Document: PAU-3-48-33

Effects of exogenous N addition, mammalian exclusion, and detritivore diversity on decomposition in old fields.

MAYER, P.*, E.JORGENSEN and A.WEST

U.S. Environmental Protection Agency, National Risk Management Research Laboratory, Robert S. Kerr Laboratory, Ada, OK 74820 ¹

Abstract:
Plant litter decomposition strongly controls C and N flux in terrestrial ecosystems. Anthropogenic inputs of N may influence decomposition by changing N supply to microbes or by changing litter quality and quantity. Detritivore diversity also may influence decomposition rates when diverse functional groups process litter more efficiently, whereas, mammalian consumers may, in turn, affect detritivore diversity. This study was designed to test the effects on litter decomposition of 1) exogenous N inputs, 2) detritivore diversity, and 3) mammal diversity. N and mammals were manipulated in 16 plots in a factorial experiment where 4 plots each were treated with fertilizer only (48 kg/ha/yr), mammal exclusion only, a combination of fertilizer and exclusion, or no treatment. A mixture of grass and forb litter of known quantity was contained in either fine (0.33 mm²) nylon mesh intended to exclude macro-detritivores (e.g. macroarthropods, isopods, annelid worms) or in coarse (6.35 mm²) mesh bags intended to allow access by all detritivores. Litter bags were placed randomly in each plot and collected every two months for one year. Loss of litter mass, C, and N were quantified as response variables. Neither the mammal exclusion nor N addition had significant main effects (ANOVA) on litter mass loss. However, a significant interaction between exclusion and N addition was observed (P = 0.02). Detritivore exclusion had the greatest influence on litter mass loss (P < 0.001). These results suggest that N addition and mammal exclusion have complex interactive effects on litter decomposition presumably by exercising an influence on the detritivores. The results also indicate that macro-detritivores have a large effect on litter decomposition likely by shredding and processing recalcitrant fragments of litter, a result that has implications for the maintenance of detritivore diversity. Environmental stressors, such as pesticides that remove larger detritivores from the decomposer community may affect nutrient flux patterns in terrestrial ecosystems.

Keywords: decomposition, detritivores, mammals, diversity, exogenous N

This abstract is being presented at: 3:45 PM in session:
Oral Session #67: Decomposition Processes.