Hooker,T.D., Stark,J.M., Norton,U., Leffler,A.J., Peek,M. and Ryel,R.(2008): Distribution of ecosystem C and N within contrasting vegetation types in a semiarid rangeland in the Great Basin, USA. Biogeochemistry, 90, 291-308.

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wAbstract
@Semiarid sagebrush ecosystems are being transformed by wildfire, rangeland improvement techniques, and exotic plant invasions, but the effects on ecosystem C and N dynamics are poorly understood. We compared ecosystem C and N pools to 1 m depth among historically grazed Wyoming big sagebrush, introduced perennial crested wheatgrass, and invasive annual cheatgrass communities, to examine whether the quantity and quality of plant inputs to soil differs among vegetation types. Natural abundance ƒΒ15N isotope ratios were used to examine differences in ecosystem N balance. Sagebrush-dominated sites had greater C and N storage in plant biomass compared to perennial or annual grass systems, but this was predominantly due to woody biomass accumulation. Plant C and N inputs to soil were greater for cheatgrass compared to sagebrush and crested wheatgrass systems, largely because of slower root turnover in perennial plants. The organic matter quality of roots and leaf litter (as C:N ratios) was similar among vegetation types, but lignin:N ratios were greater for sagebrush than grasses. While cheatgrass invasion has been predicted to result in net C loss and ecosystem degradation, we observed that surface soil organic C and N pools were greater in cheatgrass and crested wheatgrass than sagebrush-dominated sites. Greater biomass turnover in cheatgrass and crested wheatgrass versus sagebrush stands may result in faster rates of soil C and N cycling, with redistribution of actively cycled N towards the soil surface. Plant biomass and surface soil ƒΒ15N ratios were enriched in cheatgrass and crested wheatgrass relative to sagebrush-dominated sites. Source pools of plant available N could become ƒΒ15N enriched if faster soil N cycling rates lead to greater N trace gas losses. In the absence of wildfire, if cheatgrass invasion does lead to degradation of ecosystem function, this may be due to faster nutrient cycling and greater nutrient losses, rather than reduced organic matter inputs.

Keywords: Invasive species (cheatgrass); Ecosystem C and N storage; ƒΒ15N natural abundance isotope ratio; Sagebrush rangelandx

Introduction
Materials and methods
@Study area
@Aboveground biomass and surface litter
@Soil sampling
@Calculation of above- and belowground plant C and N inputs to soil
@Statistical analysis
Results
@Distribution of ecosystem C and N
@Estimates of plant above- and belowground inputs to soil
@Natural abundance ƒΒ15N stable isotope ratios
Discussion
@Influence of vegetation type on the quantity and quality of plant organic matter inputs to soil
@Integrating the N cycle with ecosystem ƒΒ15N
Acknowledgments
References


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