Short communicationDistribution of carbon and nitrogen in sagebrush steppe after six years of nitrogen addition and shrub removal
Introduction
There is widespread interest in understanding how disturbance modifies nutrient cycling and soil organic matter across ecosystems (Conant et al., 2001). Arid-lands, including sagebrush-steppe, comprise over 30% of the terrestrial surface of the earth. Due in part to the vast area these ecosystems cover, they have been subjected to a variety of land uses such as tilling, grazing by domestic livestock, and recreation. Some of these uses have allowed Bromus tectorum, an exotic annual grass, to invade shrub-lands and subsequently increase the occurrence of fire (Young and Allen, 1997). Increased fire regimes have led to ecosystem wide changes in plant species composition, with a shift in dominance from big sagebrush (Artemisia tridentata) to B. tectorum (Billings, 1990; Norton et al., 2004; Stewart and Hull, 1949; Whisenant, 1990). A shift of species dominance from woody to herbaceous vegetation raises the question of how changes in plant species composition alter soil nutrient pools, and if these changes can influence the current nutrient patterns across shrub landscapes.
Increased nitrogen deposition resulting from activities that include burning fossil fuels and agriculture (Asner et al., 2001) also can impact plant community composition and in turn feedback to microbial nutrient processing (Chapman et al., 2006; Knops et al., 2002; Schwinning et al., 2005). Past studies have demonstrated that additional nitrogen can decrease species richness, increase plant biomass, and shift plant community composition to a few dominant species (Bobink et al., 1998; Inouye and Tilman, 1988, Inouye and Tilman, 1995; Tilman, 1987; Wilson and Tilman, 1993). Although rates of atmospheric deposition are typically lower in the western United States than in much of the eastern US, nitrogen deposition in the west is thought to have influenced changes in nitrogen cycling and plant species composition, elevated nitrate levels in lakes and streams, changed microbial communities, and increased fire frequency (Fenn et al., 2003). Shifts in plant community composition favor species which can quickly acquire and incorporate available N into biomass. In arid-lands, N addition has been shown to decrease species richness and productivity of perennial species, to increase productivity of annual species (Carpenter et al., 1990; McLendon and Redente, 1991), and to create conditions amendable to exotic species invasion (Brooks, 2003; Norton et al., 2004; Schwinning et al., 2005).
Soil nutrients in undisturbed sage-steppe have a patchy distribution; more nutrients are typically found below shrub canopies (Noy-Meir, 1985). Modification of plant composition due to ecosystem disturbance or increased nitrogen input, may act to re-distribute nutrients, a potential detriment to sage-steppe stability and restoration. The objectives of this study were to quantify how the distribution of total carbon and nitrogen in relation to shrub canopies is altered by shrub removal and, separately, by nitrogen addition. We predicted that loss of shrubs would decrease the patchiness of soil total carbon and nitrogen, creating a more homogeneous distribution of nutrients, and change the quality of soil organic carbon, due to a change of species litter input. Secondly, we predicted that nitrogen addition would increase soil nitrogen evenly across the landscape.
Section snippets
Study site
To test the impact of shrub removal and increased nitrogen deposition on soil nutrient patterns we conducted a long term field experiment at Idaho State University's Barton Road Ecological Research Area, located in the sagebrush steppe of southeastern Idaho (42.853°N, 112.402°W) at an elevation of 1450 m. This area is cold desert that is characteristically dry, marked by low annual precipitation (150–492 mm), cold winters, and hot dry summers. The Pocatello 2NE reporting station, approximately 6
Results
There were no differences in perennial grass cover between control plots and either shrub removal plots or nitrogen addition plots in 1996, before treatments were first initiated, but from 1997 on, cover of perennial grasses was consistently greatest on shrub removal plots. There were significant differences in perennial grass cover between shrub removal plots and control plots in 1997 (, ), 1998 (, ), 1999 (, ), 2000 (, ), 2002 (,
Discussion
Soils on plots from which shrubs had been removed for six years had significantly greater soil carbon content than soils on control plots. The increase in soil carbon on shrub removal plots, which was primarily evident in the top 5 cm, was likely due to an increase in perennial grass biomass and resulting increases in carbon inputs from litter and from a greater abundance of herbaceous roots at shallower depths relative to shrub roots (Schenk and Jackson, 2002).
Chen and Stark (2000) found N and
Acknowledgements
Support for this project was provided by the Idaho State University Graduate Student Research and Scholarship Committee, the Department of Biological Sciences, the ISU Center for Ecological Research and Education, the National Science Foundation and BWB Bechtel. We thank two anonymous reviewers for the constructive comments which improved this manuscript greatly.
References (48)
- et al.
Soil microbial biomass and activity of a disturbed and undisturbed shrub-steppe ecosystem
Soil Biology and Biochemistry
(1993) - et al.
Plant species effects and carbon and nitrogen cycling in a sagebrush–crested wheatgrass soil
Soil Biology and Biochemistry
(2000) Effects of shrub removal and nitrogen addition on soil moisture in sagebrush steppe
Journal of Arid Environments
(2006)- et al.
Soil morphology and organic matter dynamics under cheatgrass and sagebrush-steppe plant communities
Journal of Arid Environments
(2004) - et al.
Effects of nitrogen deposition on an arid grassland in the Colorado plateau cold desert
Rangeland Ecology and Management
(2005) - et al.
Stemflow contribution to the fertile island effect in creosotebush, Larrea tridentata
Journal of Arid Environments
(1997) - et al.
Physical and biogeochemical controls over terrestrial ecosystem responses to nitrogen deposition
Biogeochemistry
(2001) - Bechtold, H.A., 2005. Nitrogen mineralization from resin bags following shrub removal and nitrogen addition in...
- et al.
Exploitation of springtime ephemeral N pulses by six Great Basin plant species
Ecology
(1997) Bromus tectorum, a biotic cause of ecosystem impoverishment in the Great Basin
The effects of air-borne nitrogen pollutants on species diversity in natural and semi-natural European vegetation
Journal of Ecology
Effect of increased soil nitrogen on the dominance of alien annual plants in the Mojave Desert
Journal of Applied Ecology
Reorganization of an arid ecosystem in response to recent climate change
Proceedings of the National Academy of Science
Herbicide treatment effects on properties of mountain big sagebrush soils after fourteen years
Soil Science Society of America
Plant community dynamics in a semi-arid ecosystem in relation to nutrient addition following a major disturbance
Plant and Soil
A comparative study of plant responsiveness to the duration of episodes of mineral nutrient enrichment
New Phytologist
Plants actively control nitrogen cycling: uncorking the microbial bottleneck
New Phytologist
Grassland management and conversion into grassland: effects on soil carbon
Ecological Applications
The relative abundance of three plant functional types in temperate grasslands and shrublands of North and South America: effects of projected climate change
Journal of Biogeography
Microbiotic crusts and ecosystem processes
Critical Reviews in Plant Sciences
Exotic plant invasion alters nitrogen dynamics in an arid grassland
Ecological Application
Ecological effects of nitrogen deposition in the western United States
Bioscience
On the relative importance of competition in unproductive environments
Journal of Ecology
Fine root growth and demographic responses to nutrient patches in four old-field plant species
Oecologia
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