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Prairie restoration at the northern edge of the Great Plains can be frustrated by previously established non-native perennial grasses. We compared the emergence of a widely introduced grass, Agropyron cristatum, and a common native grass, Bouteloua gracilis, in a 4-year-old field experiment in which the Agropyron-dominated vegetation had either been left intact or treated annually with herbicide. This was done at two levels of water supply, reflecting conditions expected in wet and dry years, to examine the effects of among-year variability in precipitation. Water addition significantly increased the emergence of both surface-sown and buried (1 cm deep) seeds. Herbicide treatment of neighbors did not increase the...
Three mixed prairie sites at Mandan, N.D. were grazed heavily (0.9 ha ), moderately (2.6 ha ), or left ungrazed (exclosure) since 1916. These sites provided treatments to study the effects of long-term grazing on soil organic carbon and nitrogen content and to relate changes in soil carbon and nitrogen to grazing induced changes in species composition. Blue grama [Bouteloua gracilis (H.B.K.) Lag. ex Griffiths] accounted for the greatest change in species composition for both grazing treatments. Relative foliar cover of blue grama was 25% in 1916 and 86% in 1994 in the heavily grazed pasture and 15% in 1916 to 16% in 1994 in the moderately grazed pasture. Total soil nitrogen content was higher in the exclosure (1.44...
This study investigated how CO2and temperature affect dry weight (d.wt) accumulation, total nonstructural carbohydrate (TNC) concentration, and partitioning of C and N among organs of two important grasses of the shortgrass steppe,Pascopyrum smithii Rydb. (C3) andBouteloua gracilis(H.B.K.) Lag. ex Steud. (C4). Treatment combinations comprised two temperatures (20 and 35�C) at two concentrations of CO2(380 and 750 ?mol mol-1), and two additional temperatures of 25 and 30�C at 750 ?mol mol-1CO2. Plants were maintained under favourable nutrient and soil moisture and harvested following 21, 35, and 49d of treatment. CO2-induced growth enhancements were greatest at temperatures considered favourable for growth of these...
The desert/grassland biome transition zone in central New Mexico provides an important region for testing species differences to changing environmental conditions and various land management practices. Interactions of black grama (Bouteloua eripoda) and blue grama (Bouteloua gracilis) significantly affect the resultant plant community and its influence on system structure and function. Black grama demonstrated higher productivity, especially after wet years, and this species has increased its dominance during the 20-year period since livestock grazing was removed. While black grama can alter the previous pattern of overgrazing and desertification in this transition zone, our experiments demonstrated that it was...
Invasive exotic weeds pose one of the earth's most pressing environmental problems. Although many invaders completely eliminate native plant species from some communities, ecologists know little about the mechanisms by which these exotics competitively exclude other species. Mycorrhizal fungi radically alter competitive interactions between plants within natural communities, and a recent study has shown that arbuscular mycorrhizal (AM) fungi provide a substantial competitive advantage to spotted knapweed, Centaurea maculosa, a noxious perennial plant that has spread throughout much of the native prairie in the northwestern U.S. Here we present evidence that this advantage is potentially due to mycorrhizally mediated...
A greenhouse experiment was conducted to determine the effect of watering regime on competition between the introduced annual Salsola kali var. tenuifolia and the native perennial grasses Agropyron smithii and Bouteloua gracilis. The treatments consisted of pots and had mixed cultures of Salsola with either one of the grass species, and pure cultures of all three species, under wet and dry soil moistures conditions. Plants were analyzed for leaf resistance (r"1), N, P, K, Ca, and Mg concentrations, and aboveground biomass. Both grass species had lower biomass and higher r"1 when growing in mixed culture with Salsola than in pure culture in the dry regime, but there were no significant differences in the wet regime....
In order to better elucidate fixed-C partitioning, nutrient acquisition and water relations of prairie grasses under elevated [CO2], we grew the C4 grass Bouteloua gracilis (H.B.K.) lag ex Steud. from seed in soil-packed, column-lysimeters in two growth chambers maintained at current ambient [CO2] (350 ?L L?1) and twice enriched [CO2] (700 ?L L?1). Once established, plants were deficit irrigated; growth chamber conditions were maintained at day/night temperatures of 25/16�C, relative humidities of 35%/90% and a 14-hour photoperiod to simulate summer conditions on the shortgrass steppe in eastern Colorado. After 11 weeks of growth, plants grown under CO2 enrichment had produced 35% and 65% greater total and root...
Populations of grasses exposed to grazing by vertebrates often exhibit reduced stature, increased tillering, reduced flowering, and other morphological differences which distinguish them from ungrazed populations. These differences frequently are interpreted as an adaptive response that reduces grazing damage; however, there are few experimental tests of this hypothesis. This paper describes a field experiment designed to determine whether morphological variation among genotypes of the grass Bouteloua gracilis is related to variation in their responses to grazing. Eleven genotypes differing in morphological and reproductive characters were transplanted into a shortgrass steppe community near Fort Collins, Colorado....
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Although research has shown that root associated fungi (RAF) are necessary for plant success in harsh environments, few studies have examined RAF community variability between different plant species coexisting in arid habitats. We compared the diversity and composition of the fungal communities colonizing dominant and important forage grasses, Bouteloua gracilis and Sporobolus cryptandrus, inhabiting the Sevilleta National Wildlife Refuge, a semiarid grassland in New Mexico. A third sympatric plant, Yucca glauca (Agavaceae), also was analyzed. ITS rDNA from roots, collected and amplified in 2007, yielded 447 fungal sequences. Sequences obtained from all three species suggest that grasses share a core group of RAF...
In the shortgrass steppe region of North America there is a controversy about the ability of the dominant species to recruit from seedlings. The prevailing view is that Bouteloua gracilis is incapable of recruitment from seedlings in areas receiving <380 mm of annual precipitation. A common explanation for this situation is that environmental conditions permitting seedling establishment are infrequent. To assess the frequency of environmental conditions appropriate for the recruitment of B. gracilis we used a soil water simulation model and long-term climatic data in conjunction with detailed information about the ecophysiological requirements for seed germination and growth of seminal and adventitious roots. We...
The eastern Colorado shortgrass steppe is dominated by the C4 grass, Bouteloua gracilis, but contains a mixture of C3 grasses as well, including Pascopyrum smithii. Although the ecology of this region has been extensively studied, there is little information on how increasing atmospheric CO2 will affect it. This growth chamber study investigated gas exchange, water relations, growth, and biomass and carbohydrate partitioning in B. gracilis and P. smithii grown under present ambient and elevated CO2 concentrations of 350 ?l l?1and 700 ?l l?1, respectively, and two deficit irrigation regimes. The experiment was conducted in soil-packed columns planted to either species over a 2-month period under summer-like conditions...
This research experimentally examined seasonal effects of fire on biological soil crusts and perennial grasses in shortgrass steppe. We predicted dormant-season fire would have greater negative effects on biological soil crusts than fire during the growing season, but less of an impact on perennial grasses than fire during the growing season. Treatments were dormant- and growing-season fires and unburned reference condition plots. Response variables included biological soil crust and grass percent ground cover, and crust nitrogen fixation and chlorophyll a content. Results indicated shortgrass steppe can recover from fire in three to 30 months, dependent on fire season. Burning during the dormant-season had little...
Large intact soil cores of nearly pure stands of Pascopyrum smithii (western wheatgrass, C3) and Bouteloua gracilis (blue grama, C4) were extracted from the Central Plains Experimental Range in northeastern Colorado, USA and transferred to controlled environment chambers. Cores were exposed to a variety of water, temperature and CO2 regimes for a total of four annual growth cycles. Root subsamples were harvested after the completion of the second and fourth growth cycles at a time corresponding to late winter, and were examined microscopically for the presence of mycorrhizae. After two growth cycles in the growth chambers, 54% of the root length was colonized in P. smithii, compared to 35% in blue grama. Field control...
The desert/grassland biome transition zone in central New Mexico provides an important region for testing species differences to changing environmental conditions and various land management practices. Interactions of black grama (Bouteloua eripoda) and blue grama (Bouteloua gracilis) significantly affect the resultant plant community and its influence on system structure and function. Black grama demonstrated higher productivity, especially after wet years, and this species has increased its dominance during the 20-year period since livestock grazing was removed. While black grama can alter the previous pattern of overgrazing and desertification in this transition zone, our experiments demonstrated that it was...
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We studied the diversity of arbuscular mycorrhizal fungi (AMF) in semiarid grassland and the effect of long-term nitrogen (N) fertilization on this fungal community. Root samples of Bouteloua gracilis were collected at the Sevilleta National Wildlife Refuge (New Mexico, USA) from control and N-amended plots that have been fertilized since 1995. Small subunit rDNA was amplified using AMF specific primers NS31 and AM1. The diversity of AMF was low in comparison with other ecosystems, only seven operational taxonomic units (OTU) were found in B. gracilis and all belong to the genus Glomus. The dominant OTU was closely related to the ubiquitous G. intraradices/G. fasciculatum group. N-amended plots showed a reduction...
Global environmental change is altering temperature, precipitation patterns, and resource availability in aridland ecosystems. In 2006, we established a multifactor global change experiment to determine the interactive effects of nighttime warming, increased atmospheric N deposition, and more frequent occurrence of El Ni�o years on plant community dynamics in a northern Chihuahuan Desert grassland. Here we only report the results of warming and N addition from the first monsoon growing season prior to the imposition of the precipitation treatments. Our passive nighttime warming treatment increased daily minimum temperatures by 1.4?3.0 �C. Fertilization increased NO3N supply, as measured with Root Simulator Probes,...
The distribution and turnover of plant litter contribute to soil structure, the availability of plant nutrients, and regional budgets of greenhouse gasses. Traditionally, studies of decomposition have focused on the upper soil profile. Other work has shown that temperature, precipitation, and soil texture are important determinates of patterns of decomposition. Since these factors all vary through a soil profile, it has been suggested that decomposition rates may vary with depth in a soil profile. In this work, we examine patterns of root decomposition through a shortgrass steppe soil profile. We buried fresh root litter from Bouteloua gracilis plants in litterbags at 10, 40, 70, and 100 cm. Litterbags were retrieved...
Question: What are the plant population- and community-level effects of removal of dominant plant species in the shortgrass steppe? Location: The Shortgrass Steppe Long-Term Ecological Research site in northern Colorado, USA. Methods: We annually measured plant cover and density by species for 10 years after a one-time aboveground removal of the dominant perennial grass, Bouteloua gracilis. Removal and control plots (3 m � 3 m) were within grazed and ungrazed locations to assess the influence of grazing on recovery dynamics. Our analyses examined plant species, functional type, and community responses to removal, paying special attention to the dynamics of subdominant and rare species. Results: Basal cover of B....
    map background search result map search result map A general suite of fungal endophytes dominate the roots of two dominant grasses in a semiarid grassland Effect of long-term nitrogen fertilization on mycorrhizal fungi associated with a dominant grass in a semiarid grassland A general suite of fungal endophytes dominate the roots of two dominant grasses in a semiarid grassland Effect of long-term nitrogen fertilization on mycorrhizal fungi associated with a dominant grass in a semiarid grassland