Site Description

This research is being conducted as a part of the Detritus Input and Removal Treatments Project (DIRT), a cross-continental experiment that assesses rates and sources of plant inputs control accumulation and dynamics of organic matter and nutrients in forest soils over decadal timescales. This decomposition study is being conducted at the University of Michigan Biological Station in the northern lower peninsula of Michigan. Vegetation is dominated by early successional species, including quaking aspen, red maple, and white pine. Soils are derived from glacial outwash sands. The area was logged extensively in the early 1900s, with numerous fires that swept through the area following logging, burning away most of the surface organic matter. For the last century, the forest was been left untouched.

MethodsBulk Leaf Decomposition

• Leaves collected during autumn 2007 using 21 nets across the approx. 2 ha site• Leaves were air-dried, weighed, and placed into 10x20 cm fiberglass screen bags, based on ambient litterfall composition• Five bags placed at each of 21 locations across the site• Samples being collected annually for 5 years.

Individual Species DecompositionWe are measuring decay rates of major tree species

• Four species (red maple, quaking aspen, red oak, white pine) • Leaves collected, air-dried, and placed into 10x20 cm fiberglass screen bags• Bags placed at a single location at the site• Seven 7 bags per species per year• Established for five years of collection

Root Decomposition

• Roots collected from O horizon at 21 locations across the site• Washed and separated into 0-1mm and 1-2mm diameter classes• Air-dried, weighed, and placed into fine mesh bags• Finest roots (0-1 mm diameter) collected yearly. • 1-2mm diameter roots to be collected at years 2 and 5

Analyses

• In autumn, 2007, root and leaf bags were deployed• Decomposition quantified by mass loss • Changes in litter chemistry (C, N) is measured

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Fine Roots Mixed Litter Acer rubrum Pinus strobus Populusgrandidentata

Quercus rubra

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Introduction

Forests play a key role in the global carbon (C) cycle, sequestering atmospheric C within woody biomass and soil organic matter. North temperate forests serve as important C sinks, however the dynamics of the large and heterogeneous pool of forest soil organic matter are still poorly understood. Forest soil C is derived from forest production, and is transferred to soils via decomposition of leaves and roots. Environmental change (e.g. climate alteration, atmospheric pollution, species shifts, forest management) can influence overall forest productivity as well as relative production rates of leaves and roots, thus altering inputs of organic matter into soil. Due to large differences in the chemistry of leaves and roots, leaf and root litter can decompose at drastically different rates. These differences in decomposition rates, as well as the chemistry of the organic matter remaining after decomposition, strongly dictate the contribution of different soil organic matter sources to soil C.

Study ObjectiveFew studies have simultaneously measured rates of leaf and root decomposition at the same site. To determine the relative importance of these organic matter inputs to temperate forest soils, we are comparing leaf and fine root decomposition in a temperate deciduous forest in northern Michigan.

Acknowledgements We thank Ericson Myers, Bessie and Adena Bowden, Tony Sutterley, Sherry Webster, and Sam Reese for valuable field and laboratory assistance. This project was funded by the

Allegheny College Shanbrom and Wells Student Research Funds and Class of ‘39 Fund.

Placing root bags under the forest floor

Installing litter bags

University of Michigan Field Site

UMBS

Collecting Root “Brownies”

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Decomposition of Roots and Leaves in a Northern Temperate ForestRichard D. Bowden1, Elizabeth Fager1, Knute Nadelhoffer2, Jim LeMoine2

1 Allegheny College 2 University of Michigan2

Litter Nitrogen Concentration after One Year of Decomposition

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Fine Roots Mixed Litter Acer rubrum Pinus strobus Populusgrandidentata

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Litter Decomposition Expected v. Actual Decomposition

• Litter N concentrations after one year of decomposition were as high in fine roots as in mixed litter and P. strobus and Q. rubra.

• Root N concentrations alone would have suggested higher rates of root litter mass loss

• Annual loss rates ranged from 27 to 50%

• Fine roots decomposed most slowly

• Mixed leaf litter decomposed twice as fast as roots, and more quickly than single species

• Expected loss rates were calculated from loss rates of individual species and mass of each species within the mixed litter bags

• Mass loss of mixed litter was greater than expected

Conclusion: Inputs from dead roots to the soil organic matter pool appear to be slow, however, slowly decaying root litter may represent an important pool of soil carbon. Furthermore, root-derived organic matter, at least in some forest ecosystems, may provide more long-term soil organic matter than organic matter inputs derived from aboveground sources. Enhanced decomposition of mixed litter suggests that nutrient release form litter is enhanced by a diversity of resources.