Leaf Litter Decomposition at Missouri Ozarks Managed Landscape

Qinglin Li

The Objectives:

• 1. Determine mixed leaf litter decomposition rates.

• 2. Quantify mixed leaf litter chemistry composition during decay.

• 3. Identify forest management effects on leaf litter decomposition and leaf litter chemistry.

Introduction

• Decomposition of litter (including root litter) contributes about 70% to the total annual carbon flux, which is estimated at 68 Pg C yr-1. (Raich & Schlesinger, 1992)

• Litter decomposition rates are controlled by environmental conditions, the chemical composition of the litter, and by soil organisms.

Conceptual model for describing plant litter decomposition

Model for chemical changes and rate-regulating factors during decomposition (Berg & Matzner, 1997)

Asymptotic model for estimating limit values for plant litter decomposition. Limited value indicated by the dashed line (Berg and Ekbohm, 1991)

Quantitative models

Formula Comments characteristic Reference

Unified-substrate qualityMt=A+Brt Asymptotic Leaves a residual Howard and Howard,

1974

Lt=m(1-e-kt/m) Asymptotic Leaves a residual Berg & Ekbohm, 1991

Mt = M0e-kt Single exponential Leaves no residual Jenny et. al., 1949; Olson, 1963

Two or three substrate-quality componentsMt = Ae-k1t + Be-k2t Double

exponentialLeaves no residual Bunnel et. al., 1977;

Lousier & Parkinson, 1976

Mt = Ae-k1t + Be-k2t + Ce-k3t

Triple exponential Leaves no residual Couteaux et. al., 1998

Environmental conditions

Climate

Litter chemistry

Soil organisms

Generalized model of the changes in the slope and intercept of the relationship between initial lignin concentrations (%) and annual weight loss (%) with climatic actual evapotranspiration (AET in millimeters, Meentemeyer, 1978)

Litter Quality

Climate

Litter chemistry

Soil organisms

Enzyme activities

Climate

Litter chemistry

Soil organisms

Manipulation (anthropogenic) effects

• 1. N fertilization

Linear relationships between N and lignin concentrations in needle litter from N-fertilized Scots Pine plot. (Black dots 50 kg N ha-1 yr-1, triangle 100 kg N ha-1 yr-1 , square 150 kg N ha-1 yr-1 , circle – control., Berg and Tamm 1991).

2. Elevated CO2 effects

C:N ratios of mixed-species litter collected from the field open-top chamber experiment from the sandstone (filled circles) and serpentine (open circles) grassland, solid line show 1:1 relationship. (Dukes & Hungate 2002)

3. Forest Management

• I. Clear cuttings had more rapid rate of mass loss. (Gadgil & Gadgil, 1978; Prescott et. al. 2000).

• II. Clear-felling had a large decrease in mass loss relative to a control stand, with first year mass loss of 25 and 37%, respectively. (Cortina & Valejo, 1994)

• III. Whole tree harvesting had the highest mass loss rates comparing to stem and whole tree harvesting with forest floor removal. (Kranabetter & Chapman, 1999)

The hypothesis:

Leaf litter decomposition rate was regulated by species composition, leaf litter chemistry, management activities, or any of the combinations.

Study Site & Design

Even age

Uneven age

No Harvest

Manipulation Type

10 Kilometers

Shannon

Reynolds

Carter

Design: 3 block x 3 treatment x 3 reps per site x 3 reps per location; even age (clear cut--CC, intermediate cut--INT, old growth--Old), Uneven age (single tree selection--Sin, group opening--Gro, and old growth--Old).

Block 1

Block 2

Block 3

Forest type

Forest types at selected decomposition plot– Oak -- O – Oak hickory -- OH– Oak Pine -- OP

Methodology

• 1. Litter bag

– Litter bags were made by vinyl standard mesh.

– 5 gram of mixed litter was put in each bag.

– Litter bags were retrieved after 3, 6, 9, 19 months of field incubation

• 2. Litter chemistry– Soluble in water and ethanol.– Cellulose removed by sulfuric acid digestion– Lignin was acid insoluble.

• 3. Analysis– Repeated analysis– Simple ANOVA

Primary Results

Source of variance  df 

Soluble

p-value

Cellulose

p-value

Lignin

p-value

Within subject         Harvest treatment 4 0.0157* 0.0325* 0.1921 Forest type 2 0.5329 0.5250 0.1711

Harvest treatment x forest type 3 0.0138* 0.0030* 0.0195*

Between subject        

Time 3 <.0001* <.0001* <.0001*

Time x harvest treatment 11 0.0319* 0.0602 0.2782

Time x Forest type 6 0.1892 0.2351 0.1358

Repeated measures analysis of variance -- chemistry

 

Source of variance

 

df

Soluble

p-value

Cellulose

p-value

Lignin

p-value

Site 1 0.7416 0.2547 0.3313

Harvest treatment 3 0.7344 0.7014 0.9357

Forest type 2 0.2746 0.5173 0.6242

Harvest treatment x forest type 4 0.6475 0.3355 0.3142

Analysis of variance of initial chemistry

Single exponential fit of percentage accumulated mass loss by treatments

Group: y = 89.102e-0.0483x

R2 = 0.945

CC: y = 96.659e-0.0298x

R2 = 0.9481

Single: y = 97.259e-0.0339x

R2 = 0.9908INT: y = 94.693e-0.0252x

R2 = 0.9097

Old: y = 97.536e-0.0374x

R2 = 0.9951

20

40

60

80

100

0 5 10 15 20

months

% a

ccum

ulat

ed m

ass

loss

CC Group INT Old Single

Percentage accumulated mass loss by treatments

0

20

40

60

80

CC INT Group Single Old

Treatments

% a

ccu

mu

late

d m

ass

loss

a

b bc bc c

Percentage accumulated mass loss by forest types

60

65

70

75

80

O OH OP

Forest Type

% a

ccu

mu

late

d m

ass

loss

a

b

c

Treatments effects on chemical components

0

50

100

150

200

250

300

350

CC INT Gro Sin Old

Treatment

rem

aini

ng m

ass

chem

ical

com

pone

nts

(mg) Soluble

Cellulose

Lignin

Conclusion

• Forest management activities had significant effects on leaf litter decomposition. They also had significant effects on leaf litter chemistry during decay courses.

• Initial litter chemistry was not affected by any of the factors in this experiments

• Forest type (species composition) had significant effects on mass losses, however, it had no effects on leaf litter chemistry.

Acknowledgement:• This project was founded by MDC MOFEP research

• Daryl Moorhead provided all the facilities for chemical analysis.

• Field and lab assistants for litter bag retrievals and chemical analysis.

• John Rademacker & Mark Johanson for litter bag preparing and burying

• All LEES lab members assistants

Thank you!

Questions?

• 60 species was cited by Berg for litter decomposition research

• John Blair: measurement of N & C flux in single species litterbags may not reflect actual N & C flux in the field. The differences in N flux between single- and mixed species litterbags can affect ecosystem-level N flux at study site. Single litter bag underestimate of N release about 64% by 75 day, overestimate of N accumulation 183% in litter by 375 day.