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NSF IRCEB interannual climate variability and ecosystem processes in tallgrass prairie: Controls on litter decomposition.
Weatherly, Heather*,1, Su, Bo2, Wallace, Linda2, Arnone, John1, 1 Desert Research Institute-Reno, Reno, NV, USA2 University of Oklahoma, Stillwater, Oklahoma, USA
ABSTRACT- The 4°C increase in average air temperature that is expected to occur over the next decade is likely to result in an increase in the decomposition of plant litter and potentially enhance the rate of nutrient return to the soil. Evidence for the positive relationship between temperature and decomposition is abundant. This may be especially significant in a tallgrass prairie ecosystem where moisture is not typically a limiting factor for microbial-mediated decomposition processes, in contrast to more arid systems. In the first year of a four-year study to determine the effects of a 4°C increase in air temperature on ecosystem processes, we decomposed representative mixtures of tallgrass prairie litter in litterbags, as well as standard cotton and popsicle sticks, for 8 months in laboratory mesocosms (EcoCells) in order to determine what may control decomposition under current ambient temperature in the tallgrass prairie ecosystem. One half of the litterbags were exposed under the intact canopy, while the remaining half were exposed under a mowed layer. We also decomposed the same litter in field plots in Oklahoma to eliminate possible artifacts of the controlled laboratory conditions. Linear regressions of percent decomposition with above-ground net primary production (both during the year the litter was produced and during the period of litterbag exposure) showed no relationship. Furthermore, no relationships existed between percent decomposition and species diversity or between percent decomposition and average soil moisture in the top 15 cm of soil (TDR) over the duration of litterbag exposure. However, litterbags that were exposed beneath the intact canopy of each monolith (plot) decomposed more rapidly (35%) than those exposed on the mowed side (26%) of each monolith (P=0.005). Both temperature and relative humidity (averaged over the exposure period) were higher on the soil surface of the mowed canopy than on the soil surface beneath the intact canopy (P<0.000 for both temperature and relative humidity), suggesting that abiotic factors may be less important in controlling decomposition than microbial processes in this system. The possibility that microbial activity is localized in areas that are more nutrient rich (i.e. not mowed) may explain the faster decomposition observed in the intact canopy.
Key words: Bromus, grassland, Andropogon gerardii, ANPP