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 FormulaCommentscharacteristicReference Unified-substrate quality M t =A+Br t AsymptoticLeaves a residual Howard and Howard, 1974 L t =m(1-e -kt/m )AsymptoticLeaves a residual Berg & Ekbohm, 1991 M t = M 0 e -kt Single exponentialLeaves no residual Jenny et. al., 1949; Olson, 1963 Two or three substrate-quality components M t = Ae -k 1 t + Be -k 2 t Double exponential Leaves no residual Bunnel et. al., 1977; Lousier & Parkinson, 1976 M t = Ae -k 1 t + Be -k 2 t + Ce -k 3 t Triple exponentialLeaves 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 CO 2 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 *0.0325* Forest type Harvest treatment x forest type *0.0030*0.0195* Between subject Time 3<.0001* Time x harvest treatment * Time x Forest type Repeated measures analysis of variance -- chemistry

Source of variance df Soluble p-value Cellulose p-value Lignin p-value Site Harvest treatment Forest type Harvest treatment x forest type Analysis of variance of initial chemistry

Single exponential fit of percentage accumulated mass loss by treatments

Percentage accumulated mass loss by treatments a b bc c

Percentage accumulated mass loss by forest types a b c

Treatments effects on chemical components

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.