lecture for ‘biogeochemistry and global change’ lowland ...aibrom/bggc/lecture veldkamp effects...

Effects of N-deposition on tropicallowland and montane forests

Lecture for ‘Biogeochemistry and Global Change’

Edzo Veldkamp

Are tropical forests Nitrogen or Phosphoruslimited?

How is the internal N- Cycle affected by theabundance of Nitrogen in P-limited tropicallowland forests?

What will happen to tropical forests if the depositionof nitrogen-containing compounds will increase in thefuture?

Soil Scientist‘s view:

Trop. Lowland forest

Trop. Montane forest

Trop. Lowland 'Podzol'

Temperate forest

N in Litterfall (kg ha-1 yr-1)

0

40

80

120

160

200

0 50 100 150 200 250

Based on Vitousek (1984)

Are tropical forests N limited?D

ry m

ass/

N r

atio

0

2

4

6

8

10

12

14

16

18

0 0,5 1 1,5 2 2,5N Concentration in litterfall (% dry mass)

Trop. Lowland Forest

Trop. Montane Forest


Does nitrogen control fine litter fall?Li

tter

dry

mas

s (M

g ha

-1 y

r-1 )

• Most lowland tropical forestsdo not have efficient within-stand nitrogen economiescompared to temperate forests.

• The few tropical forestswith an efficient within-standnitrogen use are eithermontane forests or arelocated on podzols

Indirect evidence shows that:

Also direct evidence startsto emerge with fertilizationexperiments

Trop. Lowland forest

Trop. Montane forest


Temperate forest

00 2 4 6 8 10 12 14 16

P in Litterfall (kg ha-1 yr-1)

2000

4000

6000

8000


Are tropical forests P limited?D

ry m

ass/

P ra

tio


0

2

4

6

8

10

12

14

16

18

0 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08

P. concentration in litterfall (% dry mass)



Does phosphorus control fine litter fall?Li

tter

dry

mas

s (M

g ha

-1 y

r-1 )

• Many (but not all!!) lowlandtropical forests have moreefficient within-standphosphorus economies thanmost temperate forests.

•The tropical forests withthe most efficient within-stand phosphoruseconomics include some ofthe montane forests

Why are within-stand P-economy of tropical lowlandforests more efficient than most temperate forests?

•Endproduct of chemical weatheringin humid tropics are sequioxides,which can bind Phosphorus almostirreversible

•Phosphorus content of a site cannotbe replenished by the fixation of anabundant gas like is the case forNitrogen

Source: UNEP

Source: ISRIC

How much tropical rainforest is situated on soils withsesquioxides?

•Most lowland tropical forests are P limitedbecause they are situated on old, heavily weatheredtropical soils which contain sesquioxides

•P-limited lowland tropical forests normally have anexcess of Nitrogen

•How is the internal N-Cycle affected by the relativeexcess of Nitrogen in P-limited tropical lowland forests?

N2O NOx

Gaseous losses

LeachingClay minerals

NO2- NH3

NH4+

NO3-

Soil Organic Matter

Organisms

Residues,Manures

N2

Nitrification Denitrification

N cycling in soils

NO3- N2NH4

+

NO N2ONO N2O

OrganicMatter

Firestone & Davidson, 1989

•The trace gasses NO and N2O are linked throughtheir common processes of microbial production.

•NO + N2O emissions are correlated with the rateat which Nitrogen cycles through the ecosystem.

NO + N2O emissions should covary with indexesof nitrogen availability.

NO + N2O emissions should be high in tropicallowland forests

--------------------Tg N y-1 -----------------•Natural sources

Ocean 3.0 (1-5)Tropical forest soils 3.0 (2.2-3.7)Tropical savanna soils 1.0 (0.5-2.0)Temperate forest soils 1.0 (0.1-2.0)Temperate grasslands 1.0 (0.5-2.0)

•Anthropogenic sourcesAgricultural soil 3.3 (0.6-14.8)Biomass burning 0.5 (0.2-1.0)Industrial Sources 1.3 (0.7-1.8)Cattle and feedlots 2.1 (0.6-3.1) Σ 16.2 (6.4-34.4)

•Sinks Atmospheric Increase 3.9 (3.1-4.7)Soils ?Stratospheric Sink 12.3 (9-16) Σ 16.2 (12.1-20.7)

Global N2O budget (IPCC, 1997)

Log Y = -0,0563X + 2,331

R2 = 0,70

Sum of annual estimates of NO + N2O emissions as afunction of litterfall C/N

-1,5

-1

-0,5

0

0,5

1

1,5

10 20 30 40 50 60 70

Litterfall C/N (Davidson et al, 2000)

Log(

NO

+ N

2O) f

lux

(kg

N h

a-1 y

r-1 )

0

1

2

3

4

5

6

7

8

0 50 100 150 200 250

N in Litterfall (kg ha-1 yr-1)




Possible relation between annual litterfall N and sum ofannual NO + N2O emission

Pred

icte

d N

O +

N2O

flu

x (k

g N

ha-

1 yr-

1 )

•The low efficiency of within-stand nitrogen economies oftropical lowland forests lead tohigh emissions of NO + N2O.

•I speculate that tropicalmontane forest will have lowNO + N2O emissions becauseof their relatively efficientwithin-stand nitrogeneconomy

•What will happen to tropical lowland forests ifthe deposition of nitrogen-containing compoundswill increase in the future?

Legume crops

Fossil fuel

N fertilizer

1970 1980 1990Year

19600

20

40

60

80

100

120

140

160

Terr

estr

ial N

-fixa

tion

Tg N

yr-1

Range of estimates ofnatural N fixation

Galloway et al., (1995)

Comparison of natural and human-drivenNitrogen sources

0

20

40

60

80

100

120

Tg N

yr-1

20

40

60

80

100

120

Present 20200

Present 2020

Tg N

yr-1

Temperate area

FertilizerEnergy

Tropical area

Present and future anthropogenic N production

Adapted from Galloway et al., 1995

Increasing N deposition is already happening!

0

1

2

3

4

5

6

7

8

9

Banana Plantation Agriculture in temperateareas

N2O NO

N2O

and

NO

loss

es (%

of

appl

ied

fert

ilize

r

Adapted from Veldkamp & Keller 1997

Hall & Matson, 1999

N2O & NO emissions from soil in N-limited and P-limitedtropical forests before and after N addition

•P-limited forest lostmore NO + N2O than N-limited forest

•P-limited forests seemto be less able to retainanthropogenic N as N-limited forests

0

5

10

15

20

25

-7 0 7 14

N limited

N2O

-N (n

g cm

-2 h

-1)

0

5

10

15

20

25

30

-7 0 7 14

N limited

NO

-N (n

g cm

-2 h

-1)

N a

dditi

onN

add

ition

0 7 14

P limited

0 7 14

P limited

N a

dditi

onN

add

ition

•Increasing N deposition in lowland tropicalforests will almost certainly lead to even higherN-trace gas (NO + N2O) emissions as theseecosystems seem to be less able to retainanthropogenic N than temperate forests

•Increasing energy production and fertilizeruse will lead to higher N deposition in thetropics in the near future

lecture for ‘biogeochemistry and global change’ lowland ...aibrom/bggc/lecture veldkamp effects...

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