Photodegradation as a Factor in the Decomposition of Surface Litter in Grassland Ecosystems

EPA Grant Number: F6F10361
Title: Photodegradation as a Factor in the Decomposition of Surface Litter in Grassland Ecosystems
Investigators: Brandt, Leslie A.
Institution: University of Minnesota
EPA Project Officer: Hahn, Intaek
Project Period: September 1, 2006 through September 1, 2009
Project Amount: $109,402
RFA: STAR Graduate Fellowships (2006) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Ecological Indicators/Assessment/Restoration , Fellowship - Terrestrial Systems Ecology


Photodegradation, the break-down of chemical compounds by ultraviolet radiation, may contribute substantially to decomposition of surface litter, especially in areas with high penetration of solar radiation to the litter layer and relatively low microbial activity such as arid and semi-arid grasslands. Few studies in terrestrial ecosystems have quantified the contribution of photodegradation to decomposition rates or elucidated the mechanisms by which photodegradation affects carbon and nutrient cycling. My proposed work will address this significant lack of understanding.

The objectives of my study are to:

  1. Quantify the relative contribution of photodegradation to surface litter decomposition in grasslands across a gradient of solar radiation and aridity in the central United States.
  2. Determine the mechanisms by which photodegradation affects carbon cycling through a series of laboratory experiments.


Objective 1: I will establish a 2-year field experiment at three grassland sites across the United States that contrast in ultraviolet radiation and mean annual precipitation. I will place litterbags filled with 2 species of native grass litter that contrast in chemistry under screens that either block or pass ultraviolet radiation (<400 nm), while keeping visible radiation (400-700 nm) constant. I will measure mass loss and changes in carbon, nitrogen, fiber content, and microbial biomass and enzyme activity. I will compare results between the different radiation treatments, between litter types and among sites.

Objective 2: Using the same litter species and simulating radiation conditions at one of my sites, I will conduct two laboratory experiments to determine how much photodegradation contributes directly to decomposition as an abiotic process and indirectly by increasing microbial decomposition by increasing the bioavailability of labile carbon substrates. In my first experiment, I will incubate sterile litter under contrasting regimes of radiation (including a dark control) and measure direct oxidation to CO2 and changes in mass loss and litter chemistry. In my second experiment, I will incubate litter that has been pre-irradiated and litter that has not been irradiated under conditions ideal for microbial decomposition and compare microbial respiration rates, enzyme activity, and biomass between treatments.

Expected Results:

I expect exposure to ultraviolet radiation will increase rates of decomposition, especially in arid systems. I expect exposure to ultraviolet radiation will increase decomposition both directly by the abiotic process of photodegradation and indirectly by facilitating microbial decomposition. This study will increase our understanding of how photodegradation may contribute to decomposition, help us better predict decomposition rates in grasslands, and increase our ability to predict how future environmental changes in solar radiation may affect decomposition rates of surface litter.

Supplemental Keywords:

decomposition, ultraviolet radiation, photodegradation, grasslands, global change, carbon cycling, ecosystems,, RFA, Scientific Discipline, Air, INTERNATIONAL COOPERATION, POLLUTANTS/TOXICS, Chemicals, climate change, Air Pollution Effects, Environmental Monitoring, Atmosphere, Global Climate Change, atmospheric carbon dioxide, carbon sequestration, ozone, emissions impact, methane, grasslands, carbon dioxide, CO2 concentrations, greenhouse gases

Progress and Final Reports:

  • 2007
  • 2008
  • Final