Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 29, 2012
Publication Date: January 2, 2013
Citation: Jin, V.L., Haney, R.L., Fay, P.A., Polley, H.W. 2013. Soil type and moisture regime control microbial C and N mineralization in grassland soils more than atmospheric CO2-induced changes in litter quality. Soil Biology and Biochemistry. 58:172-180. Available: http://dx.doi.org/10.1016/j.soilbio.2012.11.024. Interpretive Summary: Temperate grassland soils are expected to have high carbon (C) sequestration potential compared to other terrestrial ecosystems. Atmospheric CO2 could be stored in grassland soils as soil organic matter (SOM), but the decomposition of plant biomass and SOM could also return some CO2 to the atmosphere. Decomposition is affected by the quantity and quality of plant litter and SOM, but it will also depend on potential changes in precipitation and how precipitation, plant inputs, and soils interact with each other. Results from this study suggest that grassland CO2 emissions will be controlled in the short-term by changes in the timing and amount of precipitation and its interactions with soil type more so than by changes in litter quality. Because both soil moisture and soil type are dependent on landscape features, this study could have important implications for changes in grassland CO2 emissions across the landscape in response to different global changes. Specifically, the decomposition of litter could play a more important role in soil C emissions from better-drained landscape positions and in coarse- than fine-textured soils, whereas C emissions from more poorly-drained landscape positions with finer-textured soils will be more responsive to changes in litter quality but dominated by SOM decomposition.
Technical Abstract: Decomposition in grassland soils and subsequent impacts on grassland C storage will depend on how global change effects on litter quality and soil moisture interact with edaphic characteristics across the landscape. We measured grass litter decomposition in a full-factorial incubation experiment (112 days) to test interactive effects of soil type, litter quality (as affected by growth CO2 concentration), soil moisture level (% water-holding capacity, WHC), and soil drying-rewetting. Four levels of litter quality (no litter; or Bouteloua curtipendula litter grown under 280, 380, 500 µL L-1 CO2) were surface-applied to three contrasting Blackland Prairie soils (Alfisol, Mollisol, Vertisol) under different mean daily soil moisture (air-dry, 25%, 35%, 55% WHC) and drying-rewetting (D-RW; 0, 1, 2, 4, 8 times) treatments. Litter quality and D-RW frequency effects were minor compared to soil type and WHC effects on soil CO2 emissions. Litter additions had a greater impact overall than litter quality on soil C and N mineralization, increasing total CO2 production by 13% to 88% and decreasing net N mineralization (i.e. greater microbial N immobilization) compared to soils-only controls. Soil type, however, controlled the effect of litter quality on litter decomposition (i.e. the relative contribution of litter-C to total C mineralized), and %WHC affected how much litter-C was mineralized. Total CO2 production increased with increasing litter growth-CO2 in the two fine-textured soils (Mollisol, Vertisol) but not in the coarser-textured Alfisol. Our results suggest that litter decomposition may dominate grassland C losses from coarse-textured soils (i.e. better-drained landscape positions), whereas litter quality and SOM decomposition could dominate C emitted from finer-textured soils (i.e. more poorly-drained landscape positions). Overall, short-term C mineralization in grasslands will likely be controlled by precipitation changes and its interactions with soil type, with soil-specific response to changes in litter quality (i.e. C:N ratio) due to increasing atmospheric CO2.