2000

2500

3000

0,0 2,0 4,0 6,0 8,0 10,0

pH-KCl

C/P

• NL higher anorg. P fraction

• SLK higher org. P and extremely low C/P ratio’s

(C/P < 50) • Upon acidification decreased humification

Case 2 Phosphorus behaviourResults suggest that: Under wet conditions P is immobilized by

microbes through (anaerobic) humification Upon drainage and oxidation acidification will

occur P will be released by decomposition and

mineralisation and Taken up by vegetation or Excess will be bound by Ca, Fe or Al (what we see

in NL)

A shift from organic bound P to inorganic bound P occurs during degradation

What do we learn from these cases ? Microbes are of main importance in controlling

low levels of plant available nutrients by immobilisation in pristine calcareous fens

Microbes are outcompeting plants for nutrients and are playing a key role in maintaining primary production at a low level

A divers food web of soil organisms (browsers, grazers and predators) is controlling nutrient cycling and availability in soils

Hypothesis

Plant biodiversity is controlled by soil biodiversity

Conclusion: In restoration ecology we are fueling the cars by

amelioration of abiotic conditions, but indeed we left the batteries unloaded by ignoring soil fauna as the main driving force of nutrient cycling.

So: Future restoration efforts should focus on soil

biodiversity !

Thank you

© Wageningen UR

Food leagues and ammonium

NH4+ min.

2. Microbes

4. Predatores

3. Bacterivores/Fungivores

R2 = 0,417

-0,05

0,00

0,05

0,10

0,15

0,20

0,25

0 100 200 300 400

C14 inc. Leucine

Nm

in/m

in-N