Factors Influencing Decomposition of Surface Litter from the Cerrado in Central Brazil

R.G. ZeppR.G. Zepp11, M. Molina, M. Molina11, M. , M. CyterskiCyterski11, K. Kisselle, K. Kisselle22, A.R. , A.R.

KozovitsKozovits33, M.R.S.S. Silva, M.R.S.S. Silva44, D.A. da , D.A. da SilvaSilva44, and M.M.C. Bustamante, and M.M.C. Bustamante44

11U.S. EPA, Athens GA; U.S. EPA, Athens GA; 2 2 Austin College, Austin College, Sherman TX; Sherman TX; 33Universidade Federal de Universidade Federal de Ouro Preto; Ouro Preto; 44Universidade de Universidade de Brasília Brasília

OUTLINEOUTLINE

Pathways for effects of light and Pathways for effects of light and fertilization on surface litter fertilization on surface litter decompositiondecomposition

Action spectra for Action spectra for photodecompositionphotodecomposition

Comparisons to field studiesComparisons to field studiesFertilization effects Fertilization effects

Projected Changes in Amazon Vegetation CoverProjected Changes in Amazon Vegetation CoverCox et al, 2004Cox et al, 2004

Pathways for Plant Litter Pathways for Plant Litter Transformation and TransportTransformation and Transport

COCO22

Litter Litter Microbial biomassMicrobial biomassRefractory OMRefractory OM

Leaching, runoffLeaching, runoff

DOM(CDOM)DOM(CDOM)Leaching, runoffLeaching, runoff

CDOM is colored (chromophoric) dissolved organic matter-important in remote sensing of color; UV protection

Light,Fertilization

H C2 O

Formaldehyde Acetaldehyde

H C2 O

H

Acetone

C

O

H C3 H 3C

Glyoxal

C

O

H C

O

H

Methylglyoxal

CH C3 C

O O

HCO

Carbon Monoxide

COS

Carbonyl Sulfide

Biologically Labile and/or Biologically Labile and/or VolatileVolatile Photoproducts of Aquatic Dissolved Photoproducts of Aquatic Dissolved

Organic Matter (DOM)Organic Matter (DOM)

Volatile Organic Compounds

Glyoxylate

COOC

O

H

Ammonium

NH4+

Carbon Dioxide

CO2R-C C -R'

C2 - C4

Light-induced Litter Decomposition in Patagonian Steppe

Austin and Vivanco, 2006

Competing Effects of Solar Ultraviolet Competing Effects of Solar Ultraviolet Radiation on Plant Litter DecompositionRadiation on Plant Litter Decomposition

• Enhances decomposition by direct Enhances decomposition by direct photoreactions (open, arid ecosystems)photoreactions (open, arid ecosystems)

• Slows decomposition by inhibition ofSlows decomposition by inhibition ofdecomposers (e.g. fungi)decomposers (e.g. fungi)

• Changes leaf composition in growing Changes leaf composition in growing plants thus altering decompositionplants thus altering decomposition

Processes Driving Trace Gas Exchange Processes Driving Trace Gas Exchange In Terrestrial EcosystemsIn Terrestrial Ecosystems

microbial recycling

degradation

root turnover

groundwater loss

runoff litter

photosynthesisCO22

CO22

CO

CH44

CO NMHCCH4(?)

microbial oxidation

respiration

abioticproduction

litter

Species

CO

flux

, m

ol m

-2 h

r-1

0

10

20

30

40

50

60

70Kielmeyera coriaceaQualea grandifloraBrachiaria sp.Sheflera macrocarpumVochysia ellipticaVochysia thyrsoidea

CO Fluxes From Sunlight-Exposed LitterCO Fluxes From Sunlight-Exposed Litter

Developing Relationships Required to Developing Relationships Required to ModelModel

Sunlight-Induced Decomposition of Plant Sunlight-Induced Decomposition of Plant LitterLitter

General Approach: Determine action spectra using Rundel General Approach: Determine action spectra using Rundel technique (Rundel, technique (Rundel, Physiol. Plant.Physiol. Plant., 58, (1986) 360-366.), 58, (1986) 360-366.)

Steps: -Determine decomposition rates by following certain-Determine decomposition rates by following certain indicators, e.g. weight loss, COindicators, e.g. weight loss, CO22 or CO production or CO production using filters that block UV using filters that block UV-Measure irradiance of filtered light-Measure irradiance of filtered light-Fit the data using exponential (or other) equation -Fit the data using exponential (or other) equation of form (EXP (a + b * Wavelength) of form (EXP (a + b * Wavelength) -Use Excel Solver to compute values of a and b

that minimize difference between observed and computed decomp rates

Filtered Irradiance Used to Determine Action Spectra For Litter Decomposition

Wavelength, nm

300 400 500 600 700

Irra

dian

ce, W

m-2

nm

-1

0.0

0.5

1.0

1.5

2.0

305 nm320 nm360 nm385 nm

CO Production from Various Cerrado Litter SourcesCO Production from Various Cerrado Litter SourcesExposed to Filtered Simulated Solar RadiationExposed to Filtered Simulated Solar Radiation

Filter Cutoff Wavelength (nm)

AM1 385 nm 360 nm 320 nm 305 nm

CO

Pro

duct

ion

(nL

CO

s-1

cm

-2)

0.00

0.01

0.02

0.03

0.04

Kielmeyera coriacea Qualea grandiflora Brachiaria sp. Sheflera macrocarpum Vochysia elliptica Vochysia thyrsoidea

SpeciesSpecies a b RMSESun Sun FluxFlux

Kielmeyera coriaceaKielmeyera coriacea -2.37 -0.0198 0.00131 0.0028

Qualea grandifloraQualea grandiflora 3.12 -0.0348 0.00165 0.0031

Brachiaria sp.Brachiaria sp. 8.63 -0.0507 0.00417 0.0034

Sheflera Sheflera macrocarpummacrocarpum 2.78 -0.0314 0.00484 0.0073

Vochysia ellipticaVochysia elliptica 7.55 -0.0448 0.00421 0.0085

Vochysia thyrsoideaVochysia thyrsoidea -0.40 -0.0219 0.00677 0.0093

Flux = a expFlux = a exp-b-bλλ

Equation and Data Describing LitterEquation and Data Describing LitterPhotodegradation FluxesPhotodegradation Fluxes

Action Action SpectraSpectra for Plant Litter Photodecomposition for Plant Litter Photodecomposition

Wavelength, nm

300 350 400 450 500

Rel

ativ

e A

ctio

n

1e-5

1e-4

1e-3

1e-2

1e-1

1e+0

1e+1

Brachiaria sp Kielmeyera coriacea Qualea grandiflora Sheflera macrocarpum Vochysia elliptica Vochysia thyrsoidea

Wavelength Effects for Sunlight-inducedDecomposition of Brachiaria sp

Wavelength, nm

300 320 340 360 380 400

Rel

ativ

e A

ctio

n

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Irra

dian

ce o

r W

eigh

ted

irrad

ianc

e

(W m

-2 n

m-1

)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

UVB

IrradianceWavelength

Weighted irradiance

CO flux = 7.5 x 10-6 x (PAR)

CO2 flux = (7.5 -15) x 10-6 x (PAR)(PAR expressed as W m-2)

For Cerrado CO2 in dry season

est. 0.3-0.6 µmol m-2 s-1

~15-30% of observed

Estimated Relationship Estimated Relationship Between Degradation and Between Degradation and Photosynthetically Active Photosynthetically Active

Radiation (PAR)Radiation (PAR)

Litter CO Fluxes Observed in Cerrado SitesLitter CO Fluxes Observed in Cerrado SitesKisselle et al., 2002Kisselle et al., 2002

With litterWithout litter

Fertilizer Effects: Long-term Fertilizer Effects: Long-term Incubation ExperimentIncubation Experiment

Collect Soil samples 0-10 cm10-20 cmSieving

Addition of Soil and Nutrients to Jars

Measure

•CO2 (Licor)

•CO (Trace A)

•Fertilizers added: N, P, N+P•All fertilizers added in granular form•Jars were incubated in the dark at room temperature, at 60% WHC for 143 days.

Fertilization Effects on Average COFertilization Effects on Average CO22 Flux Flux from Soils (0-10 cm Depth)from Soils (0-10 cm Depth)

0

1

2

3

4

5

6

1 11 20 32 41 53 62 82 102 126 143Days

CO2

flux

(um

oles

CO

2 m

-2 s

-1)

Control 0-10cm

N 0-10 cm

P 0-10 cm

N+P 0-10 cm

Fertilization Effects on Exponential Decay Constants for the Active and

Slow C Pools in Cerrado Soils

TreatmentsOriginal Soil Depth (cm)

Act. C ka

Slow C ks

Control 0-10 0.52 0.03

N 1.03 0.03

P 2.26 0.02

N+P 0.62 0.03

Control 10-20 0.06 0.00

N 0.13 0.00

P 0.23 0.01

N+P 0.13 0.01

Time, min.

0 2 4 6 8 10 12 14 16

[CO

] t/[C

O] 0

1

P N Control

CO Uptake By Cerrado SoilCO Uptake By Cerrado Soil Treated with FertilizerTreated with Fertilizer

De

po

sitio

n V

elo

city

, cm

s-1

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

ControlNP

Deposition Velocities for CO UptakeDeposition Velocities for CO Uptake By Soil Treated With FertilizerBy Soil Treated With Fertilizer

Summary of Results Summary of Results and Conclusionsand Conclusions

• Litter photodegradation is a significant CO source and loss pathway for surface litter in the Cerrado during dry season.

• Action spectra for litter photodegradation are species dependent and induced primarily by UV component of sunlight

• Fertilizer addition, esp. P, increases the microbial respiration of the labile C of surface SOM from Cerrado s.s. and enhances CO uptake