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Soil type and moisture regime control microbial C and N mineralization in grassland soils more than atmospheric CO2-induced changes in litter quality

Jin, Virginia L., Haney, Richard L., Fay, Philip A., Polley, H. Wayne
Soil biology & biochemistry 2013 v.58 pp. 172
Alfisols, Bouteloua curtipendula, Mollisols, Vertisols, biodegradation, carbon dioxide, carbon nitrogen ratio, elevated atmospheric gases, gas production (biological), grasses, grassland soils, highlands, immobilization in soil, landscapes, lowlands, microbial activity, mineralization, organic nitrogen compounds, plant litter, prairies, rain, soil analysis, soil microorganisms, soil organic matter, soil quality, soil respiration, soil water, soil water regimes, water holding capacity
Global change-induced alterations in litter quality and soil moisture regime will likely impact grassland C and N dynamics, but how these changes interact with edaphic properties across the landscape is unclear. We measured the effects of litter quality, soil type, soil moisture level, and soil drying-rewetting frequency (D-RW) on microbial C and N mineralization of litter and soil organic matter (SOM) in a full-factorial, controlled incubation experiment. Four levels of litter quality (no litter; or litter from Bouteloua curtipendula grown under 280, 380, 500 μL L−1 CO2) were surface-applied to three contrasting soils common to Blackland Prairie landscapes: an upland Mollisol, a lowland Vertisol, and a fluvial Alfisol. Different soil moisture regimes were tested by incubating soils at four moisture levels (air-dry, 25%, 35%, or 50% water-holding capacity, WHC) and by drying-rewetting soils 0, 1, 2, 4 or 8 times over the 112-d incubation period. Litter additions stimulated microbial activity, increasing total CO2 production (i.e. C mineralized from litter + SOM decomposition) up to 17× more than no-litter controls (average 3×) and decreasing net N mineralization up to −3× less (average −0.5×) due to greater microbial N immobilization. Neither C nor N mineralization, however, was affected by litter quality. For all soils, litter decomposition increased with increasing WHC and D-RW frequency, but the average percent of total CO2 derived from litter was a negative function of SOM content. Similarly, net N mineralization also was positively correlated with soil WHC and affected most strongly by soil type (Alfisol < Mollisol < Vertisol). Net N mineralization responses to D-RW events was also soil-specific, with Alfisol soils showing no response and Mollisol and Vertisol soils decreasing after 4 D-RW events. Our results suggest that predicted changes in rainfall patterns and its interactions with soil type across the landscape will control short-term C and N mineralization responses in grasslands to a greater extent than atmospheric CO2-induced changes in litter C:N ratio for this common species of prairie grass.